Cover : Coherent Ising Machine for Combinatorial
Optimization Problems
Combinatorial optimization problems can be mapped onto ground-state-search problems of
the Ising model, which can be solved efficiently with the artificial spin system. We realized acoherent Ising machine based on networked 2048 degenerate optical parametric oscillators tosolve the Ising problem. The coherent Ising machine could obtain good approximate solutionsfor MAX-CUT problems on 2000 node graphs. (see page 40)(left) Figure shows the structure of a G39 graph, which is a scale-free graph with 2000 nodes and 11778 edges.
(right) A solution to the MAX-CUT problem on the G39 graph obtained with the coherent Ising machine in 5 ms.
The red and blue nodes correspond to up and down spin states of the Ising model, respectively. The green lines
show the edges between the divided subsets.

Message from the Director
We at NTT Basic Research Laboratories(BRL) are extremely grateful for your interestand support of research activities. BRL’s
mission is to promote progress in science andinnovations in leading-edge technology toadvance NTT's business. To achieve thismission, researchers in fields including physics,
chemistry, biology, mathematics, electronics,
informatics, and medicine, conduct basic
research in the fields of 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, the 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 ouractivities and to encourage 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.
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, 2017

Tetsuomi Sogawa
Director
NTT Basic Research Laboratories

Table of Contents◆ Cover : Coherent Ising Machine for Combinatorial Optimization Problems◆ Message from the Director◆ Organogram1◆ Member List

2

Ⅰ Research Topics◇ Overview of Research in Laboratories

20

Materials Science Laboratory◆

Surface Morphology Control of Nonpolar m-plane AlN Homoepitaxial Layers by

22

Flow-rate Modulation Epitaxy◆

Enhancement of Heat Dissipation in AlGaN/GaN High-electron-mobility Transistors

23

Using Substrate-transfer Technique◆Atmospheric Pressure Chemical Vapor Deposition Growth of Millimeter-scale

24

Single-crystalline Graphene on the Copper Surface with a Native Oxide Layer◆

Theory of a Carbon-nanotube Polarization Switch

25◆

Shubnikov-de Haas Quantum Oscillations Reveal a Reconstructed Fermi Surface

26

Near Optimal Doping in a Thin Film of the Cuprate Superconductor Pr1.86Ce0.14CuO4±δ
◆Conductive Silk Film Electrode for Manipulation and Electrical Stimulation of

27

Adherent Cells◆

Fabrication of a Hydrogel Array for Facilitating Lipid Membrane Formation

28◆

Bio-interface on Graphene for Protein Detection

29

Physical Science Laboratory◆

World-record Accuracy of Gigahertz High-speed Single-electron Transfer

30◆

A Planar Cold Cathode Based on Multilayer-graphene/SiO2/Si Heterostructure

31◆

Experimental Test of Macroscopic Realism Using a Superconducting Flux Qubit

32◆

Coherent Coupling Between 4300 Superconducting Qubits and a Superconducting

33

Resonator◆

Simulating the Spin Ising Model with Phonons

34◆

A Strongly Coupled Λ-type Micromechanical System

35◆

Engineering Quantum Spin Hall Insulators by Strained-layer Heterostructures

36◆

Andreev Reﬂection and Bound State Formation in a Ballistic Two-dimensional

37

Electron Gas Probed by a Quantum Point Contact◆

Evaluation of Disorder Introduced by Electrolyte Gating through Transport
Measurements in Graphene

38

Optical Science Laboratory◆

Spectroscopic Analysis for Measuring Quantum Phase Transitions of Bosonic Atoms

39

in an Optical Lattice◆

Coherent Ising Machine for Combinatorial Optimization Problems

40◆

Quantum State Tomography for High-dimensional Time-bin States

41◆

Fundamental Rate-loss Trade-off for the Quantum Internet

42◆

Hybrid Quantum Engineering Using Spectral Hole Burning in Microwave Photonics

43◆

Generation of Low-noise Millimeter-wave by Using an
Electro-optics-modulator-based Optical Frequency Comb◆

Light-Field Driven Petahertz Electronic Oscillation with Attosecond Periodicity in
GaN Semiconductor◆

Bridging the Gap Between the Nanometer-scale Bottom-up and Micrometer-scale
Top-down Approaches for Site-defined InP/InAs Nanowires

44
45
46

Nanophotonics Center◆

Demonstration of Efficient Mode Conversion for Deep-subwavelength Plasmonic

47

Waveguides◆

Subwavelength Nanowire-induced Silicon Photonic Crystal Lasers

48◆

Efficient Light-to-voltage Conversion by Ultralow-capacitance49

Nano-photodetector◆

Superconducting Nanowire Single Photon Detector on Si Platform

50◆

LEAP Lasers Integrated on Si Waveguides

51

Ⅱ Data◇ The 9th Advisory Board

54◇ Science Plaza 201655

◇ List of Visitors’ Talks

56◇ List of Award Winners

58◇ List of In-house Award Winners

59◇ Number of Papers

60◇ Number of Presentations

61◇ Number of Patents

61◇ Publication List

62

◇ List of Invited Talks

69

NTT Basic Research Laboratories

Organogram

As of March 31, 2017
Director

Research Planning Section
Executive Manager

Tetsuomi Sogawa

Hideki Gotoh

Quantum and Nano Device Research
Senior Distinguished Researcher

Hiroshi Yamaguchi

Nanophotonics Center
Project Manager

Masaya Notomi
Biomedical • Exercise Physiology Research
Senior Distinguished Researcher

Shingo Tsukada

Materials Science Laboratory
Executive Manager

Hideki Yamamoto

Physical Science Laboratory
Executive Manager

Akira Fujiwara

Optical Science Laboratory
Executive Manager

Hideki Gotoh

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)1

Member List
As of March 31, 2017(*/ 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

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

Dr. Hideki Gotoh
Dr. Yoshitaka Taniyasu
Dr. Katsuhiko Nishiguchi
Dr. Shiro Saito*
Dr. Norio Kumada

NTT Research Professor
Prof. Yasuhiro Tokura
Prof. Hiroki Hibino

2

University of Tsukuba
Kwansei Gakuin University

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Executive Manager

NTT Basic Research Laboratories

Materials Science Laboratory

Dr. Hideki Yamamoto
Dr. Yuko Ueno
Dr. Hisashi SatoThin-Film Materials Research Group
Dr. Kazuhide Kumakura (Group Leader)
Dr. Tetsuya Akasaka

Dr. Kouta Tateno

Dr. Masanobu Hiroki

Dr. Kazuaki Ebata

Dr. Kazuyuki Hirama

Dr. Junichi Nishinaka

Low-Dimensional Nanomaterials Research Group
Dr. Kazuhide Kumakura (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. Ai Ikeda

Molecular and Bio Science Research GroupDr. Hiroshi Nakashima (Group Leader)
Dr. Shingo Tsukada

Dr. Yuko Ueno

Dr. Nahoko Kasai

Dr. Yoshiaki Kashimura

Dr. Aya Tanaka

Dr. Azusa Oshima

Dr. Tetsuhiko Teshima

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)3

Physical Science Laboratory

Executive Manager

Dr. Akira Fujiwara
Dr. Takeshi Ota
Takeshi Karasawa

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

Dr. Toshiaki Hayashi

Hirotaka Tanaka

Dr. Jinichiro Noborisaka

Dr. Gento Yamahata

Dr. Kensaku Chida

Dr. Rento Osugi

Dr. Nicolas Clement

Hybrid Nanostructure Physics Research GroupDr. Hiroshi Yamaguchi (Group Leader)
Dr. Shiro Saito

Dr. Imran Mahboob

Dr. Hajime Okamoto

Dr. Kosuke Kakuyanagi

Dr. Yuichiro Matsuzaki

Dr. Daiki Hatanaka

Dr. Hiraku Toida

Dr. Ryuichi Ohta

Dr. Rangga Budoyo

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

Dr. Satoshi Sasaki

Dr. Kyoichi Suzuki

Dr. Takeshi Ota

Dr. Keiko Takase

Dr. Hiroshi Irie

Dr. Takafumi Akiho

Dr. Francois Couedo*

Dr. Ngoc Han Tu

4

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

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. Tetsuya Mukai
Dr. Toshimori Honjo
Dr. Fumiaki Morikoshi
Dr. Takahiro Inagaki
Dr. Hsin-Pin Lo

Dr. Makoto Yamashita
Dr. Hiroyuki Tamura
Dr. Kensuke Inaba
Dr. Nobuyuki Matsuda
Takuya Ikuta

Theoretical Quantum Physics Research GroupDr. William John Munro (Group Leader)
Dr. Kiyoshi Tamaki
Dr. Fabian Furrer*
Dr. Yanbao Zhang

Dr. Koji Azuma
Dr. Stefan Bäuml

Quantum Optical Physics Research GroupDr. Hideki Gotoh (Group Leader)
Dr. Katsuya Oguri
Dr. Atsushi Ishizawa
Dr. Haruki Sanada
Dr. Hiroki Mashiko
Dr. Kenichi Hitachi
Dr. Yoji Kunihashi

Dr. Takehiko Tawara
Dr. Guoqiang Zhang
Dr. Keiko Kato
Dr. Tomoya Akatsuka
Dr. Hiromitsu Imai
Dr. Yusuke Tanaka

Photonic Nano-Structure Research Group
Dr. Masaya Notomi (Group Leader)
Dr. Akihiko Shinya
Dr. Eiichi Kuramochi
Dr. Kengo Nozaki
Dr. Masato Takiguchi
Dr. Kenta Takata
Dr. Feng Tian
Dr. Shota Kita

Dr. Atsushi Yokoo
Dr. Hisashi Sumikura
Dr. Hideaki Taniyama
Dr. Masaaki Ono
Dr. Devin Smith*
Dr. Sylvain Sergent

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

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. Kouta Tateno

Dr. Guoqiang Zhang

Nanostructured Device Research Group
Dr. Shinji Matsuo

Dr. Hiroshi Fukuda

Dr. Tai Tsuchizawa

Dr. Takaaki Kakitsuka

Dr. Koichi Hasebe*

Dr. Koji Takeda

Hidetaka Nishi

Dr. Kota Okazaki*

Tatsurou Hiraki

Ryo Nakao

Takuro Fujii

6

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

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.S., M.S. in physics and Ph.D. degrees inengineering from Osaka University in 1984, 1986, and 1993, respectively. He joined
NTT Basic Research Laboratories, Nippon Telegraph and Telephone Corporationin 1986 and has been engaged in the study of compound semiconductor surfaces
using electron diffraction and scanning tunneling microscopy. His current
interests are micro/nanomechanical devices using semiconductor heterostructures.
He was a visiting research fellow in Imperial College, University of London, U.K. during 19951996 and a visiting research staff in Paul Drude Institute, Germany in 2003. He is a guest professor
in Tohoku University from 2006 and a director of the Japanese Society of Applied Physics (JSAP) in2008 and 2009. He served as more than 40 committee members of academic societies and international
conferences. He was appointed as Senior Distinguished Scientist of NTT since 2011. He is currently
an executive manager of Quantum and Nano Device Research and a group leader of Hybrid NanoStructure 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. 27 (2016)7

Koji MURAKI received his B.E., M.E., 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, theJapan 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. 27 (2016)

NTT Basic Research Laboratories

Akira FUJIWARA received his B.E., M.E., 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 in1994 and moved to NTT Basic Research Laboratories in 1996. Since 1994, hehas been engaged in research on silicon nanostructures and their application to
single-electron devices. He was a guest researcher at the National Institute ofStandards and Technology (NIST), Gaithersburg, MD, USA during 2003-2004. He was a director of theJapanese Society of Applied Physics in 2010 and 2011 and a visiting professor of Hokkaido University
in 2013. He was appointed as Distinguished Scientist of NTT in 2007 and Senior Distinguished
Scientist of NTT in 2015. He is currently a senior manager of Physical Science Laboratory and a groupleader 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.

William J. MUNRO received his B.Sc in Chemistry, M.Sc and D.Phil degrees inPhysics from the University of Waikato, NZ in 1989, 1991, and 1995 respectively.
He was a research fellow at the University of Queensland, Australia from1997-2000 and then a staff scientist at Hewlett Packard Laboratories in Bristol(2000-2010). He joined NTT Basic Research Laboratories, Nippon Telegraphand Telephone Corporation in 2010 as a research specialist and from 2014 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 and its
practical realization.
He is currently a visiting professor at the National Institute of Informatics in Japan (2006 - ), theUniversity of Leeds in the UK (2009 - ) and the University of Queensland in Australia (2012 - ). He
was appointed as Distinguished Scientist of NTT in 2015 and Senior Distinguished Scientist of NTT in
2016. He is currently the group leader of the theoretical quantum physics research group. He was madea fellow of the Institute of Physics (UK) in 2009, the American Physical Society (APS) in 2013 andthe Optical Society of America (OSA) in 2014. He is also a member of the International Society for
Optical Engineering (SPIE).

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

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 Corporation in
2003. Since then, he has been engaged in the study of highly correlated electronic
states in two-dimensional systems. He was a visiting researcher at CEA Saclay
during 2013-2014. He was appointed as Distinguished Scientist of 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 and the IEEE.

10

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

NTT Basic Research Laboratories

Shiro SAITO received his B.E., M.E., and Ph.D. degrees in applied physics fromThe University of Tokyo, Japan, in 1995, 1997, and 2000, respectively. He joined
NTT Basic Research Laboratories, Nippon Telegraph and Telephone Corporationin 2000. Since then, he has been engaged in quantum information processing
using superconducting circuits. He was a guest researcher at Delft University ofTechnology, 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 Research Group.
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(2nd place) 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. 27 (2016)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 2012 asa Senior Research Scientist. During this period he studied nonlinear dynamics in electromechanicalresonators with notable achievements including mechanical memory and logic processors, parametricfrequency conversion, parametric mode coupling, all-mechanical phonon-lasing, two-mode squeezed
states all using phonons for the first time. Since 2017 he has been engaged in the development of
microwave quantum optics for quantum technology applications. He was appointed as Distinguished
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 electrical engineeringfrom Tohoku University, Japan, in 2001, 2002, and 2005 respectively. He joined
NTT Basic Research Laboratories, Nippon Telegraph and Telephone Corporationin 2005. His research interests are optical and spin properties of low-dimensional
semiconductor nanostructures, and their application to solid-state quantum
information processing. He is a visiting researcher at Chalmers University ofTechnology, Sweden in 2015. He was appointed as Distinguished Scientist of NTT in 2014. He iscurrently 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, the RIEC Award from Tohoku University
in 2014, and the Commendation for Science and Technology by the Minister of Education, Culture,
Sports, Science and Technology of Japan (the Young Scientists' Prize) in 2016. He is a member of theJapan Society of Applied Physics.

12

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

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 Ph.D. 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 in engineeringfrom Hokkaido University, Japan, in 1993, 1995, and 1998, respectively. He
joined NTT Basic Research Laboratories, Nippon Telegraph and Telephone
Corporation in 1998. His current interests are highly efficient energy conversion
devices using nitride semiconductors and two-dimensional layered materials. He
was a visiting researcher at Paul-Drude-Institute, Germany during 2007-2008.
He was appointed as Distinguished Scientist of NTT in 2015. He is currently a group leader of ThinFilm Materials Research Group and Low-Dimensional Nanomaterials 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. 27 (2016)13

Kengo NOZAKI received his B.E., M.E., and Ph.D. degrees in electrical engineeringfrom Yokohama National University, Japan, in 2003, 2005, and 2007 respectively.
He joined NTT Basic Research Laboratories, Nippon Telegraph and Telephone
Corporation in 2008. His current interests are ultralow-power nanophotonic
semiconductor devices based on photonic crystal. He was appointed asDistinguished Scientist of NTT in 2016. He is currently a member of Photonic
Nanostructure Research Group.
He received the Best Paper Award at Photonics in Switching 2012, and the Young Researchers Award
from IEICE Lasers and Quantum Electronics in 2014, and the Best Paper Award from OECC/PS in
2016. He is a member of the Japan Society of Applied Physics.

14

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

NTT Basic Research Laboratories

Advisory Board Members
Name

Affiliation

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. 27 (2016)15

Overseas Trainees

16

Name

Affiliation

PeriodAndrew Browning

The University of British Columbia,
CanadaMay 2015 - Apr. 2016

Jun Ki Kim

Georgia Institute of Technology,
U.S.A.

Sep. 2015 - Apr. 2016

Isabel Gonzalvez

University of Edinburgh, U.K.

Sep. 2015 - Aug. 2016

Monika Schied

Ulm University, GermanyJan. 2016 - Aug. 2016

Veronika Zagar

University of Ljubljana, Slovenia

Jan. 2016 - Aug. 2016

Carla Garcia

Carlos III University of Madrid, Spain

Jan. 2016 - Aug. 2016

Giacomo Mariani

Politecnico di Milano, Italy

Jan. 2016 - Aug. 2016

Dominika Gnatek

Jagiellonian University, Poland

Jan. 2016 - Aug. 2016

Javier Cambiasso

Imperial College London, U.K.

Jan. 2016 - Apr. 2016

Paul Brasseur

Ecole Centrale de Paris, France

May 2016 - Nov. 2016

Caleb John

University of Calgary, Canada

May 2016 -Alice Dearle

University of Edinburgh, U.K.

July 2016 -Calum Henderson

University of Edinburgh, U.K.

July 2016 -Harry Parke

University of Bath, U.K.

July 2016 - Dec. 2016

Romain Monsarrat

ESPCI Paris Tech (École supérieure dephysique et de chimie industrielles de July 2016 - Dec. 2016
la ville de Paris), France

Ruben Ohana

ESPCI Paris Tech (École supérieure dephysique et de chimie industrielles de July 2016 - Dec. 2016
la ville de Paris), France

Vincent Vinel

ESPCI Paris Tech (École supérieure dephysique et de chimie industrielles de July 2016 - Dec. 2016
la ville de Paris), France

Alexandre Gourmelon

ESPCI Paris Tech (École supérieure dephysique et de chimie industrielles de July 2016 - Dec. 2016
la ville de Paris), France

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Elizabeth Brockman

University of Victoria, Canada

Sep. 2016 -Luca Rigovacca

Imperial College London, U.K.

Sep. 2016 - Nov. 2016

David Wood

Imperial College London, U.K.

Sep. 2016 - Nov. 2016

Dino Ibrahimagic

Lund University, Sweden

Jan. 2017 -Fabian Böhm

Technische Universität Berlin,
Germany

Jan. 2017 -Mark IJspeert

Delft University of Technology,
The Netherlands

Jan. 2017 -Tiffany Tsu

University of British Columbia,
CanadaJan. 2017 -Thuong Phan

Georgia Institute of Technology,
U.S.A.

Jan. 2017 -Tommy Boykin II

University of Central Florida, U.S.A.

Jan. 2017 -Anthony Hayes

University of Leeds, U.K.

Feb. 2017 -Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

NTT Basic Research Laboratories

Paul Renault

ESPCI Paris Tech (École supérieure dephysique et de chimie industrielles de July 2016 - Dec. 2016
la ville de Paris), France

17

Domestic Trainees

18

Name

Affiliation

PeriodMasafumi Horio

The University of Tokyo

Apr. 2016 - Mar. 2017

Takuya Ohrai

Tokyo University of Science

Apr. 2016 - Mar. 2017

Megumi Kurosu

Tohoku University

Apr. 2016 - Mar. 2017

Gento Nakamura

The University of Electro-Communications

Apr. 2016 - Mar. 2017

Kzutaka Hara

Tokyo Denki University

Apr. 2016 - Mar. 2017

Go Taniguchi

Tokyo Denki University

Apr. 2016 - Mar. 2017

Yuya Hasegawa

Tokyo Denki University

Apr. 2016 - Mar. 2017

Hisashi Chiba

Tokyo Institute of Technology

Apr. 2016 - Mar. 2017

Masanori Hata

Tokyo Institute of Technology

Apr. 2016 - Mar. 2017

Suguru Endo

Keio University

Apr. 2016 - Dec. 2016

Hiroyuki Masuda

Yokohama National University

Apr. 2016 - Mar. 2017

Yuta Chisuga

Yokohama National University

Apr. 2016 - Mar. 2017

Takuya Ikemachi

The University of Tokyo

June 2016 - Mar. 2017

Keita Nakagawara

Tohoku University

July 2016 - Sep. 2016

Kan Hayashi

Kyoto University

Aug. 2016

Wataru Tomita

Tohoku University

Aug. 2016 - Mar. 2017

Rina Asai

Kyushu University

Aug. 2016 - Sep. 2016

Yoshiaki Taniguchi

Tokushima University

Aug. 2016 - Sep. 2016

Yuki Itoh

Tohoku University

Aug. 2016 - Sep. 2016

Tatsuya Ogawa

Hirosaki University

Sep. 2016 - Jan. 2017

Takahito Saito

Tohoku University

Sep. 2016 - Nov. 2016

Yoshifumi Suzuki

Tokyo Institute of Technology

Oct. 2016 - Mar. 2017

Yoshiko Nanao

Tokyo University of Agriculture andTechnology

Nov. 2016 - Mar. 2017

Kenta Imai

Toyohashi University of Technology

Jan. 2017 - Feb. 2017

Kento Toume

Tokyo University of ScienceFeb. 2017 - Mar. 2017

Riku Takahashi

Hokkaido University

Feb. 2017

Taiki Yoda

Tokyo Institute of Technology

Feb. 2017 - Mar. 2017

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

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
including typical compound semiconductors such as GaAs and GaN, two-dimensional
materials such as graphene, high-T c oxide superconductors, and biological molecules. We areconducting innovative materials research based on advanced thin-film growth technologies
and high-precision and high-resolution measurements of structures and properties along withtheoretical studies.
This year, we succeeded in controlling the surface morphologies of non-polar AlN
heteroepitaxial layers, which points toward the realization of high-performance light emitting
devices operating in the deep ultraviolet spectral region. We also prepared millimeterscale single-crystalline graphene. Our high-quality samples allowed us to observe quantum
oscillations for the first time using high-temperature superconductor thin films. Furthermore,
we fabricated conductive and highly biocompatible silk gel films with which we havedeveloped a new method for cell manipulation and the electrical stimulation of specific cells.
Last but certainly not least, electrodes and electrical leads made of a functional sensing fabric“hitoe”, which we developed in collaboration with Toray Industries Inc., have been officiallyregistered as general medical devices and offer a broad scope for medical use.

Physical Science Laboratory

Akira Fujiwara

The aim of the Physical Science Laboratory is to develop semiconductor- and superconductorbased devices and hybrid-type devices, which will have a revolutionary impact on future ICT
society. Utilizing the high-quality crystal growth techniques and nanolithography techniquesthat we have developed, research groups in our laboratory are exploring novel properties
that could lead to nanodevices for ultimate electronics and sensors and novel information
processing devices based on new degrees of freedom such as single electrons, mechanicaloscillations, quantum coherent states, electron correlation, and spins.
This year we achieved the world’s most accurate gigahertz single-electron transfer using
a silicon nanotransistor, and we performed an experimental test on the macroscopic realism
problem using a superconducting flux qubit. We also studied the quasi-Ising coupling ofelectromechanical resonators and coherent coupling between thousands of superconducting
qubits and a superconducting resonator to explore functional physical coupled systems.
Moreover, we developed novel material and device technology including band-engineered
two-dimensional topological insulators in InAs/InxGa1-xSb heterostructures and graphenebased electron emitters and liquid-gated transistors.

20

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Optical Science Laboratory

Hideki Gotoh

Optical Science Laboratory

Nanophotonics Center

Materials Science Laboratory Physical Science Laboratory

The aims of the Optical Science Laboratory is 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 as regards quantum computers has been thedemonstration of a new computing scheme with a laser cavity composed of an optical fiberand a phase sensitive amplifier. This scheme, known as a “quantum neural network”, hasbeen employed to solve a max-cut problem, which is a combinatorial optimization problem,and has realized a 50 times faster computation time than conventional computers. Moreover,
we have achieved the electronic oscillation of the 1 PHz regime with attosecond opticaltechnologies and suppressed the noises of microwave sources by employing optical-comb
technologies.

Masaya Notomi

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

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 Technology Laboratories. Our aim is to develop a full-fledged largescale photonic integration technology that will allow the dense integration of a large numberof nano-scale photonic devices with various functions in a single chip. Furthermore, we aretargeting a huge reduction in energy consumption for photonic information processing by
taking advantage of nanophotonics technology.
This year, we achieved super-efficient optical-to-electrical energy conversion by using
ultrasmall-capacitance nano-photodetectors integrated with resistors. We have also
demonstrated the high-speed modulation of sub-wavelength nanowire photonic-crystal lasers.
Furthermore, we have achieved various nanophotonic devices (deep sub-wavelength plasmonic
waveguides, superconducting single-photon detectors, and photonic-crystal lasers) efficiently
coupled to Si waveguides.

21

Surface Morphology Control of Nonpolar m -plane AlN Homoepitaxial
Layers by Flow-rate Modulation Epitaxy
Junichi Nishinaka, Yoshitaka Taniyasu, Tetsuya Akasaka, and Kazuhide Kumakura
Materials Science Laboratory
AlGaN is an attractive material for light-emitting devices in the deep ultraviolet spectral
region. Particularly, nonpolar AlGaN-based heterostructures can improve internal quantum
efficiency and light extraction efficiency compared to the conventional c-plane devices [1].
However, it is difficult to obtain m-plane AlN and AlGaN with a flat surface, although highquality m-plane AlN bulk substrates have become available. It has been reported that a highgrowth temperature is required for promoting adatom migration to achieve smooth a surfaceof the m-plane AlN homoepitaxial layers [2]. On the other hand, flow-rate modulation epitaxy(FME) can also promote adatom migration by modulating the amount of source gas [3]. In thisstudy, we investigated the surface morphologies of nonpolar m-plane AlN homoepitaxial layersgrown by the FME technique.
The samples were grown by metalorganic chemical vapor deposition with trimethylaluminum(TMA) and ammonia (NH3). We employed four types of source supply sequences: continuous
supply, group-III-source FME (III-FME), group-V-source FME (V-FME), and FME withgroups III and V alternated (A-FME).
Figure 1 shows the source supply sequences and corresponding atomic force microscopy(AFM) images of the m-plane AlN homoepitaxial layers grown by (a) continuous supply, (b)V-FME, and (c) A-FME. The flow rates of TMA and NH3 were unchanged, but the average
V/III ratios differed depending on the source supply sequences. We found that a-steps tend to
appear when the average V/III ratio is large [Fig. 1(a)], whereas +c-steps tend to appear when
it is small [Fig. 1(c)]. This is probably because the a- and +c-steps have different dangling
bonds and because the average V/III ratio affects the anisotropic step-flow velocity in a- and+c-directions, which determines step direction. Atomically flat surfaces can be obtained bychoosing appropriate growth conditions [Fig. 1(b)]. In addition, +c-steps tend to bunch under
the V-FME or A-FME with N-poor conditions. This is probably due to enhanced adatom
migration in the absence of the NH3 flow. Thus, we can control the surface morphologies ofm-plane AlN homoepitaxial layers by using the FME technique.
This work was supported by JSPS KAKENHI JP25246022.
[1] R. Banal et al., Appl. Phys. Lett. 105, 053104 (2014).
[2] I. Bryan et al., J. Appl. Phys. 116, 133517 (2014).
[3] T. Akasaka et al., Appl. Phys. Lett. 90, 121919 (2007).

Fig. 1. Source supply sequences and 10×10 μm2 AFM images of m-plane AlN homoepitaxial layers.
(a) Continuous (average V/III: 8.8). (b) V-FME (average V/III: 6.3). (c) A-FME (average V/III: 1.8).
22

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Enhancement of Heat Dissipation in AlGaN/GaN High-electron-mobility
Transistors Using Substrate-transfer Technique
Masanobu Hiroki, Kazuhide Kumakura, and Hideki Yamamoto
Materials Science Laboratory

Materials Science Laboratory

III-nitride semiconductor materials can be applied for high-power devices by exploiting
their high critical electric field. Under high current operation, however, power performance islimited due to the generation of Joule heat. We transferred AlGaN/GaN high electron mobility
transistors (HEMTs) from a sapphire substrate to a copper plate using the hexagonal boron
nitride epitaxial lift-off technique [1,2]. In this study, we transferred the HEMTs to a copper
plate using Au-Au thermocompression bonding and found an increase in drain current (Id) andsignificant improvement of the heat dissipation [3].
Figure 1 shows an I-V characteristics of an AlGaN/GaN HEMT before release and after
transfer. Before release, a large reduction in drain current Id vs drain bias (Vds) was observedin the saturation region. In contrast, for the HEMT after transfer, the negative slope of Id vsVds decreased. In addition, we found a significant increase in maximum Id from 0.72 to 0.91
A/mm after transfer. The maximum transconductance also increased from 110 to 140 mS/mm.
These indicate an increase in two-dimensional electron gas (2DEG) density. The increase in
2DEG density is likely caused by the reduction in compressive stress in the GaN layer, whichis revealed from the E2 peak shift of –1.3 cm–1 in Raman spectroscopy measurement.
Figure 2 shows temperature maps of a HEMT transferred to a copper plate and another
HEMT on a sapphire substrate. For the transferred HEMT, the temperature increased from 50
to 150°C with increasing power dissipation (P) from 0.3 to 1.5 W. For the HEMT on sapphire(before release), the temperature reached 240°C at P of 0.7 W. Our results indicate that thetransfer technique using the h-BN release layer can enhance the heat dissipation and boost thepower performance of GaN-based devises.
[1] Y. Kobayashi et al., Nature 483, 223 (2012).
[2] M. Hiroki et al., Appl. Phys. Lett. 105, 193509 (2014).
[3] M. Hiroki et al., Jpn. J. Appl. Phys. 55, 05FH07 (2016).

Fig. 1. I-V characteristics of AlGaN/GaN
HEMT before release and after transfer.

Fig. 2. Temperature maps of a HEMT transferred to copperand another HEMT on sapphire.

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)23

Atmospheric Pressure Chemical Vapor Deposition Growth ofMillimeter-scale Single-crystalline Graphene on the Copper Surface witha Native Oxide Layer
Shengnan Wang, Hiroki Hibino, Satoru Suzuki, and Hideki Yamamoto
Materials Science Laboratory
Graphene fabricated by “bottom-up” methods always contains various kinds of structuraldefects, which are introduced during the fabrication process. For example, 1 mm2 chemical
vapor deposition (CVD) grown graphene can be composed of over ten thousand single
crystalline domains and centimeter-long domain boundaries [1]. These domain boundaries,
as well as lattice defects, have been identified as main disorders to affect the electrical andmechanical performance of graphene. Thus, fabrication of large scale single crystalline
graphene is important for its potential technological applications in nanoelectronics and related
fields.
Here, we present an atmospheric pressure CVD approach to synthesize millimeter-scalegraphene single crystals on commercial Cu foils [2]. A hydrogen-excluded annealing step isused to flatten the Cu surface and maintain the native oxide layer, which is catalytic inactive
and is used to restrict the nucleation of graphene on Cu surface in the following growth
process. A resulted density of ~12 nuclei cm–2 is obtained with an optimized annealing period.
Combined with the annealing step, the growth of graphene is further modified by placing thecatalyst foils on roughness-defined solid supports (quartz or sapphire), which generate twodifferent types of reaction space: open and confined space on the double sides of the foils. Dueto the variation in the kinetics role of oxide layer, reproducible results are observed that thedomain size of as-grown graphene is larger on the confined surface, as shown in Fig. 1. With apolished quartz support, ~3 mm isolated graphene islands with an average growth rate of ~25
μm/min are achieved. The as-grown hexagonal domains are confirmed to be single-crystalline
monolayer graphene with a field-effect mobility of ~4900 cm2/Vs at room temperature.
[1] S. Wang et al., Nanoscale 6, 13838 (2014)[2] S. Wang et al., Chem. Mater. 28, 4893 (2016).

Fig. 1. Schematic and optical images of single crystalline graphene domain grown on the Cu surface w/ and w/osupport under same CVD procedure.
24

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Theory of a Carbon-nanotube Polarization Switch
Ken-ichi Sasaki
Materials Science Laboratory

Materials Science Laboratory

Polarized light is one of the most-familiar natural phenomena as the origin of variety seen
in reflection and transmission of light at the surface of a physical object. On the other hand, as
the profound spin degree of freedom (helicity) possessed by a massless gauge boson (photon),
two components of polarized light have been used to acquire a new knowledge on so many
natural laws [1]. Therefore, it would be beneficial if there is a device by which the polarization
direction is switched by an electrical means.
We predicted a novel phenomenon that the polarization direction of light transmission ofcarbon nanotube (CNT) changes by charge doping [2]. A CNT absorbs light whose linear
polarization is parallel to the tube’s axis, but not when the polarization is perpendicular toit [Fig. 1(left)]. This is a well-known property of an undoped CNT, which enables aligned
CNTs to function as an optical polarizer [3]. Charge doping of a CNT inverts the polarization
dependence. That is, a doped CNT transmits parallel polarized light and absorbs perpendicularpolarized light [Fig. 1(right)].
To change the polarization direction of light transmitted through a typical Polaroid lens, itis necessary to rotate the lens itself. However, according to the theory of doping dependence,a CNT polarizer can invert the polarization of the transmitted light by 90 degrees without
having to spatially rotate the polarizer; in other words, it is expected to function as anelectrnoic polarization switch. In regard to cutting-edge optical transmission technology, thetwo degrees of freedom of polarized light are utilized to double the amount of information
being transmitted. Different information like images and sound is transcribed to orthogonal
polarization and transmitted. A polarization switch based on CNTs can be used to manipulate
information within highly miniaturized structure for optical transmission.
[1] B. H. Billings, Ed., Selected Papers on Applications of Polarized Light (2012); W. K. Wootters and W. H.
Zurek, Nature 299, 802 (1982).
[2] K. Sasaki, S. Murakami, and H. Yamamoto, Appl. Phys. Lett. 93, 125402 (2016).
[3] S. Shoji et al., Phys. Rev. B 77, 153407 (2008); B. G. Kang et al., Nanotechnology 21, 405202 (2010).

Fig. 1. (left) Undoped CNTs transmit only perpendicular polarized light. (right) Doped CNTs transmit only
parallel polarization. Since the polarization of the transmiited light rotates 90 degrees by doping, the aligned CNTs
function as a polarization switch.

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)25

Shubnikov-de Haas Quantum Oscillations Reveal a ReconstructedFermi Surface Near Optimal Doping in a Thin Film of the Cuprate
Superconductor Pr1.86Ce0.14CuO4±δ
Yoshiharu Krockenberger1, Ai Ikeda1, Hiroshi Irie2, Hideki Yamamoto1,
Nicholas P. Breznay3, Ian M. Hayes3, Ross McDonald4, and James G. Analytis3
1
Materials Science Laboratory, 2Physical Science Laboratory,
3
University of California, Berkeley, 4NHMFL, Los Alamos National Laboratory
Understanding the ordering phenomena that compete or coexist with superconductivity inthe cuprate superconductors remains an outstanding challenge. Central to this effort is theidentification of Fermi surface topology and evolution with doping via studies of magnetic
quantum oscillations (QO), led by initial observations of QO in hole-doped YBa2Cu3O6.5 [1].
We reported [2] on the Fermi surface topology and effective mass in the electron-doped cuprate
superconductor Pr2–xCexCuO4 (PCCO) with x = 0.14. PCCO thin films have been grown by
molecular beam epitaxy onto (001) SrTiO3 substrates and annealed in order to maximize themean-free path length [3]. We observe Shubnikov-de Haas QO in a PCCO thin film measured
under extreme magnetic fields up to 92 T, where magneto-transport data [Fig. 1(A)] show
evidence for a small Fermi surface pocket (255 T), a light quasi-particle with effective massof m* = 0.43 me, allowing direct determination of the orbitally averaged Fermi velocity ofvF = 2.4×105 m/s. For comparison, the Hall conductivity at 2 K is 0.9×10–9 Ωm/T, resulting in acharge carrier density per CuO2 plane of 0.66 by assuming a single parabolic band [Fig. 1(B)].
The small Fermi surface pocket indicates a reconstruction [Fig. 1(C)], coupled with a similar
observation of Ce-free Pr2CuO4 films [4], suggests that small Fermi surface pockets are auniversal feature of cuprate superconductors with square-planar coordinated copper.
[1] D. LeBoeuf et al., Nature 450, 533 (2007).
[2] N. P. Breznay, I. M. Hayes, B. J. Ramshaw, R. D. McDonald, Y. Krockenberger, A. Ikeda, H. Irie,
H. Yamamoto, and J. G. Analytis, Phys. Rev. B 94, 104514 (2016).
[3] A. Ikeda, H. Irie, H. Yamamoto, and Y. Krockenberger, J. Mater. Res. 31, 3522 (2016).
[4] N. P. Breznay, R. McDonald, Y. Krockenberger, K. A. Modic, Z. Zhu, I. M. Hayes, N. L. Nair, T. Helm,
H. Irie, H. Yamamoto, and J. G. Analytis, arXiv:1510.04268 (2015).

Fig. 1. (A) Low-temperature magneto-resistance of a superconducting Pr2-xCexCuO4 thin film measured up to
92 T at temperatures between 2 and 30 K. (B) 2D Fermi surface area [ABand = 43% of Brillouin zone (BZ)]
estimated using Hall effect measurements as discussed in the text. (C) 2D Fermi surface area (red pockets)
estimated from magnetic quantum oscillations [AQO = 0.97% of Brillouin zone (BZ)].

26

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Conductive Silk Film Electrodefor Manipulation and Electrical Stimulation of Adherent Cells
Tetsuhiko Teshima, Hiroshi Nakashima, and Shingo Tsukada
Materials Science Laboratory

Materials Science Laboratory

Action potentials generated by ion channels are involved in a wide range of cellular
processes. Microelectrode arrays (MEAs) or transistor biosensors have been developed tostimulate cells or measure electrical signals. However, there is a technical issue as regards
controlling the location of cells on the electrodes. This is because the cells adhere randomly
to the surface, which hampers experimental reproducibility and accuracy. We thus approach
this issue by developing a mobile, conductive film-based interface (nano-pallet) that enables
us to manipulate and electrically activate specific cells. We fabricated the nano-pallet byusing a combination of silk fibroin hydrogel and PEDOT:PSS [1] to improve transparency,
biocompatibility, mechanical stiffness, and electrical conductivity.
The micropatterned nano-films were formed with a controllable size and shape by using aphotolithographic technique [Fig. 1(a)] [2]. The silk fibroin matrix with embedded PEDOT:PSS
is optically transparent in both the visible and ultraviolet regions, enabling the observation withvarious types of microscopes. The FTIR spectra had peaks at 1535 and 1630 cm–1 assigned tothe amino-1 band, which indicated that the film contained β-sheet crystalline fractions. The
gelled silk fibroin proteins improved the mechanical properties of the film (elastic coefficient= 100 MPa). Interestingly, the fabricated nano-film realized 500 times higher conductivity (ata maximum of 1 mS) than pristine PEDOT:PSS film, implying that the silk fibroin molecules
help the rearrangement of the PEDOT:PSS chains and enhance charge transfer in inter-chains
or inter-particles.
Since silk fibroin and PEDOT:PSS are highly biocompatible, the cells tend to migrate andproliferate at the nano-pallet surface [Fig. 1(b)]. We micropatterned the film to modulate thebehavior of specific cells and activate them while retaining their adhesive property. We further
utilized these films to individually measure and apply cellular action potentials to a target
cell by incorporating them in capillary electrodes. By applying a voltage to cell-laden nanofilms, cells expressing P/Q-type calcium channels (Cav2.1) were selectively activated under ahomogeneous condition [Fig. 1(c)]. These properties along with non-cytotoxicity and long-term
implantation capability could provide a prototype biocompatible electrode for cells and tissues.
We believe that the nano-films can be used for both in vitro electrophysiological analysis andvarious biomedical applications.
[1] S. Tsukada et al., PLoS One 7, e33689 (2012).
[2] T. Teshima et al., Adv. Funct. Mater. 26, 8185 (2016).

Fig. 1. (a) Schematic illustration of cell-laden nano-pallet electrodes. (b) Micrograph of cell-laden nano-pallets.
(c) Merged micrographs of phase-contrast and confocal images of voltage-applied nano-pallets.
Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)27

Fabrication of a Hydrogel Array for Facilitating Lipid Membrane Formation
Aya Tanaka, Yoshiaki Kashimura, and Hiroshi Nakashima
Materials Science Laboratory
The integration of biological substances in electronic devices has great potential for various
applications such as biosensing and drug discovery. Of the many kinds of biological molecules,
membrane proteins have received a lot of attention due to their importance in relation tocellular survival and communication. We have already developed nano-bio devices for the
optical and electrophysiological analysis of membrane proteins by using microwells on asilicon substrate covered with lipid bilayers [1]. In addition, we have improved the fragility of asuspended lipid membrane by using hydrogel as a water permeable and mechanical support [2].
Here, we describe the fabrication of a cationic hydrogel array that can electrostatically facilitate
the formation of a planar lipid membrane over microwells by the fusion of negatively charged
small unilamellar vesicles (SUVs) with a diameter smaller than the microwell aperture (Fig. 1) [3].
The hydrogel array was produced as follows: microwells 1, 2, 4, and 8 μm in diameter and1 μm deep were fabricated on a silicon substrate using a conventional lithographic andetching technique. The hydrogel was prepared by photo-initiating free radical polymerizationfrom a cationic gel-precursor aqueous solution including a green fluorescent dye, calcein.
The hydrogel precursor solution was dropped onto the substrate and polymerized by UVlight irradiation through a photomask covering half the area of the substrate. After removing
excess hydrogel from the substrate, a lipid membrane was prepared on the hydrogel-confined
microwell by rupturing negatively charged SUVs with a diameter smaller than the microwellaperture. The lipid membrane formation on the hydrogel-confined microwell array wasobserved with fluorescence microscopy (Fig. 2).
The positively charged hydrogels were only confined in the microwells on the substrate
where light was irradiated [Fig. 2(a)]. Planar lipid membranes were formed on the microwells
confining the positively charged hydrogels [Fig. 2(b)]. By comparison, lipid membranes were
not formed in microwells with no positively charged hydrogels [Fig. 2(c)]. These results
indicate that the function of the hydrogels confined in the microwells is to both stabilize
the lipid membranes mechanically and facilitate the formation of a lipid membrane via an
attractive electrostatic interaction between SUVs and hydrogels. We expect these hydrogel
supports to allow us to prepare a lipid membrane from a proteoliposome. Since the chemicalcomposition of a hydrogel is easily modified, we can obtain a hydrogel array with desirable
properties such as high mechanical strength, electric charge, and responsiveness to a stimulus.
[1] K. Sumitomo et al., Biosens. Bioelectron. 31, 445 (2012).
[2] A. Tanaka et al., Appl. Phys. Express 7, 017001 (2014).
[3] A. Tanaka et al., Colloids Surf. A 477, 63 (2015).

Fig. 1. Schematic illustration of lipid membrane
formation by fusing SUVs on a hydrogel array.

28

Fig. 2. (a) Fluorescence image of a substrate after light irradiation
over half the substrate area. (b, c) Lipid membrane formation on thesubstrate (b) without and (c) with light exposure. Scale bar: 20 μm

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Bio-interface on Graphene for Protein Detection
Yuko Ueno1 and Kazuaki Furukawa2
1
Materials Science Laboratory, 2Meisei University

Materials Science Laboratory

We have developed a two-dimensional graphene biomolecular interface to detect biologicallyimportant proteins such as cancer markers. Until this work, water-dispersive graphene oxide(GO) in aqueous media has been preferred as a biosensor platform. By contrast, we havedesigned and demonstrated a protein detection system on a solid surface where we can use
either water-dispersive GO or hydrophobic graphene as the sensor platform [Fig. 1(left)]. This
allows us to combine the protein detection system with microfluidic techniques to realize an
on-chip type sensor. We have successfully demonstrated the quantitative detection of multiple
targets by using a sensor array built in a multichannel configuration [1].
We compared the protein detection performance quantitatively by using graphene and GO
biosensors prepared on the same chip. We fixed graphene and GO on the SiO2 surface of asolid substrate and modified both surfaces with a dye-labeled aptamer (single-stranded DNA
that recognizes and forms a complex with a specific target molecule such as a protein) under
the same conditions. Here we used prostate specific antigen (PSA, a cancer marker) as thetarget molecule. We observed increases in the fluorescence intensity on both the graphene andGO surfaces when we added PSA (33 μg/mL @ t = 100 s) [Fig. 1(right)]. After performing
several observations under constant PSA concentration conditions, we added deionized water
to dilute the PSA solution. The fluorescence intensities became weaker as the concentration of
the PSA solution decreased (20, 14, 11, 9 μg/mL @ t = 300 s, 400 s, 500 s, and 600 s). We thus
demonstrated the successful operation of the sensor on both graphene and GO surfaces. We
compared the performance of the graphene sensor with that of the GO sensor by subtracting
the average fluorescence intensities before PSA addition from the maximum fluorescenceintensities after PSA detection. The graphene sensor yielded a larger intensity than GO, and theratio exceeded 3 [2]. We conclude that the graphene is superior to GO in terms of building a
biomolecular interface for fluorescence-based sensors.
This work was supported by JSPS KAKENHI JP26286018.
[1] Y. Ueno, K. Furukawa et al., Anal. Chim. Acta 866, 1 (2015): Featured on Cover[2] K. Furukawa, Y. Ueno et al., ACS Sens. 1, 710 (2016).

Fig. 1. (Left) Schematic of graphene biosensor.
(Right) Quantitative comparison of PSA detection performance of graphene and GO sensors.

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)29

World-record Accuracy of Gigahertz High-speed Single-electron Transfer
Gento Yamahata1, Stephen P. Giblin2, Masaya Kataoka2,
Takeshi Karasawa1, and Akira Fujiwara1
1
Physical Science Laboratory, 2National Physical Laboratory
A single-electron (SE) pump can transfer electrons one by one with clock control. When theclock frequency is f, the pump generates accurate electric current ef, where e is the elementarycharge. The accurate current can be used for the current standard, which corresponds to a ruler
with which to measure electric current. Although there are many reports on SE transfer, it has
been difficult to achieve high-accuracy operation at more than 1 GHz. Here, using a highaccuracy measurement system, we precisely measure a current generated by a Si SE pump [1]and demonstrate an ultralow transfer error rate of less than 9.2 × 10 7 at 1 GHz [2].
Figure 1(a) shows a schematic of the device, which has double-layer gate electrodes on a Si
wire with a diameter on the order of 10 nm. By applying a DC voltage to the upper gate, we
induce electrons in the Si wire. In addition, by applying a high-frequency clock signal and DC
voltage (VG2) to lower gates G1 and G2, respectively, an electron from the source is capturedby the island between G1 and G2, followed by its ejection to the drain. We measure the transfer
current using a high-accuracy current measurement system [Fig. 1(b)], which has an ultralow
measurement uncertainty of 8.8 × 10–7 achieved by the calibration using the Josephson voltage
standard and quantum Hall resistance standard.
Figure 1(c) shows the ratio of the difference from ef at 1 GHz as a function of VG2. While
the standard uncertainty of the measurements is 9.2 × 10–7, the mean of the measured values(normalized by ef) in the current plateau deviates only –6.4 × 10–7. This means that themeasured current matches ef in the range of the standard uncertainty. In addition, the current
plateau is flat with the level of 9.2 × 10–7. These results indicate that the transfer error rate isless than 9.2 × 10–7, which is a world-record accuracy in the gigahertz regime. Furthermore, we
observe a transfer error rate of about 3 × 10–6 at 2 GHz. This indicates that our device breaks
the 1-GHz barrier and is suitable for high-speed operation. In future work, we will optimize
the measurement system and device structure to further improve accuracy, with the aim ofrealizing a high-accuracy current standard.
[1] A. Fujiwara, K. Nishiguchi, and Y. Ono, Appl. Phys. Lett. 92, 042102 (2008).
[2] G. Yamahata et al., Appl. Phys. Lett. 109, 013101 (2016).

Fig. 1. (a) Schematic of the SE pump. (b) High-accuracy current measurement system, which has a 1-GΩ standard
resistor and voltmeter calibrated by the primary standards. When IR ~ ef by setting the value of the voltage source,
ID << ef. In this case, we can neglect the measurement uncertainty of ID.
(c) High-accuracy measurement results at 1 GHz.
30

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

A Planar Cold Cathode Based on
Multilayer-graphene/SiO2/Si Heterostructure
Katsuhiko Nishiguchi1, Daisuke Yoshizumi2, Yoshiaki Sekine3, Kazuaki Furukawa3,
Akira Fujiwara1, and Masao Nagase2
1
Physical Science Laboratory, 2Tokushima University, 3Materials Science Laboratory

Physical Science Laboratory

Cathodes that emit electrons are used for various applications such as electron microscopy,
electron beam lithography, material reformation, and vacuum gauges. The most commonly usedcathode is a hot cathode that uses a filament heated up by current, and a Spindt-type cathodecomposed of a sharp cone [1] has been studied as a cold cathode with high functionality. Whileeach cathode type has some advantages, there are also some problems: cathodes operate byusing a high voltage supply in a high vacuum and electrons emitted spread widely; both ofwhich lead to complicated systems. In this work, we demonstrated a planar cold cathode basedon a multilayer-graphene/SiO2/Si heterostructure [2] to solve these problems.
Figure 1 shows the schematic and cross-sectional views of the cold cathode based on amultilayer-graphene (~10 nm)/SiO2 (6 nm)/Si heterostructure. Figure 2 shows the mechanismof electron emission from the cathode. When voltage V graphene is applied to the multilayer
graphene, electrons in the Si layer tunnel to the multilayer graphene through the SiO2. Electrons
with energy larger than the work function (~5 eV) of the multilayer graphene are emitted
from it to a vacuumed space and reach the anode, which leads to current Ianode. However,when the energy of electrons in the multilayer grapheme is smaller than its work function, theelectrons (current Igraphene) flow into the multilayer graphene without electron emission. Figure
3 shows the electron-emission characteristics. The increase in Vgraphene increases the tunnelingcurrent Igraphene. At Vgraphene larger than the work function of the multilayer-graphene, Ianode flows
because the electrons are emitted from the cathode and reach the anode. The electron-emission
efficiency is defined as 0.3%, which is four orders of magnitudes larger than in our previous
results using polycrystalline Si instead of multilayer graphene [3]. This improvement originatesfrom a small scattering of electrons in the multilayer graphene due to its thinness, whichmeans that single-layer graphene is promising for further improvement of the efficiency. On
the other hand, since multilayer-graphene’s conductivity is not sensitive to electron-emission
characteristics, wide graphene grown by chemical vapor deposition can be used to make awide-area cathode. Additionally, since electrons are emitted perpendicular to the multilayer
graphene with a small voltage in low vacuum, a simple system for electron emission targeting
various applications can be achieved.
[1] C. A. Spindt, J. Appl. Phys. 39, 3504 (1968).
[2] K. Nishiguchi et al., Appl. Phys. Express 9, 105101 (2016).
[3] K. Nishiguchi et al., Jpn. J. Appl. Phys. 47, 5106 (2008).

(a)

(b)

Fig. 1. (a) Schematic and (b) cross-sectional viewof the cathode.

Fig. 2. A mechanism ofelectron emission.

Fig. 3. Electron-emission
characteristics.

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)31

Experimental Test of Macroscopic Realism Usinga Superconducting Flux Qubit
Kosuke Kakuyanagi1, George C. Knee2, Mao-Chuang Yeh3,
Yuichiro Matsuzaki1, Hiraku Toida1, Hiroshi Yamaguchi1, Shiro Saito1,
Anthony J. Leggett3, and William J. Munro2
1
Physical Science Laboratory, 2Optical Science Laboratory, 3University of Illinois
Realism is an idea that a state of the object is determined before its observation. Although
this idea is widely believed to hold in our lives, it has been shown that “realism” is broken
in a microscopic world. The microscopic world is governed by the principles of quantum
mechanics that allows a state to have a superposition. For a superposed state, the measurable
values are not determined until they are observed. Since the macroscopic world is composedof microscopic objects, quantum mechanics could be valid even in this macroscopic world. Or
there could be so limitation to the application of the quantum mechanics to the macroscopic
world. Currently, there is still no consensus about which is likely to be true.
Here we aim to address this. A superconducting flux qubit is a circuit composed of several
Josephson junctions and a superconducting loop. Due to the non-linearity of the Josephson
junctions, this device provides a two-level system with clockwise and anti-clockwise current
states. These two states contain 1012 electrons flowing around the circuit per a second. We test
whether realism is broken with this macroscopic device or not.
In our normal world, it is accepted that we can measure macroscopic objects without
disturbing them (non-invasiveness). If realism is true, any non-invasively measured results on
this device should satisfy the Leggett-Garg inequality. However, if quantum mechanics is true,
we could observe a violation of the inequality using non-invasive measurements.
We show that the Leggett-Garg inequality is mathematically equivalent to an experimental
test to check if the non-invasive measurements affect the state of the device. Interestingly, even
if the measurement is designed to be non-invasive, observation by the measurement induces a
projection according to quantum mechanics. This can change the state of the device.
In our test, we perform two experiments. First we check the non-invasiveness of themeasurements by evaluating the classical disturbance that our measurement device on the flux
qubit has. Second, we compare the measured state of the flux qubit with a not measured stateof the flux qubit. From these experiments, we have shown that there is a large difference inthese measured results, which cannot be explained by the classical disturbance [Fig.1(a)]. Thisis a manifestation of quantum superposition. Our results conclusively demonstrate that “realism”
is broken even for a macroscopic device such as a superconducting qubit [Fig. 1(b)] [1].
This work was partly supported by JSPS KAKENHI JP15H05870 and JP15H05867.
[1] G. C. Knee, K. Kakuyanagi, M-C. Yeh, Y. Matsuzaki, H. Toida, H. Yamaguchi, S. Saito, A. J. Leggett, andW. J. Munro, Nature Commun. 7, 13253 (2016).

Fig. 1. (a) Differences by observation. (b) Quantum superposition of current state.
32

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Coherent Coupling Between 4300 Superconducting Qubits and aSuperconducting Resonator
Kosuke Kakuyanagi1, Yuichiro Matsuzaki1, Corentin Déprez1, Hiraku Toida1,
Kouichi Semba2, Hiroshi Yamaguchi1, William J. Munro3, and Shiro Saito1
1
Physical Science Laboratory, 2NICT, 3Optical Science Laboratory

Physical Science Laboratory

Hybridization between a superconducting resonator and ensembles of two level systems
has been considered as a promising way to realize quantum technologies. The conventional
approaches have used natural systems such as atoms & molecules to realize the ensemble
where the properties of such “atoms” are difficult to tailor to the properties of the device [1].
Our approach is to create the ensemble from artificial atoms such as superconducting qubits.
The properties such superconducting qubits are not intrinsic but can be largely changed evenafter the fabrication. Moreover, due to their large size, we can in principle achieve individual
controllability. In this direction, only a small number of superconducting qubits (8 in total
and not an ensemble) has shown collective coupling to a resonator [2]. Here, we fabricate ahybrid device composed of 4300 superconducting flux qubits embedded in a superconducting
resonator [3]. We observe a large dispersive frequency shift in the spectrum of 250 MHz as
shown in Fig. 1. From our theoretical analysis, we show that this frequency shift is evidence ofa coherent coupling between the resonator and thousands of flux qubits. Although the couplingstrength of a single flux qubit with the resonator is much smaller than the inhomogeneous
width of the ensemble, the coupling can be enhanced by collective effects. This provides us
with a measurable signal for the experiments. Our results represent the largest number ofcoupled superconducting qubits realized so far.
This work was supported by JSPS KAKENHI JP15K17732 and JP25220601. This work wasalso partly supported by MEXT KAKENHI JP15H05869 and JP15H05870.
[1] Z-L. Xiang et al., Rev. Mod. Phys. 85.2 623 (2013).
[2] P. Macha et al., Nature Commun. 5, 5146 (2014).
[3] K. Kakuyanagi et al., Phys. Rev. Lett. 117, 210503 (2015).

Fig. 1. Energy spectrum of a superconducting microwave resonator coupled to an ensemble of flux qubits.
(Left) Experimental results. (Right) Theoretical analysis.

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)33

Simulating the Spin Ising Model with Phonons
Imran Mahboob and Hiroshi Yamaguchi
Physical Science Laboratory
Physical simulators, composed of atoms, ions, photons or electrons, have emerged as anovel means for solving intractable mathematical problems [1]. Here this concept is extended
to phonons that are localised in spectrally pure resonances in an electromechanical system[Fig. 1(a)] which enables their interactions to be exquisitely fashioned via piezoelectricity [2].
Specifically the electromechanical system is developed to mimic the spin Ising Hamiltonian
where its spin 1/2 particles are replicated by the phase bi-stable vibration from a mechanicalparametric resonance where multiple resonances play the role of a spin bath [Figs. 1(c),(d)].
The coupling between the mechanical spins is created via non-degenerate parametric downconversion which entwines the resonances resulting in correlated vibrations [Fig. 1(b)]. The
combination of parametric resonance and parametric down-conversion can then be harnessed
to imitate a ferromagnetic, random or an anti-ferromagnetic state on-demand, whose statistical
dynamics are consistent with the idealized spin Ising interaction. These results suggest that theelectromechanical system could be further developed to imitate the spin Ising model in a nontrivial configuration, namely with a large number of spins with multiple degrees of coupling, atask that would overwhelm a conventional computer [3].
This work was supported by MEXT KAKENHI JP15H05869.
[1] I. Buluta and F. Nori, Science 326, 108 (2009).
[2] I. Mahboob et al., New J. Phys. 18, 083009 (2016).
[3] I. Mahboob et al., Sci. Adv. 2, e1600236 (2016).

Fig. 1. (a) A false colour scanning electron micrograph of the electromechanical system. Each mechanicalresonator (1 and 2) has a vibration in its position which can be decomposed into in-phase (Q) and quadrature (P)components. (b) The vibration of the resonators, with frequency ω, can be visualised as balls rolling in harmonic
potentials driven by thermal energy kBT. The parametric down-conversion correlates the vibration of the two
resonators, effectively coupling them, which is confirmed via a linear inter-dependence of the in-phase andquadrature components of the two resonator’s motion. (c) and (d) Parametric resonance is manifested as either
resonator having two large amplitude vibrations, with opposite phases, in phase-space and an off thermal stateat the origin. This behaviour corresponds to the underlying harmonic potential of the resonators evolving into adouble well potential, with barrier energy E being greater than kBT thus enabling spin information to be encoded.
34

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

A Strongly Coupled Λ-type Micromechanical System
Hajime Okamoto and Hiroshi Yamaguchi
Physical Science Laboratory

Physical Science Laboratory

The ability to control phonon transport in semiconductor micromechanical systems has
important consequences for applications, such as ultralow-power-consumption mechanicalmemories and logic gates [1,2]. Such phonon manipulation requires strong coupling of adjacentmechanical resonators, that is, energy exchange between the resonators at a rate larger than theenergy dissipation. Parametrically coupling mechanical resonators via the periodic modulationof stress is an effective way to realize strong coupling. This has been recently demonstrated
in GaAs mechanical systems using the piezoelectric or photothermal effect [1,3], where themodulation with the frequency difference between the mechanical resonators (modes) allows
strong on-chip coupling as well as its on-off switching. However, such a demonstration has
been limited to two-resonator systems and not yet expanded to multiple-resonator (array) ones.
Here, we demonstrate strong coupling among three SiN mechanical resonators via dielectric
stress modulation with an electric field [4].
The sample consists of three SiN doubly clamped beams, where the middle beam (beam M)
is sandwiched by two metalized beams (beams L and R) [Fig. 1(a)]. Because the mode
frequency of beam M (fM) is higher than that of beams L (fL) and R (fR), it forms a Λ-type
three-level system as shown in Fig. 1(b). All the levels are frequency-shifted in an electric field
applied between beams L and R, that is, the three resonators are coupled via the dielectricallyinduced attractive force. However, strong coupling is not achieved only with this DC field
because of the frequency mismatch between beam M and beam L (R). To compensate forthis frequency mismatch, the electric field is AC-modulated with the frequency difference
between the two modes (ΔL(R) = fM – fL(R)). Then, beam M and beam L (R) are parametricallycoupled, leading to the splitting of each level. When the two modulation tones (ΔL, ΔR) are
simultaneously applied, each of the three levels splits into three. Here, one state of beam M is“dark”, where the vibration amplitude is canceled out [Fig. 1(b)]. This is due to the destructive
interference of the three beams and is evidence of the formation of a strongly coupled Λ-typemechanical system.
This work was supported by MEXT KAKENHI JP15H05869, JP15K21727 and collaborated
with Swiss Federal Institute of Technology in Lausanne (EPFL).
[1] H. Okamoto et al., Nature Phys. 9, 480 (2013).
[2] T. Faust et al., Nature Phys. 9, 485 (2013).
[3] R. Ohta et al., Appl. Phys. Lett. 107, 091906 (2015).
[4] H. Okamoto et al., Appl. Phys. Lett. 108, 153105 (2016).
Fig. 1. (a) Scanning electron micrographof the device: red, SiN (100 nm thickness);yellow, Au (45 nm thickness); grey, Si
substrate. Simulated mode shape of thethree mechanical resonators is also shown.
(b) Energy level diagram of the Λ-type
micromechanical system. Each of thethree levels splits into three when the two
frequency modulation tones (ΔL, ΔR) are
simultaneously applied. Notably, one stateof beam M is “dark” in the sense that it
involves no motion of the middle beam.

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)35

Engineering Quantum Spin Hall Insulators
by Strained-layer Heterostructures
Takafumi Akiho1, François Couëdo1, Hirhoshi Irie1, Kyoichi Suzuki1,
Koji Onomitsu2, and Koji Muraki1
1
Physical Science Laboratory, 2 Materials Science Laboratory
Quantum spin Hall insulators (QSHIs) have insulating bulk and conductive edges originatingfrom nontrivial inverted band structures. Owing to these unique properties of the spin-helicaledge modes, QSHIs have been proposed as a platform for exploring spintronics applications
and exotic quasiparticles useful for topological quantum computation. InAs/GaSb quantum
wells (QWs) have been predicted to offer a QSHI and have a key advantage of being insitu tunable between trivial and topological insulating phases. However, the residual bulk
conductivity associated with the small energy gap in the QSHI phase has been an obstacle tothe unambiguous identification of edge properties. In this study, we propose a strained InAs/
InGaSb heterostructure as a QSHI candidate and demonstrate that the strain enhances theenergy gap and leads to superior bulk insulation properties [1].
The QWs were grown by MBE and comprise InAs with the thickness of t (8.5~10.9 nm) and
5.9-nm-thick In0.25Ga0.75Sb layers, sandwiched between AlSb barrier layers. Compressive strain
induced in the InGaSb layer enhances heavy-hole light-hole splitting and impacts the energy
dispersion in the QSHI phase.
We determined the density of electrons (ne) and holes (nh) separately through the fast Fouriertransform (FFT) analysis of the longitudinal resistance (Rxx) vs. magnetic field (B) trace [Fig.
1(a)]. We confimed the coexsitence of electrons and holes at high densities, which indicatesthat the QW is deep in the band-invered regime. From the linear fit of gate voltage (VFG)
dependence of ne and nh (inset), we obtained the density ncross at the charge neutrality point(where ne = nh) to be 3.6 × 1015 m–2, which gives a quantitative measure of the band overlap.
We emphasize that the linear fit in the two-carrier regime gives an accurate evaluation of theband overlap.
The Rxx peak height at the the charge neutrality point, which mainly reflects in-gap statesin the bulk, increased with decreasing InAs thickness and reached 889 kΩ (corresponding
resistivity of ~10h/e2) [Fig. 1(b)]. All samples have bulk resistivity two orders of magnitude
higher than those of the InAs/GaSb system. These results demonstrate that InAs/InGaSb
strained QWs are promising for investigating edge transport properties.
This work was supported by JSPS KAKENHI JP15H05854 and JP26287068.
[1] T. Akiho et al., Appl. Phys. Lett. 109, 192105 (2016).

Fig. 1. (a) Rxx vs. B trace. (Inset) VFG dependence of ne and nh. (b) Rxx peaks with different InAs thickness.
36

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Andreev Reflection and Bound State Formation in a Ballistic
Two-dimensional Electron Gas Probed by a Quantum Point Contact
Hiroshi Irie1, Clemens Todt1, Norio Kumada1, Yuichi Harada1, Hiroki Sugiyama2,
Tatsushi Akazaki1, and Koji Muraki1
1
Physical Science Laboratory, 2 NTT Device Technology Laboratories

Physical Science Laboratory

The superconducting proximity effect in superconductor-semiconductor hybrid structures
has gained increased interest for studying exotic quantum phases [1] and developing novel
electronic devices [2]. In such hybrid structures, charge transport near the interface is governedby Bogoliubov quasiparticles generated by Andreev reflections. Better control and sensitive
detection of electronic properties of the quasiparticle are among the major challenges in thestudies of the proximity effect.
We study transport properties of Bogoliubov quasiparticles in a high-mobility In0.75Ga0.25As
two-dimensional electron gas (2DEG) coupled to a superconducting Nb electrode [3]. By using
a quantum point contact (QPC) formed in the vicinity of the InGaAs/Nb interface as a singlemode probe with a tunable transmission [Fig. 1 (a)], we can study the effects of the boundary
condition on the quasiparticle transport in the ballistic regime. Figure 1 (b) shows a differential
conductance spectrum of a fully open QPC. The QPC shows a single-channel conductancegreater than the conductance quantum 2e2/h at zero bias, which indicates the presence ofAndreev-reflected quasiparticles returning back through the QPC. When the QPC transmission
TQPC is reduced to the tunneling regime, the differential conductance spectrum probes the
single-particle density of states in the proximity area. Measured conductance spectra exhibit
a double peak within the superconducting gap of Nb [Fig. 1 (c)], demonstrating the formationof Andreev bound states in the 2DEG. Both of these results, obtained in the open and closed
geometries, underpin the coherent nature of quasiparticles, i.e., phase-coherent Andreev
reflection at the InGaAs/Nb interface and coherent propagation in the ballistic 2DEG.
[1] V. Mourik et al., Science 336, 1003 (2012).
[2] T. W. Larsen et al., Phys. Rev. Lett. 115, 127001 (2015).
[3] H. Irie et al., Phys. Rev. B 94, 155305 (2016).

Fig. 1. (a) Superconductor/semiconductor hybrid device studied. The distance between QPC and Nb contact Lch
is 220 nm. (b,c) Differential conductance spectra measured in (b) the open-channel regime and (c) the tunnelingregime. The grey areas represent the superconducting gap energy of Nb (1.3 meV).

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)37

Evaluation of Disorder Introduced by Electrolyte Gating throughTransport Measurements in Graphene
Norio Kumada1, Andrew Browning1, Yoshiaki Sekine2, Hiroshi Irie1, Koji Muraki1,
and Hideki Yamamoto2
1
Physical Science Laboratory, 2Materials Science Laboratory
Owing to the large capacitance as well as the flexibility, transparency, and facile processingof ionic liquids, electrolyte gating has been used for widespread applications. However its
drawback, namely contamination of the surface of the base material, has been overlooked. In
this work, we evaluate the degree of disorder introduced by the electrolyte gating structureusing graphene, in which the carrier transport is sensitive to disorder scattering [1].
We used graphene grown by thermal decomposition of a 6H-SiC(0001) substrate. Two
different types of samples were fabricated; one using an ionic liquid gate and the other having a
metal gate for reference. For the ion-gated samples, the graphene Hall bar and coplanar Cr/Au
gate electrode were coated by EMIM-TFSI [Fig. 1(a)]. To quantitatively investigate the disordereffects from the ionic liquid, we compare the transport properties for the ion- and metal-gatedsamples through a wide range of the carrier densities. From the slope of the conductivity as
a function of the carrier density, we found that the deposition of the ionic liquid introducescharged impurities with a density of approximately 6 × 1012 cm–2 [Fig. 1(b)]. This limits the
low-temperature mobility of graphene to 3 × 103 cm2/Vs [Fig. 1(c)]. We also found that at
higher temperature (> 50 K), phonons in the ionic liquid further reduce the mobility; restricting
the upper limit at room temperature to approximately 2 × 103 cm2/Vs at room temperature.
Since the degree of disorder does not depend on the base material, our results provide useful
information on estimating the disorder effects in any type of electrolyte gating experiments.
[1] A. Browning et al., Appl. Phys. Express 9, 065102 (2016).

Fig. 1. (a) Schematic top view of the ion-gated sample. (b) and (c) Conductivity and mobility, respectively, as afunction of the carrier density at 4 K for the ion-gated sample (red dots) and metal-gated sample (blue dots). The
solid lines in (b) represent results of the fitting.

38

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Spectroscopic Analysis for Measuring Quantum Phase Transitions ofBosonic Atoms in an Optical LatticeKensuke Inaba and Makoto Yamashita
Optical Science Laboratory

Optical Science Laboratory

Ultra-cold atoms in an optical lattice, which are highly controllable and quite clean quantum
systems, allow us to simulate quantum many-body phenomena found in condensed matters andrelated fields. As a typical example, a quantum phase transition from superfluid (SF) to Mott
insulator (MI) of bosons has been experimentally demonstrated by tuning lattice depths [1].
However, systematic and comprehensive measurements across the two phases, SF and MI, arestill lacking. This is because measurement methods used in the previous works are basicallystanding on the strategy to detect a certain characteristic signal for one of the two phases andthen to determine the critical point where such a signal disappears: For example, the time-offlight imaging has been used to identify SF-MI transitions by detecting the disappearance ofthe coherent peak that characterizes the existence of SF states [1].
Kyoto Univ. and NTT collaboratively developed high-resolution spectroscopy [2] anda numerical scheme for calculating observed spectra [3], respectively. The developed
spectroscopy has been used to comprehensively measure spectra of bosons in a threedimensional optical lattice across the SF and MI phases [2]. Our numerical scheme takes
into account the physical sum rule [3], which allows us to systematically analyze the spectra
without any fitting parameters. As shown in Fig. 1, experiments and calculations show good
agreements with each other, and the obtained spectra clearly capture the signatures of theexistence of both SF and MI states in shallow and deep lattices, respectively [2]. Furthermore,
we found that SF and MI states coexist in a middle lattice [2]. A combination of the highresolution spectroscopy and the numerical scheme can determine quantum phase transitions ofbosons in detail, and in addition, it will be applicable to the future quantum simulation on thevarious systems, e.g., fermions or boson-fermion mixtures confined in optical lattices.
This work was partly supported by CREST (JPMJCR08F5), JST and JSPS KAKENHI
JP25287104.
[1] I. Bloch, J. Dalibard, and W. Zwerger, Rev. Mod. Phys. 80, 885 (2008), and references therein.
[2] S. Kato, K. Inaba et al., Nature Commun. 7, 11341 (2016).
[3] K. Inaba and M. Yamashita, Phys. Rev. A 93, 043608 (2016).

Fig. 1. Spectrum of bosons obtained experimentally (blue circles) and those calculated numerically (orange solidlines) in (a) shallow, (b) middle, and (c) deep optical lattices. The broadened spectra originate from the superfluid
states, and the discrete narrow spectra result from the Mott insulators. The both characteristics can be seen in the
middle region. The data is extracted from Ref. [2].

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)39

Coherent Ising Machine for Combinatorial Optimization Problems
Takahiro Inagaki, Kensuke Inaba, Toshimori Honjo, and Hiroki Takesue
Optical Science Laboratory
It is known that combinatorial optimization problems can be mapped onto ground-statesearch problems of the Ising model. Recently, several approaches have been demonstrated tosolve the Ising problems using artificial spin systems. A coherent Ising machine (CIM) can
simulate the Ising model with networked degenerate optical parametric oscillators (DOPOs).
A DOPO takes only a 0 or π phase relative to the pump pulse, so this binary phase mode canrepresent the binary spin state of the Ising model. To solve complex problems with the CIM,
we need to prepare a large number of DOPOs and connect them with each other throughmutual optical couplings. We generated over 10,000 DOPOs via time-domain multiplexing
in a 1-km fiber ring cavity [1,2]. Using those DOPOs, a one-dimensional Ising model was
simulated by introducing nearest-neighbor optical coupling with a 1-bit delay interferometer.
We observed the ferromagnetic and anti-ferromagnetic behavior of low-temperature Ising spinswith the networked DOPOs.
To implement all-to-all optical couplings among DOPOs, we employed a measurement andfeedback (MFB) scheme [Fig. 1 (left)]. A portion of the DOPOs are measured using a balanced
homodyne detector. The measured signals are then input into a field-programmable gate array(FPGA) module, where a feedback signal for each DOPO is calculated according to the network
structure. The calculated feedback signals are converted into optical pulses, and launched into
the cavity to achieve the virtual optical couplings between DOPOs. With the MFB scheme,
we developed a CIM that could find solutions to optimization problems on arbitrary graphstructures with up to 2,048 nodes [3]. We performed a benchmark study to investigate theperformance of our CIM to solve an optimization problem and compared it with a simulated
annealing (SA) algorithm. We used the CIM and SA to solve the maximum-cut (MAX-CUT)
problem for a 2,000-node complete graph with 1,999,000 undirected edges. The times needed
to reach the target Ising energy were about 70 μs for the CIM and 3.2 ms for SA [Fig. 1, (right)].
The CIM obtained the benchmark Ising energy nearly 50 times faster than SA. These results
suggest that a CIM can outperform SA on a CPU when solving dense graph problems.
This work was supported by the ImPACT Program.
[1] T. Inagaki et al., Nature Photon. 10, 415 (2016).
[2] H. Takesue et al., Opt. Lett. 41, 4273 (2016).
[3] T. Inagaki et al., Science 354, 603 (2016).

Fig. 1. (Left) Experimental setup of CIM with measurement and feedback scheme.
(Right) Time evolutions of Ising energy when solving the MAX-CUT problem for a 2000-node complete graph.
40

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Quantum State Tomography for High-dimensional Time-bin States
Takuya Ikuta and Hiroki Takesue
Optical Science Laboratory

Optical Science Laboratory

High-dimensional quantum states are being investigated as resources of advanced quantum
information processing. Because a high-dimensional state has multiple orthogonal states, forexample, we can increase the information that a particle can carry (multiple bits per particle).
A time-bin state is often used in photonic quantum communication systems because a time
bin state is robust against disturbances caused by optical fiber transmission. Furthermore, we
can easily enlarge the number of dimensions of the state simply by increasing the number oftime slots that form it. To evaluate the quality of the state, it is important to fully characterize
the quantum state via quantum state tomography [1,2]. However, a method of quantum state
tomography for high-dimensional time-bin states was not known prior to our research. Here,
we demonstrated a quantum state tomography scheme for high-dimensional time-bin statesusing cascaded Mach-Zehnder interferometers [3]. With this scheme, the number of themeasurement settings scales linearly with the dimension of the state [3].
Figure 1 shows the concept of quantum state tomography using cascaded Mach-Zehnderinterferometers. The information of a high-dimensional time-bin state is encoded at multiple
temporal positions and in the relative phases between the positions. After a photon passes
through the cascaded Mach-Zehnder interferometers, it makes an interference pattern of
single photon counts depending on its state and the settings of the interferometers. By
observing the interference pattern while changing the settings of the interferometers, we canobtain information on the temporal positions and relative phases encoded in the photon andreconstruct the state with that information.
We performed quantum state tomography on four-dimensional time-bin entangled states
generated via spontaneous parametric down-conversion in a periodically poled lithium niobate
waveguide. We obtained a reconstructed state that was close to the four-dimensional maximallyentangled time-bin state (Fig. 2). The number of measurement settings was 16, which was equal
to the dimension of the Hilbert space for the two entangled photons. Thus, we successfully
demonstrated an efficient quantum state tomography for high-dimensional time-bin states.
[1] D. F. V. James et al., Phys. Rev. A 64, 052312 (2001).
[2] R. T. Thew et al., Phys. Rev. A 66, 012303 (2002).
[3] T. Ikuta and H. Takesue, New J. Phys. 19, 013039 (2017).

Fig. 1. Concept of the quantum state tomography using cascaded
Mach-Zehnder interferometers.

Fig. 2. Real parts of the reconstructed fourdimensional maximally entangled state.

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)41

Fundamental Rate-loss Trade-off for the Quantum Internet
Koji Azuma1, Akihiro Mizutani2, and Hoi-Kwong Lo3
1
Optical Science Laboratory, 2Osaka University, 3University of Toronto
The quantum internet holds promise for accomplishing many quantum communication tasks—such as quantum teleportation and quantum key distribution (QKD)—freely between
any clients all over the globe, as well as the simulation of the evolution of quantum manybody systems. The most primitive function of the quantum internet is to provide quantum
entanglement or a secret key (for secure communication) to two points in the network [such as
A and B in Fig. 1(a)] efﬁciently.
In our work, we present a general theoretical limit on the performance of such quantum
internet protocols [Fig. 1(b)], determined only by the properties of communication channels
in the network [1]. This theoretical limit is obtained by generalizing the Takeoka-GuhaWilde (TGW) bound [2] which upper bounds the private/quantum capacities of single
communication channels. Therefore, our theoretical limit inherits a feature of the TGW boundthat it can be estimated for any communication channel, and our limit can thus be estimatedirrespectively of what kind of communication channel constructs the quantum network. In fact,
for any quantum communication protocol working over linear networks composed of opticalfibres, this feature enables us to derive a trade-off relation between the communication rate
and the loss in the network. This trade-off has essentially no scaling gap with the quantum
communication efﬁciencies of known protocols such as intercity QKD protocols and quantum
repeater protocols. In other words, this implies that there remains not much room to improve
known intercity QKD protocols and quantum repeater protocols with respect to the efficiency.
As another example of applications of our theoretical limit, we apply the limit to one ofmost famous quantum repeater schemes, called Duan-Lukin-Cirac-Zoller-type (DLCZ-type)schemes [3]. As a result, we conclude that the matter quantum memories in the DLCZ-type
schemes should have coherence time (T2) larger than 0.1 ms at least, in order to enjoy theblessing of the DLCZ-type schemes. Our result—reveraling a practical but general limitationon the quantum internet—enables us to grasp the potential of the future quantum internet.
[1] K. Azuma, A. Mizutani, and H.-K. Lo, Nature Commun. 7, 13523 (2016).
[2] M. Takeoka, M. Guha, and M. M. Wilde, Nature Commun. 5, 5245 (2014).
[3] N. Sangouard et al., Rev. Mod. Phys. 83, 33 (2011).

Fig. 1. (a) Quantum network. (b) General quantum internet protocol. In the protocol, quantum channels, local
operations and classical communication (LOCC) are freely combined.
42

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Hybrid Quantum Engineering Using Spectral Hole
Burning in Microwave Photonics
Stefan Putz1, Andreas Angerer1, Dmitry O. Krimer1, Ralph Glattauer1,
William J. Munro2, Stefan Rotter1, Jorg Schmiedmayer1, and Johannes Majer1
1
TU Wien, 2Optical Science Laboratory

Optical Science Laboratory

Spectral hole burning of inhomogeneously broadened ensembles using optical fields is
now a well-established technique [1] that allows one to selectively bleach the absorption
spectrum of materials. These spectral holes have been used in a variety of applications ranging
from spectroscopy in photochemistry to slow light in photonics, and the storage of quantum
information by the creation of optical solid-state frequency combs. Similarly, in microwave
photonics hybrid solid-state devices with ensembles of electron spins are considered as aversatile component for future quantum memories with high storage capacities [2], but theiroperational capability lag behind those of full optical systems. To demonstrate the potential ofelectron spin ensembles in circuit-QED (Quantum Electrodynamics) systems, we implement
spectral hole burning using a cavity in the microwave domain. This enables us to selectively
bleach the ensembles microwave absorption spectrum and thus engineer long-lived collective
dark states in a hybrid system, composed of an ensemble of electron spins hosted by nitrogenvacancy centers in diamond strongly coupled to a superconducting microwave cavity.
We show how to eliminate the ensembles inhomogeneous broadening, which is a severe
issue that limits the memory’s storage time. The coherence rates are significantly better thaneither those given by the ensembles free induction decay or the bare cavity dissipation rate.
Our hybrid quantum system truly lives up to the promise of this technology to perform better
than its individual subcomponents as is shown in Fig. 1. To further demonstrate the potential of
our approach for the selective preparation of “decoherence-free” states, we engineer multiple
long-lived dark states [3], a key step towards a solid-state microwave frequency comb. Our
technique allows the advantages given by spectral hole burning using optical fields to cometo the solid-state microwave world opening up the way for long-lived quantum memories,
spin squeezed states, optical-to-microwave quantum transducers and novel metamaterials.
Furthermore, our approach also paves the way for a new class of cavity QED experiments with
dense spin ensembles, where dipole spin-spin interactions become important and many-bodyphenomena are directly accessible on a chip.
[1] W. E. Moerner, Persistent Spectral Hole-Burning: Science and Applications (Springer Science & BusinessMedia, 2012).
[2] J. Nunn et al., Phys. Rev. Lett. 101, 40 260502 (2008).
[3] S. Putz et al., Nature Photon. 11, 3639 (2016).

Fig. 1. (Left) Image of the hybrid system composed of a superconducting resonator and NV- electron spin
ensemble. (Middle) Cavity response to a weak driving pulse without spectral hole burning (Right) Cavity response
to a weak driving pulse after spectral holes are burnt.
Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)43

Generation of Low-noise Millimeter-wave by Using an Electro-opticsmodulator-based Optical Frequency Comb
Atsushi Ishizawa1, Kenichi Hitachi1, Tadashi Nishikawa2,
Takahiro Goto2, Tetsuomi Sogawa1, and Hideki Gotoh1
1
Optical Science Laboratory, 2Tokyo Denki University
We are trying to generate ultralow-noise microwave and millimeter-waves using an opticalfrequency standard toward high-accuracy time and frequency synchronization. We havefocused on an electro-optics-modulator-based optical frequency comb (EOM comb), whichacts as an optical ruler and developed one with 25-GHz mode spacing. The EOM comb is a
useful light source for large capacity optical transmission systems and astronomy. On the other
hand, the noise increases and the spectral linewidth widens with distance from the frequency
comb’s center wavelength.
We exploited this “disadvantage” to demonstrate that an EOM comb can work as a noise
booster and a high-sensitivity detector for detecting the magnified noise from microwave andmillimeter-wave signal generators [1]. Our method can generate low-noise and continuously
frequency-variable microwave and millimeter-wave signals. In addition, we can overcome thedisadvantage of the EOM comb. The interference signal between an optical frequency comb
and reference laser with narrow linewidth (i.e. low noise) includes information about the noisefrom microwave and millimeter-wave signal generators. The noise information is converted
into an electrical signal and detected with high sensitivity. Finally, by using the electricalsignal, the noise from microwave and millimeter-wave signal generators is reduced with afeedback circuit [Fig. 1(a)]. The further the wavelength is away from the center wavelengthof the semiconductor laser, the wider the spectral linewidth becomes. The noise in 25-GHz
millimeter-wave signals can be reduced to –110 dBc/Hz at a 1-kHz offset frequency from thecenter frequency [Fig. 1(b)]. The noise with our method is one-hundred times lower than thelowest noise reported for commercially available signal generators. Even lower noise will beachieved if we use a reference laser that is further away from the center wavelength of thesemiconductor laser. In addition, the output frequency of microwave and millimeter-wave
signal generators can be expanded for their universal use. We succeeded in generating lownoise signals at continuously variable frequencies over the range from 6 to 72 GHz.
[1] A. Ishizawa et al., Sci. Rep. 6, 24621 (2016).

(a)

(b)

Fig. 1. (a) Diagram showing how the noise of microwave and millimeter-wave signal generators is reduced.
(b) Experimental noise reduction results for 25-GHz signal.

44

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Light-Field Driven Petahertz Electronic Oscillation
with Attosecond Periodicity in GaN Semiconductor
Hiroki Mashiko, Katsuya Oguri, and Hideki Gotoh
Optical Science Laboratory

Optical Science Laboratory

High-speed photonic and electronic devices at present rely on radio-frequency (RF) electricfields to control the physical properties of a semiconductor, which limits their operating speed
to terahertz (1012 Hz) frequencies. Using the electric field from light pulses, however, could
extend the operating frequency into the petahertz (1015 Hz: PHz) regime. Here we demonstrate
optical drive at 1.16-PHz frequency in the gallium nitride (GaN) semiconductor characterized
by an isolated attosecond (10–18 Hz: as) pulse (IAP) [1].
Figure 1(a) shows a schematic view of the transient absorption spectroscopy. The collinearly
propagated IAP (660-as duration, 20.5-eV center photon energy [2]) and near-infrared (NIR)
pulse (7-fs duration, 1.6-eV center photon energy, 1×1010 W/cm2) are focused onto stand-alone
102-nm thick GaN[0001] (bandgap energy: 3.4 eV). The NIR pulse induces ultrafast electronicinterband polarization with the three photon process. Figure 1(b) displays the measured
transient absorption trace. The trace shows the deviation of optical density (ΔOD) with andwithout the NIR pulse as a function of time delay. The coherent broadband IAP excites thesuperposition state of electrons in the valence band (VB) and conduction band (CB). Figure 1(c)shows the electric oscillation with 860-as periodicity. The resultant frequency reaches 1.16
PHz, making this the first time the ultrafast electric dipole oscillation with PHz frequency
is observed in Solid-state materials [1]. This study shows the potential of future PHz signal
processing technology based on the semiconductor devices.
This work was supported by JSPS KAKENHI JP16H05987 and JP16H02120.
[1] H. Mashiko et al., Nature Phys. 12, 741 (2016) : Featured on cover.
[2] H. Mashiko et al., Nature Commun. 5, 5599 (2014) .

Fig. 1. Experimental setup and as transient absorption trace. (a) Schematic view of experimental setup.
(b) Measured transient absorption trace of GaN. (c) The upper graph shows the integrated line profile structure forthe photon energy region in Fig. 1(b). The bottom graph shows the profile in the shorter delay region.
Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)45

Bridging the Gap Between the Nanometer-scale Bottom-up andMicrometer-scale Top-down Approaches for Site-defined InP/InAs
Nanowires
Guoqiang Zhang1,2 and Hideki Gotoh1
1
Optical Science Laboratory, 2NTT Nanophotonics Center
The field of microelectronics has been attempting to come to grips with the issue ofminiaturization for decades as the demand for ever-smaller products puts pressure on
manufacturers to make smaller components [1]. Despite the state-of-the-art Extreme
Ultraviolet (EUV) photolithography technique, the low cost feature of the conventional UV
photolithography is greatly advantageous over the high-cost EUV photolithography. Thisissue has opened the door to the development of other device fabrication methods [2]. Anothercompeting method, self-assembly, relies on a bottom-up process that is driven energetically as
the system reaches a lower energy state.
III-V compound semiconductor nanowires (NWs) are successful example of the bottomup approach. For site-defined growth of III-V NWs with nanoscale diameter, top-down
techniques like conventional photolithography are not feasible. This work presents a methodthat bridges the gap between the nanometer-scale bottom-up and micrometer-scale top-down
approaches for site-defined NWs, which has long been a significant challenge for applications
that require low-cost and high-throughput manufacturing processes [3]. We realized thebridging by controlling the seed indium nanoparticle position inside the open window throughthe optimization of the temperature and the pitch size. Site-defined InP NWs were then grownfrom the indium-nanoparticle array [Fig. 1(left)]. We demonstrated that the developed method
can be used to grow a uniform InP/InAs axial-heterostructure NW array. The ability to form aheterostructure NW array makes it possible to tune the emission wavelength over a wide range
through quantum confinement [Fig. 1(right)]. Successful pairing of a controllable bottomup growth technique with a top-down substrate preparation technique greatly improves thepotential for the mass-production and widespread adoption of this technology.
This work was supported by JSPS KAKENHI JP15H05735 and JP16H03821.
[1] G. A. Brown et al., Mater. Today 7, 20 (2004).
[2] B. D. Gates et al., Annu. Rev. Mater. Res. 34, 339 (2004).
[3] G. Zhang et al., ACS Nano 9, 10580 (2015).

Fig. 1. (Left) Schematic diagram of absorption, decomposition, surface diffusion, and accumulation of materials
on the surface of SiO2 film and circular InP open windows. SEM images of indium seed particle array by selfassembly of indium adatoms and InP NWs grown from the particle array. (Right) SEM image of InP/InAs
NWs with two InAs segments. Schematic structure and band diagram of the NW and spatial PL image withluminescence spots from InAs quantum disks.
46

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Demonstration of Efficient Mode Conversion for Deep-subwavelength
Plasmonic Waveguides
Masaaki Ono1,2, Hideaki Taniyama1,2, Hao Xu1,2, Masato Tsunekawa2,3, Eiichi Kuramochi1,2Kengo Nozaki1,2, and Masaya Notomi1,2,3
1
NTT Nanophotonics Center, 2Optical Science Laboratory, 3Tokyo Institute of Technology

Nanophotonics Center

Plasmonic waveguides enable us to utilize light-propagating modes much smaller thana wavelength dimension in photonic integrated circuits. In particular, nanomaterials suchas nanowires and two-dimensional (2D) materials interact efficiently with light in deepsubwavelength plasmonic waveguides, and their combination may lead to ultracompact,
ultrahigh-speed photonic devices. On the other hand, plasmonic waveguides have a large
propagation loss, and thus conventional low-loss dielectric waveguides are needed for long
distance propagation. However, it is difficult to efficiently connect two waveguide modes
that have fundamentally different sizes and characteristics. Thus, the waveguide thickness
was almost unchanged in previously reported mode converters. In this study, we demonstrate
highly efficient (–1.7 dB) mode conversion between a Si-wire waveguide (400 × 200 nm2 coresize) and a plasmonic waveguide with a metal-insulator-metal (MIM) structure (50 × 20 nm2
core size) [1]. The waveguide thickness was reduced from 200 nm to 20 nm, resulting in a large
reduction in core size. In addition, the core size of the connected MIM waveguide decreased to(λ/n)2/2000 (λ = wavelength, n = reflective index).
Our converter consists of a 2D laterally tapered structure, and there is a small gap between
the Si and the metal [Fig. 1(a)]. Figures 1(b) and (c) show the calculated field profile at awavelength of 1.55 μm. The eigenmode of the Si-wire waveguide has side lobes, which
are attracted to the air gap and are adiabatically connected to the MIM mode. Investigating
the structural parameter dependence of the coupling efficiency, we found that the coupling
efficiency is greatly increased both by optimizing the taper length and by introducing the small
air gap. This enables highly efficient, full three-dimensional (3D) mode conversion, where
the mode size is squeezed laterally and vertically, without the need to introduce a 3D tapered
structure accompanied by a complicated fabrication process. We measured the fabricatedsamples and estimated the coupling efficiency. The experimentally obtained coupling efficiency
was very high and –1.7 dB for an air gap width of 40 nm and a taper length of 600 nm. Thisefficiency value was consistent with the calculated result (–1.4 dB). We believe that our mode
converter will provide a new deep-subwavelength photonic platform.
This work was supported by JSPS KAKENHI JP15H05735.
[1] M. Ono et al., Optica 3, 999 (2016).

Fig. 1. (a) Schematic structure of the mode converter. (b) Cross-sectional top view of the calculated field profile
for an air gap width of 40 nm and a taper length of 400 nm at y = 10 nm. Scale bar, 500 nm. (b) Cross-sectional
side views of the calculated field profile. Scale bar, 200 nm.
Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)47

Subwavelength Nanowire-induced Silicon Photonic Crystal Lasers
Masato Takiguchi1,2, Atsushi Yokoo1,2, Kengo Nozaki1,2,
Muhammad Danang Birowosuto1,2, Kouta Tateno1,3, Guoqiang Zhang1,2,
Eiichi Kuramochi1,2, Akihiko Shinya1,2, and Masaya Notomi1,2
1
NTT Nanophotonics Center, 2Optical Science Laboratory, 3Materials Science Laboratory
While many nanowire (NW) lasers have been demonstrated at visible and near-visible
wavelengths, it is difficult to make nanowire lasers that operate in telecom-bands because thegain is too small. In this study, we devised an NW induced photonic crystal cavity by using
atomic force microscopy [Fig. 1(a)] [1] and demonstrated telecom-band nanowire lasers on Si.
This is a new technique to build nano-lasers in Si photonic circuits [2,3].
In the experiment, the number of quantum wells in each NW was increased to 100 toincrease the gain volume. In addition, the quality of the NW’s crystal was improved so thatthe polarization of the intrinsic emission of the nanowire could be optimized to the cavity
polarization therefore increasing the extraction efﬁciency. The NW was 2.5 µm long and about
111 nm in diameter. The emission was at about 1330 nm. Figure 1(b) shows the spectrum of a
NW laser under 0.25 and 2.5 mW continuous wave (CW) pumping conditions at 4K. Figure1(c) shows the light-in vs light-out (L-L) property and full width at half maximum. It shows akink structure in the L-L plot and that indicates lasing. We also measured photon statistics [Fig.
1(d)] and confirmed that the sample truly achieves CW lasing [3]. The lasing wavelength canbe tuned by moving the NW [Fig. 1(e)] [1,2]. Next we estimated the dynamic property of thelaser. The single NW laser was pumped by a modulated laser (pseudo-random bit sequence),
and the signal from the NW laser was measured with a superconducting single photon detector.
It is generally difficult to measure a modulation signal in micro-photoluminescence because
the coupling efficiency to the vertical direction is very low. However our measurement system
is very sensitive and makes it possible to obtain the signal. We also obtained 10 Gbps opened
eye-pattern from the measured modulated signal [Fig. 1(f)] [3]. This is the first demonstrationof directly modulated nanowire lasers.
[1] M. D. Birowosuto et al., Nature Mater. 13, 279 (2014).
[2] A. Yokoo, M. Takiguchi et al., ACS Photonics 4, 355 (2017).
[3] M. Takiguchi et al., APL Photonics 2, 046106 (2017).

Fig. 1. (a) Schematic image. (b) PL spectrum. (c) L-L. (d) Photon correlation. (e) Tuned spectrum. (f) Eye diagram.
48

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Efficient Light-to-voltage Conversion by Ultralow-capacitanceNano-photodetector
Kengo Nozaki1,2, Shinji Matsuo1,3, Takuro Fujii1,3, Koji Takeda1,3, Masaaki Ono1,2,
Eiichi Kuramochi1,2, and Masaya Notomi1,2
1
NTT Nanophotonics Center, 2Optical Science Laboratory,
3
NTT Device Technology Laboratories
Photodetectors (PDs) to use as a receiver in a dense on-chip photonic processor requires
low-energy consumption and small size. However, the energy consumption of a conventional
photoreceiver is dominated by the electric amplifiers connected to the PD. An ultralowcapacitance PD can overcome this limitation, because it can generate large voltage without
an amplifier when connected with a high-impedance load. By our fabrication technique of theburied heterostructure to embed the compact InGaAs absorber in the photonic crystal (PhC)
waveguide [Fig. 1(a)] [1], we demonstrated the ultrasmall PD with a length of 1.7 μm and atheoretical capacitance of only 0.6 fF. Such a short PD still showed the optical responsivity
as high as 1 A/W and the fast response with a bit rate of 40 Gbit/s. A resistor-loaded PD was
also fabricated to evaluate the light-to-voltage conversion [Fig. 1(b)]. We utilized an electrooptic probing method to measure the voltage across the strip lines, which is generated fromthe photocurrent and the load resistor. As a result, we obtained a light-to-voltage conversion
efficiency of 4 kV/W [Fig. 1(c)], which is actually as large as conventional receivers integrated
with amplifiers. Although the operation bandwidth was limited by the parasitic capacitance ofthe strip lines that were required in the EO probe measurement, a 40 Gbit/s operation will be
expected if we only take the ultrasmall PD capacitance into account. These results offer therealization of an ultralow-energy amplifier-less receiver by using an ultrasmall-capacitance PD,
and therefore are step toward a densely-integrated photonic network/processor on a chip.
This work was partly supported by CREST (JPMJCR15N4), JST.
[1] K. Nozaki et al., Optica 3, 483 (2016).

Nanophotonics Center

Fig. 1. (a) Photonic crystal PD. Insets show the optical field distribution (upper) and the cross-sectional
photograph (lower). (b) Resistor-loaded PD and its equivalent circuit. (c) Light-to-voltage conversion efficiency
vs load resistance characteristic.
Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)49

Superconducting Nanowire Single Photon Detector on Si Platform
Tatsurou Hiraki1,2, Tai Tsuchizawa1,2, Hiroyuki Shibata3, and Shinji Matsuo1,2
1
NTT Nanophotonics Center, 2NTT Device Technology Laboratories,
3
Kitami Institute of Technology.
Quantum photonics technology has attracted attentions for quantum computing and quantumcode communications. In particular, a silicon (Si) photonics technology is widely studied
for the scalable quantum photonics system. One of key challenges for the Si photonics is tointegrate a single-photon detector, because traditional Si avalanche photodiodes cannot detect
infrared photons. The promising solution is a waveguide-integrated superconducting nanowire
single-photon detector (SNSPD) [1] on Si platform, because it can detect infrared photons
with low noise and small jitter. However, the system detection efficiency of the SNSPD isstill limited by a large fiber coupling loss [2]. In this work, we demonstrated a high-systemdetection SNSPD integrated with Si nanowire waveguide and spot-size converter (SSC), whichefficiently couples to the fiber.
Figure 1(a) shows a schematic of waveguide-integrated SNSPD with SSC. The
superconducting nanowire was comprised of niobium nitride (NbN) whose thickness andwidth were 7 nm and 60 nm, respectively. The NbN nanowire was evanescently coupled to the
Si nanowire waveguide. The Si waveguide has inverse taper structure, which is covered witha 3-μm-square SiOx waveguide to construct SSC [3]. The mode-field diameter of the SiOx corenearly matched that of the high-numerical aperture fiber. The key fabrication process is the
low-temperature formation of the SiOx waveguide (< 200°C), which prevents thermal damage
to the NbN film.
We measured the system detection efficiency of the fabricated SNSPD in a cryostat. In theexperiment, input continuous-wave light power was attenuated to have 106 photons per second
outside the cryostat. The cryostat state was at 0.3 K. Figure 1(b) shows measured relationshipbetween system detection efficiency and bias current. The system detection efficiency was around32%, which is over ten times larger than that of the previous devices. The fiber-chip couplingloss was remarkably small (1.9 dB/facet). It is notable that the on-chip detection efficiencyof the SNSPD was over 90%. It means the low-temperature integration process successfully
prevent thermal damages to NbN nanowires. These results indicated the Si-NbN-SiOx integration
technology is a promising solution for constructing future quantum photonics systems.
[1] J. P. Sprengers et al., Appl. Phys. Lett. 99, 181110 (2011).
[2] O. Kahl et al., Sci. Rep. 5, 10941 (2015).
[3] T. Hiraki et. al., Proc. in Frontiers in Optics, FW5F.3 (2016).

(a)

(b)

Fig. 1. (a) Schematic of SNSPD with SSC. (b) measured system detection efficiency.
50

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

LEAP Lasers Integrated on Si Waveguides
Koji Takeda1,2, Takuro Fujii1,2, Akihiko Shinya1,3, Tai Tsuchizawa1,2, Hidetaka Nishi1,2,
Eiichi Kuramochi1,3, Masaya Notomi1,3, Takaaki Kakitsuka1,2, and Shinji Matsuo1,2
1
NTT Nanophotonics Center, 2NTT Device Technology Laboratories,3
Optical Science Laboratory
Data transfer is becoming a performance bottleneck in datacenters and high-performancecomputing. For further improvement, short-distance optical interconnects with large capacity
and low energy cost are desired [1]. Since the required bandwidth is large in such interconnects,
many photonic devices, which can operate with very small energy, need to be integrated withlarge bandwidth density [2]. In this context, we are studying photonic crystal (PhC) lasers
integrated on Si waveguides, which enables large density owing to the large refractive index
contrast. Here, we report the first continuous-wave (CW) operation of our PhC lasers on Si
waveguides.
The device fabrication procedure was as follows. First, InGaAsP 6-quantum wells and
InGaAs etch stop layers were grown on InP substrates and Si waveguides were formed byusing silicon-on-insulator (SOI) substrates. SiO2 layers were deposited on InP substrates, and
InP and Si substrates were bonded by oxygen-plasma-assisted bonding. After removing the InP
substrate and InGaAs layer, we defined buried heterostructure patterns, followed by etching
and regrowth to bury the active regions with InP. After fabricating the buried active region, alateral p-i-n junction was formed by implantation and diffusion. Then we formed PhC air holes
by electron-beam lithography and dry etching. Finally, electrodes were formed on top of the
III-V slab. A schematic of a fabricated laser is shown in Fig. 1(a). From their structural feature,
we call our lasers lambda-scale embedded active region PhC (LEAP) lasers.
We measured output light power and applied voltage as a function of injected current at
25°C, and the results are shown in Fig. 1(b). CW operation was successfully achieved witha threshold current of 42 μA. Maximum output power from the device was 0.72 μW at thelensed fiber at an injected current of 0.5 mA. The inset in Fig. 1(b) shows an infrared image ofthe device taken during measurements. From this image, we confirmed that the lasing light was
successfully guided through the Si waveguides. We believe this achievement is an important
step towards realizing short-distance, large-bandwidth-density optical interconnects.
Nanophotonics Center[1] A. Benner, Proc. OFC Tutorial (2012).
[2] Y. Arakawa et al., Com. Mag. IEEE, 51, 72 (2013).

Fig. 1. (a) Schematic of LEAP lasers fabricated on Si waveguides. (b) L-I-V characteristic and infrared image ofthe device.
Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

51

Ⅱ．Data

The 9th Advisory Board
The NTT BRL Advisory Board, which was first convened in 2001, held its 9th meeting on
January 30 - 31, 2017. The aim of the Advisory Board is to provide an objective evaluationof our research plans and activities to enable us to employ strategic management in a timely
manner. On this occasion, we had the meeting with five board members.
Over the course of the two days, the board made valuable suggestions and comments inrelation to our research and management activities. They commented that the research level
was generally high on a worldwide point of view, and that it was important for us to maintainthis top-level research and transmit information on our research achievements to the world.
They also raised several issues related to human resources, the research budget and internaland external collaboration. We will improve research issues and managements based on thesevaluable suggestions.
At this meeting, the BRL researchers had a lunch with the board members and a poster
session, where they had chances to present their researches to the board members. The
poster session was performed with the dinner party where the board members and the BRL
researchers were able to interact in a casual atmosphere. For the BRL and NTT executives,
we organized a Japanese style dinner, which provided a good chance to discuss the future
management strategy of NTT BRL from an international perspective. The next board meeting
will be held in two years.

54

Board members

Affiliation

Research field

Prof. John Clarke
Prof. Evelyn Hu
Prof. Mats Jonson
Prof. Sir Peter Knight
Prof. Anthony J. Leggett
Prof. Allan H. MacDonald
Prof. Andreas Offenhäusser
Prof. Halina Rubinsztein-Dunlop
Prof. Klaus von Klitzing

Univ. California, Berkeley
Harvard Univ.
Univ. Gothenburg
Imperial College London
Univ. Illinois
Univ. Texas
Forschungszentrum Jülich
Univ. Queensland
Max-Planck-Inst.

Superconductor physics
Nanodevice
Condensed matter
Quantum optics
Quantum physics
Condensed matter
Nano-bio electronics
Quantum electronics
Semiconductor physics

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Science Plaza 2016
“Science Plaza 2016”, an NTT Basic Research Laboratories (BRL) open-house event,
was held at NTT Atsugi R&D Center on 23rd November, 2016. Under the banner “Frontier
Science: Open Door to the Future”, Science Plaza aimed at disseminating our latest researchaccomplishments to various groups of people inside and outside NTT and to gather diverse
opinions. This event was held jointly with NTT Device Innovation Center, NTT Device
Technology Laboratories, and NTT Communication Science Laboratories.
Following an opening address by Dr. Tetsuomi Sogawa (director of BRL) and an
introduction to NTT Laboratories by the Executive Managers, Dr. Akira Fujiwara (SeniorDistinguished Researcher) presented a symposium lecture entitled “Ultimate Electronics
Using Nano-devices”. In the afternoon session, Prof. Hiroshi Amano (Nagoya University)
gave a special lecture entitled “Illuminating the World by LEDs”. Each lecture was wellattended and followed by lively question and answer sessions.
In the poster session, 52 posters were presented, including 13 from joint research institutes.
These posters described the originality and impact of various areas of research as well as
outlining future prospects. They provoked intense discussions, and many meaningful opinions
were heard. This year’s “Lab Tour”—a guided tour of the research facilities that has been
receiving high praise from visitors over the years—took place at ten different labs. After all
the lectures, presentations, and exhibitions had finished, a banquet was held in the Center’sdining room, and friendships were established and deepened by the lively conversations
engaged in by the participants.
198 people from research institutes, universities, and industries as well as from NTT Group
companies attended Science Plaza 2016. Thanks to the efforts of all the participants, theconference ended on a high note. We would therefore like to express our sincere gratitude to
all who took part.

Data

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

55

List of Visitors’ Talks
Date
Apr. 26

Speaker (Affiliation)

Title

Prof. Peter Smith

Integrated photonic circuits for quantum(University of Southampton, U.K.)

information processing

Prof. Jacob. M. Taylor
June 22(National Institute of Standards andTechnology, U.S.A.)

June 22
June 24
July 4

Hydrogen - For developing functional(Hokkaido University, Japan)

biocompatible materials -Dr. Zhechao Wang

Monolithic integration of III-V semiconductor(Ghent University-IMEC, Belgium)

lasers on Si

Dr. Rakchanok Rungsawang

Wavefront sensing, adaptive optics for microscopy(Imagine Optic, France)and optical metrology(Paul Drude Institut for Solid StateElectronics, Germany)
Dr. David Elkouss

July 19(Delft University of Technology,
The Netherlands)
Dr. Erika KawakamiAug. 9(Delft University of Technology,
The Netherlands)

Aug. 9Sep. 9Sep. 26

light

Mr. Riku Takahashi

Prof. Henning Riechert
July 4

Solving quantum information challenges with

III-nitride nanowires ― understanding MBE
growth and pathways towards true nanostructures
Benchmarking quantum channels for private
communications
All­electrical universal control of electron spin
qubits in Si/SiGe quantum dots

Dr. Fabien Lafont

New paradigm for edge reconstruction of(Weizmann Institute, Israel)hole-conjugate fractional states

Prof. Hideki Kawakatsu

Introduction of the international Lab LIMMS at(The University of Tokyo, Japan)

Tokyo University and Development of

Dr. Eric Leclerc

microfluidic devices for hepatic induced(The University of Tokyo, Japan)

pluripotent stem cell differentiation

Prof. Christian A. Nijhuis

Mechanisms of charge transport and(National University of Singapore,light-matter interactions across (bio) molecular

Singapore)tunnel junctions

Dr. Takeshi Ohtsuka(Gunma University, Japan)
Oct. 3

Dr. Vladimír Chalupecký

Mathematical aspects of crystal growth : recent(Fujitsu Limited, Japan)

topics on growth dynamics

Dr. Norbert Požá(Kanazawa University, Japan)

56

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Prof. Shinobu Ohya
Oct. 11(The University of Tokyo, Japan)

Spintronics with ferromagnetic epitaxial single-

Mr. Kento Takeshima

crystalline heterostructures(The University of Tokyo, Japan)
Dr. Yuxi Fu
Oct. 18

Recent progress on high-energy ultrafast laser(RIKEN Center for Advanced

systems in RIKEN

Photonics, Japan)
Oct. 27

Nov. 1

Prof. Toshiharu Saiki

Nanoscale light-matter and nanofluidics(Keio University, Japan)

interactions in biomaterials
High-quality graphene films obtained fromProf. Ryota Negishi

graphene oxides ― Syntheses and bio-sensing(Osaka University, Japan)

applications

Dr. Stefan Fölsch
Nov. 15

Artiﬁcial lattices created by electrostatic gating of(Paul Drude Institut for Solid Statesurface state electrons

Electronics, Germany)
Dr. Takuya Higuchi
Dec. 15(Friedrich-Alexander University ofLight-field controlled currents in graphene

Erlangen-Nürnberg, Germany)
Dec. 16
Dec. 26
Jan. 25
Mar. 2Mar. 9Prof. Hidetoshi Nishimori(Tokyo Institute of Technology, Japan)
Mr. Cheng Wang

Progress of quantum annealing
Lithium niobate nonlinear nanophotonics(Harvard University, U.S.A.)
Dr. Pooya Ronagh

Global optimization of quadratic functions(1Qbit, Canada)
Dr. Frank Deppe

Continuous-variable propagating quantum(Walther-Meißner-Institut, Germany)

microwaves

Dr. Sébastien Gleyzes

A sensitive electrometer based on a Rydberg atom

(Laboratoire Kastler Brossel, France)

in a Schrödinger-cat state

Data

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

57

List of Award Winners
AwardAward Winners

Title

Date

JSAP Spring Meeting,2016, Poster Award

M. OnoH. Taniyama
M. Tsunekawa
E. Kuramochi
K. Nozaki
M. Notomi

Demonstration of Efficient Mode
Conversion to Slot Waveguides
with λ2/2000 Cross-Sectional Area

Apr. 1, 2016

The Young Scientists' Prizeof the Commendation for
Science and Technology
by the Minister of
Education, Culture, Sports,
Science and Technology

H. Sanada

Electron spin manipulation insemiconductor quantum structures

Apr. 20, 2016

OECC/PS 2016
Best Paper Award

K. Nozaki
S. Matsuo
T. Fujii
K. Takeda
M. OnoA. Shakoor
E. Kuramochi
M. Notomi

Sub-fF-capacitance photoniccrystal photodetector towards fJ/bit
on-chip receiver

July 6, 2016

The Japan Society ofApplied Physics (JSAP)
Fellow

T. SogawaControl of Photonic and Spin-Related
Properties in Semiconductor Quantum Sep. 13, 2016
Structures by Surface Acoustic Waves

The Japan Society ofApplied Physics (JSAP)
Young Scientist AwardP. A. Carles

Deviation from the law of energy
equipartition in a small
dynamic-random-access memory

Sep. 13, 2016

The Chemical Society ofJapan, Division of Colloid
and Surface Chemistry
Early Career Award

T. Teshima
H. Nakahsima
Y. UenoS. Sasaki
S. Tsukada

Self-folded Thin Polymer Film for
Encapsulation and Manipulation of
Cells

Nov. 10, 2016

IOP Publishing
Outstanding Reviewer
Award 2016

W. J. Munro

Outstanding Reviewer for New
Journal of Physics in 2016

Feb. 3, 2017

The Japan Societyof Applied Physics(JSAP) Young Scientist
Presentation Award

M. Kurosu

Dispersion effects on phonon
temporal waveforms in a phononic
crystal waveguideMar. 14, 2017

T. Ikuta

Implementation of quantum state
tomography for high-dimensional
time-bin entanglements

Mar. 14, 2017

The Japan Societyof Applied Physics(JSAP) Young Scientist
Presentation Award

58

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

List of In-house Award Winners
Award Winners

Title

Date

NTT Corporation
President Award

H. Takesue
T. Inagaki
K. Inaba
T. Honjyo
T. Umeki

Coherent Ising Machine for
Combinatorial Optimization Problems

Oct. 24, 2016

NTT Science and CoreTechnology Laboratory
Group Director’s Award

I. Mahboob
D. Hatanaka
H. Okamoto
H. Yamaguchi

Proposal and demonstration of
nonlinear phononics devices

Dec. 12, 2016

BRL Director’s Award
Award for Achievements

S. Tsukada
T. Ogasawara
H. Kurasawa
M. Yamaguchi
N. Kasai
H. Nakashima

Creation, demonstration and practicalrealization of "hitoe" wear and systemfor precise vital signal measurement

Mar. 27, 2017

BRL Director’s Award
Award for Achievements

K. Kakuyanagi
G. KneeY. Matsuzaki
H. Toida
W. J. Munro
S. Saito

Development of proof-of-principle
experiments for testing quantumness
in superconducting circuits

Mar. 27, 2017

BRL Director’s Award
Award for Achievements

H. Mashiko
K. KatoK. Oguri

Pioneering ultrafast dynamics based on
attosecond pulse generation technology

Mar. 27, 2017

BRL Director’s Award
Award for Excellent
PapersS. Wang
H. Hibino
S. Suzuki
H. Yamamoto"Atmospheric Pressure Chemical Vapor
Deposition Growth of Millimeter-Scale
Single-Crystalline Graphene on theMar. 27, 2017
Copper Surface with a Native Oxide
Layer"
Chemistry of Materials 28, 4893 (2016).

BRL Director’s Award
Award for Excellent
PapersT. Inagaki
T. Honjo
T. Umeki
K. Enbutsu
O. Tadanaga
H. Takenouchi
H. Takesue"A coherent Ising machine for 2000node optimization problems"
Science 354, 603 (2016).

Mar. 27, 2017

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

K. Nishiguchi
A. Fujiwara"Single-electron counting statistics ofshot noise in nanowire Si metal-oxidesemiconductor field-effect transistors"
Applied Physics Letters 98, 193502(2011).

Mar. 27, 2017

BRL Director’s Award
Award for Encouragement

Y. Kunihashi

Control of electron spin dynamics
using spin-orbit interaction insemiconductors

Mar. 27, 2017

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Data

Award

59

Number of Papers
The number of papers published in international journals in fiscal 2016 is 104. The number of papers
published in major journals are listed below.

Journals

IF2015

Numbers

Physical Review A

2.765

10

Physical Review B

3.718

8

Applied Physics Express

2.265

8

Applied Physics Letters

3.142

7

Nature Communications

11.3296

Scientific Reports

5.228

5

New Journal of Physics

3.570

5

Japanese Journal of Applied Physics

1.122

5

Optics Express

3.148

4

Science34.661

3

Optica5.205

3

Nature Photonics

31.1672

Nature Physics

18.791

2

Chemistry of Materials

9.407

2

Physical Review Letters

7.645

2

Optics Letters

3.040

2

Journal of the Physical Society of Japan

1.559

2

APL Photonics―

2

Advanced Functional Materials

11.382

1

Nanoscale

7.760

1

ACS Photonics

5.404

1

Journal of Materials Chemistry C

5.066

1

Nanophotonics

4.333

1

Science Advances―

1*IF2015 Impact Factor 2015
The average IF2015 for all research papers from NTT Basic Research laboratories is 5.568

60

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

Number of Presentations
The number of presentations at international conferences in fiscal 2016 is 173. The number ofpresentations in major conferences are listed below.

Conferences

Numbers

The 2016 Compound Semiconductor Week (CSW2016) : The 43rd International
Symposium on Compound Semiconductors / The 28th International Conference on
Indium Phosphide and Related Materials

10

The 22nd International Conference on High Magnetic Fields in Semiconductor Physics(HMF-22)9

Conference on Lasers and Electro-Optics (CLEO2016)9

33rd International Conference on the Physics of Semiconductors (ICPS2016)

7

International Conference on Quantum Communication, Measurement and Computing(QCMC2016)

6

Joint Center for Quantum Information and Computer Science (QuICS2016)

62016 International Conferences on Solid State Devices and Materials (SSDM2016)5

The 11th SPSJ International Polymer Conference (IPC2016)

5

Number of Patents
The number of applied patents in fiscal 2016 is 44.

Data

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)61

Publication List
(1)
(2)
(3)

T. Akasaka, C. H. Lin, H. Yamamoto, and K. Kumakura, "Surface Supersaturation in Flow-rate
Modulation Epitaxy of GaN", J. Cryst. Growth. 468, 821 (2017).
T. Akiho, F. Couedo, H. Irie, K. Suzuki, K. Onomitsu, and K. Muraki, "Engineering Quantum Spin Hall
Insulators by Strained-layer Heterostructures", Appl. Phys. Lett. 109, 192105 (2016).
K. Azuma, A. Mizutani, and H. K. Lo, "Fundamental Rate-loss Trade-off for the Quantum Internet",Nature Commun. 7, 13523 (2016).
S. Bevilacqua, E. Novoselov, S. Cherednichenko, H. Shibata, and Y. Tokura, "Wideband MgB2 Hot-(4)

electron Bolometer Mixers: IF Impedance Characterisation and Modeling", IEEE Trans. Appl.
Supercond. 26, 2300105 (2016).
M. D. Birowosuto, M. Takiguchi, A. Olivier, L. Y. Tobing, E. Kuramochi, A. Yokoo, W. Hong, and(5)M. Notomi, "Temperature-dependent Spontaneous Emission of PbS Quantum Dots inside Photonic
Nanostructures at Telecommunication Wavelength", Opt. Commun. 383, 555 (2017).
N. P. Breznay, I. M. Hayes, B. J. Ramshaw, R. D. McDonald, Y. Krockenberger, A. Ikeda, H. Irie,(6)

H. Yamamoto, and J. G. Analytis, "Shubnikov-de Haas Quantum Oscillations Reveal a ReconstructedFermi Surface Near Optimal Doping in a Thin Film of the Cuprate Superconductor Pr1.86Ce0.14CuO4 ±δ",
Phys. Rev. B 94, 104514 (2016).
A. Browning, N. Kumada, Y. Sekine, H. Irie, K. Muraki, and H. Yamamoto, "Evaluation of Disorder(7)

Introduced by Electrolyte Gating through Transport Measurements in Graphene", Appl. Phys.
Express 9, 065102 (2016).
R. J. Collins, R. Amiri, M. Fujiwara, T. Honjo, K. Shimizu, K. Tamaki, M. Takeoka, E. Andersson,(8)

G. S. Buller, and M. Sasaki, "Experimental Transmission of Quantum Digital Signatures over 90 km of
Installed Optical Fiber Using a Differential Phase Shift Quantum Key Distribution System", Opt. Lett.
41, 4883 (2016).

(9)
(10)

F. Couedo, H. Irie, K. Suzuki, K. Onomitsu, and K. Muraki, "Single-edge Transport in an InAs/GaSb
Quantum Spin Hall Insulator", Phys. Rev. B 94, 035301 (2016).
S. Dooley, W. J. Munro, and K. Nemoto, "Quantum Metrology Including State Preparation and Readout
Times", Phys. Rev. A 94, 052320 (2016).
S. Dooley, E. Yukawa, Y. Matsuzaki, G. C. Knee, W. J. Munro, and K. Nemoto, "A Hybrid-systems(11) Approach to Spin Squeezing Using a Highly Dissipative Ancillary System", New J. Phys. 18, 053011(2016).
S. N. A. Duffus, K. N. Bjergstrom, V. M. Dwyer, J. H. Samson, T. P. Spiller, A. M. Zagoskin,(12)

W. J. Munro, K. Nemoto, and M. J. Everitt, "Some Implications of Superconducting Quantum
Interference to the Application of Master Equations in Engineering Quantum Technologies",
Phys. Rev. B 94, 064518 (2016).

(13)

62

K. Furukawa, Y. Ueno, M. Takamura, and H. Hibino, "Graphene FRET Aptasensor", ACS Sens. 1, 710(2016).

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

(14)T. Goto, N. Kasai, R. Lu, R. Filip, and K. Sumitomo, "Scanning Electron Microscopy Observation ofInterface Between Single Neurons and Conductive Surfaces", J. Nanosci. Nanotechnol. 16, 3383 (2016).
R. Hamerly, K. Inaba, T. Inagaki, H. Takesue, Y. Yamamoto, and H. Mabuchi, "Topological Defect(15) Formation in 1D and 2D Spin Chains Realized by Network of Optical Parametric Oscillators",
Int. J. Mod. Phys. B 30, 1630014 (2016).
(16)

K. Hirama, Y. Taniyasu, S. Karimoto, H. Yamamoto and K. Kumakura, "Heteroepitaxial Growth ofSingle-domain Cubic Boron Nitride Films", Appl. Phys. Express 10, 035501 (2017).
H. Hibino, S. Wang, C. M. Orofeo, and H. Kageshima, "Growth and Low-energy Electron Microscopy(17) Characterizations of Graphene and Hexagonal Boron Nitride", Prog. Cryst. Growth Charact. Mater. 62,
155 (2016).
M. Hiroki, K. Kumakura, and H. Yamamoto, "Enhancement of Performance of AlGaN/GaN High(18) electron-mobility Transistors by Transfer from Sapphire to a Copper Plate", Jpn. J. Appl. Phys. 55,
05FH07 (2016).
A. Ikeda, H. Irie, H. Yamamoto, and Y. Krockenberger, "Clean Superconductivity in Electron Doped(19) Pr2−xCexCuO4+δ Thin Films Hetero-epitaxially Grown on SrTiO3 by Reactive Molecular Beam Epitaxy",
J. Mater. Res. 31, 3522 (2016).
(20)
(21)

A. Ikeda, H. Irie, H. Yamamoto, and Y. Krockenberger, "Incommensurate Defect-driven Electron
Correlations in Pr1.85Ce0.15CuO4+δ", Phys. Rev. B 94, 054513 (2016).
A. Ikeda, Y. Krockenberger, H. Irie, M. Naito, and H. Yamamoto, "Direct Observation of Infinite NiO2
Planes in LaNiO2 Films", Appl. Phys. Express 9, 061101 (2016).
R. Ikuta, T. Kobayashi, K. Matsuki, S. Miki, T. Yamashita, H. Terai, T. Yamamoto, M. Koashi, T. Mukai,(22) and N. Imoto, "Heralded Single Excitation of Atomic Ensemble via Solid-state-based Telecom Photon
Detection", Optica 3, 1279 (2016).
(23)
(24)

T. Ikuta and H. Takesue, "Implementation of Quantum State Tomography for Time-bin Qudits", New J.
Phys. 19, 013039 (2017).
K. Inaba and M. Yamashita, "Theoretical Analysis of the Spectroscopy of Atomic Bose-Hubbard
Systems", Phys. Rev. A 93, 043608 (2016).
T. Inagaki, Y. Haribara, K. Igarashi, T. Sonobe, S. Tamate, T. Honjo, A. Marandi, P. L. McMahon,(25)

T. Umeki, K. Enbutsu, O. Tadanaga, H. Takenouchi, K. Aihara, K. Kawarabayashi, K. Inoue, S.
Utsunomiya, and H. Takesue, "A Coherent Ising Machine for 2000-Node Optimization Problems",
Science 354, 603 (2016).

(26)

T. Inagaki, K. Inaba, R. Hamerly, K. Inoue, Y. Yamamoto, and H. Takesue, "Large-scale Ising Spin
Network Based on Degenerate Optical Parametric Oscillators", Nature Photon. 10, 415 (2016).
H. Irie, C. Todt, N. Kumada, Y. Harada, H. Sugiyama, T. Akazaki, and K. Muraki, "Andreev Reflection(27) and Bound State Formation in a Ballistic Two-dimensional Electron Gas Probed by a Quantum Point
Data

Contact", Phys. Rev. B 94, 155305 (2016).
A. Ishizawa, T. Nishikawa, T. Goto, K. Hitachi, T. Sogawa, and H. Gotoh, "Ultralow-phase-noise(28) Millimetre-wave Signal Generator Assisted with an Electro-optics-modulator-based Optical Frequency
Comb", Sci. Rep. 6, 24621 (2016).

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

63

K. Kakuyanagi, Y. Matsuzaki, T. Baba, H. Nakano, S. Saito, and K. Semba, "Characterization and(29) Control of Measurement-induced Dephasing on Superconducting Flux Qubit with a Josephson
Bifurcation Amplifier", J. Phys. Soc. Jpn. 85, 104801 (2016).
K. Kakuyanagi, Y. Matsuzaki, C. Deprez, H. Toida, K. Semba, H. Yamaguchi, W. J. Munro, and S. Saito,(30) "Observation of Collective Coupling Between an Engineered Ensemble of Macroscopic Artificial Atoms
and a Superconducting Resonator", Phys. Rev. Lett. 117, 210503 (2016).
(31)
(32)

N. Kasai, "Nano-biointerfaces for Detection and Control of Biological Information", Electrochemistry84, 688 (2016).
N. Kasai, R. Lu, R. Filip, T. Goto, A. Tanaka, and K. Sumitomo, "Neuronal Growth on a-Si and Au
Nanopillars", Electrochemistry 84, 296 (2016).
M. Kasu, K. Hirama, K. Harada, and T. Oishi, "Study on Capacitance-voltage Characteristics of(33) Diamond Field-effect Transistors with NO2 Hole Doping and Al2O3 Gate Insulator Layer", Jpn. J. Appl.
Phys. 55, 041301 (2016).
S. Kato, K. Inaba, S. Sugawa, K. Shibata, R. Yamamoto, M. Yamashita, and Y. Takahashi, "Laser(34) Spectroscopic Probing of Coexisting Superfluid and Insulating States of an Atomic Bose-Hubbard
System", Nature Commun. 7, 11341 (2016).
(35)

G. Kato and K. Tamaki, "Security of Six-state Quantum Key Distribution Protocol with Threshold
Detectors", Sci. Rep. 6, 30044 (2016).
S. Kita, K. Takata, M. Ono, K. Nozaki, E. Kuramochi, K. Takeda, and M. Notomi, "Coherent Control of(36) High Efficiency Metasurface Beam Deflector with a Back Partial Reflector", APL Photonics 2, 046104(2017).
G. C. Knee, K. Kakuyanagi, M. C. Yeh, Y. Matsuzaki, H. Toida, H. Yamaguchi, S. Saito, A. J. Leggett,(37) and W. J. Munro, "A Strict Experimental Test of Macroscopic Realism in a Superconducting Flux
Qubit", Nature Commun. 7, 13253 (2016).
(38)

P. A. Knott, W. J. Munro, and J. A. Dunningham, "Correspondence: Enhancing a Phase Measurement by
Sequentially Probing a Solid-state System", Nature Commun. 7, 11520 (2016).
R. Kou, Y. Hori, T. Tsuchizawa, K. Warabi, Y. Kobayashi, Y. Harada, H. Hibino, T. Yamamoto,(39) H. Nakajima, and K. Yamada, "Ultra-fine Metal Gate Operated Graphene Optical Intensity Modulator",Appl. Phys. Lett. 109, 251101 (2016).
(40)
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(43)
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64

E. Kuramochi, "Manipulating and Trapping Light with Photonic Crystals from Fundamental Studies toPractical Applications", J. Mater. Chem. C 4, 11032 (2016).
N. Lambert, K. Debnath, A. F. Kockum, G. C. Knee, W. J. Munro, and F. Nori, "Leggett-Garg Inequality
Violations with a Large Ensemble of Qubits", Phys. Rev. A 94, 012105 (2016).
N. Lambert, Y. Matsuzaki, K. Kakuyanagi, N. Ishida, S. Saito, and F. Nori, "Superradiance with an
Ensemble of Superconducting Flux Qubits", Phys. Rev. B 94, 224510 (2016).
C. H. Lin, T. Akasaka, and H. Yamamoto, "N-Face GaN(0001) Films with Hillock-free Smooth Surfaces
Grown by Group-III-source Flow-rate Modulation Epitaxy", Jpn. J. Appl. Phys. 55, 04EJ01 (2016).
I. Mahboob, R. Dupuy, K. Nishiguchi, A. Fujiwara, and H. Yamaguchi, "Hopf and Period-doubling
Bifurcations in an Electromechanical Resonator", Appl. Phys. Lett. 109, 073101 (2016).

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

(45)
(46)
(47)
(48)
(49)

I. Mahboob, H. Okamoto, and H. Yamaguchi, "An Electromechanical Ising Hamiltonian", Sci. Adv. 2,
E1600236 (2016).
I. Mahboob, H. Okamoto, and H. Yamaguchi, "Enhanced Visibility of Two-mode Thermal Squeezed
States via Degenerate Parametric Amplification and Resonance", New J. Phys. 18, 083009 (2016).
I. Mahboob, M. Villiers, K. Nishiguchi, D. Hatanaka, A. Fujiwara, and H. Yamaguchi , "A CorrelatedElectromechanical System", New J. Phys. 19, 033026 (2017).
H. Mashiko, K. Oguri, T. Yamaguchi, A. Suda, and H. Gotoh, "Petahertz Optical Drive with Widebandgap Semiconductor", Nature Phys. 12, 741 (2016).
N. Matsuda and H. Takesue, "Generation and Manipulation of Entangled Photons on Silicon Chips",
Nanophotonics 5, 440 (2016).
Y. Matsuzaki, H. Morishita, T. Shimooka, T. Tashima, K. Kakuyanagi, K. Semba, W. J. Munro,(50) H. Yamaguchi, N. Mizuochi, and S. Saito, "Optically Detected Magnetic Resonance of High-density
Ensemble of NV Centers in Diamond", J. Phys. : Condens. Matter 28, 275302 (2016).
Y. Matsuzaki, T. Shimo-Oka, H. Tanaka, Y. Tokura, K. Semba, and N. Mizuochi, "Hybrid Quantum(51) Magnetic-field Sensor with an Electron Spin and a Nuclear Spin in Diamond", Phys. Rev. A 94, 052330(2016).
(52)

Y. Matsuzaki and S. Benjamin, "Magnetic-field Sensing with Quantum Error Detection under the Effectof Energy Relaxation", Phys. Rev. A 95, 032303 (2017).
P. L. McMahon, A. Marandi, Y. Haribara, R. Hamerly, C. Langrock, S. Tamate, T. Inagaki, H. Takesue, S.

(53) Utsunomiya, K. Aihara, R. L. Byer, M. M. Fejer, H. Mabuchi, and Y. Yamamoto, "A Fully Programmable
100-spin Coherent Ising Machine with All-to-all Connections", Science 354, 614 (2016).
(54)
(55)

A. Morinaga, M. Murakami, K. Nakamura, and H. Imai, "Scalar Aharonov-Bohm Phase in Ramsey
Atom Interferometry under Time-varying Potential", Atoms 4, 23 (2016).
D. Morita, T. Kubo, Y. Tokura, and M. Yamashita, "Spin-1 Quantum Walks", Phys. Rev. A 93, 063625(2016).

(56) W. J. Munro and K. Nemoto, "Optical Circulators Reach the Quantum Level", Science 354, 1532 (2016).
Y. Nagamatsu, A. Mizutani, R. Ikuta, T. Yamamoto, N. Imoto, and K. Tamaki, "Security of Quantum(57) Key Distribution with Light Sources that are Not Independently and Identically Distributed", Phys. Rev.
A 93, 042325 (2016).
M. Naito, Y. Krockenberger, A. Ikeda, and H. Yamamoto, "Reassessment of the Electronic State,(58) Magnetism, and Superconductivity in High-TC Cuprates with the Nd2CuO4 Structure", Physica C 523, 28(2016).
(59)

K. Nemoto, M. Trupke, S. J. Devitt, B. Scharfenberger, K. Buczak, J. Schmiedmayer, and W. J. Munro,"Photonic Quantum Networks Formed from NV-centers", Sci Rep. 6, 26284 (2016).
Data

H. Nishi, T. Fujii, K. Takeda, K. Hasebe, T. Kakitsuka, T. Tsuchizawa, T. Yamamoto, K. Yamada, and(60) S. Matsuo, "Membrane Distributed-reflector Laser Integrated with SiOx -based Spot-Size Converter on
Si Substrate", Opt. Express 24, 18346 (2016).
(61)

K. Nishiguchi, D. Yoshizumi, Y. Sekine, K. Furukawa, A. Fujiwara, and M. Nagase, "Planar Cold
Cathode Based on a Multilayer-graphene/SiO2/Si Heterodevice", Appl. Phys. Express 9, 105101 (2016).
Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)65

J. Nishinaka, Y. Taniyasu, T. Akasaka, and K. Kumakura, "Surface Morphology Control of Nonpolar(62) M-plane AlN Homoepitaxial Layers by Flow-rate Modulation Epitaxy", Phys. Status Solidi B 254,
1600545 (2017).
(63)

M. Y. Niu, F. H. Xu, J. H. Shapiro, and F. Furrer, "Finite-key Analysis for Time-energy High-dimensional
Quantum Key Distribution", Phys. Rev. A 94, 052323 (2016).
K. Nozaki, S. Matsuo, T. Fujii, K. Takeda, M. Ono, A. Shakoor, E. Kuramochi, and M. Notomi,(64) "Photonic-crystal Nano-photodetector with Ultrasmall Capacitance for On-chip Light-to-voltage
Conversion without an Amplifier", Optica 3, 483 (2016).
R. Ohsugi, Y. Kunihashi, H. Sanada, M. Kohda, H. Gotoh, T. Sogawa, and J. Nitta, "Bias Dependence(65) of Spin Injection/transport Properties of a Perpendicularly Magnetized FePt/MgO/GaAs Structure",
Appl. Phys. Express 9, 043002 (2016).
(66)
(67)

R. Ohta, H. Okamoto, and H. Yamaguchi, "Feedback Control of Multiple Mechanical Modes in Coupled
Micromechanical Resonators", Appl. Phys. Lett. 110, 053106 (2017).
R. Ohta, Y. Ueno, and K. Ajito, "Raman Spectroscopy of Pharmaceutical Cocrystals in Nanosized Poresof Mesoporous Silica", Anal. Sci. 33, 47 (2017).
M. Ohtomo, Y. Sekine, S. N. Wang, H. Hibino, and H. Yamamoto, "Etchant-free Graphene Transfer(68) Using Facile Intercalation of Alkanethiol Self-assembled Molecules at Graphene/metal Interfaces",
Nanoscale 8, 11503 (2016).
(69)
(70)
(71)

H. Okamoto, R. Schilling, H. Schutz, V. Sudhir, D. J. Wilson, H. Yamaguchi, and T. J. Kippenberg,"A Strongly Coupled Λ-type Micromechanical System", Appl. Phys. Lett. 108, 153105 (2016).
Y. Okazaki, I. Mahboob, K. Onomitsu, S. Sasaki, and H. Yamaguchi, "Gate-controlled Electromechanical
Backaction Induced by a Quantum Dot", Nature Commun. 7, 11132 (2016).
M. Ono, E. Kuramochi, G. Q. Zhang, H. Sumikura, Y. Harada, D. Cox, and M. Notomi, "Nanowirenanoantenna Coupled System Fabricated by Nanomanipulation", Opt. Express 24, 8647 (2016).
M. Ono, H. Taniyama, H. Xu, M. Tsunekawa, E. Kuramochi, K. Nozaki, and M. Notomi, "Deep-(72) subwavelength Plasmonic Mode Converter with Large Size Reduction for Si-wire Waveguide",
Optica 3, 999 (2016).
(73)
(74)
(75)
(76)
(77)
(78)

66

K. Onomitsu, A. Krajewska, R. A. E. Neufeld, F. Maeda, K. Kumakura, and H. Yamamoto, "Epitaxial
Growth of Monolayer MoSe2 on GaAs", Appl. Phys. Express 9, 115501 (2016).
F. D. Parmentier, T. Cazimajou, Y. Sekine, H. Hibino, H. Irie, D. C. Glattli, N. Kumada, and P. Roulleau,"Quantum Hall Effect in Epitaxial Graphene with Permanent Magnets", Sci. Rep. 6, 38393 (2016).
N. L. Piparo, M. Razavi, and W. J. Munro, "Measurement-device-independent Quantum Key
Distribution with Nitrogen Vacancy Centers in Diamond", Phys. Rev. A 95, 022338 (2017).
S. Punniyakoti, R. Sivakumarasamy, F. Vaurette, P. Joseph, K. Nishiguchi, A. Fujiwara, and N. Clement,"Hydrogen Silsesquioxane-based Nanofluidics", Adv. Mater. Interf. 1601155 (2017).
S. Putz, A. Angerer, D. O. Krimer, R. Glattauer, W. J. Munro, S. Rotter, J. Schmiedmayer, and J. Majer,"Spectral Hole Burning and Its Application in Microwave Photonics", Nature Photon. 11, 36 (2017).
K. Sasaki, S. Murakami, and H. Yamamoto, "Theory of Intraband Plasmons in Doped Carbon
Nanotubes: Rolled Surface-Plasmons of Graphene", Appl. Phys. Lett. 108, 163109 (2016).

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

S. Sergent, M. Takiguchi, H. Taniyama, A. Shinya, E. Kuramochi, and M. Notomi, "Design of Nanowire(79) Induced Nanocavities in Grooved 1D and 2D SiN Photonic Crystals for the Ultra-Violet and Visible
Ranges", Opt. Express 24, 26792 (2016).
A. Srinivasan, K. L. Hudson, D. Miserev, L. A. Yeoh, O. Klochan, K. Muraki, Y. Hirayama,(80) O. P. Sushkov, and A. R. Hamilton, "Electrical Control of the Sign of the g Factor in a GaAs Hole
Quantum Point Contact", Phys. Rev. B 94, 041406 (2016).
H. Sumikura, E. Kuramochi, H. Taniyama, and M. Notomi, "Purcell Enhancement of Fast-dephasing(81) Spontaneous Emission from Electron-hole Droplets in High-Q Silicon Photonic Crystal Nanocavities",
Phys. Rev. B 94, 195314 (2016).
(82)
(83)
(84)
(85)
(86)
(87)

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).
M. Taguchi, S. Nakajima, T. Kubo, and Y. Tokura, "Quantum Adiabatic Pumping by Modulating Tunnel
Phase in Quantum Dots", J. Phys. Soc. Jpn. 85, 084704 (2016).
M. Takamura, H. Hibino, and H. Yamamoto, "Applying Strain into Graphene by SU-8 Resist Shrinkage",
J. Phys. D-Appl. Phys. 49, 285303 (2016).
M. Takamura, H. Okamoto, K. Furukawa, H. Yamaguchi, and H. Hibino, "Energy Dissipation inGraphene Mechanical Resonators with and without Free Edges", Micromachines 7, 158 (2016).
Y. Takesaki, K. Kawahara, H. Hibino, S. Okada, M. Tsuji, and H. Ago, "Highly Uniform Bilayer
Graphene on Epitaxial Cu-Ni(111) Alloy", Chem. Mat. 28, 4583 (2016).
H. Takesue and T. Inagaki, "10 GHz Clock Time-multiplexed Degenerate Optical Parametric Oscillators
for a Photonic Ising Spin Network", Opt. Lett. 41, 4273 (2016).
M. Takiguchi, A. Yokoo, K. Nozaki, M. D. Birowosuto, K. Tateno, G. Zhang, E. Kuramochi, A. Shinya,(88) and M. Notomi, "Continuous-wave Operation and 10-Gb/s Direct Modulation of InAsP/InP Subwavelength Nanowire Laser on Silicon Photonic Crystal", APL Photonics 2, 046106 (2017).
(89)
(90)
(91)

K. Tamaki, M. Curty, and M. Lucamarini, "Decoy-State Quantum Key Distribution with a Leaky
Source", New J. Phys. 18, 065008 (2016).
T. Tawara, Y. Kawakami, H. Omi, R. Kaji, S. Adachi, and H. Gotoh, "Mechanism of Concentration
Quenching in Epitaxial (ErxSc1-x)2O3 Thin Layers", Opt. Mat. Express 7, 1097 (2017).
T. Tawara, G. Mariani, K. Shimizu, H. Omi, S. Adachi, and H. Gotoh, "Effect of Isotopic Purification on
Spectral-hole Narrowing in 167Er3+ Hyperfine Transitions", Appl. Phys. Express 10, 042801 (2017).
T. Teshima, H. Nakashima, N. Kasai, S. Sasaki, A. Tanaka, S. Tsukada, and K. Sumitomo, "Mobile Silk

(92) Fibroin Electrode for Manipulation and Electrical Stimulation of Adherent Cells", Adv. Funct. Mater. 26,
8185 (2016).
(93)

A. M. D. Thomasen, T. Mukai, and T. Byrnes, "Ultrafast Coherent Control of Spinor Bose-Einstein
Data

Condensates Using Stimulated Raman Adiabatic Passage", Phys. Rev. A 94, 053636 (2016).
F. Tian, H. Sumikura, E. Kuramochi, H. Taniyama, M. Takiguchi, and M. Notomi, "Optomechanical(94) Oscillator Pumped and Probed by Optically Two Isolated Photonic Crystal Cavity Systems", Opt.
Express 24, 28039 (2016).

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T. Tilma, M. J. Everitt, J. H. Samson, W. J. Munro, and K. Nemoto, "Wigner Functions for Arbitrary
Quantum Systems", Phys. Rev. Lett. 117, 180401 (2016).
J. Trasobares, D. Vuillaume, D. Theron, and N. Clement, "A 17 GHz Molecular Rectifier", Nature
Commun. 7, 12850 (2016).
T. Uchida, M. Jo, A. Tsurumaki-Fukuchi, M. Arita, A. Fujiwara, and Y. Takahashi, "Capacitance(97) Evaluation of Compact Silicon Triple Quantum Dots by Simultaneous Gate Voltage Sweeping",
J. Appl. Phys. 120, 234502 (2016).
(98)

M. Villiers, I. Mahboob, K. Nishiguchi, D. Hatanaka, A. Fujiwara, and H. Yamaguchi, "AnElectromechanical Displacement Transducer", Appl. Phys. Express 9, 086701 (2016).
S. N. Wang, H. Hibino, S. Suzuki, and H. Yamamoto, "Atmospheric Pressure Chemical Vapor(99) Deposition Growth of Millimeter-scale Single-crystalline Graphene on the Copper Surface with a Native
Oxide Layer", Chem. Mat. 28, 4893 (2016).
(100)
(101)

T. Watanabe, M. Hori, T. Tsuchiya, A. Fujiwara, and Y. Ono, "Time-domain Charge Pumping on Siliconon-insulator MOS Devices", Jpn. J. Appl. Phys. 56, 011303 (2017).
G. Yamahata, S. P. Giblin, M. Kataoka, T. Karasawa, and A. Fujiwara, "Gigahertz Single-electron
Pumping in Silicon with an Accuracy Better than 9.2 Parts in 107", Appl. Phys. Lett. 109, 013101 (2016).
G. Yamahata, S. P. Giblin, M. Kataoka, T. Karasawa, and A. Fujiwara, "High-accuracy Current(102) Generation in the Nanoampere Regime from a Silicon Single-trap Electron Pump", Sci. Rep. 7, 45137(2017).
A. Yokoo, M. Takiguchi, M. D. Birowosuto, K. Tateno, G. Zhang, E. Kuramochi, A. Shinya, H.
(103) Taniyama, and M. Notomi, "Subwavelength Nanowire Lasers on a Silicon Photonic Crystal Operating at
Telecom Wavelengths", ACS Photonics 4, 355 (2017).
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68

F. Yoshihara, T. Fuse, S. Ashhab, K. Kakuyanagi, S. Saito, and K. Semba, "Superconducting Qubitoscillator Circuit beyond the Ultrastrong-coupling Regime", Nature Phys. 13, 44 (2017).

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

List of Invited Talks
Ⅰ.

Materials Science Laboratory

M. Hiroki, K. Kumakura, and H. Yamamoto, "Improvement in Thermal Resistance of Substrate(1) transferred GaN-HEMT Using Layered h-BN", 7th International Symposium on Control of
Semiconductor Interfaces (ISCSI-VII), Nagoya, Japan (June 2016).
H. Hibino, "Structural analysis of heterostructures of 2D materials by low-energy electron microscopy(2) and diffraction," 18th International Conference on Crystal Growth and Epitaxy (ICCGE-18), Nagoya,
Aichi, Japan (Aug. 2016).
(3)

Y. Ueno and K. Furukawa, "On-chip FRET Aptasensor Built on the Graphene-biomolecular-interface",
RSC Tokyo International Conference 2016, Chiba, Japan (Sep. 2016).

H. Hibino, "Structural analysis of 2D materials and heterostructures using low-energy electron(4) microscopy and diffraction," 7th International Symposium on Practical Surface Analysis (PSA-16),
Daejeon, South Korea (Oct. 2016).
(5)

Y. Ueno and K. Furukawa, "On-chip FRET Aptasensor Built on the Graphene-biomolecular-interface",
29th International Microprocesses and Nanotechnology Conferences (NMC), Kyoto, Japan (Nov. 2016).

(6)

H. Omi and T. Tawara, "Molecular Beam Epitaxy of ErxSc2-xO3 on Si(111) and Optical Properties of theFilms", 2016 Materials Research Society Fall Meeting (MRS Meeting), Boston, U.S.A. (Nov. 2016).

Ⅱ.
(1)

Physical Science Laboratory
K. Muraki, "NMR Probing of Density-modulated Phases in the Third Landau Level", Recent
Developments in 2D systems, Okinawa, Japan (Apr. 2016).

M. Hashisaka, N. Hiyama, T. Akiho, K. Muraki, and T. Fujisawa, "Time-domain Observation of Spin(2) and Charge-wave Packet Separation in Chiral One-dimensionalchannels", EMN Optoelectronics Meeting
2016, Phuket, Thailand (Apr. 2016).
H. Yamaguchi, I. Mahboob, H. Okamoto, and D. Hatanaka, "Phonon Confinement, Transport, andPiezoelectric Manipulation in Nonlinear Electromechanical Resonators", The 11th Annual IEEE
(3)International Conference on Nano/Micro Engineered and Molecular Systems (IEEE-NEMS 2016),
Sendai, Japan (Apr. 2016).
H. Yamaguchi, D. Hatanaka, Y. Okazaki, and I. Mahboob, "Piezoelectric Phonon Manipulation in(4) Electromechanical Resonators and Waveguides", SPICE Workshop: Quantum Acoustics - Surface
Acoustic Waves meets Solid State Qubits, Mainz, Germany (May 2016).
Y. Sato, J. C. H. Chen, R. Kosaka, M. Hashisaka, K. Muraki and T. Fujisawa, "Enhanced Transition(5) Between Charge States and Spin States of a Double Quantum Dot in a Surface Acoustic Wave Cavity",
Quantum Acoustics, Mainz, Germany (May 2016).
Data

H. Okamoto, T. Watanabe, R. Ohta, K. Onomitsu, H. Gotoh, T. Sogawa, and H. Yamaguchi, "Excitonic(6) Optomechanics in a GaAs System", Frontiers in Quantum Materials & Devices Workshop 2016, Saitama,
Japan (June 2016).

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

69

S. Sasaki, "InAs/InP Core-shell Nanowire Transistors with Outstanding Device Performance", The 28th(7) International Conference on Indium Phosphide and Related Materials (IPRM2016), Toyama, Japan (June2016).
(8)

H. Yamaguchi, I. Mahboob, and H. Okamoto, "Multi-mode Nonlinear Electromechanics", OPTO-And
Electro-mechanical Technologies 2016 (OET2016), Monte Verita, Switzerland (July 2016).

A. Fujiwara, G. Yamahata, K. Nishiguchi, S. P. Giblin, and S. Kataoka, "Gigahertz Single-electron Pump(9) for Quantum Current Standard", 33rd International Conference on the Physics of Semiconductors (ICPS),
Beijing, China (July 2016).
(10)
(11)

D. Hatanaka, I. Mahboob, K. Onomitsu, and H. Yamaguchi, "An Electromechanical Phononic Crystal",
20th International Vacuum Congress (IVC-20), Busan, Korea (Aug. 2016).
K. Muraki, "Engineering a Quantum Spin Hall Insulator with InAs/GaSb Type-II Quantum Wells",
Topological Material Science TopoMat Meeting 2016, Stuttgart, Germany (Sep. 2016).
K. Muraki, "Engineering a Two-dimensional Topological Insulator with III-V Semiconductor(12) Heterostructures", International Symposium on Revolutionary Atomic-layer Materials, Sendai, Japan (Oct.
2016).
(13)
(14)
(15)

H. Yamaguchi, "Mechanical Resonators Hybridized with Semiconductor Quantum Structures", GermanJapanese Meeting on the Science of Hybrid Quantum Systems, Berlin, Germany (Nov. 2016).
N. Clement and A. Fujiwara, "10-nm-scale Nanotechnology: from Nanoarrays to 0D Nanotransistor
Biosensors", The 18th Takayanagi Kenjiro Memorial Symposium, Shizuoka, Japan (Nov. 2016).
S. Saito, "Superconducting Quantum Circuits and Electron Spin Ensembles", 6th Atom Chip Workshop,
Pangkil Island, Indonesia (Dec. 2016).
H. Yamaguchi, I. Mahboob, H. Okamoto, and D. Hatanaka, "Parametric Coupling and Correlated(16) Fluctuation in Multimode Electromechanical Resonators", Frontiers of Nanomechanical Systems(FNS2017), La Thuile, Italy (Feb. 2017).
(17)

K. Muraki, "Engineering Quantum Spin Hall Insulators with InAs/(In,Ga)Sb Quantum Wells: A Status
Report", International School on Topological Science and Topological Matters, Kyoto, Japan (Feb. 2017).
K. Kakuyanagi, G. Knee, M. C. Yeh, Y. Matsuzaki, H. Toida, H. Yamaguchi, S. Saito, A. J. Leggett, and(18) W. J. Munro, "Violation of Macroscopic Realism by Using a Superconducting Flux Qubit", Interdisciplinary
Workshop on Quantum Device (IWQD 2017), Tokyo, Japan (Mar. 2017).
(19)

Ⅲ.

S. Saito, "Collective Coupling in Hybrid Superconducting Circuits", APS March Meeting 2017, New
Orleans, U.S.A. (Mar. 2017).

Optical Science Laboratory
H. Sanada, Y. Kunihashi, H. Gotoh, K. Onomitsu, M. Kohda, J. Nitta, P. V. Santos, and T. Sogawa "Acoustic(1) Transport and Manipulation of Electron Spins in Semiconductors", SPICE Workshop: Quantum Acoustics –Surface Acoustic Waves meets Solid State Qubits, Mainz, Germany (May 2016).
K. Oguri, H. Mashiko, T. Yamaguchi, A. Suda, and H. Gotoh, "Observation of Petaherz Electronic(2) Oscillation Based on Attosecond Spectroscopy", Shanghai-Tokyo Advanced Research Symposium on
Ultrafast Intense Laser Science (STAR7), Kanagawa, Japan (May 2016).

70

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

(3)
(4)
(5)
(6)
(7)

H. Takesue, T. Sasaki, K. Tamaki, and M. Koashi, "Round-robin Differential Phase Shift Quantum Key
Distribution Experiment", Trustworthy Quantum Information 2016, Shanghai, China (June 2016).
K. Azuma, "All-photonic Measurement-device-independent Quantum Repeaters", Trustworthy Quantum
Information 2016, Shanghai, China (June 2016).
W. J. Munro, "Quantum @ NTT", International Conference on Quantum Communication, Measurement
and Computing (QCMC 2016), Singapore, Singapore (July 2016).
W. J. Munro, K. Azuma, and K. Tamaki, "Intercity Quantum Networking without Repeaters", SPIE 2016
Optics+Photonics, San Diego, U.S.A. (Aug. 2016).
W. J. Munro, "Quantum Communication for Tomorrow", Photonics Conference (IPC2016), Hawaii,
U.S.A. (Oct. 2016).
K. Oguri, H. Mashiko, T. Yamaguchi, A. Suda, and H. Gotoh, "Light-induced Electron Dynamics in(8) Semiconductor from Femtosecond to Attosecond Regime", International Symposium on Ultrafast Intense
Laser Science (ISUILS15), Cassis, France (Oct. 2016).
(9)
(10)

N. Matsuda, "Spectral and Spatial Manipulation of Single Photons Using Optical Waveguides", The 3rd
UK-Japan Quantum Technology Workshop, Tokyo, Japan (Oct. 2016).
K. Azuma, "Theory of the Quantum Internet", Quantum Science Symposium Europe-2016, Cambridge,
U.K. (Nov. 2016).
K. Oguri, H. Mashiko, T. Yamaguchi, A. Suda, and H. Gotoh, "Petaherz Electronic Response in(11) Semiconductor", The 9th Asian Symposium on Intense Laser Science (ASILS 9), Ninh Binh, Vietnam(Nov. 2016).
G. Zhang and H. Gotoh, "InP/InAs Heterostructure Nanowires Grown by Indium-particle-assisted Vapor(12) liquid-solid Mode", 31st DGKK Workshop: Epitaxy of III/V Semiconductor, Duisburg, Germany (Dec.
2016).
(13)
(14)
(15)

W. J. Munro, "Quantum Communication: A primer", Mini-School on Quantum Information Science,
Taipei, Taiwan (Dec. 2016).
W. J. Munro, "Quantum Hybridization: Why One Plus One is Now Greater than Two", 8th International
Workshop on Solid State Quantum Computing, Taipei, Taiwan (Dec. 2016).
W. J. Munro, "New Century Engineering Using the Age Old Principles of Quantum Mechanics",
Conference on 90 Years of Quantum Mechanics (QM90), Singapore, Singapore (Jan. 2017).
H. Takesue, T. Inagaki, K. Inaba, R. Hamerly, K. Inoue, and Y. Yamamoto, "Large-scale Artificial Spin

(16) Network Based on Time-multiplexed Degenerate Optical Parametric Oscillators for Coherent Ising
Machine", SPIE Photonics West 2017, San Francisco, U.S.A. (Jan. 2017).
(17)

N. Matsuda, "Spectral and Spatial Manipulation of Single Photons", The JSAP Workshop on Quantum
Information and Related Fields, Tokyo, Japan (Mar. 2017).
K. Oguri, H. Mashiko, and H. Gotoh, "Petahertz Semiconductor Drive Characterized by Isolated(18) Attosecond Pulse", The 8th Asian Workshop on Generation and Application of Coherent XUV and X-ray
Data

Radiation (8th AWCXR), Hsinchu, Taiwan (Mar. 2017).

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

71

Ⅳ.
(1)

Nanophotonics Center
M. Notomi, "Nanomaterial-nanophotonics Hybrid Systems for Novel Photonic Platform", SPIE
Photonics Europe 2016, Brussel, Belgium (Apr. 2016).
K. Takeda, T. Fujii, A. Shinya, E. Kuramochi, M. Notomi, K. Hasebe, T. Kakitsuka, and S. Matsuo,(2)"Electrically Driven Nanocavity Lasers on Silicon with Photonic-crystal Cavity and Ultrasmall Buried
Heterostructure", International Nanotechnology Conference & Expo (Nanotech 2016), Baltimore, U.S.A.
(Apr. 2016).
M. Notomi, "Hybrid Nanophotonics-nanomaterial Platforms with III/V Semiconductor Nanowires(3) on Si", 5th International Conference on Smart and Multifunctional Materials Structures & Systems(CIMTEC 2016), Perugia, Italy (June 2016).
(4)

S. Matsuo, K. Takeda, and T. Fujii, "Heterogeneously Integrated Photonic Crystal Laser on Si", 2016 the Premier International Laser and Electro-Optics Event (CLEO/QELS), San Jose, U.S.A. (June 2016).
R. Nakao, M. Arai, T. Kobayashi, T. Kakitsuka, T. Yamamoto, and S. Matsuo, "Epitaxial Growth on(5) Lattice-mismatched Substrate for High-performance Lasers", The 43rd International Symposium on
Compound Semiconductors (ISCS), Toyama, Japan (June 2016).
(6)(7)

M. Notomi, "Integrated Nanophotonics for Optical Computation in a Chip", 18th International
Conference on Tranparent Optical Networks (ICTON 2016), Torento, Italy (July 2016).
A. Shinya, "Nanophotonics for Low-latency Optical Passgate Logic Circuits", 16th International Forumon MPSoC for Software-defined Hardware (MP SOC), Nara, Japan (July 2016).
S. Matsuo, K. Takeda, T. Fujii, H. Nishi, and T. Kakitsuka, "Directly Modulated Membrane DFB Lasers(8) and Photonic Crystal Lasers", 2016 IEEE Photonics Society Summer Topical Meeting Series (SUM),
Newport Beach, U.S.A. (July 2016).
(9)
(10)

M. Notomi, "Impact of Capacitance and Latency on Integrated Nanophotonics", The 12th International
Symposium on Photonic and Electromagnetic Crystal Structures (PECS-XII), York, U.K. (July 2016).
S. Matsuo, K. Takeda, T. Fujii, H. Nishi, and T. Kakitsuka, "Membrane DFB and Photonic Crystal Lasers
on Si", The 25th International Semiconductor Laser Conference (ISLC2016), Kobe, Japan (Sep. 2016).
S. Matsuo, "Applications of Photonic Crystal and Heterogeneous Integration to Ultra-low-energy Lasers(11) for Optical Interconnects and Datacenter Networks", 42nd European Conference and Exhibition on
Optical Communication (ECOC), Dusseldorf, Germany (Sep. 2016).
(12)

S. Matsuo, K. Takeda, and T. Fujii, "Directly Modulated Photonic Crystal Lasers for Extremely Short
Optical Links", 2016 IEEE Photonics Conference (IPC), Hawaii, U.S.A. (Oct. 2016).
H. Nishi, T. Tsuchizawa, T. Kakitsuka, K. Hasebe, K. Takeda, T. Hiraki, T. Fujii, T. Yamamoto, and(13) S. Matsuo, "SiOxNy Back-end Photonics Platform for Si-Ge-InP Integration", Pacific Rim Meeting on
Electrochemical and Solid-State Science (PRiME 2016), Hawaii, U.S.A. (Oct. 2016).
M. Notomi, "Hybrid Nanoemitterd with Nanomaterials and Nanophotonic Platforms”, Workshop on(14) Coherence and Quantum Phenomena in Small and Single-Photon
Sources (CohQuantSSPhS), Nice, France (Oct. 2016).
A. Ishihara, A. Shinya, K. Inoue, K. Nozaki, and M. Notomi, "An Integrated Optical Parallel Adder as(15) a First Step Towards Light Speed Data Processing", 13th International SoC Design Conference (ISOCC
2016), Jeju, Korea (Oct. 2016).

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Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)

T. Kakitsuka, T. Fujii, K. Takeda, H. Nishi, and S. Matsuo, "III-V Membrane Lasers on Silicon for(16) Datacom and Computercom Applications", Photonics 2017 (in IEEE Symposium on HPCA), Austin,
U.S.A. (Feb. 2017).
(17)

S. Matsuo, "High-performance Lasers on InP-SOI Platform", The Future of Optical Networking andCommunication (OFC), Los Angeles, U.S.A. (Mar. 2017).
A. Ishihara, A. Shinya, K. Inoue, K. Nozaki and M. Notomi, "An Optical Parallel Adder towards Light(18) Speed Data Processing", Design, Automation and Test in Europe (DATE 2017), Lausanne, Switzerland(Mar. 2017).

Data

Research Activities in NTT Basic Research Laboratories Vol. 27 (2016)73

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/