Cover: Optomechanics Using Excitonic Transitions

Schematic image in the middle of the cover.

Electron-hole pairs are generated by laser irradiation in the AlGaAs/GaAs cantilever. Electrons
and holes are spacially separated via the built-in electric field, leading to the piezoelectriccompressive stress in the GaAs (the green colored lower layer). This stress causes bending.
Thus, the cantilever can be driven via this opto-piezoelectric effect. Because the driving
efficiency depends on the degree of optical absorption, high-sensitivity spectroscopy isrealized by monitoring the displacement of the cantilever. The optically induced stress acts on
the cantilever in a time delay with respect to the optical excitation. Therefore, the continuous
laser irradiation results in a feedback effect on the mechanical oscillation. This enables us toreduce the thermal noise in the cantilever as well as to amplify its vibration.

Graphs on the cover (top left graphs on the cover are shown on page 34).

Top middle graph: Amplification (left) and de-amplification (right) of the thermal vibrationby continuous laser illumination. Detuning the photon energy from the exiciton resonanceenergy (1.5152 eV) causes a positive or negative feedback effect. Top right graph: Photonenergy dependence of the frequency response under modulated illumination (top) and thephotoluminescence excitation (PLE) spectrum (bottom). The driving efficiency is maximized
at the exciton resonance energy, where the PLE intensity is the maximum.

Message from the Director
We at NTT Basic Research Laboratories(BRL) are extremely grateful for your interestand support with respect to our research
activities. BRL’s missions are to promote
progress in science and innovations in leadingedge technology to advance NTT's business.
To achieve these missions, researchers infields including physics, chemistry, biology,
mathematics, electronics, informatics, andmedicine, conduct basic research on materials
science, physical science and optical science.
Since our management principle is based onan "open door" policy, we are collaboratingwith many universities and research institutes
in Japan, US, Europe, and Asia as well asother NTT laboratories. NTT-BRL regularlyorganizes international conferences related to quantum physics and nanotechnology at NTT
Atsugi R&D Center and also holds a "Science Plaza" to enhance public understanding of
our activities and to ensure a frank exchange of opinions. Moreover, one of our missions is
the education of young researchers and we sponsor the biennial "BRL School", which boasts
distinguished researchers as lecturers. In November 2015, thirty Ph.D. students and young
researchers from universities and institutes in 11 countries participated in the BRL School.
These activities enable us to realize our missions with respect to the promotion of advancesin science and the development of groundbreaking technology for NTT's business. Your
continued support will be greatly appreciated.

July, 2016

Tetsuomi Sogawa
Director
NTT Basic Research Laboratories

Table of Contents◆

Cover : Optomechanics Using Excitonic Transitions◆

Message from the Director◆

Organogram

1◆

Member List

2

Ⅰ Research Topics◇

Overview of Research in Laboratories

20

Materials Science Laboratory◆

Ion-Irradiation Effect in Ion-beam-assisted MBE Growth of c-BN Films

22◆

N-Face GaN (0001) Films with Hillock-free Smooth Surfaces Grown by

23Group-III-source Flow-rate Modulation Epitaxy◆

Determination of Intrinsic Lifetime of Edge Magnetoplasmons

24◆

Applying Strain into Graphene - toward Strain Engineering of Graphene

25◆

Er-Sc Silicate as an Optical Gain Material in Telecommunications Band

26◆

As-grown Superconducting Pr2CuO4 Thin Films

27◆

On-chip FRET Graphene Oxide Aptasensor: Enhanced Sensitivity by Using

28

Aptamer with Double-stranded DNA Spacer◆

Time-lapse Imaging of a Single Neuron During the Early Stage of Apoptosis

29

Using Scanning Ion Conductance Microscopy◆

Si and Au Nanopillar Arrays as Scaffolds for Neuronal Growth30

Physical Science Laboratory◆

Observing Semiconducting Band-gap Alignment in MoS2 Layers Using a

31

MoS2/SiO2/Si Heterojunction Tunnel Diode◆

High-speed Single-hole Transfer in a Si Tunable-barrier Pump

32◆

Thermal-noise Suppression in Nano-scale Si Field-effect Transistors by Feedback

33

Control of Single Electrons◆

Optomechanics Using Excitonic Transitions in Semiconductor Heterostructures

34◆

Optical Control of Mechanical Mode Coupling at Room Temperature

35◆

Improving the Coherence Time of a Quantum System by Coupling it to a

36

Short-lived System◆

Observation of Quantum Zeno Effect in Superconducting Flux Qubit

37◆

Electron Paramagnetic Resonance Using a SQUID Magnetometer Directly Coupled38

to an Electron Spin Ensemble◆

Shot Noise Generated by Graphene p-n Junctions in the Quantum Hall Effect Regime

39◆Gate-controlled Semimetal-Topological Insulator Transition in an InAs/GaSb

40

Heterostructure◆

Probing the Extended-state Width of Disorder-broadened Landau Levels in Epitaxial

41

Graphene

Optical Science Laboratory◆

Coherent Raman Beat Analysis of the Hyperfine Sublevel Coherence Properties of
167

42

3+

Er Ions Doped in an Y2SiO5 Crystal◆

Deterministic Wavelength Conversion of Single Photons Using Cross-phase

43

Modulation◆

An Entanglement Analogue in Light Cones

44◆

All-Photonic Intercity Quantum Key Distribution

45◆

Finite-key Security Analysis of Quantum Key Distribution with Imperfect Light

46

Sources◆

Extraction of Phonon Decay Rate in p-type Silicon Under Fano Resonance47◆

Frequency Stabilization of an Er-doped Fiber Laser with a Collinear 2f-to-3f

48

Self-referencing Interferometer◆Long-distance Transport of Electron Spins in Persistent Spin Helix State

49◆

Thresholdless Oscillation in High-β Buried Multiple-quantum-well Photonic Crystal

50

Lasers◆Wavelength-scale All-optical Photonic Crystal Nanocavity Memory Operating at

51

Nanowatt-level◆

An All-optical Packet Switch Realized by Using the Ultralow-power Optical

52

Bistability of a Nanocavity

Nanophotonics Center◆

Membrane Distributed-reflector Laser Integrated with SiOx-based Spot-size

53

Converter on Si Substrate◆

Dislocation Reduction in MOVPE-grown GaAs/Ge Layers on Si Substrates by

54

Thermal Cycle Annealing

Ⅱ Data◇7th NTT-BRL School

56◇

ISNTT 2015

57◇

List of Visitors’ Talks

58◇

List of Award Winners

60◇

List of In-house Award Winners

61◇

Number of Papers

62◇

Number of Presentations

63◇

Number of Patents

63◇

Publication List

64◇

List of Invited Talks

71

NTT Basic Research Laboratories

Organogram

As of March 31, 2016

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)1

Member List
As of March 31, 2016(*/ left in the middle of the year)

NTT Basic Research Laboratories
Director

Dr. Tetsuomi Sogawa

Quantum and Nano Device Research

Senior Distinguished Researcher

Dr. Hiroshi Yamaguchi

Biomedical Exercise Physiology Research

Senior Distinguished Researcher

Dr. Shingo Tsukada

Research Planning Section

Senior Research Scientist, Supervisor
Senior Research Scientist, Supervisor
Senior Research Scientist, Supervisor
Senior Research Scientist

Dr. Hideki Gotoh
Dr. Hideki Yamamoto*Dr. Yoshitaka Taniyasu
Dr. Shiro Saito
Dr. Masumi Yamaguchi

NTT Research Professor
Prof. Yasuhiro Tokura
Prof. Hiroki Hibino

2

University of Tsukuba
Kwansei Gakuin University

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Executive Manager

NTT Basic Research Laboratories

Materials Science Laboratory

Dr. Hideki Yamamoto
Dr. Yuko Ueno
Dr. Kazuaki Furukawa*Thin-Film Materials Research Group
Dr. Kazuhide Kumakura (Group Leader)Dr. Hisashi SatoDr. Tetsuya Akasaka

Dr. Kota Tateno

Dr. Masanobu Hiroki

Dr. Kazuyuki Hirama

Dr. Kazuaki Ebata

Dr. Junichi Nishinaka

Low-Dimensional Nanomaterials Research GroupDr. Hideki Yamamoto (Group Leader)
Dr. Satoru Suzuki

Dr. Hiroo Omi

Dr. Ken-ichi Sasaki

Dr. Koji Onomitsu

Dr. Yoshiharu Krockenberger

Dr. Shin-ichi Karimoto

Dr. Yoshiaki Sekine

Dr. Makoto Takamura

Dr. Shengnan Wang

Dr. Yui Ogawa

Dr. Adel Najar*

Dr. Manabu Ohtomo

Dr. Ai Ikeda

Molecular and Bio Science Research GroupDr. Hiroshi Nakashima (Group Leader)
Dr. Koji Sumitomo

Dr. Shingo Tsukada

Dr. Yuko Ueno

Dr. Kazuaki Furukawa

Dr. Nahoko Kasai

Dr. Yoshiaki Kashimura

Dr. Aya Tanaka

Dr. Toichiro Goto

Dr. Azusa Oshima

Dr. Tetsuhiko Teshima

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)3

Physical Science Laboratory

Executive Manager

Dr. Akira Fujiwara
Dr. Takeshi Ota
Dr. Toshiaki Hayashi*
Takeshi Karasawa

Nanodevices Research Group
Dr. Akira Fujiwara (Group Leader)
Toru Yamaguchi

Dr. Toshiaki Hayashi

Dr. Katsuhiko Nishiguchi

Hirotaka Tanaka

Dr. Jinichiro Noborisaka

Dr. Gento Yamahata

Dr. Kensaku Chida

Dr. Nicolas Clement

Hybrid Nanostructure Physics Research GroupDr. Hiroshi Yamaguchi (Group Leader)
Dr. Imran Mahboob

Dr. Hajime Okamoto

Dr. Kosuke Kakuyanagi

Dr. Yuichiro Matsuzaki

Dr. Daiki Hatanaka

Dr. Hiraku Toida

Dr. Ryuichi Ohta

Quantum Solid State Physics Research Group
Dr. Koji Muraki (Group Leader)
Dr. Kiyoshi Kanisawa

Dr. Satoshi Sasaki

Dr. Hiroyuki Tamura

Dr. Kyoichi Suzuki

Dr. Takeshi Ota

Dr. Norio Kumada

Dr. Keiko Takase

Dr. Hiroshi Irie

Dr. Takafumi Akiho

Dr. Trevor David Rhone*

Dr. Francois Couedo

4

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Executive Manager

NTT Basic Research Laboratories

Optical Science Laboratory

Dr. Hideki Gotoh
Dr. Makoto Yamashita
Kazuhiro Igeta

Quantum Optical State Control Research Group
Dr. Kaoru Shimizu (Group Leader)Dr. Hiroki Takesue

Dr. Makoto Yamashita

Dr. Tetsuya Mukai

Dr. Fumiaki Morikoshi

Dr. Kensuke Inaba

Dr. Nobuyuki Matsuda

Dr. Takahiro Inagaki

Dr. Kazuto Noda

Theoretical Quantum Physics Research GroupDr. William John Munro (Group Leader)
Dr. Kiyoshi Tamaki

Dr. Koji Azuma

Dr. George Knee*

Dr. Fabian Furrer

Dr. Stefan Bäuml

Quantum Optical Physics Research GroupDr. Hideki Gotoh (Group Leader)
Dr. Takehiko Tawara

Dr. Katsuya Oguri

Dr. Atsushi Ishizawa

Dr. Guoqiang Zhang

Dr. Haruki Sanada

Dr. Keiko Kato

Dr. Hiroki Mashiko

Dr. Kenichi Hitachi

Dr. Hiromitsu Imai

Dr. Yoji Kunihashi

Photonic Nano-Structure Research Group
Dr. Masaya Notomi (Group Leader)
Dr. Akihiko Shinya

Dr. Atsushi Yokoo

Dr. Eiichi Kuramochi

Dr. Hisashi Sumikura

Dr. Hideaki Taniyama

Dr. Kengo Nozaki

Dr. Masato Takiguchi

Dr. Masaaki Ono

Dr. Kenta Takata

Dr. Devin Smith

Dr. Feng Tian

Dr. Sylvain Sergent

Dr. Shota Kita
Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

5

Nanophotonics Center

Project Manager

Dr. Masaya Notomi

Photonic Nano-Structure Research Group
Dr. Akihiko Shinya

Dr. Atsushi Yokoo

Dr. Eiichi Kuramochi

Dr. Hisashi Sumikura

Dr. Hideaki Taniyama

Dr. Kengo Nozaki

Dr. Masato Takiguchi

Dr. Masaaki Ono

Dr. Kenta Takata

Dr. Hiroo Omi

Dr. Takehiko Tawara

Dr. Nobuyuki Matsuda

Dr. Kota Tateno

Dr. Guoqiang Zhang

Nanostructured Device Research Group6

Dr. Shinji Matuo

Dr. Tai Tsuchizawa

Dr. Takaaki Kakitsuka

Dr. Koichi Hasebe

Dr. Koji Takeda

Hidetaka Nishi

Dr. Kota Okazaki

Tatsurou Hiraki

Ryo Nakao

Takuro Fujii

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

NTT Basic Research Laboratories

Senior Distinguished Researchers
Masaya NOTOMI received his B.E., M.E. and Ph.D. degrees in applied physics
from The University of Tokyo, Japan in 1986, 1988, and 1997, respectively. He
joined NTT Optoelectronics Laboratories, Nippon Telegraph and Telephone
Corporation in 1988 and moved to NTT Basic Research Laboratories in 1999.
Since then, his research interest has been to control the optical properties ofmaterials and devices by using artificial nanostructures, and engaged in researchon quantum wires/dots and photonic crystal structures. In 1996-1997, he was a visiting researcher of
Linköping University, Sweden. He was a guest associate professor of Applied Electronics in 20032009 and is currently a guest professor of Physics in Tokyo Institute of Technology. He was appointed
as Senior Distinguished Scientist of NTT since 2010. He is currently a director of NTT Nanophotonics
Center and a group leader of Photonic Nanostructure Research Group.
He received IEEE/LEOS Distinguished Lecturer Award in 2006, Japan Society for the Promotionof Science (JSPS) prize in 2009, Japan Academy Medal in 2009, The Commendation for Scienceand Technology by the Minister of Education, Culture, Sports, Science and Technology (Prize for
Science and Technology, Research Category) in 2010, and IEEE Fellow grade in 2013. He served asa member of National University Corporation Evaluation Committee in the Japanese government. He
is a research director of JST CREST program from 2015. He is also a member of the Japan Society ofApplied Physics, APS, IEEE, and OSA.

Hiroshi YAMAGUCHI received his B.E., M.S. in physics and Ph.D. degrees
in engineering from Osaka University in 1984, 1986, and 1993, respectively.
He joined NTT Basic Research Laboratories, Nippon Telegraph and Telephone
Corporation in 1986 and has been engaged in the study of compound
semiconductor surfaces using electron diffraction and scanning tunnelingmicroscopy. His current interests are micro/nanomechanical devices using
semiconductor heterostructures. He was a visiting research fellow in Imperial College, Universityof London, U.K. during 1995-1996 and a visiting research staff in Paul Drude Institute, Germany in2003. He is a guest professor in Tohoku University from 2006 and a director of the Japanese Societyof Applied Physics (JSAP) in 2008 and 2009. He served as more than 40 committee members ofacademic societies and international conferences. He was appointed as Senior Distinguished Scientistof NTT since 2011. He is currently an executive manager of Quantum and Nano Device Research anda group leader of Hybrid Nano-Structure Physics Research Group.
He received the Paper Awards of Japan Society of Applied Physics in 1989, 2004, and 2010, MNC2008
Outstanding Paper Award in 2009, SSDM2009 Paper Award in 2010, Inoue Prize for Science in 2012,
and Commendation for Science and Technology by MEXT in 2013. He was made a Fellowship of
Institute of Physics (IOP) in 2011 and JSAP in 2013. He is a member of JSAP, the Physical Society ofJapan, Institute of Physics (IOP), American Physical Society (APS), and IEEE.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)7

Koji MURAKI received his B.S., M.S., and Ph.D. degrees in applied physics
from The University of Tokyo, Japan, in 1989, 1991, and 1994, respectively.
He joined NTT Basic Research Laboratories, Nippon Telegraph and Telephone
Corporation in 1994. Since then, he has been engaged in the growth of highmobility heterostructures and the study of highly correlated electronic states
realized in such structures. He was a guest researcher at Max-Planck Institute,
Stuttgart, Germany during 2001-2002. He served as a program committee/chair of international
conferences on High Magnetic Fields in Semiconductor Physics (HMF) and Electronic Propertiesof Two-Dimensional Systems (EP2DS). He was a leader of physics research and epitaxy group of
ERATO Nuclear Spin Electronics Project, Japan Science and Technology, during 2008-2015. He wasappointed as Distinguished Scientist of NTT in 2009 and Senior Distinguished Scientist of NTT in
2013. He is currently a group leader of Quantum Solid State Physics Research Group. He is a memberof the Physical Society of Japan and Japan Society of Applied Physics.

Shingo TSUKADA received his M.D. degrees from Toyama Medical andPharmaceutical University, Japan and his medical license in 1990. He received
the Ph.D. degrees in medicine from Tsukuba University, Japan in 2003
respectively. He was a visiting researcher at University of California at San
Diego, U.S.A. during 2003-2005. He joined NTT Basic Research Laboratories,
Nippon Telegraph and Telephone Corporation in 2010 as a Research Specialist,
and from 2013 as a Senior Research Scientist. Since then, he has been engaged in the study ofmechanism and activity control of signal transduction of brain cell. His current interests are thedetection of biomedical signals using novel wearable-type and implant-type bioelectrodes based on
the composites of conductive polymers with various fibers and textiles. He was appointed as SeniorDistinguished Scientist of NTT in 2014. He is currently a member of Molecular and Bio Science
Research Group. He is a member of Society for Neuroscience, The Physiological Society of Japan, The
Japan Society of Applied Physics, the japan Neuroscience Society, the Japanese Circulation Society,and the Japanese Orthopaedic Association.

8

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

NTT Basic Research Laboratories

Akira FUJIWARA received his B.S., M.S., and Ph.D. degrees in applied
physics from The University of Tokyo, Japan in 1989, 1991, and 1994,
respectively. He joined NTT LSI Laboratories, Nippon Telegraph and Telephone
Corporation in 1994 and moved to NTT Basic Research Laboratories in 1996.
Since 1994, he has been engaged in research on silicon nanostructures andtheir application to single-electron devices. He was a guest researcher at the
National Institute of Standards and Technology (NIST), Gaithersburg, MD, USA during 2003-2004.
He was a director of the Japanese Society of Applied Physics in 2010 and 2011 and a visiting professorof Hokkaido University in 2013. He was appointed as Distinguished Scientist of NTT in 2007 andSenior Distinguished Scientist of NTT in 2015. He is currently a senior manager of Physical Science
Laboratory and a group leader of Nanodevices Research Group.
He received the SSDM Young Researcher Award in 1998, SSDM Paper Award in 1999, and Japanese
Journal of Applied Physics (JJAP) Paper Awards in 2003, 2006, and 2013. He was awarded the Young
Scientist Award from the Minister of MEXT (Ministry of Education, Culture, Sports, Science, andTechnology) in 2006. He was supported by the funding program for Next Generation World-Leading
Researchers (NEXT Program), JSPS in 2011-2014. He is a member of the Japan Society of Applied
Physics and a senior member of the IEEE.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

9

Distinguished Researchers
Norio KUMADA received his B.S., M.S., and Ph.D. degrees in physics fromTohoku University, Japan, in 1998, 2000, and 2003, respectively. He joined NTT
Basic Research Laboratories, Nippon Telegraph and Telephone Corporationin 2003. Since then, he has been engaged in the study of highly correlated
electronic states in semiconductor heterostructures. He was a visiting researcher
at CEA Saclay during 2013-2014. He was appointed as Distinguished Scientistof NTT in 2010. He is currently a member of Quantum Solid State Physics Research Group.
He received the Young Scientist Award of the Physical Society of Japan in 2008, and the Young
Scientists’ Prize from the Minister of Education, Culture, Sports, Science and Technology in 2012. He
is a member of the Physical Society of Japan.

Katsuhiko NISHIGUCHI received his B.E., M.E., and Ph.D. in electricalengineering from Tokyo Institute of Technology, Japan in 1998, 2000, and 2002,
respectively. He joined NTT Basic Research Laboratories, Nippon Telegraph andTelephone Corporation in 2002. Since then, he has been engaged in the researchon physics and technology of Si nanometer-scale devices for LSI applications
with low power consumption and new functions. He was an invited researcher
at the National Center for Scientific Research (CNRS), France during September 2008 and also aguest researcher at Delft University of Technology, Delft, the Netherlands during 2012-2013. He
was appointed as Distinguished Scientist of NTT in 2011. He is currently a member of Nanodevices
Research Group.
He received IUPAP Young Author Best Paper Award at the International Conference on Physics of
Semiconductors 2000, Graduate Student Award Silver at the Materials Research Society 2000 Fall
Meeting, Young Scientist Award at the Japan Society of Applied Physics Spring Meeting in 2000,
JSAP Outstanding Paper Award 2013, and The Commendation for Science and Technology by the
Minister of Education, Culture, Sports, Science and Technology of Japan (the Young Scientists' Prize)in 2013. He is a member of the Japan Society of Applied Physics.

10

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

NTT Basic Research Laboratories

Shiro SAITO received his B.S., M.S., and Dr. Eng. degrees in applied physics
from The University of Tokyo, Japan, in 1995, 1997, and 2000, respectively.
He joined NTT Basic Research Laboratories, Nippon Telegraph and Telephone
Corporation in 2000. Since then, he has been engaged in quantum information
processing using superconducting circuits. He was a guest researcher at Delft
University of Technology, Delft, the Netherlands during 2005-2006. He is a guest
associate professor in Tokyo University of Science from 2012. He was appointed as Distinguished
Scientist of NTT in 2012. He is currently a member of Hybrid Nano-Structure Physics ResearchGroup.
He received the Young Scientist Presentation Award at the Japan Society of Applied Physics (JSAP)
Spring Meeting in 2004. He is a member of the Physical Society of Japan and the Japan Society ofApplied Physics.

Hiroki TAKESUE received his B.E., M.E., and Ph.D. degrees in engineeringscience from Osaka University, Japan, in 1994, 1996, and 2002, respectively.
He joined NTT Access Network Systems Laboratories, Nippon Telegraphand Telephone Corporation in 1996 and moved to NTT Basic ResearchLaboratories in 2003. Since then, he has been engaged in research on quantum
communications and novel computation schemes based on nonlinear optics.
He was appointed as Distinguished Scientist of NTT in 2013. He is currently a member of Quantum
Optical State Control Research Group.
He received several awards including the ITU-T Kaleidoscope Conference 2nd Best Paper Award (2ndplace) in 2008 and The Commendation for Science and Technology by the Minister of Education,
Culture, Sports, Science and Technology of Japan (the Young Scientists' Prize) in 2010. He was a
Visiting Scholar at Stanford University, Stanford, CA from 2003 to 2004, and a guest researcher at the
National Institute of Standards and Technology (NIST), Boulder, CO in 2014. He is a member of IEEEand the Japan Society of Applied Physics.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)11

Imran MAHBOOB received a combined B.Sc. and M.Sc. degree in Theoretical
Physics from The University of Sheffield, U.K., in 2001 and Ph.D. degreein Physics studying the electronic properties of nitride semiconductors fromThe University of Warwick, U.K., in 2004, respectively. He joined NTT Basic
Research Laboratories, Nippon Telegraph and Telephone Corporation in 2005
as a Research Associate, from 2008 as a Research Specialist, and from 2012as a Senior Research Scientist. His current interests are developing electromechanical resonators for
digital signal processing applications and to study their non-linear dynamics. He was appointed asDistinguished Scientist of NTT in 2013. He is currently a member of Hybrid Nano-Structure Physics
Research Group.
He received the Clarke Prize in Physics from the University of Sheffield in 2001 and the Young
Scientist Award at the 2003 Physics of Semiconductors and Interfaces conference. He is a member ofthe American Physical Society.

Haruki SANADA received his B.E., M.E., and Ph.D. degrees in electricalengineering from Tohoku University, Japan, in 2001, 2002, and 2005
respectively. He joined NTT Basic Research Laboratories, Nippon Telegraphand Telephone Corporation in 2005. His research interests are optical andspin properties of low-dimensional semiconductor nanostructures, and theirapplication to solid-state quantum information processing. He is a visiting
researcher at Chalmers University of Technology, Sweden in 2015. He was appointed as Distinguished
Scientist of NTT in 2014. He is currently a member of Quantum Optical Physics Research Group.
He received the Young Scientist Presentation Award at the Japan Society of Applied Physics (JSAP)
Autumn Meeting in 2004, the SSDM Paper Award in 2010, and the RIEC Award from Tohoku
University in 2014. He is a member of the Japan Society of Applied Physics.

12

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

NTT Basic Research Laboratories

Yoshiharu KROCKENBERGER received his diploma in physics from The
University of Technology of Munich, Germany, studying tunneling spectroscopy
on superconductors. Working at the Max Planck Institute for Solid State
Research in Stuttgart, Germany, on transition metal oxides with strong electron
correlations he received his PhD degree from The University of Technology
of Darmstadt, Germany in 2006. At the end of 2006 he joined the CorrelatedElectron Research Center at The Institute for Advanced Industrial Science and Technology in Tsukuba,
Japan as a research scientist. In 2008, he moved to RIKEN in Wako, Japan where he was engaged asa research scientist at the Cross-Correlated Materials Research group. He joined NTT Basic ResearchLaboratories, Nippon Telegraph and Telephone Corporation in 2010. His interests are developmentof novel superconducting materials and competing order parameters in strongly-correlated electronicsystems. He was appointed as Distinguished Scientist of NTT in 2013. He is currently a member of
Low-Dimensional Nanomaterials Research Group.
He received the Young Scientist Award for an Excellent Article from Superconductivity Divisionof Japan Society of Applied Physics in 2012. In 2016, the Society for Non-Traditional Technology
awarded his contributions to research in superconductivity. He is a member of American PhysicalSociety, Materials Research Society, and The Japan Society of Applied Physics.

Kazuhide KUMAKURA received his B.E., M.E., and Ph.D. degrees inengineering from Hokkaido University, Japan, in 1993, 1995, and 1998,
respectively. He joined NTT Basic Research Laboratories, Nippon Telegraph andTelephone Corporation in 1998. His current interests are high-power, high-speed
optoelectronic devices using nitride semiconductors. He was a visiting researcher
at Paul-Drude-Institute, Germany during 2007-2008. He was appointed asDistinguished Scientist of NTT in 2015. He is currently a group leader of Thin-Film Materials
Research Group.
He received the Young Scientist Presentation Award at the Japan Society of Applied Physics Spring
Meeting in 2000. He is a member of the Japan Society of Applied Physics.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)13

William J. MUNRO received his B.Sc in Chemistry, M.Sc and D.Phil degrees
in Physics from the University of Waikato, NZ in 1989, 1991, and 1995
respectively. He was a research fellow at the University of Queensland, Australia
from 1997-2000 and then a staff scientist at Hewlett Packard Laboratories inBristol (2000-2010). He joined NTT Basic Research Laboratories, Nippon
Telegraph and Telephone Corporation in 2010 as a research specialist and from2014 as a Senior Research Scientist. Since then, he has researched several areas of Quantum Physics
ranging from foundational issues of quantum theory through to quantum information processing andits practical realization.
He is currently a visiting professor at the National Institute of Informatics in Japan (2006 - 2015), theUniversity of Leeds in the UK (2009 - 2015) and the University of Queensland in Australia (2012 2015). He was appointed as Distinguished Scientist of NTT in 2015 and is currently the group leaderof the theoretical quantum physics research group.
He was made a fellow of the Institute of Physics (UK) in 2009, the American Physical Society (APS)
in 2013 and the Optical Society of America (OSA) in 2014. He is also a member of The International
Society for Optical Engineering (SPIE).

14

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

NTT Basic Research Laboratories

Advisory Board Members
Name

Affiliation

Prof. Gerhard Abstreiter

Walter Schottky Institute,Technische Universität München,
Germany

Prof. John Clarke

University of California, Berkeley, U.S.A.

Prof. Evelyn Hu

Harvard University, U.S.A.

Prof. Mats Jonson

University of Gothenburg, Sweden

Prof. Sir Peter Knight

Imperial College London, U.K.

Prof. Anthony J. Leggett

University of Illinois at Urbana-Champaign, U.S.A.

Prof. Allan H. MacDonald

The University of Texas at Austin, U.S.A.

Prof. Andreas Offenhäusser

Forschungszentrum Jülich, Germany

Prof. Halina Rubinsztein-Dunlop

The University of Queensland, Australia

Prof. Klaus von Klitzing

Max Planck Institute for Solid State Research, Germany

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)15

Overseas Trainees

16

Name

Affiliation

PeriodHadrien Duprez

École Polytechnique de Montréal,
CanadaMay 2014 - Apr. 2015

Sophia Chan

University of Edinburgh, U.K.

June 2014 - June 2015

Aleksandra Krajewska

University of Edinburgh, U.K.

July 2014 - June 2015

Todt ClemensTechnical University Dresden,
Germany

Sep. 2014 - Aug. 2015

Aleix Llenas

Polytechnic University of
Catalonia Barcelona Tech, Spain

Sep. 2014 - Aug. 2015

Dorota Kowalczyk

Gdansk University of Technology,
PolandSep. 2014 - Aug. 2015

Silviu Dinulescu

University Politehnica of
Bucharest, Romania

Sep. 2014 - Aug. 2015

Akie Watanabe

The University of British
Columbia, Canada

Jan. 2015 - Aug. 2015

Mats Powlowski

Corcodia University, Canada

Jan. 2015 - July 2015

Joo Whan Yoo

McGill University, Canada

May 2015 - Mar. 2016

Ziyan XuThe University of British
Columbia, Canada

May 2015 - Dec. 2015

Andrew David Browning

The University of British
Columbia, Canada

May 2015 -Samarth Desai

Padue University, U.S.A.

May 2015 - July 2015

Samuele Grandi

Imperial College London, U.K.

July 2015 - Oct. 2015

Nathaniel Walmsley

University of Bath, U.K.

July 2015 - Dec. 2015

Victoria Hamilton

University of Bath, U.K.

July 2015 - Dec. 2015

Corentin Deprez

ESPCI ParisTech(École supérieure de physique et dechimie industrielles de la villede Paris), France

July 2015 - Dec. 2015

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

July 2015 - Dec. 2015

Tom Darras

ESPCI ParisTech(École supérieure de physique et dechimie industrielles de la ville deParis), France

July 2015 - Dec. 2015

Mathieu Durand

ESPCI ParisTech(École supérieure de physique et dechimie industrielles de la ville deParis), France

July 2015 - Dec. 2015

Isabel Gonzalvez

University of Edinburgh, U.K.

Sep. 2015 -Monika Theresa Schied

Ulm University, Germany

Sep. 2015 -Veronika Zagar

University of Ljubljana, Slovenia

Sep. 2015 -Carla Maria Palomares Garcia

Carlos III University of Madrid,
Spain

Sep. 2015 -Giacomo Mariani

Politecnico di Milano, Italy

Sep. 2015 -Dominika Urszula Gnatek

Jagiellonian University, Poland

Sep. 2015 -Jun Ki Kim

Geogia Institute of Technology,
U.S.A.

Sep. 2015 -Javier Cambiasso

Imperial College London, U.K.

Jan. 2016 -Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

NTT Basic Research Laboratories

Marius Villiers

ESPCI ParisTech(École supérieure de physique et dechimie industrielles de la ville deParis), France

17

Domestic Trainees

18

Name

Affiliation

PeriodMasafumi Horio

The University of Tokyo

Apr. 2015 - Mar. 2016

Ahmad YoshinariTokyo University of Science

Apr. 2015 - Mar. 2016

Takuya Ohrai

Tokyo University of Science

Apr. 2015 - Mar. 2016

Toru Tanaka

Waseda University

Apr. 2015 - Mar. 2016

Suguru Endo

Keio University

Apr. 2015 - Mar. 2016

Yamato Ashikawa

Tohoku University

Apr. 2015 - Mar. 2016

Rento Osugi

Tohoku University

Apr. 2015 - Mar. 2016

Takahiro Gotoh

Tokyo Denki University

Apr. 2015 - Mar. 2016

Kazutaka Hara

Tokyo Denki University

Apr. 2015 - Mar. 2016

Yu Shimojo

Tokyo Denki University

Apr. 2015 - Mar. 2016

Yuya Hasegawa

Tokyo Denki University

Apr. 2015 - Mar. 2016

Masato Tsunekawa

Tokyo Institute of Technology

Apr. 2015 - Mar. 2016

Takuya Ikuta

Osaka University

Apr. 2015 - Dec. 2015

Hisashi Chiba

Tokyo Institute of Technology

Apr. 2014 - Mar. 2015

Ryo Sawaishi

Tohoku Institute of Technology

May 2015 - Dec. 2015

Daisuke Yoshizumi

Tokushima University

Aug. 2015 - Sep. 2015

Takahiro Tominaga

Hokkaido University

Aug. 2015 - Sep. 2015

Tatsuya Ogawa

Hirosaki University

Aug. 2015 - Sep. 2015

Naoki Kanazawa

Toyohashi University of Technology

Sep. 2015 - Mar. 2016

Akiyoshi Naka

Nagaoka University of Technology

Oct. 2015 - Feb. 2016

Gento Nakamura

The University of Electro-Communications

Oct. 2015 - Mar. 2016

Junpei Yamaguchi

Hokkaido University

Nov. 2015 - Mar. 2016

Yuki Hamada

The University of Tokyo

Nov. 2015 - Dec. 2015

Shuntaro Ishii

The University of Tokyo

Dec. 2015 - Mar. 2016

Shun Saito

Toyohashi University of Technology

Jan. 2016 - Feb. 2016

Thomas Tiong

Toyohashi University of Technology

Jan. 2016 - Feb. 2016

Xinwei LiuTokyo Institute of Technology

Jan. 2016 - Mar. 2016

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Ⅰ．Research Topics

Overview of Research in Laboratories
Materials Science Laboratory

Hideki Yamamoto

The aim of the Materials Science Laboratory is to contribute to progress in materials scienceand to revolutionize information communication technology by creating novel materials andfunctions through materials design at the atomic and molecular levels.
The laboratory consists of three research groups investigating a wide range of materials e.g.,
typical compound semiconductors including GaAs and GaN, two-dimensional materials suchas graphene, high-Tc oxide superconductors, and biological molecules. We are conducting
innovative materials research based on advanced thin-film growth technologies along withhigh-precision and high-resolution measurements of structures and properties.
This year, we succeeded in growing high-quality N-polar GaN, metastable c-BN, and asgrown superconducting thin films. We also applied controlled strain to graphene, which
provides way of realizing “graphene strain engineering”. Moreover, we successfully measured
mental and physical bio-signals in various use scenarios including medical, rehabilitation,
sports, worker safety control and extreme situations by using a functional sensing fabric“hitoe®”, which we developed in collaboration with Toray Industries, Inc.

Physical Science Laboratory

Akira Fujiwara

The aim of the Physical Science Laboratory is to develop semiconductor- andsuperconductor-based devices and/or hybrid-type devices, which will have a revolutionary
impact on future ICT society. Utilizing the high-quality crystal growth techniques andnanolithography techniques that we have developed, research groups in our laboratory are
exploring novel properties that can lead to nanodevices for ultimate electronics and novel
information processing devices based on new degrees of freedom such as single electrons,mechanical oscillations, quantum coherent states, electron correlation, and spins.
This year we succeeded in realizing optomechanical system using excitonic transitions
in semiconductor heterostructures and an electron beam splitter at a graphene p-n junctionin the quantum Hall regime. We also demonstrated experimentally the operation of a MoS2/
SiO2/Si tunnel diode, thermal-noise suppression by feedback control of single electrons in
Si nanotransistors, and gate-controlled semimetal-topological insulator transition in InAs/
GaSb heterostructures. We show theoretically that the spin coherence time of an NV center indiamond can be significantly improved by coupling it to a superconducting flux qubit.

20

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Optical Science Laboratory

Hideki Gotoh

Optical Science Laboratory

Nanophotonics Center

Materials Science Laboratory Physical Science Laboratory

The aims of the Optical Science Laboratory are to develop innovative core technologies for
optical communications and optical signal processing, and to make fundamental scientificprogress.
The groups in our laboratory are working to achieve quantum state control and quantum
information processing by using very weak light, to discover intriguing phenomena byusing very intense short pulse light, to control optical properties by using photonic crystals
and ultrasonic techniques, and to characterize the unique properties of semiconductor
nanostructures such as quantum dots and nanowires.
This year, one of our achievements in quantum information processing has been thedemonstration of a new scheme for manipulating the color of single phonons, which are
the main carriers of information. Moreover, we have proposed an uncrackable quantum
cryptography technique for use over double the previous distance and developed a newquantum cryptography scheme that can ensure security without us having to monitor the error
rate of a photon transmission. In the spintronics field, we have achieved spin transportation
over 100 mm in semiconductor nanostructures, which will be applied to spin functional devices
in the near future.

Masaya Notomi

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Nanophotonics Center

The Nanophotonics Center (NPC) was established in April 2012, and is now composedof several groups involved in nanophotonics research and based in NTT’s Basic ResearchLaboratories and Device Integration Laboratories. Our aim is to develop a full-fledged largescale photonic integration technology by which we will be able to densely integrate a large
number of nano-scale photonic devices with various functions in a single chip. Furthermore,
we are targeting a huge reduction in energy consumption for photonic information processing
by taking advantage of nanophotonics technology.
This year, we broke the power consumption record for photonic memories by one order ofmagnitude by using novel photonic crystal nanocavities, and demonstrated laser oscillation
with a semiconductor nanowire on a silicon photonic crystal. In addition, we demonstrated
thresholdless laser oscillation by using a special photonic crystal nanocavity, and realized
distributed feedback membrane lasers on a silicon substrate with spot-size converters.

21

Ion-Irradiation Effect in Ion-beam-assisted MBE Growth of c -BN Films
Kazuyuki Hirama, Yoshitaka Taniyasu, Hideki Yamamoto, and Kazuhide Kumakura
Materials Science Laboratory
Cubic boron nitride (c-BN) with sp3-bonding has a large bandgap energy of 6.25 eV,
which may further expand the potential of nitride-based semiconductor devices. However,conventional growth methods for group-III nitrides, such as MOVPE, have been unsuccessful
in the epitaxial growth of c-BN films because c-BN is a metastable phase in ambient
atmosphere and a thermodynamically stable sp2-bonded BN phase is easily formed. Recently,
we achieved the epitaxial growth of c-BN films by the ion-beam-assisted molecular beam
epitaxy (MBE) method, in which boron atoms are supplied by electron-beam evaporation witha simultaneous irradiation of N2+ and Ar+ [1]. Here we establish the growth phase diagram forc-BN thin-film growth and show that the flux intensity ratio of Ar+ to boron (FAr+/FB) is a key
to controlling the crystal structures of BN films.
BN films were grown on diamond(001) substrates by electron-beam evaporation of boronwith a simultaneous supply of nitrogen radical (N*) and Ar+. Instead of N2+, N* was used anitrogen source to investigate the proper ion-irradiation condition of Ar+ for c-BN growth. The
V/III ratio, defined as the flux intensity ratio of N* to boron (FN*/FB), was set at values > 1. The
growth temperature (Tg) was 920°C.
Figure 1 shows FT-IR absorption spectra of BN films with and without Ar+ irradiation.
Without Ar+ irradiation, absorption peaks attributed to BN sp2-bonding were observed ataround 780 and 1380 cm-1. On the other hand, with Ar+ irradiation (FAr+/FB>1), only an FTIR absorption peak attributed to BN sp3-bonding was observed at around 1070 cm-1. Other
peaks originating from BN sp2-bonding were not observed. From a cross-sectional TEM image
and the selective-area electron diffraction (SAED) pattern, we confirmed that the c-BN(001)film was epitaxially grown on the diamond(001) substrate from the initial growth stage (Fig. 2).
Accordingly, the Ar+ irradiation is a prerequisite for the selective formation of the sp3-bonded
c-BN.
Next, we focused on the effect of F Ar+ on the structure of BN films. We carried out
regrowth of BN films on c-BN(001) film templates on diamond substrates; FAr+ and FB weresystematically varied. Figure 3 shows the growth phase diagram plotted as functions of FAr+and FB. The c-BN(001) films are epitaxially grown at FAr+/FB larger than 1, while sp2-bonded
turbostratic BN (t-BN) films are grown at FAr+/FB smaller than 1 even on the c-BN(001)templates. Thus, FAr+/FB larger than 1 is necessary for epitaxial growth of c-BN films, inaddition to V/III larger than 1 and Tg above 750°C [1].
This work was supported by KAKENHI.
[1] K. Hirama et al., Appl. Phys. Lett. 104, 092113 (2014).

Fig. 1. FT-IR spectra of BN
films grown with and without
Ar+ irradiation.
22

Fig. 2. Cross-sectional TEM image and
SAED pattern of epitaxial c-BN(001)film.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Fig. 3. Growth phase diagram for
BN as functions of FAr+ and FB.

N-Face GaN (0001) Films with Hillock-free Smooth Surfaces
Grown by Group-III-source Flow-rate Modulation Epitaxy
Chia-Hung Lin, Tetsuya Akasaka, and Hideki Yamamoto
Materials Science Laboratory

Materials Science Laboratory

Low incorporation efficiency of nitrogen atoms has been a problem in the growth of nitride
semiconductors, such as InN and InGaN, with the conventional group-III-face (0001) surface.
Improvement of the crystal quality is expected by using N-face (0001) surface, since one can
avoid re-evaporation of nitrogen compared with the group-III-face (0001) surface. However, aserious problem in N-face (0001) nitride films has been a high density of hillocks on the film
surface. Here, we report that N-face GaN (0001) films with hillock-free smooth surfaces canbe grown by group-III-source flow-rate modulation epitaxy (FME), wherein the flow-rates ofgroup-III sources are sequentially modulated under a constant supply of NH3 [1].
In the group-III-source FME, NH3 was continuously supplied, while the group-III source(trimethylgallium or triethylgallium) was supplied at a higher (21 µmol/min) or lower(10 µmol/min) flow rate alternately. The durations of the higher and lower flow-rate periods
for one cycle were 1 and t s, respectively. The t value was varied from 0 to 10 s. Neither
deposition nor etching of GaN occurs during the period of the lower flow rate t. Totally, 900
cycles were repeated, resulting in the total film thickness of approximately 450 nm.
Figure 1 shows optical micrographs of N-face GaN (0001) films. Hillocks are observedin the samples grown by conventional continuous growth (t = 0). On the other hand, there
are no hillocks on the surface prepared by group-III-source FME (t = 10 s). Hillock-freesurfaces are achieved over almost the whole sample area (10 × 5 mm2) for t longer than 5 s.
As shown in Fig. 2, the hillock density on the surface decreases drastically with increasing t.
We have confirmed by cross-sectional transmission electron microscopy that there is a screwtype dislocation or micro-pipe at around the center of a hillock. This indicates that a hillock
develops by spiral growth originating from a screw-type dislocation or micro-pipe. The
reason for the decrease in hillock density by group-III-source FME is considered to be theenhancement of the surface migration of Ga atoms under low surface supersaturation during
the lower Ga supply period t. The spiral growth rate of GaN rapidly decreases with decreasing
surface supersaturation, while the step-flow growth rate decreases linearly. Therefore, under
low surface supersaturation, the spiral growth rate can be lower than the step-flow growth one
so that hillock formation is suppressed.
[1] C. H. Lin, T. Akasaka, and H. Yamamoto, Jpn. J. Appl. Phys. 55, 04EJ01 (2016).

Fig. 1. Optical micrographs of the surfaces of N-face GaN(0001) films grown by (a) conventional continuous growth(t = 0) and (b) group-III-source FME (t = 10 s).

Fig. 2. Hillock density on N-face GaN (0001)
film surfaces plotted as a function of t.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)23

Determination of Intrinsic Lifetime of Edge Magnetoplasmons
Ken-ichi Sasaki1, Shuichi Murakami2, and Yasuhiro Tokura3,4
1
Materials Science Laboratory, 2Tokyo Institute of Technology, 3Optical Science Laboratory,
4
University of Tsukuba
Many types of intriguing phenomena can emerge at the edge of a material that are invisibleor hiding in the interior for some reason. Edge magnetoplasmon is such an example; it is agapless collective excitation that appears at the edge of a two-dimensional electron gas (2DEG)
under the application of an external magnetic field [1]. The properties unique to the edge
magnetoplasmons, such as the localization length and dispersion relation, were calculatedby Volkov and Mikhailov [2]. They succeeded in solving an integral equation of the electric
potential using the Wiener-Hopf method. Meanwhile, an internal magnetic field, which is
coupled to the potential through Maxwell equations, is neglected, and this simplification
prevents the lifetime of the edge magnetoplasmon from being determined and also obscures themagnetic configurations of the excitations. The fact that the localization length and dispersion
relation are dependent on the lifetime makes it difficult to analyze experimental results.
In Ref. [3], we determine the intrinsic lifetime of the edge magnetoplasmon. Our analyses
are based on two observations. The first is that there is a purely relaxational state with avery long lifetime in the interior of a 2DEG. The second is that the state acquires a non-zeroreal part of the frequency through localization and starts to propagate. By showing that theproperties of the localized state are consistent with those of the edge magnetoplasmons, we
identified the purely relaxational state as the bulk counterpart of the edge magnetoplasmonsand determined the lifetime of the edge magnetoplasmons (Fig. 1). Our results show that theinternal magnetic field normal to the layer is strongly suppressed in the interior, which partly
justifies the assumption used in the past and may lead us to a more complete description of theedge magnetoplasmons.
[1] H. Yan, et al., Nano Lett. 12, 3766 (2012).
[2] V. A. Volkov and S. A. Mikhailov, Sov. Phys. JETP 67, 1639 (1988).
[3] K. Sasaki, S. Murakami, Y. Tokura, and H. Yamamoto, Phys. Rev. B 93, 125402 (2016).

Fig. 1. Our result on the lifetime of edge magnetoplasmons is applied to a
recent experiment reported in Ref. [1]. The close agreement between thecircle and open square plots supports the validity of our result.

24

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Applying Strain into Graphene - toward Strain Engineering of Graphene
Makoto Takamura1, Hiroki Hibino1,2, and Hideki Yamamoto1
1
Materials Science Laboratory, 2Kwansei Gakuin University

Materials Science Laboratory

The strain engineering of graphene is expected to make breakthroughs for graphene-based
electronics. Graphene's high Young's modulus of 1 TPa and high elastic strain limit of 15%
allow us to widely tune its electronic properties. However, applying strain under control is stillchallenging in experiments.
We thus investigated the strain in graphene induced by thermal shrinkage of SU-8 resist
to establish a method for applying a strain with high controllability [1]. The SU-8 resist
significantly shrinks ~10-20% when annealed at over 300oC, which is caused by dissociationof oxygen or hydrogen in SU-8. We studied two types of samples: grounded graphene (GG)
[Fig. 1(a)], where two resist bars were deposited on graphene that had been transferred onto thesubstrate, and suspended graphene (SG) [Fig. 2(a)], where graphene was suspended between
two bars of resist deposited on the substrate. In both samples, tensile strain is induced ingraphene by shrinking the resist, where the resist pulls the graphene.
We first show results for GG samples. When we annealed a GG sample, the gap between
the bars expanded [Fig. 1(b), (c)] and 2D peak position shifted to lower frequencies[Fig. 1(d)]. These results indicate that the tensile strain was applied into graphene by shrinking
the SU-8. From the 2D peak position maps [Fig. 1(c)], we also found that the applicable areaof the shrinkage-induced strain is limited to near the resist (1-2 µm from it), which suggeststhat designing the resist deposition will allow us to locally control the strain in GG samples.
Meanwhile, for SG samples, a larger tensile strain is induced. After annealing an SG sample,
the 2D peak largely shifted to lower frequencies [Fig. 2(b)] and the amount of strain was
three times larger than that for GG samples. We can conclude that a larger strain was induced
because of the lack of adhesion between the graphene and substrate. We found that theconfiguration of SG will take full advantage of the large shrinkage of SU-8 for inducing a large
strain, while GG allow us to induce a local strain. Our findings provide an avenue to the spatial
control of graphene's mechanical, and consequently its electronic properties.
[1] M. Takamura et al., Proc. 15th IEEE Int. Conf. on Nanotechnology, Rome, Italy, 33 (2015).

(Left) Fig. 1. (a) A schematic of GG sample. Optical microscopy images and the corresponding Raman 2D peak
position maps (b) before and (c) after annealing at 300oC. (d) Raman spectra before and after annealing.
(Right) Fig. 2. (a) A schematic of SG sample. (b) Raman spectra before and after annealing.
Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)25

Er-Sc Silicate as an Optical Gain Material in Telecommunications Band
Adel Najar1, Hiroo Omi1,3, and Takehiko Tawara2,3
1
Materials Science Laboratory, 2Optical Science Laboratory, 3NTT Nanophotonics Center
Photonic interconnects requires the development of new efficient and reliable on-chip
optical device elements, including light sources, modulators, amplifiers, buffers, switches,and detectors. The realization of a silicon-based light source is considered to be one of themost challenging tasks. One of the possible solutions for the realization of silicon based
light source is to use the emission from Er-silicates. Er silicates (Er2SiO5 and Er2Si2O7) havebeen attracting considerable attention as Er based materials for small size and high optical
gain light source in silicon photonics integration, because they contain a higher Er density of1022 cm−3 than Er doped Si-based materials. However, such a high concentration of Er results in
up-conversion due to closely neighboring Er ions which limits the Er luminescence. Therefore,
it is necessary to characterize and control the distance between Er ions in such Er silicates. An
effective strategy for reducing this up-conversion is to incorporate yttrium (Y) cations into thestructure, where they substitute Er ions in the silicate lattice and prevent neighboring Er ionsfrom causing up-conversion due to the similar ionic radius between Y and Er. Scandium ions
(Sc3+), on the other hand, are small (ionic radius = 0.75 Å) than erbium (Er3+) (ionic radius =0.881 Å). Generally, this can result in enhancing the crystal field strength for Er doped silicatesand oxides. In fact, Sc3+ ions in Er doped Sc silicate single crystals would increase the Starksplitting of the thermally populated erbium ground state as well as that of other electronicenergy levels of the silicates and thereby reduce re-absorption losses. In this work, we
successfully synthesized a polycrystalline Er-Sc silicate and discilicate compounds in which
Er and Sc are homogeneously distributed using RF-sputtering with multilayer Er2O3, Sc2O3,
and SiO2 deposited on SiO2/Si (100) substrate and thermal annealing at high temperature[Fig. 1(Left)]. Photoluminescence (PL) measurements show the presence of Er xSc2-xSiO5
with an emission peak at 1528 nm for annealing from 900 to 1100oC, and ErxSc2-xSi2O7 with
an emission peak at 1537 nm for higher annealing temperature. The PL intensity of the
ErxSc2-xSi2O7 phase is five times stronger than that of the ErxSc2-xSiO5 phase at 1250oC. From
PL excitation and PL spectra of ErxSc2-xSi2O7 thin film [Fig. 1(Middle), (Right)], we determinedthe energy levels of Er3+ ions in the silicates. Temperature-dependent PL of the ErxSc2-xSi2O7
phase exhibits a variation of the full-width at half-maximum (FWHM) from 1.1 to 2.3 nm. The
narrow FWHM is due to the small ionic radii of Sc3+, which enhance the crystal field strength
affecting the optical properties of Er3+ ions located at the well-defined lattice sites of Sc silicate.
[1] A. Najar, H. Omi, and T. Tawara, Opt. Express 23, 7021 (2015).

Fig. 1. (Left) Fabricated structures, (Middle) PLE color plot measured at 4 K obtained from the sample
annealed at 1250oC. (Right) PLE and PL spectra at 4K.

26

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

As-grown Superconducting Pr2CuO4 Thin Films
Yoshiharu Krockenberger1, Masafumi Horio1,2, Ai Ikeda1, Hiroshi Irie3,
Atsushi Fujimori2, and Hideki Yamamoto1
1
Materials Science Laboratory, 2The University of Tokyo, 3Physical Science Laboratory

Materials Science Laboratory

The synthesis of electron doped cuprate superconductors, i.e. cuprates with square-planar
coordinated copper, is entangled to a delicate problem arising from imperfection on the oxygen
sub-lattice of the crystal. In particular, superconductivity in electron doped cuprates is known
to appear only after an elaborate annealing process. While we have shown earlier that a proper
tuning of the annealing process allows the induction of superconductivity even in the undoped
cuprate [1], the thought of circumventing the annealing procedure by optimizing the growth
conditions is tempting. Using molecular beam epitaxy, we have grown Pr2CuO4 (PCO) thinfilms coherently onto (110) GdScO3 substrates (Fig. 1) as a negligible lattice mismatch is to be
expected. For coherently grown PCO thin films one may raise the synthesis temperature wellbeyond the point usually considered to result in disorder of the material. More importantly,
it is now possible to further ease the oxidation power during the growth. We systematicallyvaried the growth temperature, the oxidizing potential, and the substrate material in order toelucidate the very best combination possible. The results are circled in Fig. 1. Ultimately, PCO
thin films grown at such conditions are superconducting and this is shown in Fig. 2 where weplot the temperature dependency of the resistivity of a PCO thin film coherently grown onto(110) GdScO3. At high temperatures, the PCO is metallic as the resistivity value monotonicallydecreases and superconductivity sets in at 27 K. In Fig. 2, we also show the resistivity responsewhen a magnetic field is applied perpendicular to the CuO2 planes of PCO [2].
In summary, we have shown that superconducting PCO thin films can be synthesized in situ
and such a method is important if one needs to avoid surface contaminations as is the case forangle resolved photoemission spectroscopy.
[1] Y. Krockenberger et al. , Sci. Rep. 3, 2235 (2013).
[2] Y. Krockenberger, M. Horio, H. Irie, A. Fujimori, and H. Yamamoto, Appl. Phys. Express 8, 053101 (2015).

Fig. 1. Synthesis conditions for coherently grown PCO thinfilms.

Fig. 2. Resistivity vs temperature ofa coherently grown PCO thin film
without annealing.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)27

On-chip FRET Graphene Oxide Aptasensor: Enhanced Sensitivity by
Using Aptamer with Double-stranded DNA Spacer
Yuko Ueno and Kazuaki Furukawa
Materials Science Laboratory
Graphene and graphene oxide (GO) behave as efficient acceptors for energy transfer between
a graphene/GO surface and molecules located close to it. By combining the energy transfer
reaction with a biomolecule reaction, we can visualize an invisible biological response to ameasurable physical quantity such as fluorescence.
We have successfully demonstrated a unique type of fluorescence biosensor, namely agraphene/GO aptasensor, for selective and highly sensitive protein detection. We realized
this sensor by modifying the graphene/GO surface with a pyrene-aptamer-dye probe that wedeveloped (biomolecular interface). These three components of the probe work as a linker tothe GO surface, a protein recognition part, and a fluorescence detection tag, respectively [1].
The system allows us to perform molecular detection on a solid surface, which is a powerfultool for realizing an on-chip sensor, and especially for forming a multichannel configurationand for micropatterning probes [2]. The on-chip sensor allows us to evaluate the sensor
response quantitatively by using one of the channels/patterns as an internal standard.
The most attractive feature of aptamers is that they can be flexibly designed without loss ofactivity. We designed biomolecular probes for highly sensitive protein detection by modifying
an aptamer with (i) a single-stranded DNA spacer between the aptamer sequence and the dye[3] and (ii) a double-stranded DNA spacer between the aptamer sequence and the graphene/
GO [Fig. 1(Left)] [4]. The spacer controls the distance between the dye and the graphene/
GO, which is crucial for the energy transfer reaction (FRET, fluorescence resonance energy
transfer). We improved the sensitivity of an on-chip GO aptasensor by using a longer spacer
for probes (i) and (ii) [Fig. 1(Right)]. By using the best probe design, we achieved a detection
limit of ~1 nM for thrombin, which is in the in vivo concentration range during blood clotting[3].
[1] K. Furukawa et al., J. Mater. Chem. B, 1, 1119 (2013).
[2] Y. Ueno et al., Anal. Chim. Acta, 866, 1 (2015): Featured on cover.
[3] Y. Ueno et al., Chem. Commun., 49, 10346 (2013): Featured on cover.
[4] Y. Ueno et al., Anal. Sci., 31, 875 (2015): Hot Article Award.
(a)

(b)

Fig. 1. (a) Molecular design of the probe (ii) for enhancing sensitivity of the aptasensor.
(b) Quantitative comparison of enhancement effect depending of the spacer length.

28

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Time-lapse Imaging of a Single Neuron During the Early Stages of
Apoptosis Using Scanning Ion Conductance Microscopy
Aya Tanaka, Koji Sumitomo, and Hiroshi Nakashima
Materials Science Laboratory

Materials Science Laboratory

It is known that neural morphologies change dynamically during neural network formation.
Since the morphological changes are strongly associated with neural functions, it is important
to obtain the morphological details of individual neurons. Here, we use scanning ion
conductance microscopy (SICM) to describe the series of neural morphological changes that
occurs during the early stages of apoptosis, which is well defined as programmed cell deathand one of key events in neural network formation [1].
Neurons were prepared from the cortex of a Wistar Rat (18-day embryo) and cultivated on a
glass substrate for 8 to 10 days in vitro. Apoptosis was induced by adding staurosporine (STS),
whose function is to activate caspase-3, to the culture solution during the SICM observation.
Images of apoptotic neurons were obtained every 20 min.
The SICM images show the formation of a spherical shape on the cell surface after theneurons had been exposed to STS for 180 min [Fig. 1(a), white arrows]. This morphologicalchange is similar to blebbing, which is the formation of a bulge in a plasma membrane,
caused by decoupling from an underlying cytoskeleton. We performed time-course imaging
experiments for five different neurons and thus estimated their volume change over time asa ratio of volume to initial volume, v/v0 [Fig. 1(b)]. The graph shows that the neural volume
decreases from 80 to 120 min after exposure to STS, which is known as an apoptotic volume
decrease. These results indicate that apoptosis induces a reduction in cellular volume andsubsequent membrane blebbing.
This is the first report to use SICM to describe the series of morphological changes ranging
from an apoptotic volume decrease to membrane blebbing that occurs during the early stagesof apoptosis. In future work, we expect to reveal the relationship between the apoptotic
morphological changes and biological events using the simultaneous observation ofmorphology and conventional live cell imaging equipment such as a fluorescence microscope.
[1] A. Tanaka, R. Tanaka, N. Kasai, S. Tsukada, T. Okajima, and K. Sumitomo, J. Struct. Biol. 191, 32 (2015).

Fig. 1. Morphological changes in apoptotic neurons induced by STS. (a) Time-lapse SICM images of apoptotic
neurons induced by STS. White arrows indicate membrane blebs. (b) Time-course graph of volume change of 5neurons. The vertical axis is the ratio of volume to the initial volume. v is the neuron volume at each time point,
and v0 is the volume at 0 min.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)29

Si and Au Nanopillar Arrays as Scaffolds for Neuronal Growth
Nahoko Kasai and Koji Sumitomo
Materials Science Laboratory
Neuronal in vitro cultivation has been widely used with the aim of elucidating neuronalsignaling mechanisms and for applications in the neuro-engineering field. Our group has
cultivated neurons on various substrates to create interfacial devices for neuronal guidance andthus realize artificial synapses. Neuronal guidance using nano-scale structures has also attracted
attention thanks to recent advancements in nanotechnology. In this study, we examinedneuronal guidance using nanopillar arrays made of amorphous silicon (a-Si) and gold (Au) as
scaffolds for neuronal growth [1].
Nanopillars 100 and 500 nm in diameter were fabricated on quartz substrates using electronbeam lithography, and rat cortical neurons were cultivated on them for 7 days. The samples
were then fixed and observed by using scanning electron microscopy and confocal laser
scanning microscopy after the treatment.
Neurons cause neurites to lengthen on an a-Si pillar as shown in Fig. 1. The neurites behaved
differently in terms of width; they were wider on 500-nm-diameter pillars than on 100-nmdiameter pillars. This implies that the adhesion of neurites to pillars promotes skeletal protein
expression, and thus neurite width is dependent on adhesion area size.
Then we examined neurons on different pillar materials as shown in Fig. 2. Neurons grew
randomly on Au pillars while they became longer along with the patterns on a-Si pillars[Fig. 2(A)]. A quantitative analysis demonstrated that there was a higher ratio of neurite
tips on the a-Si pillars than on the Au pillars [Fig. 2(B)]. This low affinity of neurons for
Au corresponds to neuronal cross-sections results obtained using FIB/SEM, which showed
less attachment of soma to the Au substrate [2]. These results demonstrate the possibility ofneuronal guidance using nanopillars made of appropriate materials.
This work was supported by JSPS/MEXT KAKENHI Grant Number 15H03541.
[1] N. Kasai, R. Lu, R. Filip, T. Goto, A. Tanaka, and K. Sumitomo, Electrochemistry. 84, 296-298 (2016).
[2] T. Goto, N. Kasai, R. Lu, R. Filip, and K. Sumitomo, J. Nanosci. Nanotechnol. 16, 3383 (2016).

Fig. 1. Neurites grown on different
patterned a-Si pillars. Scale: 2 μm.

30Fig. 2. Neurons grown on a-Si or Au pillar substrate (A)and neurite tip position on different pillar materials (B).
Scale: 50 μm.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Observing Semiconducting Band-gap Alignment in MoS2 Layers
Using a MoS2/SiO2/Si Heterojunction Tunnel Diode
Katsuhiko Nishiguchi1, Andres Castellanos-Gomez2, Hiroshi Yamaguchi1, Akira Fujiwara1,
Herre van der Zant2, and Gary Steele2
1
Physical Science Laboratory, 2Delft University of Technology

Physical Science Laboratory

The performance of Si transistors, the main fundamental devices in logic circuits, increases
with miniaturization. When their size reaches from a few to ten nanometers, they gain new
functionalities, such as single-electron manipulation [1], high-sensitivity charge detection [2],and photo emission [3]. However, even as miniaturization proceeds, it is essentially impossible
to change the fundamental characteristics of Si material. On the other hand, graphene andother two-dimensional layered materials have been actively studied due to their remarkablecharacteristics, such as high carrier mobility and transparency. However, such materials still
face technological difficulties for their applications. Therefore, we have been studying new
devices that integrate Si and two-dimensional layered material in order to combine theirremarkable characteristics. In this work, we demonstrate a tunnel diode composed of Si and
MoS2 [4].
The tunnel diode is based on a Si transistor, except that its gate terminal is replaced withmultiple-layer MoS2 film as shown in Fig. 1. This MoS2 film is formed on the Si channel
by means of an exfoliation method using a bulk MoS2. The Si channel and MoS2 film havep-type and n-type transistor characteristics, respectively. Since there is a gate oxide SiO2
between the Si channel and MoS2 film, a p/insulator/n heterostructure is constructed (Fig. 2).
Since the SiO2 is thin (6 nm), tunnel current flows between the Si and MoS2 when voltage isapplied between them as shown in Figs. 2 and 3. Multiple current peaks indicating negative
differential resistance (NDR) are clearly observed at room temperature. The mechanism of
NDR is the same as that in a tunnel or Esaki diode composed of heavily doped p-n junctions,though current tunnels through the SiO2 layer in our device. The appearance of the four NDR
peaks originates from the fact that the MoS2 film has four areas of different thickness andthat the bandgap of layered MoS2 varies with its thickness. From voltages giving NDR peaks,
we can evaluate the energy-band alignment of the heterostructure in our device. Using theheterostructure even for other two-dimensional layered materials, we can obtain information
about their energy-band structure in a simple system under various conditions, e.g., lowtemperature and magnetic field. The heterostructure is also promising for new functional
devices.
[1] K. Nishiguchi et al., Appl. Phys. Lett. 88, 183101 (2006).
[2] K. Nishiguchi et al., Jpn. J. Appl. Phys. 47, 8305 (2008).
[3] J. Noborisaka, K. Nishiguchi, and A. Fujiwara, Sci. Rep. 4, 6940 (2014).
[4] K. Nishiguchi et al., Appl. Phys. Lett. 107, 053101 (2015).

Fig. 1. Photograph of thefabricated device.

Fig. 2. Schematic view ofthe device.

Fig. 3. Current characteristics.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)31

High-speed Single-hole Transfer in a Si Tunable-barrier Pump
Gento Yamahata, Takeshi Karasawa, and Akira Fujiwara
Physical Science Laboratory
A single-electron (SE) pump can transfer SEs in synchronization with a clock signal. It is
expected to be used for low-power-consumption devices, current standards, and single-photon
sources. In particular, high-accuracy and high-speed operation is necessary for the current
standard, but there is so far no device that has a performance suitable for practical use (gigahertz
operation with an error rate of less than 10-8). A tunable-barrier pump is a promising device,with which we can achieve gigahertz SE pumping [1]. One factor determining its accuracy
is the effective mass of charge carriers. We expect an accuracy improvement by using a hole(electric charge e), which has a heavy effective mass. However, there is no report on highspeed single-hole (SH) transfer. Here, we report the achievement of high-speed SH transfer
using a Si tunable-barrier pump [2].
Figure 1(a) shows a schematic of the device. It has a double-layer gate structure on a Si wire.
S and D are heavily doped to form p-type leads. We apply negative voltage VUG to the uppergate (UG) to generate holes in the Si wire and apply positive voltages to the two lower gates (G1,
G2) to form hole potential barriers. As a result, there is an SH island in the Si wire between G1and G2. In addition, we apply a high-frequency signal with frequency f to G1 to transfer SHs
from S to D [Fig. 1(b)]. When the barrier under G1 is low, holes are loaded to the island. Since
the island potential rises when the barrier is raised because of a capacitive coupling, the loaded
holes escape to S. However, when the rise rate of the barrier is much larger than the escaperate, holes are captured by the island at a non-equilibrium state. The captured holes are ejected
to D. Since our device has a very small island, SH addition energy Eadd is much larger than theenergy of thermal fluctuations. In this case, a rate of SH escape from the island with two holes
can be much larger than that from the island with one hole, leading to capture of an SH in theisland. When the number of transferred holes is n, the current is nef. The n can be tuned bychanging the island potential by applying VUG.
Figure 1(c) shows a measurement result for the current at 1 GHz (red circles). We observea current plateau with decreasing VUG. A fit using a theoretical model of the non-equilibriumhole capture agrees well with the data (blue curve), indicating non-equilibrium hole transfer.
From the fit, the transfer error rate is estimated to be about 10-3 at 17 K. A theory predicts thata transfer accuracy of 10-8 can be achieved at 9 K. These results pave the way for accurate
manipulation of SHs and its application to metrological standards.
[1] A. Fujiwara, K. Nishiguchi, and Y. Ono, Appl. Phys. Lett. 92, 042102 (2008).
[2] G. Yamahata, T. Karasawa, and A. Fujiwara, Appl. Phys. Lett. 106, 023112 (2015).

Fig. 1. (a) Schematic of the device. (b) Hole potential diagram and SH transfer mechanism. (c) Measurement
data for the high-speed SH transfer and a fit.
32

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Thermal-noise Suppression in Nano-scale Si Field-effect Transistors
by Feedback Control of Single Electrons
Kensaku Chida, Katsuhiko Nishiguchi, Gento Yamahata,
Hirotaka Tanaka, and Akira Fujiwara
Physical Science Laboratory

Physical Science Laboratory

Feedback control is a way to put target objects in desired conditions by controlling outputs
based on measurement outcomes. For example, an air conditioner keeps a room temperature
at a pleasant temperature by changing its output power based on the outcome of temperature
measurements. The function cannot be achieved without proper measurement of the target
object, the room temperature.
In this study, we performed feedback control on single electrons (SEs) using nano-scale
Si field-effect transistors, which can detect SEs. Our device has an SE-resolution charge
detector, an SE box, and an electron reservoir (Fig. 1). We can monitor the number n of SEs in
the SE box by measuring current Id through the charge detector. Id fluctuates among discretevalues with 5-nA intervals [Fig. 2(a)]. This fluctuation corresponds to the fluctuation of ncaused by thermal motion of SEs between the SE box and electron reservoir [1]. Based on themeasurement outcome of n, we changed the voltage Vres applied to the electron reservoir to fix
n as a value (here, we define the value as n = 0): we changed Vres to -310 mV when n > 0, -470
mV when n < 0, and -390 mV when n = 0. The feedback control modifies the rate at which an
SE enters to the SE box: when n > 0 (n < 0), the rate is decreased (increased) to reduce (increase)possibility of an increase in n. As a result, we achieved about a 60% reduction in the thermal
fluctuation of n; variance σ of n is reduced from 1.5 to 0.5 [Fig. 2(b)] [2]. Feedback control
of SEs can be used to correct errors at the SE level for achieving current standards with SE
pumps, and to realize Maxwell’s demon in electrical devices [3].
This work was partially supported by the Funding Program for Next Generation WorldLeading Researchers of JSPS.
[1] K. Nishiguchi, Y. Ono, and A. Fujiwara, Nanotechnology 25, 275201 (2014).
[2] K. Chida et al., Appl. Phys. Lett. 107, 073110 (2015).
[3] J. V. Koski et al., Proc. Natl. Acad. Sci. U.S.A. 38, 13786 (2014); Phys. Rev. Lett. 115, 260602 (2015).

Fig. 1. Schematics of feedback control of SEs.
Number n of SEs in the SE box is monitored withcurrent Id through the detector (red line). Voltage Vres
applied to the electron reservoir was modulated basedon the n measurement outcome (blue line).

Fig. 2. Thermal-noise suppression with feedback control.
(a) Thermal fluctuation of n monitored with Id without
feedback control. (b) Suppressed thermal fluctuation
with feedback control. Vres (blue line) was modulated
based on Id (red line).

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)33

Optomechanics Using Excitonic Transitions in
Semiconductor Heterostructures
Hajime Okamoto1, Takayuki Watanabe1,2, Ryuichi Ohta1, Koji Onomitsu3,
Hideki Gotoh4, Tetsuomi Sogawa4, and Hiroshi Yamaguchi1,21Physical Science Laboratory, 2Tohoku University, 3Materials Science Laboratory,
4
Optical Science Laboratory
Optical control of micromechanical resonators has been widely demonstrated via cavityenhanced radiation pressure or photothermal backaction [1]. Such cavity optomechanics
allow highly tunable manipulation of a single mechanical resonator, including vibration
amplification and damping (i.e., mode cooling). However, it cannot be straightforwardly
extended to integrated mechanical systems because it needs delicate cavity operation, including
tapered-fiber access and coupling adjustment. Thus, an alternative cavity-free approach ishighly demanded in order to practically apply the optical control capability to integrated
micromechanical systems. Here, we present excitonic optomechanics implemented in acompound semiconductor microcantilever. By using opto-piezoelectric stress induced via
excitonic transitions, cavity-free control of a micromechanical resonator is achieved [2].
We used the AlGaAs/GaAs heterostructured cantilever shown in Fig. 1(a). In this system,
the optically excited electrons and holes are separated via the built-in electric field [Fig. 1(b)].
This causes piezoelectric (compressive) stress along the longitudinal direction in the GaAs
layer, which leads to downward bending of the cantilever [Fig. 1(a)]. This effect depends on
the optical absorption and on strain via the deformation potential. Therefore, strain-dependent
opto-piezoelectric stress appears around the exciton resonance, where the per-strain change inthe optical absorption is maximized. Since this stress acts on the cantilever in a time delay withrespect to the optical excitation, it causes a self-feedback effect on the mechanical vibration,
where the sign and gain of the self-feedback depend on the slope of the absorption spectrum[Fig. 1(c)]. We achieved both vibration amplification and mode cooling (damping) by detuning
the photon energy from the exciton resonance [Fig. 1(d), (e)].
[1] M. Aspelmeyer, T. J. Kippenberg, and F. Marquardt, Rev. Mod. Phys. 86, 1391 (2014).
[2] H. Okamoto et al., Nature Commun. 6, 8478 (2015).

Fig. 1. (a) Schematic drawing of the cantilever and opto-piezoelectric effect. (b) Calculated energy-band diagram,in which the separation of photoexcited electrons and holes is schematically drawn. (c) Photoluminescence
excitation (PLE) spectrum in the vicinity of the exciton resonance. (d) Photon-energy dependence of modetemperature (Teff) normalized by the sample temperature T = 9.2 K for the laser power of 1.19 μW. The broken line
is a theoretical fit, which depends on the slope of the PLE spectrum. (e) Laser-power dependence of the thermal
displacement noise power spectrum at 1.516 eV.
34

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Optical Control of Mechanical Mode Coupling at Room Temperature
Ryuichi Ohta1, Hajime Okamoto1, Rudolf Hey2,
Klaus-Juergen Friedland2, and Hiroshi Yamaguchi1
1
Physical Science Laboratory, 2Paul-Drude-Institut für Festkörperelektronik

Physical Science Laboratory

The ability to manipulate mechanical vibrations and their transportation in multiple
mechanical modes are of great interest for practical applications of mechanical systems, suchas to mechanical logic circuits and acoustic metamaterials. For this purpose, tunable intermodal
coupling, which is induced by the modulation of tension at the modes’ frequency difference, ishighly desired at room temperature. If the coupling rates of different mechanical modes exceed
the damping rate of each mode, called the strong coupling regime, we can quickly transfer
the vibrations from one mode to another and thereby achieve fast switching of mechanicalresonators [1]. Such a demonstration has so far been reported in GaAs mechanical resonators
at cryogenic temperatures using piezoelectric stress modulation. However, it is difficult toextend it to room temperature, because the coupling rate achieved by the piezoelectric effectis too small to overcome the mechanical damping rate at room temperature. In this work, wedemonstrate strong and tunable coupling of two mechanical modes at room temperature byusing laser-induced photothermal stress modulation [2].
Figure 1(a) shows a microscope image of two mechanical resonators connected to eachother. Figure 1(b) shows symmetric and anti-symmetric modes calculated by the finite
element method. These resonators were fabricated on a GaAs wafer containing AlAs/GaAs
superlattices. Applying a laser whose wavelength is 780 nm causes photothermal expansion
in the GaAs layer, which provides the internal stress in a mechanical resonator. The internal
stress generates the coupling of the symmetric and anti-symmetric modes, when the laser ismodulated to the difference frequency of the two modes. Figure 1(c) shows the mechanicalspectrum of the anti-symmetric mode at various frequencies of the amplitude-modulated
laser, and Fig. 1(d) shows the modulation-amplitude dependence of the spectrum. When themodulation frequency is close to the differential frequencies of the two modes, we can clearlyobserve the mode splitting, where the amount of the split corresponds to the coupling rate. As
shown in Fig. 1(d), the coupling rate can be controlled by changing the modulation amplitude.
The maximum coupling rate is 2.57 kHz. It exceeds the damping rates of both modes at room
temperature (2.14 and 1.59 kHz), which indicates that the strong coupling of two mechanicalmodes is achieved at room temperature.
This work was supported by KAKENHI.
[1] H. Okamoto et al., Appl. Phys. Lett. 105, 083114 (2014).
[2] R. Ohta et al., Appl. Phys. Lett. 107, 091906 (2015).

Fig. 1. (a) Microscope image of two mechanical resonators. (b) Schematic image of the symmetric and antisymmetric modes calculated by the finite element method. (c) Modulation-frequency dependence and (d)modulation-amplitude dependence of anti-symmetric mode. Blue dotted lines show calculated peak frequencies.
Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)35

Improving the Coherence Time of a Quantum System
by Coupling it to a Short-lived System
Yuichiro Matsuzaki1, Xiaobo Zhu1,*, Kosuke Kakuyanagi1, Hiraku Toida1,
Takaaki Shimo-Oka2, Norikazu Mizuochi2, Kae Nemoto3,
Kouichi Semba4, William J. Munro5, Hiroshi Yamaguchi1, and Shiro Saito1
1
Physical Science Laboratory, 2Osaka University,
3
NII, 4NICT, 5 Optical Science Laboratory
A single nitrogen-vacancy (NV) center is a promising candidate to realize quantum
information processing [1]. However, it is known that low frequency magnetic field noise
decreases the coherence time of the NV center [2].
We theoretically show that coupling an NV center with a short-lived superconducting flux
qubit (FQ) improves the coherence time of that NV center [3]. The NV center has two excitedstates. One of them is called a bright state coupled with the FQ while the other one is called adark state decoupled from the FQ. Since these two excited states are degenerate without theFQ, low frequency magnetic field noise can cause stochastic transitions between them, and thisdecreases the coherence time of the NV center. However, if the NV center is coupled with theFQ, these two excited states are energetically separated due to the coupling. There is an energy
gap between the bright state and dark state, and so the transition between them by the low
frequency magnetic field noise is suppressed. This improves the coherence time of the darkstate. From numerical simulations, we have confirmed that a flux qubit with a coherence timeof 10 µs can improve the coherence time of the NV center from 100 µs to nearly 1 ms via thecoupling (Fig. 1). Our proposal opens a new way to use a quantum hybrid system for therealization of robust quantum information processing.
Present address: *Chinese Academy of Sciences[1] C. Degen, Nature Nanotech. 3, 643 (2008).
[2] D. Lange et al., Science 330, 6000 (2010).
[3] Y. Matsuzaki et al., Phys. Rev. Lett. 114, 120501 (2015).

Fig. 1. Numerical simulation of the decoherence behavior of the NV center with and without coupling to the FQ.
Here, the horizontal axis denotes the time and the vertical axis denotes the coherence of the NV center.
36

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Observation of Quantum Zeno Effect in Superconducting Flux Qubit
Kosuke Kakuyanagi1, Tatsuya Baba1,2, Yuichiro Matsuzaki1, Hayato Nakano1,
Shiro Saito1, and Kouichi Semba1,3
1
Physical Science Laboratory, 2Tokyo University of Science, 3NICT

Physical Science Laboratory

It is known that an ideal quantum measurement stochastically projects a quantum state into
an energy eigenstate. As the distance between the target state and eigenstate becomes smaller,
the probability of projecting it into the eigenstate increases. If the quantum state is modified
even slightly from the initial eigenstate due to a time evolution, the probability of projecting
it into the eigenstate approaches unity. This means that frequent quantum measurements canfreeze a specific time evolution of a quantum system where the holding time of the state
depends on the measurement period. This phenomenon is both academically interesting
and useful for many applications such as the estimation of quantum measurements and therealization of a decoherence free subspace.
A superconducting flux qubit is composed of a superconducting loop circuit with Josephson
junctions. By applying a characteristic bias field, we can manipulate this circuit as a quantum
two-level system with an energy of several GHz. We implement Rabi oscillations by applying
a resonant microwave to the superconducting qubit, and attempt to freeze the Rabi oscillations
by applying periodic measurement pulses. To induce the projection, we use a Josephson
bifurcation readout, which is a quantum non-demolition measurement.
Fig. 1 (a) shows the probability of detecting excited flux qubit in the time domain with aresonant microwave pulse. Without projections, we can clearly observe Rabi oscillations
between the excited and ground states. On the other hand, with the projections, the Rabi
oscillation is suppressed, and the qubit remains in the excited state. Fig. 1 (b) shows theprobability of detecting excited flux qubit when we change the measurement period. As themeasurement period decreases, the holding time increases. These results are well explainedby a model of the quantum Zeno effect. This is the first demonstration to observe the quantum
Zeno effect on a superconducting qubit by using periodic quantum measurements [1].
[1] K. Kakuyanagi et al., New J. Phys. 17, 063035 (2015).

Fig. 1. (a) Time evolution of qubit with and without measurement pulse. (b) Holding time of quantum state withdifferent measurement periods.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)37

Electron Paramagnetic Resonance Using a SQUID Magnetometer
Directly Coupled to an Electron Spin Ensemble
Hiraku Toida1, Yuichiro Matsuzaki1, Kosuke Kakuyanagi1, Xiaobo Zhu1,*,
William J. Munro2, Kae Nemoto3, Hiroshi Yamaguchi1, and Shiro Saito1
1
Physical Science Laboratory, 2Optical Science Laboratory, 3NII
Magnetic resonance is a widely-used tool from analyzing material properties to medical
applications, for instance with electron paramagnetic resonance (EPR) or nuclear magnetic
resonance. However, conventional EPR spectrometers require a large number of spins (~1013)
for the detection and do not have high spatial resolution (~0.1 mm). To expand the field of
applications including quantum information processing, highly sensitive EPR spectrometers
are necessary.
Here, we demonstrate the detection of electron spin polarization and EPR spectroscopyusing a SQUID magnetometer directly coupled to an electron spin ensemble [1]. Our experimental
setup is shown in Figs. 1(a) and (b) where the magnetization from the sample is detected bymeasuring the critical current of the SQUID. To begin, we measure the electron spinpolarization as a function of the in-plane magnetic field and temperature. By increasing the inplane magnetic field, we observe an increase of electron spin polarization ratio due to the
reduction of the thermal fluctuations [Fig. 1(c)]. Figure 1 (d) shows the EPR spectrum of a typeIb diamond crystal containing nitrogen impurities. We confirm a linear increase of resonancefrequency. Furthermore, ~93 MHz shifted peaks are observed due to hyperfine splitting of 14N.
The minimum detectable number of spins for our method is ~106. This number is muchsmaller than the conventional EPR spectrometer and can be improved for three orders ofmagnitude by replacing the SQUID with a superconducting flux qubit. Further we estimate
the sensing volume at ~10-10 cm3 [~0.1 pL]. This is two order of magnitude smaller than thereported value in the literature [2].
This work was supported by the Commissioned Research of NICT, in part by an MEXT
Grant-in-Aid for Scientific Research on Innovative Areas, and in part by KAKENHI grant.
Present address: *Chinese Academy of Sciences[1] H. Toida et al., Appl. Phys. Lett. 108, 052601 (2016).
[2] A. Bienfait et al., Nature Nanotech. 11, 253–257 (2016).

Fig. 1. (a) Optical microscope image of the sample. (b) Cross sectional view of the experimental setup. (c)Magnetization as a function of the in-plane magnetic field and the temperature. (d) Results of EPR spectroscopy.
38

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Shot Noise Generated by Graphene p -n Junctions in the Quantum Hall
Effect Regime
Norio Kumada1, Francois D. Parmentier3, Hiroki Hibino2,
D. Christian Glattli3, and Preden Roulleau3
1
Physical Science Laboratory, 2Materials Science Laboratory, 3CEA Saclay

Physical Science Laboratory

In graphene, owing to the linear and gapless band structure, a unique p-n junction, where
n-type and p-type regions adjoin each other without a gap in between, is formed. In thequantum Hall effect regime under high magnetic field, counter-circulating electron and holeedge modes mix in the p-n junction [Fig. 1(a)]. In this work, we investigate the mode mixing
process by shot noise measurements and suggest that the p-n junction can serve as an electronic
beam splitter [1].
We used graphene grown on SiC. A p-n junction is formed by applying a gate bias to the
top gate covering half of the graphene. The current injected to the p-n junction is distributed
to electron and hole modes by the mode mixing and then partitioned at the exit of the p-njunction. We measured the shot noise generated by this mode mixing and the subsequent
partitioning process. We demonstrate the crucial role of the p-n junction length on the mode
mixing process [Fig. 1(b)]. For longer p-n junctions, the shot noise is reduced by the energy
relaxation. On the other hand, for p-n junctions with the length shorter than the relaxation
length (15 µm), the energy loss to the environment is negligible and the noise is consistent
with a quasielastic mode mixing. This suggests that a graphene p-n junction can serve as anelectronic beam splitter. Since the beam splitter is an important element of quantum optics, ourresults encourage using graphene for such applications.
[1] N. Kumada, F. D. Parmentier, H. Hibino, D. C. Glattli, and P. Roulleau, Nature Commun. 6, 8068 (2015).

Fig. 1. (a) Counter-circulating electron and hole edge modes in a bipolar graphene quantum Hall effect regime.
(b) Shot noise as a function of the source-drain bias for the samples with different p-n junction length.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)39

Gate-controlled Semimetal - Topological Insulator Transition in an
InAs/GaSb Heterostructure
Kyoichi Suzuki1, Koji Onomitsu2, Yuichi Harada3, and Koji Muraki1,
Physical Science Laboratory, 2Materials Science Laboratory, 3Kyushu University

1

Topological insulators (TIs) are new states of matter that cannot be classified into any existing
categories of materials. The insulating state in TIs cannot continue to the normal insulating stateoutside, and it is therefore necessary to break the insulating states. As a result, a conductive
channel arises at the boundary of a TI. Electron scattering in this topologically protected
conductive channel is restricted. Particularly, for two-dimensional (2D) TIs, dissipationlesstransport is expected. Therefore, TIs are promising for low power consumption electric devices.
Thus far we have succeeded in artificially realizing a 2D TI arising from the heterojunction
between InAs and GaSb, which both are commonly used in III-V semiconductors [1]. Recently,
we have further achieved in-situ semimetal-TI transition by applying a gate voltage between
the gates on both the substrate and surface sides of an InAs/GaSb heterostructure [2]. This adds
new functionality to TIs, which would enhance their device application.
Figure 1 shows the energy band profile of the InAs/GaSb heterostructure with front (surfaceside) and back (substrate side) gates. Due to the hybridization between the conduction bandof InAs and valence band of GaSb through the heterointerface, the topologically nontrivial
different energy gap opens. The energy overlap between the conduction and valence bands
can be controlled by applying a gate voltage on both sides. When the overlap is large enoughthe system becomes semimetallic as a result of the anisotropy of the GaSb valence band
[Fig. 2(a)]. By increasing the back gate voltage, the overlap becomes smaller and the band
structure becomes that of a TI [Fig. 2(b)].
This work was supported by JSPS KAKENHI Grant No. 26287068.
[1] K. Suzuki, Y. Harada, K. Onomitsu, and K. Muraki, Phys. Rev. B 87, 235311 (2013).
[2] K. Suzuki, Y. Harada, K. Onomitsu, and K. Muraki, Phys. Rev. B 91, 245309 (2015).

Fig. 1. Energy band profile of the InAs/GaSb
heterostructure with front (surface side) andback (substrate side) gates.

40

Fig. 2. Schematic illustrations of dispersion
relations for (a: semimetallic) large energy
band overlap case and (b: TI) small overlap
case .

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Probing the Extended-state Width of Disorder-broadened
Landau Levels in Epitaxial Graphene
1

Keiko Takase1, Hiroki Hibino2, and Koji Muraki1
Physical Science Laboratory, 2Materials Science Laboratory

Physical Science Laboratory

Graphene is theoretically predicted to have a zero-energy Landau level, the energy width ofwhich depends on the types of disorder; the energy width is ideally nearly zero in the presenceof typical hopping disorder such as ripples, owing to protected chiral symmetry associatedwith graphene sublattice-symmetry. Previously, we developed transport energy-spectroscopy
techniques relaying on densities of interface states involved in epitaxial graphene device [1].
Using the technique, here we report temperature dependences of the energy widths of theextended states of the zero-energy and first excited Landau levels, from which we can also
deduce exponents corresponding to the critical exponents used in the quantum Hall plateauplateau transition. The energy widths obtained from the spectroscopy technique are also
compared with the energy widths deduced from the activation gap measurements [2].
Figure 1(a) shows longitudinal resistance as a function of gate voltage (Vg) and magnetic
field (B). Due to the presence of the interface states in gate insulator or in SiC underneaththe graphene (Fig. 1(b)), trajectories of the longitudinal-resistance peaks become parabolic,reflecting the unequally-spaced graphene Landau levels. Such a Vg-B relation enables us todeduce the energy width ∆EN of the extended states of the Nth Landau level. Figure 1(c) and(d) show temperature (T) dependences of ∆E0 and ∆E1. These show that ∆E0 and ∆E1 have
similar magnitudes and are proportional to T η with η = 0.30 - 0.31 for ∆E0 and η = 0.32 - 0.35
for ∆E1. These values are comparable to the critical components previously deduced from theplateau-plateau transition in quantum Hall regimes. Moreover, we deduced the energy widths
independently using activation gap measurements. The energy width for N = 1 Landau levelshow a good agreement between two different types of measurement methods, while theenergy width for the N = 0 Landau level obtained from activation gap measurement is larger
by 30 meV than that deduced from the transport energy-spectroscopy.
Using these two different measurement techniques systematically, we demonstrate that ourdevice include random disorder rather than typical hopping disorder such as ripples.
This work was partly supported by KAKENHI.
[1] K. Takase, S. Tanabe, S. Sasaki, H. Hibino, and K. Muraki, Phys. Rev. B 86, 165435 (2012).
[2] K. Takase, H. Hibino, and K. Muraki, Phys. Rev. B 92, 125407 (2015).

Fig. 1. (a) Longitudinal resistance as a function of gate voltage (Vg) and magnetic field (B). (b) Energy diagram ofgraphene with interface states. Temperature dependence of ∆EN for the N = 0 Landau level (c) and N = 1 Landaulevel (d).

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)41

Coherent Raman Beat Analysis of the Hyperfine Sublevel Coherence
Properties of 167Er3+ Ions Doped in an Y2SiO5 Crystal
Kaoru Shimizu and Daisuke Hashimoto
Optical Science Laboratory
A metastable Λ-type three-level system of atoms and ions provides us with a medium
with which to demonstrate electromagnetically induced transparency (EIT) and coherent
population trapping (CPT). EIT and CPT media have attracted a lot of attention in the fieldof quantum optics, where they are expected to be used for devices capable of converting
quantum information between light and matter. An ensemble of Pr3+ ions doped sparsely ina host crystal Y2SiO5 cooled to a cryogenic temperature (< 4 K) has been studied intensively
for demonstrating EIT and CPT. Recently, a Λ-type three-level system was also identified for
167
Er3+ ions doped in an Y2SiO5 crystal, which had an optical transition at a telecom wavelengthand a set of hyperfine sublevels in ground and excited states [1]. Although the measured
population life time t1 of the sublevels is approximately 100 ms at 1.5 K, the phase dissipation
time t2 of the sublevel coherence has not yet been examined. To examine the feasibility of an
Er3+:Y2SiO5 crystal as a solid state medium for EIT and CPT, we must clarify the t2 value.
At first glance, Raman echoes or optically detected spin echoes appear suitable for measuring
the t2 value provided that the optical coherence time T2 or the sublevel population life time t1 islong enough. However, an Er3+:Y2SiO5 crystal cannot satisfy the conditions for the above echo
techniques. This is because an Er3+ ion is a Kramers ion and has a half-integer electronic spin,
which results in a large average magnetic moment and makes the quantum state being sensitive
to the fluctuating local magnetic field. In contrast, coherent Raman beat (CRB) spectroscopy
is insensitive to the T2 and t1 values and worth employing if we can cope with inhomogeneousdephasing in the signal.
By comparing carefully with the effects of sublevel inhomogeneous broadening ∆ sub on thevarious Raman signals (Fig. 1) that are obtained with different Er3+ ion dopant concentrations,
we can estimate the t2 value even when t2 > 1/∆ sub [2]. The ground-state t2 values of the Λ-type
three-level system identified in the 167Er3+ ions are approximately 12 and 50 µs at 2.3 K when
the dopant concentrations are 0.005 (Fig. 2) and 0.001 at%, respectively. These t2 values arelong enough to realize EIT and CPT with an Er3+:Y2SiO5 crystal at a wavelength of 1.5 µm.
[1] E. Baldit et al., Phys. Rev. B 81, 144303 (2010).
[2] D. Hashimoto and K. Shimizu, J. Lumin. 171, 183 (2016).

Fig. 1. Experimental configuration of the CRB spectroscopy.

42

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Fig. 2. Sublevel phase relaxation rate 1/t2.

Deterministic Wavelength Conversion of Single Photons
Using Cross-phase Modulation
Nobuyuki Matsuda
Optical Science Laboratory

Optical Science Laboratory

Wavelength (frequency, color) is an important physical parameter of light. Wavelength
conversion of single photons is crucial for quantum networking, which requires an interface
for photon wavelength. We have developed a lossless scheme for the wavelength conversion ofphotons using a nonlinear-optical effect called cross-phase modulation (XPM) [1].
The experimental scheme is illustrated in Fig. 1(a). XPM enables us to control the phase oflight (signal pulses) via a change in the refractive index of a medium induced by another light(control pulses). An instantaneous frequency shift is added to the signal pulses when the phaseshift is dynamic. Since XPM always occurs regardless of the intensity of the control pulses, byusing single photons as the signal pulses we can convert the wavelength of the photons withouta photon loss.
Wavelength conversion using XPM has been widely demonstrated for classical opticalpulses; however, it has not yet been demonstrated for single photons. This is because it wasdifficult to add a wavelength shift to single photons while mitigating noise photons inducedby the control pulses via other optical processes. We solved this problem by using a photonic
crystal fiber (PCF) whose dispersion property was properly designed for the experiment. As aresult, we were able to successfully convert the wavelength of telecommunication-band single
photons with a wavelength shift as large as 3 nm (0.4 THz in frequency). The amount of the
wavelength shift can be easily tuned by adjusting the intensity of the control pulses. Photon
loss due to the conversion was not observed.
Using the scheme, we further controlled the quantum correlation of pairs of photons. The
demonstrations include the modulations of non-classical frequency correlation [Fig. 1(b)],inter-packet interference, and entanglement between distant photons. These results demonstrate
our scheme’s applicability to a wide range of quantum information science and technologies,
including computation [2] and metrology.
This work was supported by KAKENHI.
[1] N. Matsuda, Sci. Adv. 2, e1501223 (2016).
[2] J. Carolan et al., Science 349, 711 (2015).

Fig. 1. (a) The illustration of the scheme. (b) Reshaping the non-classical frequency correlation between
photons. In the experiment, first, photon pairs were created via an optical process called parametric down
conversion (left). Then the wavelength of “photon A” was blue shifted with our scheme. As a result, the overall
spectral correlation was also blue shifted (right).

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)43

An Entanglement Analogue in Light Cones
Fumiaki Morikoshi
Optical Science Laboratory
In relativistic spacetime, the notion of light cones is essential and nothing can travel fasterthan light. Thus, the path of a particle stays inside the light cone. (In what follows, we takethe unit of c = 1). In this work, we drew an analogy between the structure of light cones andentanglement in quantum theory.
There are two parts in a light cone, the future cone and the past cone, as shown in Fig. 1. The
cross sections at t = ±1 become unit spheres in three dimensions (In Fig. 1, the cross sectionsof the light cone in 2+1 dimensions become unit circles in two dimensions). Each unit spherecan be identified with the Bloch sphere of a qubit in quantum information theory. Thus, we
introduce two imaginary qubits, one for the future and the other for the past. Considering worldlines of particles with constant speeds, the directions of the particles in four dimensions can be
represented by points on or inside the Bloch sphere. In other words, the directions of particles
with the light speed correspond to the points on the surface of the sphere, and the directions ofparticles travelling slower than light correspond to the points inside the sphere.
This correspondence can be seen as the one between world lines of particles and entangledstates of two imaginary qubits representing the cross sections of the light cones in the future
and the past. According to this analogy, particles with the light speed correspond to productstates, stationary particles maximally entangled states, and particles slower than light partiallyentangled states. Furthermore, by quantifying the amount of entanglement with concurrence,
we can show an intriguing relation between the concurrence E and the particle’s speed v [1],E=

1 — v2This relation allows us to interpret the factor frequently appearing in relativity,
terms of the notion of entanglement in quantum information theory.

1 — v 2 , in

[1] F. Morikoshi, Prog. Theor. Exp. Phys. 123A04 (2015).

Fig. 1. Correspondence between world lines and entanglement in a light cone (2+1 dimensions).

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Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

All-photonic Intercity Quantum Key Distribution
Koji Azuma, Kiyoshi Tamaki, and William J. Munro
Optical Science Laboratory

Optical Science Laboratory

Quantum key distribution (QKD), a technique for ultimately secure communication basedon the law of physics, usually relies on the transmission of photons over optical fibres. In fact,
based on the direct transmission of photons between a sender and a receiver, conventional
QKD schemes are already commercially available for 100-km communication distances andtestbed networks like the ‘Tokyo QKD network’ are running in Japan. Therefore, with theconventional schemes, intracity QKD links (over about 100 km) are available even at present.
However, owing to the photon loss in the optical fibre, about 400 km is considered to be themaximum distance of the conventional schemes. Thus, to connect QKD networks in different
cities above 400 km distant, it was thought that we needed ‘quantum repeaters’, rather thanthe conventional schemes based on the direct transmission. Quantum repeaters enable us
to perform QKD over any communication distance efficiently, but, they necessitate many
intermediate nodes connected with optical fibres, each of which needs challenging components
such as matter quantum memories and quantum error correction. These requisites are necessary
to achieve an extremely high goal such as intercontinental QKD connections. But, they may be
too demanding to connect different major cities below 1,000 km separation.
In this research [1], we have proposed an ‘all-photonic intercity QKD’ protocol (Fig. 1)that doubles the achievable distance of the QKD without decreasing its efficiency, using
only linear optical devices, that is, without matter quantum memories and quantum error
correction required in quantum repeaters. This scheme could outperform quantum repeaters
based on atomic ensembles for communication distances below 800 km, and it expands thecommunication range from 400 km of conventional schemes to 800 km (Fig. 2). In addition,
since the proposed scheme does not use matter quantum memories similarly to all-photonic
quantum repeaters [2], (a) it displays the communication speed in the same order of therepetition rate of optical devices, irrespective of the communication distance, (b) it does notneed a still challenging interface between matter and photons and (c) it could work at room
temperature in principle. Therefore, our scheme could work as cost-effective backbone links
to connect metropolises within a radius of 800 km. If our scheme is combined with the allphotonic quantum repeater protocol, it is made seamless to realize the high-speed and costeffective ‘all-photonic’ QKD network based only on optical devices on a global scale.
[1] K. Azuma, K. Tamaki, and W. J. Munro, Nature Commun. 6, 10171 (2015).
[2] K. Azuma, K. Tamaki, and H.-K. Lo, Nature Commun. 6, 6787 (2015).

Fig. 1. All-photonic intercity QKD. The middle point C performs
quantum nondemolition measurement (QND) on optical pulses sent bycommunicators AB. Optical switches (SW) then make only surviving
photons paired, which are subjected to the Bell measurement (BM).

Fig. 2. Communication range
expanded by our scheme.

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

45

Finite-key Security Analysis of Quantum Key Distribution with
Imperfect Light Sources
Akihiro Mizutani1, Marcos Curty2, Charles Ci Wen Lim3,
Nobuyuki Imoto1, and Kiyoshi Tamaki4
1
Osaka University, 2University of Vigo,
3
University of Geneva, 4Optical Science Laboratory
Sending confidential information such as a password over a communication channel needs
to be encrypted. Among the many encryption methods, the one-time pad is the only encryption
scheme rigorously proven to be secure. This crypt requires a key, which is a random bit string,and if its information is kept from an eavesdropper the one-time pad is secure. Therefore,
secure distribution of the key is critical, and so key distribution (QKD) has attracted muchattention as a means to accomplish this. For the secure distribution, a QKD system has tosatisfy requirements imposed by a security proof. Unfortunately, most of the requirements
in existing security proofs are hard to meet in practice. Therefore, to guarantee theimplementation security, that is the security of a real-life QKD system, we need to construct
security proofs with relaxed requirements.
In previous work [1], we modified the security proofs to accommodate the effect of imperfectphase modulation (PM) in the asymptotic limit of a large number of the pulses. In this current
work, we have generalized it to the one with a finite number of pulses [2]. Figure 1 shows oneof our results where the horizontal (vertical) axes represents the fiber distance (the secret key
generated per pulse). The solid (dashed) lines correspond to the case of the perfect (imperfectof 8.42°) PM. Moreover, the colors represent the number of pulses, and each line, form right toleft, corresponds to the asymptotic limit, 1012, 1011, 1010, 109, respectively. The small differences
between the solid and dashed lines mean that the effect of the imperfect PM is negligible. As
the clock rate of most of the QKD system is more than 1 GHz, our results show the feasibilityof secure key distribution with current QKD systems. These results constitute an important
step towards guaranteeing implementation security for QKD systems.
Our work is in part supported by NICT.
[1] K. Tamaki et al., Phys. Rev. A 90, 052314 (2014).
[2] A. Mizutani et al., New J. Phys. 17, 093011 (2015).

Fig. 1. Communication distance vs Key generation rate per pulse.

46

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Extraction of Phonon Decay Rate in p -type Silicon Under Fano
Resonance
Keiko Kato, Katsuya Oguri, Haruki Sanada, Takehiko Tawara,
Tetsuomi Sogawa, and Hideki Gotoh
Optical Science Laboratory

Optical Science Laboratory

It is of primary importance to understand phonon dynamics in Si, not only for basic physics
but also for obtaining ultrafast responses in semiconductor devices. Raman measurement is
one of the experimental methods for determining phonon decay rates. However, in doped Si,
especially p-type Si, an asymmetric lineshape appears due to Fano resonance, which makes it
difficult to evaluate them [1]. In the present study, we performed time-resolved measurements
to determine phonon decay rates free from the interaction with a continuum state in Fano
resonance [2].
Time-resolved reflectivity measurements were performed with a sub-10-fs laser pulse, whose
wavelength was centered on 780 nm. Figure 1(a) shows the time-resolved reflectivity of p-type
Si. The p-type Si exhibits an asymmetric lineshape in the Raman measurement due to Fano
resonance [inset in Fig. 1(a)]. The decay rate (Γcp) obtained from the time-resolved reflectivity
is plotted as a function of temperature in Fig. 1(b), along with the Raman linewidths (ΓRaman).
The temperature dependence of ΓRaman can be explained with the anharmonic decay model[3], but that of Γcp cannot be. The different temperature dependences between ΓRaman and Γcp
could be explained by how the Fano resonance modifies the frequency- and time-domain
spectra, respectively. The frequency-domain spectrum (i.e., Raman spectrum), on one hand,is broadened due to Fano resonance [1]. As a result, ΓRaman in the p-type Si deviates from theanharmonic decay model. The time-resolved response, on the other hand, is given by thesummation of exponential decaying and deltalike responses, originating from the discrete(i.e., phonon) and continuum states, respectively [4]. The short decay time of the continuum
state enables us to extract the exponentially phonon decay without any distortion. As a result,
the temperature dependence of Γcp of the p-type Si reveals that the anharmonic decay model
is dominant in p-type Si even under Fano resonance. We have shown that time-resolved
measurements can extract discrete-state dynamics free from the interaction with the continuum
state even under Fano resonance.
[1] F. Cerdeira, T. A. Fjeldly, and M. Cardona, Phys. Rev. B 8, 4734 (1973).
[2] K. Kato, K. Oguri, H. Sanada, T. Tawara, T. Sogawa, and H. Gotoh, AIP Advances 5, 097152 (2015).
[3] T. R. Hart, R. L. Aggarwal, and B. Lax, Phys. Rev. B 1, 638 (1970).
[4] C. Ott et al., Science 340, 716 (2013).

Fig. 1. (a) Time-resolved reflectivity of p-type Si. The inset shows the Raman spectra of p-type Si. (b) Temperaturedependence of the phonon decay rate. The solid and open symbols correspond to Γcp and ΓRaman, respectively.
Dotted lines are the fits with the anharmonic decay models.
Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)47

Frequency Stabilization of an Er-doped Fiber Laser with a Collinear
2f -to-3f Self-referencing Interferometer
Kenichi Hitachi1, Atsushi Ishizawa1, Osamu Tadanaga2, Tadashi Nishikawa3,
Hiroki Mashiko1, Tetsuomi Sogawa1, and Hideki Gotoh1
1
Optical Science Laboratory, 2NTT Device Technology Laboratories,
3
Tokyo Denki University
Techniques for stabilizing the carrier-envelope offset (CEO) frequency of an opticalfrequency comb are prerequisites for precision spectroscopy. To stabilize an optical frequency
comb, we need to generate a supercontinuum (SC) light, which broadens its spectrum. A 2f-to3f self-referencing interferometer (SRI) is used for stabilizing the CEO frequency of an opticalfrequency comb that has only a 2/3-octave bandwidth of SC light. To stabilize such an opticalfrequency comb, we constructed a collinear 2f-to-3f SRI with a dual-pitch (DP-) periodicallypoled lithium niobate (PPLN) ridge waveguide [1].
The DP-PPLN ridge waveguide has two different pitch sizes (Λ1 and Λ2) to satisfy the quasiphase matching conditions for generating second- and third-harmonic lights with a wavelengthof 600 nm [Fig. 1(a)]. In the first part, second-harmonic light with a wavelength of 900 nm
is generated from the SC component at around 1800 nm. In the second part, sum frequency
light with a wavelength of 600 nm is generated from the SC component at 1800 nm and
900-nm second-harmonic light. In addition, in the second part, second-harmonic light witha wavelength of 615 nm is involved. If 615-nm second-harmonic light and 600-nm thirdharmonic light spectrally overlap, a CEO beat signal is obtained. Figure 1(b) shows a CEO beatsignal. The SNR of the CEO beat is 52 dB at the resolution bandwidth of 100 kHz. This is thehighest SNR ever reported in a 2f-to-3f SRI.
Then, to evaluate the instability of the CEO frequency, we measured Allan deviations forboth in-loop and out-of-loop interferometers, where the former was used for stabilizing an
Er-doped fiber laser and the latter was used for monitoring the actual instability. The results
showed that both the in-loop and out-of-loop Allan deviations are 7×10-15 (= 1.4 Hz) at gate
time of 1 s [Fig. 1(c)]. Furthermore, we measured the Allan deviations after we intentionallyplaced a small pump on the breadboard near the interferometer. We found that despite thepump vibration, both the in-loop and out-of-loop Allan deviations remained almost the samevalues. These results confirmed that our collinear 2f-to-3f SRI allows us to stabilize a CEO
frequency regardless of environmental perturbation.
This work was supported by KAKENHI.
[1] K. Hitachi et al., Appl. Phys. Lett. 106, 231106 (2015).

Fig. 1. (a) DP-PPLN ridge waveguide. (b) CEO beat signal. (c) Allan deviations of CEO frequencies.
48

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Long-distance Transport of Electron Spins in Persistent Spin Helix State
Yoji Kunihashi1, Haruki Sanada1, Hideki Gotoh1, and Koji Onomitsu2
1
Optical Science Laboratory, 2Materials Science Laboratory

Optical Science Laboratory

Future information processing techniques using electron spins in non-magnetic
semiconductors will require both the manipulation and transfer of spins without their coherence
being lost. The effective magnetic field induced by a spin-orbit interaction (SOI) enables us torotate the electron spins in the absence of an external magnetic field. However, the fluctuationsin the effective magnetic field originating from the random scattering of electrons also cause
undesirable spin decoherence, which limits the length scale of the spin transport. Here we
report the electrical control of spin precession of drifting electrons in a robust spin structure,
namely a persistent spin helix (PSH) where the Rashba and Dresselhaus SOIs are the same
strength. We found that the PSH enhances the spatial coherence of drifting spins, resulting ina maximized spin decay length near the PSH condition. We also found that the spin precession
period of drifting spins can be controlled by a gate-controlled SOI [1].
The sample consisted of a 25-nm-thick GaAs QW embedded in a HEMT structure. The
wafer was processed into a cross-shaped channel with a top gate electrode (Fig. 1 inset). This
structure allowed us to use in-plane voltages Vx and Vy to create drift motion, and a verticalgate voltage Vg to tune the strengths of the SOIs. We measured the spatial spin distributionof drifting electrons using Kerr rotation microscopy at T = 8 K. A circularly polarized pumplight from a cw Ti:sapphire laser generated electron spins at a certain position and a linearlypolarized light probed the Kerr rotation θK, which was proportional to the spin density at thefocused position. Figure 2(a) shows the Vg dependence of the Kerr rotation angle θK scannedalong the [1-10] direction for Vx = 50 mV and Vy = 0 mV. Even in the absence of an external
magnetic field, we observed a spin precession resulting from the effective magnetic field
induced by the SOIs. By varying the gate voltage, the spatial frequency of the drifting spin
precession was continuously modulated via the gate control of the Rashba SOI. We also
estimated the gate voltage dependence of the spin decay length lS over which the spin density
decays to 1/e of its initial value. In Fig. 2(b), lS is plotted as a function of the spin rotation
length LSO, which is inversely proportional to the SOI. We found that lS has its maximum value
in the PSH condition, and this behavior was well reproduced by a simulation based on a spin
drift-diffusion model. A comparison of the experimental and simulation results reveals that in
the present sample the spin decay length is enhanced by suppressing the spin relaxation in the
PSH condition.
[1] Y. Kunihashi, H. Sanada, H. Gotoh, K. Onomitsu, M. Kohda, J. Nitta, and T. Sogawa, Nature Commun. 7,10722 (2016).

Fig. 1. Spatial distribution of diffusiveand drifting spins in the PSH state.
The inset shows a schematic image ofthe sample.

Fig. 2. (a) Gate voltage dependence of the spatial distribution of drifting
spins in the [1-10] direction. (b) Spin decay length lS as a function of spinrotation length LSO in which an electron spin can rotate a full cycle.
Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)49

Thresholdless Oscillation in High-β Buried Multiple-quantum-well
Photonic Crystal Lasers
Masato Takiguchi1,2, Hideaki Taniyama1,2, Hisashi Sumikura1,2,
Muhammad Danang Birowosuto1,2, Eiichi Kuramochi1,2, Akihiko Shinya1,2,
Tomonari Sato1,3, Koji Takeda1,3, Shinji Matsuo1,3, and Masaya Notomi1,2
1
NTT Nanophotonics Center, 2Optical Science Laboratory,
3
NTT Device Technology Laboratories
A photonic crystal (PhC) cavity is promising for photonic network-on-chip architecture
because its ultra-small mode volume and high quality factor will enable efficient and highspeed lasers and LEDs. To realize them, we study nano-emitters using buried multiple
quantum wells (MQW) PhC cavities [Fig.1(a)]. Conventional QW-PhC have been extensively
investigated, however they suffer from poor carrier confinement and surface non-radiative
recombination. On the other hands, our buried MQW PhC cavities can exhibit distinctive
spontaneous emission control [1] because of strong carrier confinement and low surface nonradiative recombination. Therefore spontaneous coupling factor (β) of our devices can be unity
and theoretically-predicted thresholdless laser can be realised.
In this study, we have investigated the characteristics of high-β buried MQW PhC lasers toclarify the thresholdless operation. To compare the nature of lasing operation for high and low
β values, we performed systematic measurements, such as L-L measurement and time resolved
measurement, under a large and small detuning condition (2 nm and 15 nm detuning) as
shown Fig. 1(b). From these results, we have unambiguously demonstrated high-β lasing witha smoothed transition. In addition, we systematically investigated the dependence of β on the
detuning frequency, which was in good agreement with a numerical simulation based on thefinite-difference time-domain method [Fig. 1(c)].
[1] M. Takiguchi et al., Appl. Phys. Lett. 103, 091113 (2013).
[2] M. Takiguchi et al., Opt. Express 24, 3441 (2016).

Fig. 1. (a) Schematic of L3 PhC cavity. (b) L-L curve. (c) Experimental and simulated β.

50

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Wavelength-scale All-optical Photonic Crystal Nanocavity Memory
Operating at Nanowatt-level
Eiichi Kuramochi1,2, Kengo Nozaki1,2, Akihiko Shinya1,2, Hideaki Taniyama1,2, Koji Takeda1,3,
Tomonari Sato1, Shinji Matsuo1,3, and Masaya Notomi1,2
1
NTT Nanophotonics Center, 2Optical Science Laboratory,
3
NTT Device Technology Laboratories

Optical Science Laboratory

We are developing ultralow-power-consumption large-scale photonic integrated circuits ona chip using nanophotonic technologies. All-optical memory is one of the key devices. Since
we need a considerably large memory, reducing power consumption is a crucial issue. We haverealized an optical RAM with 30-nW operation using a wavelength-scale photonic crystal (PhC)
nanocavity with a small buried heterostructure (BH) [1]. Here we describe a further one orderof magnitude reduction of power consumption by employing a novel multi-hole-tuned threemissing-hole (L3) nanocavity with a BH placed at the cavity center [Fig. 1(a)] [2]. We used
the same design as in [3], which enables large quality factor (Q) enhancement and multibit
optical RAM operation [3]. In this study, a two-port filter design [Fig. 1(b)] was employed and
Q was enhanced to 45,000 and 210,000 with and without the InGaAsP BH, where the latter isthe record high value among all InP-based nanocavities. Two multi-hole-tuned BH-L3 cavities(L3LM, L3M3) were operated as an all-optical bistable memory as shown in Fig. 1(c) andcompared to the operation of mode-gap-confined BH nanocavity (MG1) reported before [1].
As shown in Fig. 1(d), L3M3 that had Q comparable to MG1 decreased onset bias power to 10
nW thanks to the smaller mode volume (V) of the L3 nanocavity. Furthermore, L3M1 having
much higher Q (42,000) exhibited onset bias power of 2.3 nW, which is nearly 1/13 of MG1’s,
and the corresponding average number of photons in the cavity was only 0.1. Even at the 2.3nW bias power, L3M1 operated with a very good “1”/“0” switching contrast [Fig. 1(e)]. This
study paves the way for ultralow power consumption integrated photonic crystal devices andencourages the employment of multi-hole-tuned L-type nanocavities for fundamental anddevice studies.
[1] K. Nozaki et al., Nature Photon. 6, 248 (2012).
[2] E. Kuramochi et al., Appl. Phys. Lett. 107, 221101 (2015).
[3] E. Kuramochi et al., Nature Photon. 8, 474 (2014).

Fig. 1. (a) Design of systematically-tuned BH-L3. (Lattice constant (a): 426 nm. Shifts: 0.09a, 0.35a, 0.175a, and0.045a for A, B, C and D. BH is InGaAsP.) (b) SEM image of L3 optical memory. (c) Schematics of all-opticalbistable memory operation. (d) Relation between detuning (δ) and bias power for memory operation. (e) Input/
output waveforms in memory operation at 2.3 nW bias power.
Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

51

An All-optical Packet Switch Realized by Using the Ultralow-power
Optical Bistability of a Nanocavity
Kengo Nozaki1,2, Amedee Lacraz2, Akihiko Shinya1,2, Shinji Matsuo1,3, Tomonari Sato1,3,
Koji Takeda1,3, Eiichi Kuramochi1,2, and Masaya Notomi1,2
1
NTT Nanophotonics Center, 2Optical Science Laboratory,
3
NTT Device Technology Laboratories
A tiny semiconductor nanocavity allows a strong light-matter interaction with a low-power
optical input, and is used for various functional nanophotonic devices. We achieved a buried
heterostructure with which to form a nanocavity, as shown in Fig. 1(a), where an ultra-compact
InGaAsP is buried in an InP photonic crystal (PhC). This nanocavity allowed us to strongly
confine both photons and carriers, thus enabling us to realize bistable behavior even with nWlevel optical power, as shown in Fig. 1(b). Thus bistable switching between “on” and “off”
states can be obtained by combining a CW bias light and an optical pulse input, and thereby
make it possible to realize an all-optical memory. As an extended application, in this research,
we demonstrated that it can work as an all-optical packet switch [1].
For this demonstration, a write pulse (100 ps wide, 13 fJ), a CW bias light (0.8 µW), and a
reset pulse (50 ns wide) were injected to switch the bistable states, and the optical packet data
(10 Gbit/s, 1 ns long, NRZ signal) to be switched were also injected, as shown in Fig. 1(c).
As a result, we confirmed that the bistable states were switched with the output bias light,
and gate switching for the optical packet was successfully achieved, as shown in Fig. 1(d).
Furthermore, we also investigated a 1×2-port configuration, as shown in Fig. 2(a). This realized
output-port-selective switching for the optical packet via bistable memory switching as well
as gate switching, as shown in Fig. 2(b). The ultralow-power all-optical packet switch that weachieved is promising in terms of realizing a chip-scale high-speed photonic routing circuit that
does not need E-O/O-E signal conversion.
[1] K. Nozaki, A. Lacraz, A. Shinya, S. Matsuo, T. Sato, K. Takeda, E. Kuramochi, and M. Notomi, Opt.
Express 23, 30379 (2015).

Fig. 1. (a) Photograph of photonic crystal nanocavity. (b) Hysteresis
curves on optical input/output characteristic. (c) Input optical
waveforms. (d) Output waveforms showing the gate switching of
optical packet data.
52

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Fig. 2. (a) 1×2-port configuration of
nanocavity. (b) Output waveforms
showing the output-port-selective
switching of optical packet data.

Membrane Distributed-reflector Laser
Integrated with SiOx-based Spot-size Converter on Si Substrate
Hidetaka Nishi1,2, Takuro Fujii1,2, Koji Takeda1,2, Koichi Hasebe1,2,
Takaaki Kakitsuka1,2, Tai Tsuchizawa1,2, Tsuyoshi Yamamoto2, and Shinji Matsuo1,2
1
NTT Nanophotonics Center, 2NTT Device Technology Laboratories

Nanophotonics Center

To meet requirements towards the new era of datacenter networks, we have proposed andrealized membrane DFB lasers. Thanks to the strong optical confinement, the energy cost canbe reduced to 171 fJ/bit for 25.8-Gbit/s NRZ modulation signal, which is the highest energy
efficiency for DFB lasers to the best of our knowledge [1]. In addition, to obtain low-loss
fiber coupling with Si high-refractive-index-difference (high-∆) waveguides, we have also
developed a spot-size converter (SSC) based on a low-∆ silicon-oxide (SiOx) waveguide [2].
In this work, we achieved a further decrease of the energy cost by introducing a distributedreflector (DR) laser structure and a reduction of fiber-coupling loss by integrating a SiOx-based
SSC.
Figures 1(a) and (b) show a schematic of the device structure and a top-view image of afabricated device, respectively. The DR laser consists of a DFB section with uniform grating,a rear DBR section, and a front InP-wire waveguide. The DFB region has a κ of 1500 cm-1
and a buried heterostructure comprising InGaAsP-based six-QW layers (150-nm thick, 50-µm
long, 0.8-µm wide) embedded with 250-nm-thick InP. Both the rear DBR section and output
waveguide are made of InP. A compact cavity can be achieved by employing a DBR with highreflectivity. The output InP waveguide is tapered horizontally and connected with the low-∆
SiOx waveguide via the SSC.
Figure 1(c) shows current-versus-output-power (I-L) characteristics. The curve measured bya PD set in front of the SiOx waveguide facet shows a big kink with injection current between
5 and 6 mA. This is due to the reflection at the boundary between air and the SiOx waveguide.
In contrast, the curve obtained by a high-NA fiber butt-coupled to the SiOx-waveguide facet
exhibits no kink thanks to the suppression of the reflection. The threshold current is 0.6 mA
and the maximum output power is 0.7 mW. The fiber coupling loss is estimated to be 2.7 dB,
which is 6-dB lower than our previous device. Then, we measured eye diagrams for 25.8-Gbps
NRZ modulation. Figure 1(d) and (e) shows an diagram obtained with bias currents (Ib) of 5.0
and 2.5 mA, respectively. At Ib = 2.5 mA, we achieved lower an energy cost of 132 fJ/bit.
[1] S. Matsuo et al., J. Lightwave Technol. 33, 1217 (2015).
[2] T. Tsuchizawa et al., J. Sel. Top. Quantum Electron. 17, 516 (2011).

Fig. 1. (a) Schematic device structure. (b) Top-view image of a fabricated device. (c) I-L characteristics.
(d) (e) Eye diagrams for 25.8-Gbps NRZ direct modulation with Ib of 5.0 mA and 2.5 mA.
Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)53

Dislocation Reduction in MOVPE-grown GaAs/Ge Layers on
Si Substrates by Thermal Cycle Annealing
Ryo Nakao1,2, Masakazu Arai1,2, Tsuyoshi Yamamoto2, and Shinji Matsuo1,2
1
NTT Nanophotonics Center, 2NTT Device Technology Laboratories
Direct growth of III-V compound semiconductor has been desired for 30 years. Recently,
incorporating a Ge buffer layer between Si and GaAs III-V compound semiconductor has beenstudied to improve the crystalline quality because Ge’s lattice constant is very close to GaAs’s[1]. Monogermane (GeH4) is widely used as a material source for the Ge buffer layer. However,
GeH4 is explosive material. Thus, the Ge buffer layer cannot be grown in the same reactor used
for GaAs epitaxial growth [2]. Instead of using GeH4, we used metal-organic material iso-butyl
germane (IBGe) as a Ge precursor. The Ge buffer layer and GaAs were grown in the same
metal-organic vapor phase epitaxy (MOVPE) reactor. Figure 1(a) shows the cross-sectionaltransmission electron microscopy (TEM) image of a GaAs/Ge structure grown on Si substrate.
At the boundary between the GaAs and Ge layer, dislocations can be seen. The dislocations
penetrated the epitaxial layer surface. To reduce the dislocations, we performed thermal cycle
annealing (TCA) after the GaAs and Ge layer growth [3]. As shown in Fig. 1(b), the dislocations
at the GaAs/Ge boundary were significantly suppressed by TCA. Moreover, by employing
TCA, the intensity of photoluminescence (PL) measured from InGaAs/GaAs multiple quantum
wells (MQWs) grown on the GaAs epitaxial layer increased by a factor of three (Fig. 2). This
is indicates that the crystalline quality was improved by TCA. On the other hand, the PL
intensity was 11% smaller than that for MQWs on GaAs substrate. Further improvement ofgrowth and annealing conditions will provide crystalline quality comparable to GaAs substrate.
These results indicate that the MOVPE-grown GaAs/Ge layers are well-suited for integrating alight source onto Si substrate.
[1] A. Lee et al., Opt. Express 20, 22181 (2012).
[2] M. E. Groenert et al., J. Appl. Phys. 93, 362 (2003).
[3] R. Nakao et al., in Electronic Materials Symposium 34, Th-2-3 (2015).

Fig. 1. Cross-sectional TEM images of (a) as-grown GaAs/Ge structure on
Si substrate and (b) after TCA.

54

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Fig. 2. PL spectra from MQWs.

Ⅱ．Data

7th NTT-BRL School
The seventh NTT Basic Research Laboratories (BRL) School was held on November 15-17th,
2015 at NTT Atsugi R&D Center. The aim of the school was to foster young researchers working
in the material, nano and quantum science fields and to promote the international visibility of NTT
BRL. This year the theme of the school was “Nano and Optics”, and was closely related toongoing research within NTT BRL. Prestigious professors and researchers were invited toparticipate as lecturers. We accepted thirty (mainly PhD) students from eleven countries.
On the first day, Prof. Gerhard Abstreiter (Walter Schottky Institute, Technische Universität
München) gave a lecture entitled “Physics and Technology of Semiconductor Hetero- Nano- andQuantum Structures”. His lectures covered topics ranging from basic semiconductor physics tofabrication technologies, and device applications for low-dimensional structures. In addition, thedirector of NTT BRL, Dr. Tetsuomi Sogawa, provided an introduction to NTT BRL and we
conducted a laboratory tour to show our research facilities and to introduce recent research
activities at NTT BRL. On the second day, Prof. Yasuhiko Arakawa (The University of Tokyo)
gave a lecture entitled “Progress in Quantum Dot Photonics” and also introduced the“International Year of Light 2015” as the President of The International Commission for Optics(ICO). Dr. Masaya Notomi (Senior Distinguished Researcher) and Dr. William J. Munro(Distinguished Researcher) gave lectures entitled “Nanophotonics for Large-scale Integration” and“Quantum Fun with Photons”, respectively. After the lectures, the students went on an excursion
to Aikawa City, which is close to the NTT Atsugi R&D Center and enjoyed the hands-on
experience of learning indigo tie-dyeing, a traditional Japanese craft. On the third day, Prof. Tobias
Kippenberg (École Polytechnique Fédérale de Lausanne) gave a lecture on “Cavity
Optomechanics”. In the afternoon, the students attended the International Symposium on
Nanoscale Transport and Technology (ISNTT) hosted by NTT BRL. As part of this event, thestudents gave poster presentations on their research. The students, lecturers, and NTT BRL
researchers all had an excellent time exchanging information on current research topics in various
fields. At a joint BRL School and ISNTT party, “Best Poster Prizes” were awarded to three
students who gave noteworthy poster presentations. The students had the opportunity to discuss
high-quality research and build human networks and friendships within this school. NTT BRL willcontinue to provide these occasions to support young researchers and to establish researchcollaborations in the fields of material, nano and quantum science.

56

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

ISNTT2015
The International Symposium on Nanoscale Transport and Technology (ISNTT2015) was heldat NTT Atsugi R&D Center from November 17 to 20, 2015, and brought together 179 participantsfrom 15 countries. The participants enjoyed oral and poster presentations at the symposium,
exchanging their views and ideas on nanotechnology and quantum devices. Since 2009, NTT
Basic Research Laboratories (BRL) has been holding ISNTT every two years to promote mutual
exchanges between those working on different device and material technologies related to
semiconductors, superconductors, and new materials, with the aim of creating new ideas andconcepts with which to build new hybrid nanoscale and/or quantum systems.
ISNTT2015 was co-chaired by Drs. Akira Fujiwara, Hiroshi Yamaguchi, and Koji Muraki of
NTT BRL. The symposium logo of ISNTT2015 represents the combination of nanostructuresto create new functions. On the 17th, 18th, and 20th, respectively, the sessions started withkeynote lectures entitled “Semiconductor Hetero-Nanowires on Si for Photonic and Electronic
Applications” by Prof. Gerhard Abstreiter (Walter Schottky Institute, Technische UniversitӓtMünchen), “Levitons: Clean Time-Resolved Electrons for Electron Quantum Optics” by Prof.
Christian Glattli (CEA Sacley), and “Interaction between Sound and a Superconducting Qubit”
by Prof. Per Delsing (Chalmers University of Technology). During the symposium we enjoyed 13
oral sessions with 46 oral presentations including 17 invited talks by world leading researchers,
on such topics as nanophotonics, nanomechanics, quantum and spin-related electron transport,
topological insulator, spintronics, single-electron devices, and semiconductor/superconductor
quantum bit devices. On the 17th and 18th, two poster sessions
were held and the first was a joint event with the 7th NTT-BRL
School. 56 presentations were made at the poster sessions. The
symposium offered many opportunities for interaction between
senior and young researchers including 30 students. NTT BRL
believes in the importance of providing such opportunities, and it
is part of our open laboratory policy.

Data

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

57

List of Visitors’ Talks
Date

Speaker (Affiliation)
Prof. Masayuki Katsuragawa

Apr. 20(The University ofElectro-Communications, Japan)

May 12June 5June 19
June29July 3

Dr. Erik Gauger(Heriot-Watt University, U.K.)

Title
Attractive natures in optical processes driven by adiscrete coherent spectrum
Superabsorption, dark-state protection and opticalratchets: Harnessing collective effects for enhanced
light absorption with coupled nanostructures

Prof. Toshinori Suzuki

Probing chemical reactions using ultrafast lasers in(Kyoto University, Japan)

vacuum UV and hard X-ray regions

Mr. Yuya Seki

Quantum annealing: the current problems and(Tokyo Institute of Technology, Japan)

possible solutions

Prof. Takaharu Okajima

Physics of the cell: measurement of mechanical(Hokkaido University, Japan)

properties of cells

Mr. Ryan Hamerly(Stanford University, U.S.A.)

Theory of Coherent Ising Machine: Pulse-shape
Dynamics in Synchronously Pumped OpticalParametric Oscillators

Prof. John Clarke
July 14(University of California, Berkeley,

The Flux Qubit Revisited: Enhanced T1 and T2

U.S.A.)
July 23

Dr. Richard J. E. Taylor

Coherently Coupled 2D Photonic Crystal Surface(University of Sheffield, U.K.)

Emitting Laser Arrays

Dr. Stefan Heun
July 23(The National Enterprise for

2D Materials Research Activities at the NEST lab

nanoscience and nanoTechnology,

in Pisa, Italy

Italy)
Dr. Alberto Hernández-Mínguez
July 23(Paul Drude Institute for Solid StateElectronics, Germany)

July 23

July 24

Quantum Limit of Heat Flow Across a Single(CEA Saclay, France)

Electronic Channel

Mr. Robinjeet Singh(Louisiana State University, U.S.A.)(Kanagawa Academy of Science andTechnology, Japan)

58

grapheneDr. Francois D. Parmentier

Dr. Koki Kamiya
July 28

High-frequency surface acoustic waves on gatedQuantum Back-action Limited OptomechanicalCavity Using Microresonator: Towards Calibrationof Quantum Noises for LIGO
Bottom-up reconstitution of artificial cellular
systemResearch Activities in NTT Basic Research Laboratories Vol. 26 (2015)

July 31

Aug. 3

Aug. 3

Prof. Reinhold KochRadio-Frequency Scanning Tunneling Spectroscopy(Johannes Kepler University, Austria)

for Single-Molecule Spin Resonance
Extention, Fusion and Conversion of Multi-Photon

Dr. Toshiyuki Tashima

Entangled State / Quantum Information Using(Osaka University, Japan)

Solid-State Paramagnetic Center

Dr. Andrey A. Shevyrin

Suspended nanostructures with two-(Rzhanov Institute of Semiconductor

dimensional electron gas: electron transport andPhysics, Russia)

electromechanical effects

Dr. Stefan Fölsch
Aug. 3(Paul Drude Institute for Solid StateElectronics, Germany)Aug. 7
Aug. 7

Aug. 24

Controlling the charge state and conductance of asingle molecule by electrostatic gating

Dr. Hans Hübl

Hybrid Systems–Coupling spins, strings, and(Walther-Meissner-Institute, Germany)superconducting resonators

Dr. Aleksey Andreev

Modelling of Si quantum bits and light emission in(Hitachi Cambridge Laboratory, U.K.)

Si/Ge
Ultrafast probing of photoexcited molecular

Dr. Shungo Miyabe

dynamics; an investigation towards molecular(RIKEN, Japan)

control

Prof. Shiro Tsukamoto(Anan National College of Technology,
Sep. 25

Japan)

Recent progress on microscopy of graphene

Prof. Hiroki Hibino(Kwansei Gakuin University, Japan)
Sep. 25

Dr. JT Janssen (T. J. B. M. Janssen)(National Physical Laboratory, U.K.)
Dr. Benjamin Piot

Oct. 22(Grenoble High Magnetic Field
Laboratory, France)

Oct. 22
Dec. 16
Dec. 18

Mar. 22(University of Basel, Switzerland)

Low dimensional electronic systems in highmagnetic fields: Recent experiments
Breaking the mK barrier in Nanoelectronics

Dr. Michael J. Burek

Free-standing nanomechanical and nanophotonic(Harvard University, U.S.A.)

structures in single-crystal diamond

Dr. Michal Karpinski

Electro-optic spectral manipulation of pulsed(University of Oxford, U.K.)

quantum light

Dr. Tomoya Akatsuka

Development of optical lattice clocks and delivery(RIKEN, Japan)of the clock frequency using an optical fiber link

Mr. Tomoki Ito

Self assebly of light emitting Ge nanostrucutres on(Tohoku University, Japan)

Si for Si photonics

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Data

Feb. 4

Prof. Dominik Zumbuhl

Quantum Electrical Metrology with Graphene59

List of Award Winners
AwardAward Winners

Title

Date

The 62nd JSAP Spring
Meeting, 2015, Poster
Award

T. Teshima
S. Tsukada
N. Kasai
S. Sasaki
A. Tanaka
H. Nakashima
K. Sumitomo

Conductive silk films for
manipulation of adherent cells

Apr. 1, 2015

45th Senken Gousen
Prize New FrontierAward

Nippon Telegraph andTelephone Corporation
Toray Industries

Development of functional fabric“hitoe®”Apr. 24, 2015

Analytical Sciences Hot
Article Award

Y. UenoK. Furukawa
A. TinH. Hibino

On-chip FRET Graphene
Oxide Aptasensor: Quantitative
Evaluation of Enhanced Sensitivity
by Aptamer with a Double-stranded
DNA Spacer

Sep. 10, 2015

JSAP
Young Scientist AwardD. Hatanaka

Mechanical random access memory
in a phonon circuit

Sep. 13, 2015

MNC 2014 Award
for Most Impressive
Presentation

D. Hatanaka
I. Mahboob
K. Onomitsu
H. Yamaguchi

All-Mechanical Bistable Memory
In A Phonon WaveguideNov. 11, 2015

MNC 2014 Award for
Most Impressive Poster

K. Yamazaki
H. Yamaguchi

Renovation of Three-Dimensional
Electron Beam Lithography System
for Improvement of Positioning
Accuracy and Reduction of
Turnaround Time

Nov. 11, 2015

The Surface Science
Society of Japan Young
Scientist Award

M. Ohtomo
Y. Sekine
H. Hibino
H. Yamamoto

Etching-free Transfer of Highlyaligned Bottom-up Graphene
Nanoribbon Arrays on Au(788)TemplateFeb. 8, 2016

H. Yamamoto
20th Award on
Superconductivity Science Y. Krockenberger
M. Naito
and Technology

Discovery of Undoped Cuprate
Superconductors and Research on
its Physical Properties

Mar. 3, 2016

JSAP Silicon Technology
Division Incentive Award

Electric tuning of direct-indirect
optical transitions in siliconMar. 21, 2016

Nanobio-interfaces for detection
and controlling of biologicalinformation

Mar. 30, 2016

J. Noborisaka

Excellent Woman
Researcher Award of The
N. KasaiElectrochemical Society of
Japan

60

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

List of In-house Award Winners
Award Winners

Title

Date

NTT Science and CoreTechnology Laboratory
Group Director’s Award

K. Muraki
K. Suzuki
N. Kumada
K. Onomitsu

Realization of nontrivial electronic
states using semiconductor
heterostructures

Dec. 17, 2015

NTT Science and CoreTechnology Laboratory
Group Director’s Award

K. Nozaki
E. Kuramochi
A. Shinya
S. Matsuo
M. Notomi

Development of ultralow-power
many-bit optical random-accessmemory (RAM) based on photonic
crystalDec. 17, 2015

BRL Director’s Award
Award for Achievements

N. KumadaH. Hibino
K. Sasaki

Charge excitation and Relaxation
Dynamics in Graphene

Mar. 25, 2016

BRL Director’s Award
Award for Achievements

K. Azuma
K. Tamaki
W. J. Munro

Proposals of Novel Concepts in
Quantum Repeaters and Quantum
Key Distribution

Mar. 25, 2016

BRL Director’s Award
Award for Excellent
PapersK. Hirama
Y. Taniyasu
S. Karimoto
Y. Krockenberger
H. Yamamoto"Single-crystal cubic boron nitride
thin films grown by ion-beamassisted molecular beam epitaxy"
Applied Physics Letters 104, 092113(2014).

Mar. 25, 2016

BRL Director’s Award
Award for Excellent
PapersH. Okamoto
R. Ohta
K. Onomitsu
H. Gotoh
H. Yamaguchi"Cavity-less on-chip optomechanics
using excitonic transitions insemiconductor heterostructures"
Nature Communications 6, 8478
(2015).

Mar. 25, 2016

BRL Director’s Award
Award for Best Paper
for Environmental
Contribution

K. Nozaki
A. Shinya
H. Taniyama
M. Notomi"Sub-femtojoule all-opticalswitching using a photonic-crystal
nanocavity"
Nature Photonics 4, 477 (2010).

Mar. 25, 2016

BRL Director’s Award
Award for Performance

M. Yamaguchi
T. KimuraContribution to the Development of
the Sports Brain Laboratory

Mar. 25, 2016

BRL Director’s Award
Award for Encouragement

A. Tanaka

Research for Functional and
Structural Control of Neurons andArtificial Cells

Mar. 25, 2016

BRL Director’s Award
Award for Encouragement

Y. Matsuzaki

Development of a Theoretical
Framework on a Superconducting
Hybrid Quantum System

Mar. 25, 2016

Special BRL Director’sAward

H. Ueshima
H. Itou
M. Yamaguchi

Design & Establishment of a Secure
Network Environment in the Basic
Research Laboratories

Mar. 25, 2016

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Data

Award

61

Number of Papers
The number of papers published in international journals in fiscal 2015 is 98. Also the number of
papers published in major journals are shown below.

Journals

IF2014

Numbers

Physical Review A

2.808

10

Applied Physics Letters

3.302

9

Physical Review B

3.736

7

Japanese Journal of Applied Physics

1.127

7

Nature Communications

11.4706

Physical Review Letters

7.512

5

New Journal of Physics

3.558

5

IEEE Journal of Selected Topics in Quantum Electronics

2.828

4

Applied Physics Express

2.365

4

Optics Express

3.488

3

Journal of Applied Physics

2.183

3

Physical Review Applied―

3

Nano Letters13.592

2

ACS Nano

12.881

2

Scientific Reports

5.578

2

Journal of Crystal Growth

1.698

2

Journal of Physical Society of Japan

1.585

2

AIP Advances

1.524

2

Science33.6111Nature Photonics

32.386

1

Nature Physics

20.147

1

Chemistry of Materials

8.354

1

Nanotechnology

3.821

1

Science Advances

―

1

―

1

Optica*IF2014: Impact Factor 2014
The average IF2014 for all research papers from NTT Basic Research laboratories is 4.847.
62

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Number of Presentations
The number of presentations at international conferences in fiscal 2015 is 212. Also the number ofpresentations in major conferences are shown below.

Conferences

Numbers

21st International Conference on Electronic Properties of Two-Dimensional Systems /17th International Conference on Modulated Semiconductor Structures (Joint Conference
EP2DS-21/MSS17)

26

International Symposium on Nanoscale Transport and Technology (ISNTT2015)25

The Conference on Lasers and Electro-Optics (CLEO/QELS 2015)132015 International Conference on Solid State Devices and Materials (SSDM 2015)

8

APS March Meeting 20167

5th International Conference on Quantum Cryptography (QCrypt2015)

6

28th International Microprocesses and Nanotechnology Conference (MNC 2015)

5

International Workshop : Quantum Nanostructures and Electron-Nuclear Spin Interactions

4

Silicon Quantum Electronics Workshop 2015

4

Number of Patents
The number of applied patents in fiscal 2015 is 34.

Data

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)63

Publication List
H. Ago, Y. Ohta, H. Hibino, D. Yoshimura, R. Takizawa, Y. Uchida, M. Tsuji, T. Okajima, H. Mitani, and S.
(1) Mizuno, "Growth Dynamics of Single-layer Graphene on Epitaxial Cu Surfaces", Chem. Mat. 27, 53775385 (2015).
(2)
(3)
(4)
(5)

H. Akazawa and Y. Ueno, "Control of Surface Wettability of Hydroxyapatite Thin Films by Way of
Crystal Imperfections", Appl. Phys. Express 8, 107001 (2015).
R. Asaoka, H. Tsuchiura, M. Yamashita, and Y. Toga, "Dynamical Instability in the S=1 Bose-Hubbard
Model", Phys. Rev. A 93, 013628 (2016).
K. Azuma, K. Tamaki, and W. J. Munro, "All-photonic Intercity Quantum Key Distribution", Nat.
Commun. 6, 10171 (2015).
K. Azuma, K. Tamaki, and H. K. Lo, "All-photonic Quantum Repeaters", Nat. Commun. 6, 6787 (2015).
H. Cai, Y. Matsuzaki, K. Kakuyanagi, H. Toida, X. Zhu, N. Mizuochi, K. Nemoto, K. Semba, W. J.

(6)

Munro, S. Saito, and H. Yamaguchi, "Analysis of the Spectroscopy of a Hybrid System Composed of aSuperconducting Flux Qubit and Diamond NV Centers", J. Phys.: Condes. Matter 27, 345702 (2015).

(7)

P. A. Carles, K. Nishiguchi, and A. Fujiwara, "Deviation from the Law of Energy Equipartition in a
Small Dynamic-random-access Memory", Jpn. J. Appl. Phys. 54, 06FG03 (2015).
J. Carolan, C. Harrold, C. Sparrow, E. Martin-Lopez, N. J. Russell, J. W. Silverstone, P. J. Shadbolt, N.

(8)

Matsuda, M. Oguma, M. Itoh, G. D. Marshall, M. G. Thompson, J. C. F. Matthews, T. Hashimoto, J. L.
O'Brien, and A. Laing, "Universal Linear Optics", Science 349, 711-716 (2015).

(9)J. C. H. Chen, Y. Sato, R. Kosaka, M. Hashisaka, K. Muraki, and T. Fujisawa, "Enhanced Electron-phonon
Coupling for a Semiconductor Charge Qubit in a Surface Phonon Cavity", Sci. Rep. 5, 15176 (2015).
K. Chida, K. Nishiguchi, G. Yamahata, H. Tanaka, and A. Fujiwara, "Thermal-noise Suppression in(10) Nano-scale Si Field-effect Transistors by Feedback Control Based on Single-electron Detection", Appl.
Phys. Lett. 107, 073110 (2015).
(11)
(12)

S. Endo, Y. Matsuzaki, W. J. Munro, T. Koike, and S. Saito, "Spin Amplification in an Inhomogeneous
System", J. Phys. Soc. Jpn. 84, 103001 (2015).
R. Forbes, Y. Kashimura, and K. Sumitomo, "Hermetically Sealed Microwell with a Lipid Bilayer
Created Using a Self-assembled Monolayer", Appl. Phys. Express 8, 117201 (2015).
T. Fujii, T. Sato, K. Takeda, K. Hasebe, T. Kakitsuka, and S. Matsuo, "Epitaxial Growth of InP to Bury

(13) Directly Bonded Thin Active Layer on SiO2/Si Substrate for Fabricating Distributed Feedback Lasers on
Silicon", IET Optoelectron. 9, 151-157 (2015).
M. Godonoga, T. Y. Lin, A. Oshima, K. Sumitomo, M. S. L. Tang, Y. W. Cheung, A. B. Kinghorn, R. M.
(14) Dirkzwager, C. S. Zhou, A. Kuzuya, J. A. Tanner, and J. G. Heddle, "A DNA Aptamer Recognising a
Malaria Protein Biomarker Can Function as Part of a DNA Origami Assembly", Sci. Rep. 6, 21266 (2016).
T. Goto, N. Kasai, R. Lu, R. Filip, and K. Sumitomo, "Scanning Electron Microscopy Observation of(15) Interface Between Single Neurons, and Conductive Surfaces", J. Nanosci. Nanotechnol. 16, 3383-3387(2016).

64

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

(16)
(17)
(18)

J. Govenius, Y. Matsuzaki, I. G. Savenko, and M. Mottonen, "Parity Measurement of Remote Qubits
Using Dispersive Coupling and Photodetection", Phys. Rev. A 92, 042305 (2015).
D. Hashimoto and K. Shimizu, "Coherent Raman Beat Analysis of the Hyperfine Sublevel Coherence
Properties of 167Er3+ Ions Doped in an Y2SiO5 Crystal", J. Lumines. 171, 183-190 (2016).
D. Hatanaka, A. Dodel, I. Mahboob, K. Onomitsu, and H. Yamaguchi, "Phonon Propagation Dynamics
in Band-engineered One Dimensional Phononic Crystal Waveguides", New J. Phys. 17, 113032 (2015).
M. Hattori, H. Ikenoue, D. Nakamura, F. Kazuaki, M. Takamura, H. Hibino, and T. Okada, "Direct(19) Growth of Graphene on SiC(0001) by KrF-excimer-laser Irradiation", Appl. Phys. Lett. 108, 093107(2016).
M. Hiroki, K. Kumakura, and H. Yamamoto, "Enhancement of Performance of AlGaN/GaN High(20) electron-mobility Transistors by Transfer from Sapphire to a Copper Plate", Jpn. J. Appl. Phys. 55,
05FH07 (2016).
K. Hitachi, A. Ishizawa, O. Tadanaga, T. Nishikawa, H. Mashiko, T. Sogawa, and H. Gotoh, "Frequency(21) Stabilization of an Er-doped Fiber Laser with a Collinear 2f-to-3f Self-referencing Interferometer", Appl.
Phys. Lett. 106, 231106 (2015).
(22)

M. Hori, M. Uematsu, A. Fujiwara, and Y. Ono, "Electrical Activation and Electron Spin Resonance
Measurements of Arsenic Implanted in Silicon", Appl. Phys. Lett. 106, 142105 (2015).
A. Iagallo, S. Tanabe, S. Roddaro, M. Takamura, Y. Sekine, H. Hibino, V. Miseikis, C. Coletti, V. Piazza,(23) F. Beltram, and S. Heun, "Bilayer-induced Asymmetric Quantum Hall Effect in Epitaxial Graphene",
Semicond. Sci. Technol. 30, 055007 (2015).
(24)
(25)

T. Ikuta and H. Takesue, "Enhanced Violation of the Collins-Gisin-Linden-Massar-Popescu Inequality
with Optimized Time-bin-entangled Ququarts", Phys. Rev. A 93, 022307 (2016).
D. Imanaka, S. Sharmin, M. Hashisaka, K. Muraki, and T. Fujisawa, "Exchange-induced Spin Blockade
in a Two-electron Double Quantum Dot", Phys. Rev. Lett. 115, 176802 (2015).
M. Jo, T. Uchida, A. Tsurumaki-Fukuchi, M. Arita, A. Fujiwara, Y. Ono, K. Nishiguchi, H. Inokawa,(26) and Y. Takahashi, "Fabrication and Single-electron-transfer Operation of a Triple-dot Single-electronTransistor", J. Appl. Phys. 118, 214305 (2015).
(27)

K. Kakuyanagi, T. Baba, Y. Matsuzaki, H. Nakano, S. Saito, and K. Semba, "Observation of Quantum
Zeno Effect in a Superconducting Flux Qubit", New J. Phys. 17, 063035 (2015).
M. Kasu, K. Hirama, K. Harada, and T. Oishi, "Study on Capacitance-voltage Characteristics of(28) Diamond Field-effect Transistors with NO2 Hole Doping and Al2O3 Gate Insulator Layer", Jpn. J. Appl.
Phys. 55, 041301 (2016).
K. Kato, K. Oguri, H. Sanada, T. Tawara, T. Sogawa, and H. Gotoh, "Determination of Phonon Decay(29) Rate in P-Type Silicon Under Fano Resonance by Measurement of Coherent Phonons", AIP Adv. 5,097152 (2015).

(31)

Data

(30)

K. Kato, F. Furrer, and M. Murao, "Information-Theoretical Analysis of Topological Entanglement
Entropy and Multipartite Correlations", Phys. Rev. A 93, 022317 (2016).
G. C. Knee and W. J. Munro, "Optimal Trotterization in Universal Quantum Simulators Under Faulty
Control", Phys. Rev. A 91, 052327 (2015).

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

65

(32)

G. C. Knee and W. J. Munro, "Fisher Information Versus Signal-to-noise Ratio for a Split Detector",Phys. Rev. A 92, 012130 (2015).
Y. Kobayashi, S. Sasaki, S. Mori, H. Hibino, Z. Liu, K. Watanabe, T. Taniguchi, K. Suenaga, Y. Maniwa,(33) and Y. Miyata, "Growth and Optical Properties of High-quality Monolayer WS2 on Graphite", ACS Nano
9, 4056-4063 (2015).
(34)
(35)
(36)
(37)

Y. Kondo, Y. Matsuzaki, K. Matsushima, and J. G. Filgueiras , "Using the Quantum Zeno Effect for
Suppression of Decoherence", New J. Phys. 18, 013033 (2016).
Y. Krockenberger, M. Horio, H. Irie, A. Fujimori, and H. Yamamoto, "As-grown Superconducting
Pr2CuO4 Under Thermodynamic Constraints", Appl. Phys. Express 8, 053101 (2015).
N. Kumada, F. D. Parmentier, H. Hibino, D. C. Glattli, and P. Roulleau, "Shot Noise Generated byGraphene P-N Junctions in the Quantum Hall Effect Regime", Nat. Commun. 6, 8068 (2015).
Y. Kunihashi, H. Sanada, H. Gotoh, K. Onomitsu, M. Kohda, J. Nitta, and T. Sogawa, "Drift Transportof Helical Spin Coherence with Tailored Spin-orbit Interactions", Nat. Commun. 7, 10722 (2016).
E. Kuramochi, K. Nozaki, A. Shinya, H. Taniyama, K. Takeda, T. Sato, S. Matsuo, and M. Notomi,(38) "Ultralow Bias Power All-optical Photonic Crystal Memory Realized with Systematically Tuned L3
Nanocavity", Appl. Phys. Lett. 107, 221101 (2015).
(39)

C.H. Lin, T. Akasaka, and H. Yamamoto, "N-Face GaN(000-1) Films with Hillock-free Smooth Surfaces
Grown by Group-III-source Flow-rate Modulation Epitaxy", Jpn. J. Appl. Phys. 55, 04EJ01 (2016).
I. Mahboob, N. Perrissin, K. Nishiguchi, D. Hatanaka, Y. Okazaki, A. Fujiwara, and H. Yamaguchi,(40) "Dispersive and Dissipative Coupling in a Micromechanical Resonator Embedded with a
Nanomechanical Resonator", Nano Lett. 15, 2312-2317 (2015).
(41)

T. Makimoto, K. Kumakura, M. Maeda, H. Yamamoto, and Y. Horikoshi, "A New AlON Buffer Layer
for RF-MBE Growth of AlN on a Sapphire Substrate", J. Cryst. Growth 425, 138-140 (2015).
S. Mamyouda, H. Ito, Y. Shibata, S. Kashiwaya, M. Yamaguchi, T. Akazaki, H. Tamura, Y. Ootuka, and S.

(42) Nomura, "Circularly Polarized Near-field Optical Mapping of Spin-resolved Quantum Hall Chiral Edge
States", Nano Lett. 15, 2417-2421 (2015).
J. Martinez-Blanco, C. Nacci, S. C. Erwin, K. Kanisawa, E. Locane, M. Thomas, F. von Oppen, P. W.
(43) Brouwer, and S. Folsch, "Gating a Single-molecule Transistor with Individual Atoms", Nat. Phys. 11,
640-644 (2015).
(44)
(45)
(46)

J. Martinez-Blanco, S. C. Erwin, K. Kanisawa, and S. Folsch, "Energy Splitting of Image States Inducedby the Surface Potential Corrugation of InAs(111) A", Phys. Rev. B 92, 115444 (2015).
N. Matsuda, "Deterministic Reshapin of Single Photon Spectra Using Cross-phase Modulation", Sci.
Adv. 2, e1501223 (2016).
Y. Matsuzaki and H. Tanaka, "Quantum Zeno Effect in an Unstable System with NMR", J. Phys. Soc.
Jpn. 85, 014001 (2016).
Y. Matsuzaki, X. Zhu, K. Kakuyanagi, H. Toida, T. Shimooka, N. Mizuochi, K. Nemoto, K. Semba, W. J.

(47)

Munro, H. Yamaguchi, and S. Saito, "Improving the Lifetime of the Nitrogen-vacancy-center Ensemble
Coupled with a Superconducting Flux Qubit by Applying Magnetic Fields", Phys. Rev. A 91, 042329(2015).

66

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Y. Matsuzaki, X. Zhu, K. Kakuyanagi, H. Toida, T. Shimo-Oka, N. Mizuochi, K. Nemoto, K. Semba,(48) W. J. Munro, H. Yamaguchi, and S. Saito , "Improving the Coherence Time of a Quantum System Via a
Coupling to a Short-lived System", Phys. Rev. Lett. 114, 120501 (2015).
(49)
(50)

A. Mizutani, N. Imoto, and K. Tamaki, "Robustness of the Round-Robin Differential-phase-shift
Quantum-key-distribution Protocol Against Source Flaws", Phys. Rev. A 92, 060303 (2015).
A. Mizutani, M. Curty, C. C. W. Lim, N. Imoto, and K. Tamaki, "Finite-key Security Analysis of
Quantum Key Distribution with Imperfect Light Sources", New J. Phys. 17, 093011 (2015).

(51) F. Morikoshi, "An Entanglement Analogue in Light Cones", Prog. Theor. Exp. Phys. 123A04 (2015).
S. S. Mou, H. Irie, Y. Asano, K. Akahane, H. Nakajima, H. Kumano, M. Sasaki, A. Murayama, and(52) I. Suemune, "Time-resolved Measurements of Cooper-pair Radiative Recombination in InAs Quantum
Dots", J. Appl. Phys. 118, 073102 (2015).
S. S. Mou, H. Irie, Y. Asano, K. Akahane, H. Nakajima, H. Kumano, M. Sasaki, A. Murayama, and(53) I. Suemune, "Optical Observation of Superconducting Density of States in Luminescence Spectra of
InAs Quantum Dots", Phys. Rev. B 92, 035308 (2015).
(54)
(55)

W. J. Munro, K. Azuma, K. Tamaki, and K. Nemoto, "Inside Quantum Repeaters", IEEE J. Sel. Top.
Quantum Electron. 21, 6400813 (2015).
M. Naito, K. Uehara, R. Takeda, Y. Taniyasu, and H. Yamamoto, "Growth of Iron Nitride Thin Films by
Molecular Beam Epitaxy", J. Cryst. Growth 415, 36-40 (2015).
M. Naito, Y. Krockenberger, A. Ikeda, and H. Yamamoto, "Reassessment of the Electronic State,(56) Magnetism, and Superconductivity in High-Tc cuprates with the Nd2CuO4 structure", Physica C 523, 28(2016).
R. Nakao, M. Arai, W. Kobayashi, T. Yamamoto, and S. Matsuo, "1.3-μm InGaAs MQW Metamorphic(57) Laser Diode Fabricated With Lattice Relaxation Control Based on In Situ Curvature Measurement",
IEEE J. Sel. Top. Quantum Electron. 21, 1501407 (2015).
(58)
(59)

R. Namiki and K. Azuma, "Quantum Benchmark Via an Uncertainty Product of Canonical Variables",Phys. Rev. Lett. 114, 140503 (2015).
H. Nishi, K. Takeda, T. Tsuchizawa, T. Fujii, S. Matsuo, K. Yamada, and T. Yamamoto, "Monolithic
Integration of InP Wire and SiOx Waveguides on Si Platform", IEEE Photonics J. 7, 4900308 (2015).
K. Nishiguchi, A. Castellanos-Gomez, H. Yamaguchi, A. Fujiwara, H. S. J. van der Zant, and G. A.

(60) Steele, "Observing the Semiconducting Band-gap Alignment of MoS2 Layers of Different Atomic
Thicknesses Using a MoS2/SiO2/Si Heterojunction Tunnel Diode", Appl. Phys. Lett. 107, 053101 (2015).
K. Noda, K. Inaba, and M. Yamashita, "Magnetism in the Three-Dimensional Layered Lieb Lattice:(61) Enhanced Transition Temperature via Flat-band and Van Hove Singularities", Phys. Rev. A 91, 063610(2015).

(62)

Data

S. Nomura, S. Mamyouda, H. Ito, Y. Shibata, T. Ohira, L. Yoshikawa, Y. Ootuka, S. Kashiwaya, M.
Yamaguchi, H. Tamura, and T. Akazaki, "Circularly Polarized Near-field Scanning Optical Microscopefor Investigations of Edge States of a Two-dimensional Electron System", Appl. Phys. A-Mater. Sci.
Process. 121, 1341-1345 (2015).

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67

K. Nozaki, A. Lacraz, A. Shinya, S. Matsuo, T. Sato, K. Takeda, E. Kuramochi, and M. Notomi, "All(63) optical Switching for 10-Gb/s Packet Data by Using an Ultralow-power Optical Bistability of Photoniccrystal Nanocavities", Opt. Express 23, 30379-30392 (2015).
R. Ohsugi, Y. Kunihashi, H. Sanada, M. Kohda, H. Gotoh, T. Sogawa, and J. Nitta, "Bias Dependence of(64) Spin Injection/transport Properties of a Perpendicularly magnetized FePt/MgO/GaAs Structure", Appl.
Phys. Express 9, 043002 (2016).
(65)

R. Ohta, H. Okamoto, R. Hey, K. J. Friedland, and H. Yamaguchi, "Optically Induced Strong Intermodal
Coupling in Mechanical Resonators at Room Temperature", Appl. Phys. Lett. 107, 091906 (2015).
H. Okamoto, T. Watanabe, R. Ohta, K. Onomitsu, H. Gotoh, T. Sogawa, and H. Yamaguchi, "Cavity-(66) less On-chip Optomechanics Using Excitonic Transitions in Semiconductor Heterostructures", Nat.
Commun. 6, 8478 (2015).
(67)

Y. Pan, J. S. Yang, S. C. Erwin, K. Kanisawa, and S. Folsch, "Reconfigurable Quantum-dot Molecules
Created by Atom Manipulation", Phys. Rev. Lett. 115, 076803 (2015).
V. T. Renard, B. A. Piot, X. Waintal, G. Fleury, D. Cooper, Y. Niida, D. Tregurtha, A. Fujiwara, Y.

(68) Hirayama, and K. Takashina, "Valley Polarization Assisted Spin Polarization in Two Dimensions", Nat.
Commun. 6, 7230 (2015).
(69)

T. D. Rhone, L. Tiemann, and K. Muraki, "NMR Probing of Spin and Charge Order near Odd-integer
Filling in the Second Landau Level", Phys. Rev. B 92, 041301 (2015).
S. Sasaki, K. Tateno, G. Q. Zhang, H. Pigot, Y. Harada, S. Saito, A. Fujiwara, T. Sogawa, and K. Muraki,(70) "Self-aligned Gate-all-around InAs/InP Core-shell Nanowire Field-effect Transistors", Jpn. J. Appl.
Phys. 54, 04DN04 (2015).
(71)

K. Sasaki, S. Murakami, and Y. Tokura, "Determination of Intrinsic Lifetime of Edge Magnetoplasmons",
Phys. Rev. B 93, 125402 (2016).
T. Sato, K. Takeda, A. Shinya, M. Notomi, K. Hasebe, T. Kakitsuka, and S. Matsuo, "Photonic Crystal(72) Lasers for Chip-to-chip and On-chip Optical Interconnects", IEEE J. Sel. Top. Quantum Electron. 21,
4900410 (2015).
T. Satoh, Y. Matsuzaki, K. Kakuyanagi, W. J. Munro, K. Semba, H. Yamaguchi, and S. Saito, "Scalable(73) Quantum Computation Architecture Using Always-on Ising Interactions Via Quantum Feedforward",
Phys. Rev. A 91, 052329 (2015).
(74)

B. Scharfenberger, H. Kosaka, W. J. Munro, and K. Nemoto, "Absorption-based Quantum
Communication with NV Centres", New J. Phys. 17, 103012 (2015).
R. Shaikhaidarov, V. N. Antonov, A. Casey, A. Kalaboukhov, S. Kubatkin, Y. Harada, K. Onomitsu,(75)

A. Tzalenchuk, and A. Sobolev, "Detection of Coherent Terahertz Radiation from a High-temperature
Superconductor Josephson Junction by a Semiconductor Quantum-dot Detector", Phys. Rev. Appl. 5,024010 (2016).

(76)
(77)

68

H. Shibata, K. Shimizu, H. Takesue, and Y. Tokura, "Ultimate Low System Dark-count Rate forSuperconducting Nanowire Single-photon Detector", Opt. Lett. 40, 3428-3431 (2015).
K. Shimizu and Y. Tokura, "Identifying a Correlated Spin Fluctuation in an Entangled Spin Chain
Subject to a Quantum Phase Transition", Phys. Rev. E 92, 062143 (2015).

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

(78)
(79)
(80)
(81)
(82)
(83)

S. Souma, A. Sawada, H. Chen, Y. Sekine, M. Eto, and T. Koga, "Spin Blocker Using the Interband
Rashba Effect in Symmetric Double Quantum Wells", Phys. Rev. Appl. 4, 034010 (2015).
H. Sumikura, E. Kuramochi, H. Taniyama, and M. Notomi, "Enhanced Electron-hole Droplet Emission
from Surface-oxidized Silicon Photonic Crystal Nanocavities", Opt. Express 24, 1072-1081 (2016).
K. Suzuki, Y. Harada, K. Onomitsu, and K. Muraki, "Gate-controlled Semimetal-topological Insulator
Transition in an InAs/GaSb Heterostructure", Phys. Rev. B 91, 245309 (2015).
S. Suzuki and H. Hibino, "Large Optical Anisotropy for Terahertz Light of Stacked Graphene Ribbons
with Slight Asymmetry", J. Appl. Phys. 117, 174302 (2015).
S. Suzuki, M. Takamura, and H. Yamamoto, "Transmission, Reflection, and Absorption Spectroscopy ofGraphene Microribbons in the Terahertz Region", Jpn. J. Appl. Phys. 55, 06GF08 (2016).
K. Takase, H. Hibino, and K. Muraki, "Probing the Extended-state Width of Disorder-broadened Landau
Levels in Epitaxial Graphene", Phys. Rev. B 92, 125407 (2015).
H. Takesue, S. D. Dyer, M. J. Stevens, V. Verma, R. P. Mirin, and S. W. Nam, "Quantum Teleportation(84) over 100 km of Fiber Using Highly Efficient Superconducting Nanowire Single-photon Detectors",
Optica 2, 832-835 (2015).
(85)
(86)

H. Takesue, T. Sasaki, K. Tamaki, and M. Koashi, "Experimental Quantum Key Distribution without
Monitoring Signal Disturbance", Nat. Photonics 9, 827-831 (2015).
H. Takesue, E. Diamanti, R. Thew, and Z. L. Yuan, "Introduction to the Issue on Quantum
Communication and Cryptography", IEEE J. Sel. Top. Quantum Electron. 21, 0200402 (2015).
M. Takiguchi, H. Taniyama, H. Sumikura, M. D. Birowosuto, E. Kuramochi, A. Shinya, T. Sato, K.

(87) Takeda, S. Matsuo, and M. Notomi, "Systematic Study of Thresholdless Oscillation in High-beta Buried
Multiple-quantum-well Photonic Crystal Nanocavity Lasers", Opt. Express 24, 3441-3450 (2016).
T. Tanaka, P. Knott, Y. Matsuzaki, S. Dooley, H. Yamaguchi, W. J. Munro, and S. Saito, "Proposed(88) Robust Entanglement-based Magnetic Field Sensor Beyond the Standard Quantum Limit", Phys. Rev.
Lett. 115, 170801 (2015).
A. Tanaka, R. Tanaka, N. Kasai, S. Tsukada, T. Okajima, and K. Sumitomo, "Time-lapse Imaging of(89) Morphological Changes in a Single Neuron During the Early Stages of Apoptosis Using Scanning Ion
Conductance Microscopy", J. Struct. Biol. 191, 32-38 (2015).
A. Tanaka, H. Nakashima, Y. Kashimura, and K. Sumitomo, "Electrostatically Induced Planar Lipid(90) Membrane Formation on a Cationic Hydrogel Array by the Fusion of Small Negatively Charged
Unilamellar Vesicles", Colloid Surf. A-Physicochem. Eng. Asp. 477, 63-69 (2015).
H. Toida, Y. Matsuzaki, K. Kakuyanagi, X. Zhu, W. J. Munro, K. Nemoto, H. Yamaguchi, and S. Saito,(91) "Electron Paramagnetic Resonance Spectroscopy Using a Direct Current-SQUID Magnetometer Directly
Coupled to an Electron Spin Ensemble", Appl. Phys. Lett. 108, 052601 (2016).
Data

T. Uchida, M. Jo, A. Tsurumaki-Fukuchi, M. Arita, A. Fujiwara, and Y. Takahashi, "Fabrication and(92) Evaluation of Series-triple Quantum Dots by Thermal Oxidation of Silicon Nanowire", AIP Adv. 5,117144 (2015).

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)69

Y. Ueno, K. Furukawa, A. Tin, and H. Hibino, "On-chip FRET Graphene Oxide Aptasensor: Quantitative(93) Evaluation of Enhanced Sensitivity by Aptamer with a Double-stranded DNA Spacer", Anal. Sci. 31,
875-879 (2015).
(94)
(95)

S. Wang, Y. Sekine, S. Suzuki, F. Maeda, and H. Hibino, "Photocurrent Generation of a Single-gate
Graphene P-N Junction Fabricated by Interfacial Modification", Nanotechnology 26, 385203 (2015).
K. Washio, R. Nakazawa, M. Hashisaka, K. Muraki, Y. Tokura, and T. Fujisawa, "Long-lived Binary
Tunneling Spectrum in the Quantum Hall Tomonaga-Luttinger Liquid", Phys. Rev. B 93, 075304 (2016).
K. Yamazaki and H. Yamaguchi, "Renovation of Three-dimensional Electron Beam Lithography for(96) Improvement of Positioning Accuracy and Reduction of Turnaround Time", Jpn. J. Appl. Phys. 54,
06FD02 (2015).
(97)

N. Zen, H. Shibata, Y. Mawatari, M. Koike, and M. Ohkubo, "Biomolecular Ion Detection Using Hightemperature Superconducting MgB2 Strips", Appl. Phys. Lett. 106, 222601 (2015).
G. Zhang, C. Rainville, A. Salmon, M. Takiguchi, K. Tateno, and H. Gotoh, "Bridging the Gap between(98) the Nanometer-scale Bottom-up and Micrometer-scale Top-down Approaches for Site-defined InP/InAs
Nanowires", ACS Nano 9, 10580-10589 (2015).

70

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List of Invited Talks
Ⅰ.

Materials Science Laboratory
H. Hibino, S. Wang, C. M. Orofeo, and S. Suzuki, "Synthesis and Functionalization of Two-Dimensional(1)

Materials: Graphene, Hexagonal Boron Nitride, and Transition Metal Dichalcogenides", The 22ndInternational Workshop on Active-Matrix Flatpanel Displays and Devices -TFT Technologies and FPD
Materials- (AM-FPD '15), Kyoto, Japan (July 2015).

(2)
(3)
(4)

Y. Ueno and K. Furukawa, "On-Chip Graphene FRET Biosensor for Protein Detection", The FifteenthInternational Symposium on Electroanalytical Chemistry (15th ISEAC), Changchun, China (Aug. 2015).
Y. Taniyasu, "Progress in AIN-Based Deep UV Emitters and Lasers", 2015 IEEE Photonics Conference(IPC), Reston, U.S.A. (Oct. 2015).
K. Furukawa, "Controlling Self-Spreading of Lipid Bilayer on Patterned Surface", Tethered Membrane2015 Conference (TethMem 2015), Singapore, Singapore (Nov. 2015).
Y. Ueno, K. Furukawa, T. Teshima, M. Takamura, and H. Hibino, "Fabrication of Patterned Graphene(5) Electrode by a Transfer Process Assisted by a Parylene Thin Film", The International Chemical Congressof Pacific Basin Societies 2015 (Pacifichem 2015), Honolulu, U.S.A. (Dec. 2015).
(6)

N. Kasai and K. Sumitomo, "Neuronal Guidance Using Nanopillars", 9th International Symposium on
Nanomedicine (ISNM 2015), Tsu, Japan (Dec. 2015).
Y. Krockenberger, N. Breznay, N. Nair, H. Irie, R. McDonald, J. Analytis, and H. Yamamoto, "Snatching(7) the Cuprates' Fermi Pockets", International USMM & CMSI Workshop: Frontiers of Materials andCorrelated Electron Science-from Bulk to Thin Films and Interfaces, Tokyo, Japan (Jan. 2016).

Ⅱ.
(1)

Physical Science Laboratory
A. Fujiwara, "Silicon Single-Electron Devices for Ultimate Electronics", DC & Quantum Metrology
Meeting, Bern, Switzerland (May 2015).
I. Mahboob and H. Yamaguchi, "An Electromechanical Van der Pol Resonator", 3rd International(2) Conference on Phononic Crystals/Metamaterials, Phonon Transport and Phonon Coupling (Phononics
2015), Paris, France (May 2015).
(3)

K. Muraki, "Probing and Controlling Disorder Effects for the Studies of Fractional Quantum Hall
effects", Quantum transport on 2D systems Session Workshop II (W2), Luchon, France (May 2015).
K. Nishiguchi, "What happens in a Small Transistor with Single-Electron Resolution?", The 5th(4) International Symposium on Organic and Inorganic Electronic Materials and Related Nanotechnologies(EM-NANO 2015), Niigata, Japan (June 2015).
J. Noborisaka, K. Nishiguchi, and A. Fujiwara, "Gate Tuning of Direct Optical Transitions in Silicon",Data(5) 2015 Asia-Pacific Workshop on Fundamentals and Applications of Advanced Semiconductor Devices,Jeju, Korea (June 2015).
N. Clement, G. Larrieu, K. Nishiguchi, and A. Fujiwara, "Ultra-Low Noise Nanoscale Transistors for(6) Metrology of Noise, Energy Harvesting and Biosensing Applications", International Conference on Noiseand Fluctuation (ICNF), Xi'an, China (June 2015).

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)71

D. Hatanaka, I. Mahboob, K. Onomitsu, and H. Yamaguchi, "Phononic Crystal Waveguides with
(7) Dynamic Control",19th International Conference on Electron Dynamics in Semiconductors,
Optoelectronics and Nanostructures (EDISON-19), Salamanca, Spain (June 2015).
(8)

A. Fujiwara, G. Yamahata, J. Noborisaka, and K. Nishiguchi, "Nanoscale Silicon MOSFET for Metrology
and Valleytronics Applications", 2015 UK-Japan Si Nano2 Symposium, Southampton, U.K. (July 2015).
I. Mahboob, H. Okamoto, and H. Yamaguchi, "Correlated Phonon Pair Generation in an(9) Electromechanical Resonator",17th International Conference on Modulated Semiconductor Structures(MSS-17), Sendai, Japan (July 2015).
S. Foelsch, J. Martinez-Blanco, J. Yang, K. Kanisawa, and S. C. Erwin, "Quantum Dots with Single(10) Atom Precision", 17th International Conference on Modulated Semiconductor Structures (MSS-17),
Sendai, Japan (July 2015).
(11)

Y. Matsuzaki, "Quantum Sensing Basics", Diamond Quantum Sensing Workshop 2015, Takamatsu, Japan(Aug. 2015).
H. Yamaguchi, D. Hatanaka, I. Mahboob, and H. Okamoto, "III-V Semiconductor Micro/Nanomechanical(12) Resonators", 5th International Workshop on Epitaxial Growth and Fundamental Properties of
Semiconductor Nanostructures (SemiconNano 2015), Hsinchu, Taiwan (Sep. 2015).
A. Fujiwara, G. Yamahata, and K. Nishiguchi, "Gigahertz Single-Electron Pump Towards a(13) Representation of the New Ampere", 2015 International Conference on Solid State Devices andMaterials, Sapporo, Japan (Sep. 2015).
(14)

I. Mahboob and H. Yamaguchi, "Phonon Dynamics in Electromechanical Resonators", 2015 IEEE
International Ultrasonics Symposium (2015 IUS), Taipei, Taiwan (Oct. 2015).
H. Yamaguchi, D. Hatanaka, I. Mahboob, and H. Okamoto, "Phonon Confinement, Transport, and(15) Piezoelectric Manipulation in Semiconductor Micromechanical Structures", Material Research Society(MRS) 2015 Fall meeting, Boston, U.S.A. (Nov. 2015).
K. Muraki, T. D. Rhone, K. Yonaga, and N. Shibata, "NMR Probing of Charge-Density-Wave States in(16) the Third Landau Level", International Workshop on Emergent Phenomena in Quantum Hall Systems,
Mumbai, India (Jan. 2016).
(17)

Ⅲ.
(1)

H. Yamaguchi, "Mechanical Systems Hybridized with Semiconductor Quantum Structures", Gordon
Research Conference (GRC) - Mechanical Systems in the Quantum Regime -, Ventura, U.S.A. (Mar. 2016).

Optical Science Laboratory
W. J. Munro and K. Nemoto, "Quantum Repeaters: Form the First Generation to the Third?", 1stWorkshop on Quantum Repeaters and Quantum Networks, Pacific Grove, U.S.A. (May 2015).
K. Oguri, H. Mashiko, T. Yamaguchi, K. Kato, A. Suda, and H. Gotoh "Dynamical Core-Level Spectroscopy(2) Based on Attosecond High-Order Harmonic Pulse Sources", The 6th Shanghai-Tokyo Advanced Research
Symposium on Ultrafast Intense Laser Science(STAR6), Hangzhou, China (May 2015).
H. Takesue, T. Inagaki, K. Inoue, and Y. Yamamoto, "Time-Division-Multiplexed Degenerate Optical(3) Parametric Oscillator for Coherent Ising machine", IEEE Photonics Society Summer Topical Meeting on
Nonlinear-Optical Signal Processing (NOSP), Nassau, Bahamas (July 2015).

72

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

K. Oguri, T. Tsunoi, K. Kato, H. Nakano, T. Nishikawa, K. Tateno, T. Sogawa, and H. Gotoh, "High(4)Order Harmonic Source Based Femtosecond Core-Levelphotoelectron Spectroscopy for Carrier Transport
Dynamics on Semiconductor Surface", The International Conference on Advanced Laser Technologies(ALT 15), Faro, Portugal (Sep. 2015).
H. Sanada, Y. Kunihashi, H. Gotoh, K. Onomitsu, M. Kohda, J. Nitta, and T. Sogawa, "Transport of(5) Electron Spin Coherence in Persistent Spin Helix Condition", 12th Sweden-Japan QNANO Workshop,
Hindas, Sweden (Sep. 2015).
(6)(7)

K. Azuma, "All-Photonic Quantum Internet", Physical Science Symposium-2015-Boston, Boston, U.S.A.
(Sep. 2015).
K. Tamaki, "Security of Quantum Key Distribution with Imperfect Light Sources", Physical Science
Symposium-2015-Boston, Boston, U.S.A. (Sep. 2015).
K. Tamaki, "Security of Quantum Key Distribution with Imperfect Light Sources", 3rd the European(8) Telecommunications Standards Institute/Institute for Quantum Computing Workshop on Quantum-Safe
Cryptography (ETSI/IQC), Seoul, Korea (Oct. 2015).
Y. Kunihashi, H. Sanada, H. Gotoh, K. Onomitsu, and T. Sogawa, "Electrical Control of Drifting Spin
(9) Coherence", International Workshop : Quantum Nanostructures and Electron-Nuclear Spin Interactions,Sendai, Japan (Oct. 2015).
H. Mashiko, K. Oguri, T. Yamaguchi, A. Suda, and H. Gotoh, "Characterizing Ultrafast Dipole Dynamics(10) with Isolated Attosecond Pulse", Sino-German Symposium on Attosecond Photonics 2015 (SGSAP-2015),
Shanghai, China (Nov. 2015).
(11)

H. Takesue, "Towards Large Scale Coherent Ising Machine", US-Japan Workshop; New-Generation
Computers: Quantum Annealing and Coherent Computing, Stanford, U.S.A. (Dec. 2015).
W. J. Munro, Y. Matsuzaki, K. Kakuyanagi, K. Nemoto, and S. Saito, "Hybridization, a Nice Tool for(12) Quantum Engineering", ARC Centre of Excellence for Engineered Quantum Systems Annual Workshop
2015 (EQuS), Benowa QLD, Australia (Dec. 2015).
W. J. Munro, Y. Matsuzaki, S. Dooley, E. Yukawa, K. Kakuyanagi, H. Toida, K. Semba,(13)

H. Yamaguchi, K. Nemoto, and S. Saito, "Quantum Engineering Using Hybridization: When 1+1 >2", RIKEN Center for Emergent Matter Science International Symposium on Dynamics in Artificial
Quantum Systems (DAQS 2016), Tokyo, Japan (Jan. 2016).

(14)
(15)

Ⅳ.

Technology Workshop, Tokyo, Japan (Mar. 2016).
N. Matsuda, "Spectral Engineering of Single Photon Wave Packets Using Cross Phase Modulation",Spectral and Spatial Engineering of Quantum Light (SSEQL), Warsaw, Poland (Mar. 2016).

Nanophotonics Center
E. Kuramochi and M. Notomi, "All-Optical Memories on a Photonic Crystal Chip", SPIE Optics +Optoelectronics 2015, Praha, Chech (Apr. 2015).

Data

(1)

W. J. Munro, K. Azuma and K. Nemoto, "Towards Quantum Networking for QKD", UK-Japan Quantum

M. Notomi, A. Yokoo, M. D. Birowosuto, M. Takiguchi, K. Tateno, G. Zhang, and(2) E. Kuramochi, "Hybrid Nanohpotonics Systems Combined with Functional Nanomaterials", The 20th
Opto Electronics and Communications Conference (OECC), Shanghai, China (June 2015).

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

73

(3)

S. Matsuo, K. Takeda, T. Fujii, and T. Satou," Photonic Crystal Lasers on Si ", The European Conferenceon Lasers and Electro-Optics (CLEO 2015), Munchen, Germany (June 2015).
S. Matsuo, T. Fujii, and K. Takeda, "Low-Operating-Energy Membrane-Buried Heterostructure Lasers(4) on SiO2/Si Substrate", The 20th Opto Electronics and Communications Conference (OECC), Shanghai,
China (June 2015).
(5)

A. Shinya and M. Notomi, "Nanophotonics Technology Toward Optical Logic Circuits", 15th
International Forum on MPSoC for Software-defined Hardware, Ventura, U.S.A. (July 2015).
M. Notomi, A. Yokoo, M. D. Birowosuto, M. Takiguchi, K. Tateno, G. Zhang, and(6) E. Kuramochi, "III-V Nanowire-Induced Nanocavity in Si Photonic Crystals", 17th International
Conference on Modulated Semiconductor Structures (MSS-17), Sendai, Japan (July 2015).
S. Matsuo, T. Fujii, K. Takeda, H. Nishi, K. Hasebe, and T. Kakitsuka, "On-Silicon Integration of(7) Compact and Energy-Efficient DFB Laser with 40-Gbit/s Direct Modulation", 2015 IEEE International
Conference on Group IV Photonics (IEEE), Vancouver, Canada (Aug. 2015).
(8)
(9)
(10)

M. Notomi, "Ultralow-Power Integrated Photonic Crystal Devices", European Conference on OpticalCommunication (ECOC), Valencia, Spain (Sep. 2015).
S. Matsuo, T. Fujii, and K. Takeda, "Directly Modulated Membrane Lasers on Si ", The 76th JSAP
Autumn Meeting, 2015, Nagoya, Japan (Sep. 2015).
A. Yokoo, "Nano-Fabrication for Photonic Crystal Functional Device - a Route for Functional Photonic
Integration -", International Symposium on Frontier Applied Physics 2015, Bandung, Indonesia (Oct. 2015).
K. Nozaki, S. Matsuo, T. Fujii, K. Takeda, E. Kuramochi, and M. Notomi, "Photonic Crystal(11) Photodetector-Modulator Integration for Ultra-Compact Wavelength Converter", 2015 IEEE Photonics
Conference (IPC), Reston, U.S.A. (Oct. 2015).
M. Notomi, A. Yokoo, M. D. Birowosuto, M. Takiguchi, M. Ono, K. Tateno, G. Zhang, and E.
(12) Kuramochi, "Hybrid Nanophotonics Systems Based on Sub-Wavelength Nanowires", NANOWIRES
2015, Barcelona, Spain (Oct. 2015).
K. Takeda, T. Fujii, A. Shinya, E. Kuramochi, M. Notomi, K. Hasebe, T. Kakitsuka, and S. Matsuo,(13) "Photonic-Crystal Lasers on Silicon for Chip-Scale Optical Interconnects", SPIE Photonics West 2015,
San Francisco, U.S.A. (Feb. 2016).
A. Shinya, K. Nozaki, E. Kuramochi, K. Takeda, T. Kakitsuka, H. Taniyama, T. Fujii, K. Hasebe, S.
(14) Mastuo, and M. Notomi, "Integrated Nanophotonics for fJ/Bit on-Chip Optical Communications",
Design, Automation and Test in Europe (DATE), Dresden, Germany (Mar. 2016).
(15)
(16)

74

M. Notomi, "Enhanced Light-Matter Coupling in Nanoemitters and Nanolasers in Nanophotonic
Systems", Physics of Light-Matter Coupling in Nanostructures (PLMCN 17), Nara, Japan (Mar. 2016).
S. Matsuo, "Ultra-Low Threshold Semiconductor Lasers", Optical Fiber Communication Conference
and Exhibition 2015 (OFC), Anaheim, U.S.A. (Mar. 2016).

Research Activities in NTT Basic Research Laboratories Vol. 26 (2015)

Research Activities in NTT-BRL
Editorial Committee
NTT Basic Research Laboratories
3-1 Morinosato Wakamiya, Atsugi
Kanagawa, 243-0198 Japan
URL: http://www.brl.ntt.co.jp/