Annealing Paths of Pr2CuO4 and the Resulting Electronic Phase
Diagrams
Annealing is an exigency to induce superconductivity in cuprates built up of CuO2 planes withsquare-planar coordinated copper, aka "electron-doped" cuprates: e.g., RE2–xCexCuO4 (RE = rare-earth
elements). Our analysis revealed that the electronic phase diagram for Pr2–xCexCuO4 depends strongly
on the annealing path. Even undoped Pr2CuO4 is superconducting after an elaborate 2-step annealing
process [Y. Krockenberger et al., Sci. Rep. 3 (2013) 2235], which is in stark contrast with a widely
accepted assumption that undoped cuprates are antiferromagnetic insulators. Note that the data points
denoted by ﬁlled triangles in the ﬁgure are taken from [M. Brinkmann et al., Phys. Rev. Lett. 74 (1995)
4927]. (Page 22)

Schematic of the sample (left) and the pumping protocolon the energy scale (right)

Pump voltage dependence ofthe coherent oscillations

Coherent Phonon Manipulation in Coupled Mechanical Resonators
We realized the coherent manipulation of coupled GaAs mechanical beams by the parametricpumping. The piezoelectric modulation of the spring constant of one beam at the frequency difference
between the two beams via the gate voltage leads to the cyclic (Rabi) oscillations of phonons between
the beams. The oscillation period is inversely proportional to the pump amplitude, enabling the timedomain control of the mechanical vibration via the gate control. (Page 31)－Ⅰ－Schematic structure (left) and scanning-electron-microscope
image (right) of InAs nanowire FET

Output characteristics of InAs nanowire
FET at room temperature

Encapsulated Gate-All-Around InAs Nanowire Field-Effect Transistors
We have fabricated ﬁeld-effect transistors using an InAs nanowire as a channel with high electron
mobility at room temperature. Gate-all-around geometry is used to improve electrostatic control. The
gate also overlaps the source and drain electrodes, fully encapsulating the nanowire channel. This
reduces the series resistance of the channel, leading to large drive current and transconductance that
surpass those of conventional non-gate-overlap devices. (Page 36)

Ultracold atoms trapped in
an optical lattice.

Entangled cluster state.

Cluster State Generation for Ultracold Atoms in an Optical Lattice
We theoretically propose a method for generating entanglement of the ultracold atoms trapped in
an optical lattice. Our simple method can be implemented with a combination of some establishedexperimental techniques, such as, irradiating lasers and tuning their intensities. Precise numericalsimulation conﬁrms that our method can create a high-ﬁdelity multipartite entanglement, that is, thecluster state, in a short operation time with scalability. Our proposal paves the way for creating alarge-scale multipartite entanglement that is useful for the measurement based quantum computation.
(Page 38)

－Ⅱ－

Spectral distribution of attosecond pulse with(a) carbon ﬁlter and (b) carbon and boron ﬁlters.

Fourier-transform-limited pulse.

Generation of Isolated Attosecond Pulse in Carbon K-Edge (284 eV)
Region with Double Optical Gating
An attosecond (10–18 s: as) pulse is shortest laser pulse in the world. We successfully generated
isolated attosecond pulse with 284 eV photon energy (4.4 nm wavelength) using a driving laser
with only 247 µJ pulse energy, which pulse energy is lowest value ever reported. Since the K-shellabsorption edge in carbon exists in 284 eV region, the laser would be useful for visualizing of living
cell structure. (Page 43)(a) Diagram of cavity creation by installing a nanowire into a trench in a line defect of photonic crystal.
Emission spectrum shows an resonant peak of the nanowire-induced cavity.
(b) SEM image of a nanowire installed into a trench in a line defect of photonic crystal.

Optical Nanocavity Formed by a Semiconductor Nanowire
and a Si Photonic Crystal
We demonstrate that a nanocavity can be created in a photonic crystal by placing a nanowire ina trench in a line defect of Si photonic crystal (Maximum Q-factor : 9500). We move the nanowire
using a nanoprobe. In addition, the position of the nanocavity can be shifted by moving the nanowire
in the trench. We obtain a photon lifetime of 91 ps for a nanowire-induced photonic crystal cavity,
which can be attributed to the Purcell effect. It is the shortest lifetime ever reported for a III-V semiconductor nanowire. (Page 45)－Ⅲ－Message from the Director
We at NTT Basic Research Laboratories (BRL)
are extremely grateful for your interest and support
with respect to our research activities. BRL ’ smissions are to promote progress in science andinnovations in leading-edge technology to advance
NTT's business. To achieve these missions,researchers in fields including physics, chemistry,
biology, mathematics, electronics, informatics,
and medicine, conduct basic research on materials
science, physical science and optical science.
Since our management principle is based on an"open door" policy, we are collaborating with many
universities and research institutes in Japan, US,
Europe, and Asia as well as other NTT laboratories.
NTT-BRL regularly organizes international
conferences related to quantum physics andnanotechnology at NTT Atsugi R&D Center andalso holds a "Science Plaza" to enhance public understanding of our activities and to ensure afrank exchange of opinions. Moreover, one of our missions is the education of young researchers
and we sponsor the biennial "BRL School", which boasts distinguished researchers as lecturers.
In November 2013, thirty-five Ph.D. students and young researchers from universities andinstitutes in 14 countries participated in the BRL School.
These activities enable us to realize our missions with respect to the promotion of advances inscience and the development of groundbreaking technology for NTT's business. Your continued
support will be greatly appreciated.

July, 2014

Tetsuomi Sogawa
Director
NTT Basic Research Laboratories－Ⅴ－Contents
page◆ Cover♦ Sensing Fabric "hitoe" to Continuously Monitor Bioelectrical Signals◆ Color Frontispiece ............................................................................................................Ⅰ♦ Annealing Paths of Pr2CuO4 and the Resulting Electronic Phase Diagrams♦ Coherent Phonon Manipulation in Coupled Mechanical Resonators♦ Encapsulated Gate-All-Around InAs Nanowire Field-Effect Transistors♦ Cluster State Generation for Ultracold Atoms in an Optical Lattice♦ Generation of Isolated Attosecond Pulse in Carbon K-Edge (284 eV) Region with Double

Optical Gating♦ Optical Nanocavity Formed by a Semiconductor Nanowire and a Si Photonic Crystal◆ Message from the Director ................................................................................................Ⅴ◆ NTT Basic Research Laboratories Organogram ................................................................ 1◆ Member List ....................................................................................................................... 2
I. Research Topics◇ Overview of Research in Laboratories ............................................................................................... 17◇ Materials Science Laboratory ............................................................................................................ 19♦ Single-Crystal Cubic Boron Nitride Thin Film Growth by Ion-Beam-Assisted Molecular

Beam Epitaxy♦ Nucleus and Spiral Growth of N-face GaN (000-1) Obtained by Selective-Area Metalorganic

Vapor Phase Epitaxy♦ Enhanced Deep-UV Light Emission from Nonpolar M-plane AlGaN Quantum Wells♦ Superconductivity Hidden beneath Charge-Transfer Insulators♦ Broadening Light Emission at the Telecommunications Wavelengths by Material Engineeringof Rare-Earth Compounds on Silicon♦ Synthesis of Ultrathin Hexagonal Boron Nitride for Tunneling Applications♦ Thermal Instability of Graphene on a Substrate♦ Sensing Fabric "hitoe" to Continuously Monitor Bioelectrical Signals♦ Stable Sealing of Microcavities with a Lipid Membrane for Nanobiodevices♦ Ligand-Induced Structural Changes in a Single Ion Channel Receptor◇ Physical Science Laboratory ............................................................................................................... 29♦ Fast and High-Sensitivity Charge Sensor Combined with a Resonance Circuit♦ Accuracy Evaluation of Si Single-Electron Transfer Devices at Extremely Low Temperature♦ Coherent Phonon Manipulation in Coupled Mechanical Resonators♦ An Electromechanical Phonon Laser♦ Storage and Retrieval of Quantum States in a Hybrid Quantum System♦ Quantum State Projection with Various Measurement Strengths♦ Realizing Topological Insulating Phase in the Heterostructure Composed of Direct

Transition Band Gap Semiconductors♦ Encapsulated Gate-All-Around InAs Nanowire Field-Effect Transistors♦ AC Admittance of DNTT-Based MIS Capacitors◇ Optical Science Laboratory ................................................................................................................ 38♦ Cluster State Generation for Ultracold Atoms in an Optical Lattice♦ An On-Chip Single Photon Buffer Based on Coupled Resonator Optical Waveguide♦ Long-Term Performance of Quantum Key Distribution over 90-km Optical Links Installed

in a Field Environment of Tokyo Metropolitan Area
♦ Growth of InP Nanowires on Graphene-Covered Fe♦ Topological Raman Band in the Carbon Nanohorn♦ Generation of Isolated Attosecond Pulse in Carbon K-Edge (284 eV) Region with Double

Optical Gating♦ Modiﬁcation of Exciton Optical Properties with Coherent Phonons in Quantum Dots
♦ Optical Nanocavity Formed by a Semiconductor Nanowire and a Si Photonic Crystal♦ InGaAs Photodetectors Based on Photonic Crystal Waveguide Including Ultrasmall Buried

Heterostructure♦ Enhanced and Suppressed Spontaneous Emission from a Buried Heterostructure Photonic

Crystal Cavity◇ Nanophotonics Center ........................................................................................................................ 48♦ Low Energy Consumption Direct Modulation of Lambda-Scale Embedded Active-Region

Photonic-Crystal Lasers♦ Significant L-Band Responsivity Improvement of Germanium Waveguide Photodiode byFranz-Keldysh Effect

II. Data◇ 6th NTT-BRL School...................................................................................................................... 51◇ International Symposium on Nanoscale Transport and Technology (ISNTT 2013)....................... 52◇ List of BRL Seminars (Fiscal 2013) ................................................................................................... 53◇ Award Winners’ List (Fiscal 2013)................................................................................................. 56◇ In-house Award Winners’ List (Fiscal 2013).................................................................................. 57◇ Numbers of Papers, Presentations and Patents (2013)................................................................... 58◇ List of Invited Talks at International Conferences (2013).............................................................. 60

NTT Basic Research Laboratories Organogram
As of March 31, 2014

Director

Tetsuomi Sogawa, Dr.

Research Planning Section
Quantum and Nano Device Research
Senior Distinguished Researcher

Executive Manager

Hideki Yamamoto, Dr.

Hiroshi Yamaguchi, Dr.
Materials Science Laboratory
Executive Manager

Hiroki Hibino, Dr.

Physical Science Laboratory
Executive Manager

Akira Fujiwara, Dr.

Optical Science Laboratory
Executive Manager

Tetsuomi Sogawa, Dr.

Nanophotonics Center
Executive Manager

Masaya Notomi, Dr.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)1

Member List
As of March 31, 2014(*/ left NTT BRL during the year)

NTT Basic Research Laboratories
Director, Dr. Tetsuomi Sogawa

Quantum and Nano Device Research

Senior Distinguished Researcher,Dr. Hiroshi Yamaguchi

Research Planning Section

2

Executive Research Scientist,

Dr. Hideki Yamamoto

Senior Research Scientist,

Dr. Hiroshi Nakashima

Senior Research Scientist,

Dr. Katsuya Oguri

NTT Research Professor

Prof. Yasuhiro Tokura (University of Tsukuba)

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Materials Science Laboratory

Executive Manager,
		

Dr. Hiroki Hibino
Dr. Tetsuya Akasaka

Thin-Film Materials Research Group:
Dr. Hideki Yamamoto (Group Leader)
Dr. Yasuyuki Kobayashi*
Dr. Kazuhide Kumakura
Dr. Tetsuya Akasaka
Dr. Yoshitaka Taniyasu
Dr. Yoshiharu Krockenberger Dr. Shin-ichi Karimoto
Dr. Kazuyuki Hirama
Dr. Chia-Hung Lin

Dr. Hisashi Sato
Dr. Koji Onomitsu
Dr. Masanobu Hiroki
Dr. Ryan Banal

Low-Dimensional Nanomaterials Research Group:
Dr. Hiroki Hibino (Group Leader)
Dr. Fumihiko Maeda
Dr. Kazuaki Furukawa
Dr. Hiroo Omi
Dr. Yuko Ueno
Dr. Shin-ichi Tanabe*
Dr. Makoto Takamura
Dr. Yuya Murata*
Dr. Carlo M. Orofeo

Dr. Satoru Suzuki
Dr. Yoshiaki Sekine
Dr. Shengnan Wang
Dr. Adel Najar

Molecular and Bio Science Research Group:
Dr. Koji Sumitomo (Group Leader)
Dr. Shingo Tsukada
Dr. Nahoko Kasai
Dr. Touichiro Goto
Dr. Aya Tanaka

Dr. Yoshiaki Kashimura
Dr. Azusa Oshima

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)3

Physical Science Laboratory

Executive Manager,

Dr. Akira Fujiwara
Dr. Toshiaki Hayashi
Takeshi Karasawa

Nanodevices Research Group:
Dr. Akira Fujiwara (Group Leader)Dr. Hiroyuki Kageshima
Toru Yamaguchi
Hirotaka Tanaka
Dr. Jin-ichiro Noborisaka
Dr. Kensaku Chida
Hybrid Nanostructure Physics Research Group:
Dr. Hiroshi Yamaguchi (Group Leader)
Dr. Yuichi Harada
Dr. Hayato Nakano
Dr. Shiro Saito
Dr. Masumi Yamaguchi*
Dr. Hajime Okamoto
Dr. Kousuke Kakuyanagi
Daiki Hatanaka
Dr. Hiraku Toida
Quantum Solid State Physics Research Group:
Dr. Koji Muraki (Group Leader)
Dr. Kiyoshi Kanisawa
Dr. Satoshi Sasaki
Dr. Kyoichi Suzuki
Dr. Toshiaki Hayashi
Dr. Norio Kumada
Dr. Keiko Takase
Dr. Takashi Kobayashi*
Dr. Trevor David Rhone

4

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Dr. Katsuhiko Nishiguchi
Dr. Gento Yamahata

Dr. Kenji Yamazaki
Dr. Imran Mahboob
Dr. Yuichiro Matsuzaki
Dr. Yuma Okazaki

Dr. Hiroyuki Tamura
Dr. Takeshi Ohta
Dr. Hiroshi Irie

Optical Science Laboratory

Executive Manager,

Dr. Tetsuomi Sogawa
Dr. Tetsuya Mukai

Quantum Optical State Control Research Group:
Dr. Kaoru Shimizu (Group Leader)Dr. Hiroki Takesue
Dr. Masami Kumagai
Dr. Hiroyuki Shibata
Dr. Makoto Yamashita
Dr. Fumiaki Morikoshi
Dr. Kiyoshi Tamaki
Daisuke Hashimoto
Dr. Nobuyuki Matsuda
Dr. Hiromitsu Imai
Dr. Takahiro Inagaki
Dr. Kazuto Noda
Quantum Optical Physics Research Group:
Dr. Hideki Gotoh (Group Leader)
Dr. Takehiko Tawara
Dr. Kouta Tateno
Dr. Guoquiang Zhang
Dr. Haruki Sanada
Dr. Hiroki Mashiko
Dr. Ken-ichi Hitachi
Dr. Ken-ichi Sasaki
Photonic Nano-Structure Research Group:
Dr. Masaya Notomi (Group Leader)
Dr. Akihiko Shinya
Dr. Atsushi Yokoo
Dr. Hideaki Taniyama
Dr. Hisashi Sumikura
Dr. Masato Takiguchi
Dr. Masaaki Ono
Dr. Hao Xu*
Dr. Abdul Shakoor

Kazuhiro Igeta
Dr. Tetsuya Mukai
Dr. Kensuke Inaba
Dr. Koji Azuma
Dr. William John Munro

Dr. Atsushi Ishizawa
Dr. Keiko Kato
Dr. Yoji Kunihashi

Dr. Eiichi Kuramochi
Dr. Kengo Nozaki
Dr. Danang Birowosuto*

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

5

Nanophotonics Center

Executive Manager,

Dr. Masaya Notomi

Photonic Nano-Structure Research Team:
Dr. Masaya Notomi
Dr. Akihiko Shinya
Dr. Eiichi Kuramochi
Dr. Hideaki Taniyama
Dr. Kengo Nozaki
Dr. Masato Takiguchi
Dr. Hiroo Omi
Dr. Takehiko Tawara
Dr. Nobuyuki Matsuda

6

Dr. Atsushi Yokoo
Dr. Hisashi Sumikura
Dr. Masaaki Ono
Dr. Hiroyuki Shibata

InP Compound Device Research Team:Dr. Shinji Matsuo
Dr. Takaaki Kakitsuka
Dr. Koji Takeda
Dr. Koichi Hasebe

Tomonari Sato
Takuro Fujii

Silicon Photonics Research Team:
Dr. Koji Yamada
Dr. Tai Tsuchizawa
Hidetaka Nishi
Tatsurou Hiraki

Rai Kou (Rai Takahashi)
Dr. Kotarou Takeda

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Senior Distinguished Researcher
Masaya Notomi was born in Kumamoto, Japan, on 16 February 1964. Hereceived his B.E., M.E. and Ph.D. degrees in applied physics from Universityof Tokyo, Japan in 1986, 1988, and 1997, respectively. In 1988, he joined NTT
Optoelectronics Laboratories. Since then, his research interest has been to control
the optical properties of materials and devices by using artiﬁcial nanostructures,and engaged in research on quantum wires/dots and photonic crystal structures.
He has been in NTT Basic Research Laboratories since 1999, and currently agroup leader of Photonic Nanostructure Research Group and a director of NTT
Nanophotonics Center. He is also entitled as Senior Distinguished Scientistof NTT since 2010. In 1996-1997, he was a visiting researcher of Linköping
University (Sweden). He was a guest associate professor of Applied Electronics
in 2003-2009 and is currently a guest professor of Physics in Tokyo Instituteof Technology. He received IEEE/LEOS Distinguished Lecturer Award in2006, JSPS (Japan Society for the Promotion of Science) prize in 2009, Japan
Academy Medal in 2009, The Commendation for Science and 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 is serving as a member of National University Corporation Evaluation
Committee in the Japanese government. He is also a member of the Japan
Society of Applied Physics, APS, IEEE, and OSA.

Hiroshi Yamaguchi was born in Osaka Japan on October 30, 1961. Hereceived the B.E., M.S. in physics and Ph.D. degrees in engineering from the
Osaka University in 1984, 1986 and 1993, respectively. He joined NTT Basic
Research Laboratories in 1986 and has engaged in the study of compound
semiconductor surfaces using electron diffraction and scanning tunnelingmicroscopy. His current interests are micro/nanomechanical devices using
semiconductor heterostructures. He was a visiting research fellow in Imperial
College, University of London, U.K. during 1995-1996 and a visiting researchstaff 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) in 2008 and 2009. He served as more than 40 committee members ofacademic societies and international conferences. He received JSAP Fellowship(2013), Commendation for Science and Technology by MEXT (2013), Inoue
Prize for Science (2012), Institute of Physics (IOP) Fellowship (2011),
SSDM2009 Paper Award (2010), MNC2008 Outstanding Paper Award (2009),
and the Paper Awards of Japan Society of Applied Physics (1989, 2004, 2010).
He is currently an executive manager of Quantum and Nano Device Research
and a group leader of Hybrid Nanostructure Physics Research Group. He is amember of JSAP, the Physical Society of Japan, IOP, American Physical Society(APS), and IEEE.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)7

Koji Muraki was born in Tokyo, Japan in 1965. He received his B.S., M.S., andPh.D. degrees in applied physics from The University of Tokyo, Japan, in 1989,
1991, and 1994, respectively. In 1994, he joined Basic Research Laboratories,
Nippon Telegraph and Telephone (NTT) Corporation, Kanagawa, Japan. Since
then, he has been engaged in the growth of high-mobility heterostructures andthe study of highly correlated electronic states realized in such structures. He
was a guest researcher at Max-Planck Institute, Stuttgart, Germany during 20012002. He served as a program committee/chair of international conferenceson High Magnetic Fields in Semiconductor Physics (HMF) and Electronic
Properties of 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 2008-2013. He was appointed as Distinguished
Scientist of NTT in 2009 and Senior Distinguished Scientist of NTT in 2013.
He is a member of the Physical Society of Japan and Japan Society of Applied
Physics.

8

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Distinguished Researchers
Akira Fujiwara was born in Tokyo, Japan in 1967. He received his B.S., M.S.,
and Ph.D. degrees in applied physics from The University of Tokyo, Japan in
1989, 1991, and 1994, respectively. In 1994, he joined NTT LSI Laboratories
and moved to NTT Basic Research Laboratories in 1996. Since 1994, he has
been engaged in research on silicon nanostructures and their application to
single-electron devices. He is a senior manager of Physical Science Laboratory
and a group leader of Nanodevices Research Group since April 2012. He was aguest researcher at the National Institute of Standards and Technology (NIST),
Gaithersburg, MD, USA during 2003-2004. He was a director of the JapaneseSociety of Applied Physics in 2010 and 2011 and a visiting professor of
Hokkaido University in 2013. He received the SSDM Young Researcher Awardin 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, and Technology) in 2006. He is a member of the Japan Societyof Applied Physics and the IEEE.

Yoshitaka Taniyasu was born in Toyama, Japan on June 10, 1973. He received
his B.E., M.E., and Dr. Eng. degrees in electrical engineering from Chiba
University, Chiba, Japan in 1996, 1998, and 2001, respectively. He joined
NTT Basic Research Laboratories in 2001. He has been engaged in researchon wide-bandgap nitride semiconductors. He was a visiting researcher at Ecolepolytechnique fédérale de Lausanne (EPFL) during 2011-2012. He received theYoung Scientist Award for the Presentation of the Excellent Paper at the Japan
Society of Applied Physics (JSAP) in 2001, the Young Scientist Award at the
14th Semiconducting and Insulating Materials Conference in 2007, the Young
Scientists’ Prize from the Minister of Education, Culture, Sports, Science andTechnology, the Young Scientist Award at the 38th International Symposiumon Compound Semiconductors in 2011, and the Best Paper Award at theInternational Workshop on Nitride Semiconductors in 2012. He is a member of
the JSAP.

Norio Kumada was born in Gifu, Japan in 1975. He received his B.S., M.S.,
and Ph.D. degrees in physics from Tohoku University, Japan, in 1998, 2000,
and 2003, respectively. In 2003, he joined NTT Basic Research Laboratories,
Kanagawa, Japan. Since then, he has been engaged in the study of highly
correlated electronic states realized in semiconductor heterostructures. He
received Young Scientist Award of the Physical Society of Japan in 2008, and theYoung Scientists’ Prize from the Minister of Education, Culture, Sports, Scienceand Technology in 2012. He is a member of the Physical Society of Japan.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)9

Katsuhiko Nishiguchi was born in Hiroshima, Japan in 1975. He received
the B.E., M.E., and Ph.D. in electrical engineering in 1998, 2000, and 2002,
respectively, from Tokyo Institute of Technology, Tokyo, Japan. Since joining
NTT Basic Research Laboratories in 2002, 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 a guest researcher at Delft University of Technology, Delft, theNetherlands during 2012-2013. 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 Commendationfor Science and Technology by the Minister of Education, Culture, Sports,
Science and Technology of Japan (The Young Scientists' Prize) in 2013. He is amember of the Japan Society of Applied Physics.

Shiro Saito was born in Tokyo, Japan in 1972. He received his B.S., M.S.,
and Dr. Eng. degrees in applied physics from the University of Tokyo, Japan,
in 1995, 1997, and 2000, respectively. In 2000, he joined NTT Basic ResearchLaboratories, Nippon Telegraph and Telephone Corporation, Kanagawa,Japan. Since then, he has been engaged in quantum information processing
using superconducting circuits. He was a guest researcher at Delft Universityof Technology, Delft, the Netherlands during 2005-2006. He received Young
Scientist Award at the Japan Society of Applied Physics Spring Meeting in 2004.
He is a guest associate professor in Tokyo University of Science from 2012. He
is a member of the Physical Society of Japan and the Japan Society of Applied
Physics.

Hiroki Takesue was born in Wakayama, Japan, on May 10, 1971. He received
B.E., M.E., and Ph.D. degrees in engineering science from Osaka University,
Osaka, Japan, in 1994, 1996, and 2002, respectively. In 1996, he joined NTT
Access Network Systems Laboratories, Ibaraki, Japan, where he engaged inresearch on optical access networks using wavelength division multiplexing.
In 2003, he moved to NTT Basic Research Laboratories, Atsugi, Japan. Since
then, he has been engaged in experimental quantum optics and quantum
communications. He is the recipient of several awards, including the ITU-T
Kaleidoscope Conference 2nd Best Paper Award in 2008 and The Commendationfor Science and Technology by the Minister of Education, Culture, Sports,
Science and Technology of Japan (The Young Scientists' Prize) in 2010. From2004 to 2005, he was a Visiting Scholar at Stanford University, Stanford, CA.
He is a member of IEEE and the Japan Society of Applied Physics.

10

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Imran Mahboob was born in Shefﬁeld, England on 20 April, 1978. He received
a combined B.Sc. and M.Sc. degree in Theoretical Physics from The Universityof Sheffield in 2001 and Ph.D. degree in Physics studying the electronic
properties of nitride semiconductors from The University of Warwick in 2004.
He joined NTT Basic Research Laboratories in 2005 as a Research Associate,from 2008 as a Research Specialist, and from 2012 as a Senior Research
Scientist. His current interests are developing electromechanical resonators for
digital signal processing applications and to study their non-linear dynamics. He
received the Clarke Prize in Physics from the University of Shefﬁeld in 2001 andthe Young Scientist Award at the 2003 Physics of Semiconductors and Interfaces
conference.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)11

Advisory Board (2013 Fiscal Year)

12

Name

Afﬁliation

Prof. Gerhard Abstreiter

Walter Schottky Institute, Technical University of Munich,Germany

Prof. John Clarke

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

Prof. Evelyn Hu

School of Engineering and Applied Sciences, Harvard University,
U.S.A.

Prof. Mats Jonson

Department of Physics, University of Gothenburg, Sweden

Prof. Sir Peter Knight

Department of Physics, Imperial College/The Kavli Royal SocietyInternational Centre at Chicheley Hall, U.K.

Prof. Anthony J. Leggett

Department of Physics, University of Illinois, U.S.A.

Prof. Allan H. MacDonald

Department of Physics, The University of Texas, Austin, U.S.A.

Prof. Andreas Offenhäusser

Institute of Complex Systems, Forschungszentrum Julich,
Germany

Prof. Halina Rubinsztein-Dunlop

School of Physical Sciences, University of Queensland, Australia

Prof. Klaus von Klitzing

Max Planck Institute for Solid State Research, Germany

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Invited / Guest Scientists (2013 Fiscal Year)Name

Afﬁliation

PeriodProf. Koichi Semba

National Institute of Informatics (NII),
Japan

Apr. 2013 – Mar. 2014

Overseas Trainees (2013 Fiscal Year)Name

Afﬁliation

PeriodRuaridh Forbes

University of Edinburgh, U.K.

Jul. 2012 – Apr. 2013

Pawel Pactwa

AGH University of Science and Techonology,
PolandSep. 2012 – Aug. 2013

Justin Yan

The University of British Columbia, Canada

Jan. 2013 – Aug. 2013

Thomas Ziebarth

University of Victoria, Canada

Jan. 2013 – Aug. 2013

Joey Chau

University of Toronto, Canada

Jan. 2013 – Dec. 2013

Punn Augsornworawat

McGill University, Canada

Jan. 2013 – Dec. 2013

Amedee Lacraz

ESPCI ParisTech (École supérieure de physiqueet de chimie industrielles de la ville de Paris),
FranceApr. 2013 – Aug. 2013

Anthony ParkThe University of British Columbia, Canada

May 2013 – Dec. 2013

Jing Wang

Georgia Institute of Technology, U.S.A.

May 2013 – Dec. 2013

Samuel Metais

ESPCI ParisTech (École supérieure de physiqueet de chimie industrielles de la ville de Paris),
FranceJul. 2013 – Dec. 2013

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

13

14

Name

Afﬁliation

PeriodSimon YvesESPCI ParisTech (École supérieure de physiqueet de chimie industrielles de la ville de Paris),
FranceJul. 2013 – Dec. 2013

Nicolas Perrissin

ESPCI ParisTech (École supérieure de physiqueet de chimie industrielles de la ville de Paris),
FranceJul. 2013 – Dec. 2013

Malo Tarpin

ESPCI ParisTech (École supérieure de physiqueet de chimie industrielles de la ville de Paris),
FranceJul. 2013 – Dec. 2013

Sophie De La Vaissiere

ESPCI ParisTech (École supérieure de physiqueet de chimie industrielles de la ville de Paris),
FranceJul. 2013 – Dec. 2013Louise Waterston

University of Edinburgh, U.K.

Jul. 2013 –Paul Knott

University of Leeds, U.K.

Sep. 2013 – Dec. 2013

Rick Lu

University of Waterloo, Canada

Sep. 2013 –Anna Fomitcheva
Khartchenko

University of Barcelona, Spain

Sep. 2013 –Jose Alberto Rodriguez
Santamaria

University of Burgos, Germany

Sep. 2013 –Krzysztof Jan
Gibasiewicz

Warsaw university of Technology, Poland

Sep. 2013 –Gianfranco D'Ambrosio

Politecnico di Milano, Italy

Sep. 2013 –Logan G. Blackstad

Georgia Institute of Technology, U.S.A.

Sep. 2013 –Peter Karkus

Budapest University of Technology andEconomics, Hungary

Sep. 2013 –Henry Pigot

The University of British Columbia, Canada

Jan. 2014 –Ryan Neufeld

University of Waterloo, Canada

Jan. 2014 –Adrian Salmon

Georgia Institute of Technology, U.S.A.

Jan. 2014 –Andrew Tin

McGill University, Canada

Feb. 2014 –Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Domestic Trainees (2013 Fiscal Year)Name

Afﬁliation

PeriodShun Dai

The University of Tokyo

Apr. 2013 – Mar. 2014

Rento Osugi

Tohoku University

Apr. 2013 – Mar. 2014

Shunichi Matsumoto

Tokyo University of Science

Apr. 2013 – Mar. 2014

Hajime Suzuki

Tokyo University of Science

Apr. 2013 – Mar. 2014

Takahiko SatoThe University of Tokyo

Apr. 2013 – Mar. 2014

Nuremy Binti Che Ani

Tokyo Denki University

Apr. 2013 – Mar. 2014

Takahiro Gotoh

Tokyo Denki University

Apr. 2013 – Mar. 2014

Keisuke Noguchi

Tokyo Institute of Technology

Apr. 2013 – Mar. 2014

Takanobu Tsunoi

Yokohama National University

Apr. 2013 – Mar. 2014

Tomohiko Yamaguchi

Tokyo University of Science

Apr. 2013 – Mar. 2014

Toru Tanaka

Waseda University

Apr. 2013 – Mar. 2014

Ahmad YoshinariTokyo University of Science

May 2013 – Mar. 2014

Ken-ichi Suzuki

Tokyo Denki University

Jun. 2013 – Mar. 2014

Akihiro Fushimi

Keio University

Jun. 2013 – Mar. 2014

Saki Tanaka

Keio University

Jul. 2013 – Aug. 2013

Kenta Inoue

University of Tsukuba

Aug. 2013– Sep. 2013

Han CaiTohoku University

Oct. 2013 – Mar. 2014

Kazuki Moriya

The University of Tokyo

Oct. 2013 – Mar. 2014

Shingo Kanouchi

Nagaoka University of Technology

Oct. 2013 – Feb. 2014

Shouhei Takagi

Nagaoka University of Technology

Oct. 2013 – Feb. 2014

Saki Tanaka

Keio University

Oct. 2013 – Mar. 2014

Teo Dong Sheng

Toyohashi University of Technology

Jan. 2013 – Feb. 2014

Tomohiro Tamaki

Toyo University

Jan. 2013 – Mar. 2014

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)15

Ⅰ．Research Topics

Overview of Research in Laboratories
Materials Science Laboratory

Hiroki Hibino

This laboratory aims at contributing to progress in materials science and revolutionizing
information communication technology by creating new materials and functions throughmaterials design at the atomic and molecular levels.
This laboratory consists of three research groups investigating a wide range of materials
such as nitride semiconductors, graphene, superconductors, and biological molecules. We areconducting innovative materials research based on the technologies of growing high-quality
thin ﬁlms and precisely measuring the structure and physical properties of materials.
This year, we succeeded in clarifying microscopic state changes during the annealing
treatment which induces superconductivity in undoped cuprates so far believed as insulatorsand growing single-crystal cubic BN thin ﬁlm on diamond and single-layer hexagonal BN on
Co films, respectively. We also succeeded in developing new sensing fabric "hitoe", whichenables to acquire biomedical signals by simply wearing the clothes, in collaboration with
Toray Industries, Inc.

Physical Science Laboratory

Akira Fujiwara

The aim of this laboratory is to develop semiconductor- and superconductor-based solidstate devices, which will have a revolutionary impact on future communication and information
technologies. Utilizing high-quality crystal growth techniques and nanolithography techniques
we have developed, research groups in our laboratory are working on nanodevices, quantum
information processing devices, and high-sensitivity sensors based on new degrees of freedom
such as single electrons, mechanical oscillations, quantum coherent states, and spins.
This year we succeeded in realizing phonon lasing in an electromechanical resonator andcoherent phonon manipulation in coupled mechanical resonators. We also demonstrated
storage and readout of quantum states in a superconductor/diamond hybrid system. Progress
was made in the research on topological insulating phase in InAs/GaSb heterostructures,
accuracy evaluation of single-electron transfer, FET sensors with a resonance circuit, and gate
overlapped InAs nanowire FETs.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)17

Optical Science Laboratory

Tetsuomi Sogawa

This laboratory aims for the development of core-technologies that will innovate on opticalcommunications and optical signal processing, and seeks fundamental scientiﬁc progresses.
The groups in our laboratory are working for the quantum state control by very weak light,
the search for intriguing phenomena using very intensive and short pulse light, and control
of optical properties by using photonic crystals and ultrasonic techniques, based on uniqueproperties of semiconductor nanostructures such as quantum dots and nanowires.
In this year, we achieved an on-chip single photon buffer by using a coupled resonator
optical waveguide based on silicon photonic crystal cavities. We examined the long-term
operation performance of a long-distance (90 km) differential phase shift key distribution
service using a test-bed optical network in the Tokyo metropolitan area. We also proposedthat a very high-fidelity entangled cluster state can be formed with a combination of laser
irradiation and intensity tuning. In addition, we have successfully demonstrated control of
excitonic optical properties in quantum dots by using coherent phonons and generation of
an isolated attosecond pulse in Carbon K-edge (284 eV) region with a double optical gating
method.

Nanophotonics Center

Masaya Notomi

Nanophotonics Center (NPC) was established in April 2012 by several research groups
involved with nanophotonics in Basic Research Laboratories, Photonics Laboratories, andMicrosystem Integration Laboratories in NTT. We are aiming for developing a full-ﬂedgedlarge-scale photonic integration technology by which we will be able to densely integratea large number of nano-scale photonic devices with various functions in a single chip.
Furthermore, we are targeting extreme reduction of the consumption energy for photonic
information processing by taking advantage of the nanophotonics technology.
This year, we demonstrated a novel way to form a nanocavity by placing a III/V
semiconductor nanowire on a Si photonic crystal, and we also realized a novel multi-layer
waveguide on Si for mode-division multiplexing. As regards nanophotonic device research,
we have realized a novel nano-photodetector based on photonic crystals, and succeeded inlargely reducing the operation energy-per-bit of electrically-pumped nanolasers. In addition,
we achieved accelerated spontaneous emission rate of quantum wells in photonic crystal
nanocavities.

18

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Single-Crystal Cubic Boron Nitride Thin Film Growth
by Ion-Beam-Assisted Molecular Beam Epitaxy
Kazuyuki Hirama, Yoshitaka Taniyasu, Shin-ichi Karimoto,
Yoshiharu Krockenberger, and Hideki Yamamoto
Materials Science Laboratory
Cubic boron nitride (c-BN) with sp3-bonding has a large bandgap energy of 6.25 eV and ahigh breakdown ﬁeld of ~ 8 MV/cm, which may further expand the potential of nitride-based
semiconductor devices. However, conventional growth methods for group-III nitrides, such as
MOVPE, have been unsuccessful in the growth of single-crystal c-BN ﬁlms because c-BN is ametastable phase at ambient atmosphere. Here we report the epitaxial growth of single-crystal
c-BN ﬁlms by the ion-beam-assisted molecular beam epitaxy (MBE) method. We show thata proper adjustment of acceleration voltage for N2+ and Ar+ ions is the key to the selective
formation of the c-BN phase.
BN thin ﬁlms were grown on diamond(001) substrates by electron-beam evaporation of B ina ﬂux of N2+ and Ar+ ions. The acceleration voltage (Vacc) for the ions was varied in the range
from 200 to 450 V. The growth temperature (Tg) was varied in the range from 400 to 820oC.
The supplied nitrogen/boron ratio was set at values > 1.
Single-crystal c-BN(001) ﬁlms were obtained at Tg ≥ 750oC with Vacc = 280 V. The formationof the single-crystal c-BN was confirmed by cross-sectional TEM, selective area electron
diffraction (SAED) and RHEED (Figs. 1 and 2) [1]. Although the designated thickness ofthe c-BN film was 160 nm, the resultant c-BN films were about 30-nm thick. This meansthat ~ 80 % of supplied B atoms were etched by ion bombardments during the c-BN growth.
To obtain a clue to the growth mechanism of c-BN in the ion-beam-assisted MBE processes,
we also carried out regrowth of BN films on single-crystal c-BN thin film templates on
diamond substrates with the growth parameters systematically varied. A summary of thoseresults provided us a phase diagram of BN, which was plotted as a function of Vacc and Tg(Fig. 3). The phase diagram indicates a strong dependence on Vacc with much less dependence
on Tg. At Vacc < 220 V (Region I), sp2-bonded turbostratic BN (t-BN) is predominantly formed.
At Vacc between 220 and 450 V (Region II), single-crystal c-BN continues to grow. At Vacc >450 V (Region III), the c-BN template is etched out as evidenced by an instantaneous changeof the RHEED pattern back to that of the diamond(001) substrate. In short, at low acceleration
voltages, sp2-bonded BN is dominantly formed, while at high acceleration voltages, etching
dominates, irrespective of the bonding characteristics of BN. Consequently, the formationand epitaxial growth of metastable c-BN are achieved as a result of the interplay between
competitive phase formation and selective etching [1].
This work was supported by KAKENHI.
[1] K. Hirama et al., Appl. Phys. Lett. 104 (2014) 092113.

Fig. 1. Cross-sectional TEM and SAED
images of single-crystal c-BN(001).

Fig. 2. RHEED pattern ofFig. 3. Phase diagram of BN ﬁlms insingle-crystal c-BN(001).
ion-beam-assisted MBE process.
Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)19

Nucleus and Spiral Growth of N-face GaN (000-1)
Obtained by Selective-Area Metalorganic Vapor Phase Epitaxy
Chia-Hung Lin, Tetsuya Akasaka, and Hideki Yamamoto
Materials Science Laboratory
Step-free surfaces without any ﬂuctuation of thickness are promising for developing highperformance quantum devices with abrupt hetero-interfaces. We have recently succeeded in
preparing a step-free Ga-face GaN (0001) surface by selective-area metalorganic vapor phase
epitaxy (SA-MOVPE) [1]. An N-face GaN (000–1) surface is also attractive for obtaining
high-quality InN and InxGa1–xN ﬁlms because of its higher afﬁnity to N. However, it is difﬁcult
to achieve an atomically smooth N-face GaN (000–1) surface since the surface usuallycontains a high density of hexagonal hillocks. In this study, we investigated the formation of astep-free N-face GaN (000–1) surface using SA-MOVPE.
GaN films were grown selectively on an N-face GaN (000–1) bulk substrate coveredby SiO2 masks with a set of hexagonal openings 16 μm in diameter. Source gases weretrimethylgallium (TMG) and NH3, and puriﬁed H2 was the carrier gas. The NH3 ﬂow rate was
kept at 6.7x10–2 mol/min, while the TMG ﬂow rate was varied from 9.7 to 20.8 μmol/min.
The growth temperature was 1015oC.
Figure 1 shows an almost step-free N-face GaN (000–1) surface with few atomic steps. The
surface was formed by two-dimensional (2D) nucleus growth in the absence of screw-type
dislocations (STDs) within a hexagonal opening. Meanwhile, in the same sample, growth
spirals with atomic steps were also observed within another hexagonal opening having STDs.
Figure 2 shows nucleus and spiral growth rates of GaN plotted as a function of the TMG ﬂow
rate. The nucleus growth rates are all very low even for a higher TMG flow rate, whereas
spiral growth ones increase rapidly with increasing TMG ﬂow rate [2]. The slow growth rates
in 2D nucleus growth indicate that the growth proceeds under low surface supersaturation,
which results in an extremely low 2D nucleus density. The low 2D nucleus density is
considered a key factor for achieving a step-free N-face GaN (000–1) surface.
This work was partly supported by KAKENHI.
[1] T. Akasaka, Y. Kobayashi, and M. Kasu, Appl. Phys. Express 2 (2009) 091002.
[2] C.H. Lin, T. Akasaka, and H. Yamamoto, Appl. Phys. Express 6 (2013) 035503.

Fig. 1. Atomic force microscopic image of analmost step-free N-face GaN (000–1) surface.
Vertical stripes are due to the optical noise.

20

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Fig. 2. Nucleus and spiral growth rate of GaN
plotted as a function of TMG ﬂow rate.

Enhanced Deep-UV Light Emission from Nonpolar M-plane
AlGaN Quantum Wells
Ryan Banal, Yoshitaka Taniyasu, and Hideki Yamamoto
Materials Science Laboratory
Demonstrations of AlGaN quantum well (QW) light-emitting diodes (LEDs) have opened
up a new possibility of semiconductor light sources in the deep-UV region. However, theiremission efficiencies are still lower than InGaN QW near-UV/visible LEDs. One intrinsic
reason for the low emission efﬁciency is the low light extraction efﬁciency from the C-plane
AlGaN surface due to its optical polarization anisotropy (Fig. 1) [1]. In addition, the quantumconﬁned Stark effect (QCSE) has a signiﬁcant impact on the internal quantum efﬁciency ofthe polar C-plane QW, as has been reported for the InGaN QWs (Fig. 2) [2]. In this work,
we study the deep-UV light emission properties of the nonpolar M-plane and polar C-plane
AlGaN QWs [3].
The M-plane and C-plane AlGaN QW structures were epitaxially grown on M-plane andC-plane AlN bulk substrates by MOVPE, respectively. The M-plane AlGaN QWs show
higher emission intensity than the C-plane ones (Fig. 3). The deep-UV light emission from
the M-plane and C-plane AlGaN QWs was polarized for electric ﬁeld (E) parallel to the c-axis(E||c). It turned out that the M-plane AlGaN QWs show stronger E||c polarization than the
C-plane ones. Hence, the M-plane AlGaN QWs have higher light extraction efﬁciency thanthe C-plane ones. The stronger emission from the M-plane QWs can be partially attributed tothe absence of the QCSE, as evidenced by emission at shorter wavelength from the M-plane
AlGaN QWs than the C-plane ones (Fig. 3). Our results indicate that nonpolar AlGaN QW
structures are promising approach for increasing the emission efﬁciency of AlGaN deep-UV
LEDs due to their strong E||c polarization, along with the absence of the QCSE.
This work was partly supported by MEXT KAKENHI.
[1] Y. Taniyasu et al., Appl. Phys. Lett. 90 (2007) 261911.
[2] P. Waltereit et al., Nature 406 (2000) 865.
[3] R. Banal et al., Appl. Phys. Lett. (2014) submitted.

Fig. 1. Schematic of polarized
light emission from AlGaN
crystal.

Fig. 2. Band diagram of M-plane
and C-plane AlGaN QWs.

Fig. 3. Photoluminescence (PL) fromM-plane and C-plane AlGaN QWs.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)21

Superconductivity Hidden beneath Charge-Transfer Insulators
Yoshiharu Krockenberger, and Hideki Yamamoto
Materials Science Laboratory
High temperature superconductivity (HTS) remains a mystery. For hole-doped cuprate
superconductors doping is sufﬁcient to induce superconductivity but such an approach does
not hold for electron-doped cuprates. Moreover, while hole-doped cuprates are a build-up of
CuO2 planes with copper being either ﬁve- or six-fold coordinated, electron doping only works
when copper is four-fold coordinated. The fact that an annealing procedure is mandatory forthe induction of superconductivity in cuprates with square-planar coordinated copper has
obscured physicists for long while, hampering the development of effective theoretical models
describing superconductivity in cuprates. Since the electron-doped side of the electronic
phase diagram represents not only the quantity of doped electrons but to a much higher
extent the influence of annealing, it is about time to liberate the phase diagram from thesemurky parameters. Quite in contrast to common belief (undoped cuprates are charge-transfer
insulators), we have shown that electron doping does not represent an exigency but an option,i.e. superconductivity can be induced at any doping level, even zero, subject to an appropriate
annealing treatment [1]. While the consequences of such elaborate annealing treatments for the
induction of superconductivity are far reaching, the actual crystallographic changes within the
crystal are subtle. Namely, as shown in Fig. 1, in Pr2CuO4, while the in-plane lattice constantremains constant (as-grown = 1st step = 2nd step) the c-axis length shrinks, particularly after the
2nd annealing step. Upon annealing an overstoichiometric oxygen at apical sites [2] are being
evacuated thus causing a reduction of the c-axis length. Most importantly, the occupationof apical sites by oxygen
have a dramatic influenceon the overall electronicand magnetic properties as
they are the trigger for the
insulator to metal transition inthese systems. It is the local
binding energy of these extra
oxygen ions that is inﬂuenced
by the amount of electron
doping (Ce4+ substitution forPr3+). For low Ce substitution
levels, this bond strengthens
and annealing conditions
become delicate in order toavoid decomposition of thematerials. Using a 2-stepannealing scheme [3] may
hold the key to effectively
Fig. 1. Microscopic model of different states of Pr2CuO4 together withtemperature dependence of resistivity and lattice parameters after
evacuate apical sites while
each annealing step [3].
""keeping the crystal alive .
[1] Y. Krockenberger et al., Phy. Rev. B 85 (2012) 31.
[2] P. G. Radaelli et al., Phy. Rev. B 49 (1994) 15322.
[3] Y. Krockenberger et al., Sci. Rep. 3 (2013) 2235.
22

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Broadening Light Emission at the Telecommunications Wavelengths byMaterial Engineering of Rare-Earth Compounds on SiliconHiroo Omi and Takehiko Tawara*
Materials Science Laboratory, *Optical Science Laboratory
Erbium silicates (e.g. Er2SiO5 and Er2Si2O7) and erbium oxide (Er2O3) have great potential
as optical ampliﬁer materials in silicon photonics. Recent research has shown optical gain inwaveguide erbium-doped ampliﬁers. However, the luminescence is limited by concentrationquenching mechanisms, such as energy migration and up-conversion between Er3+ ions.
Therefore, yttrium (Y), which has almost the same ionic radius as erbium (Y3+ of 0.9 Å, Er3+of
0.89 Å) and is optically inactive is incorporated to increase the luminescence efficiency of
the Er ions in the silicates and oxides by forming ErxY2–xSiO5 and ErxY2–xO3. In addition, forfurther enhancement of the emission, ytterbium (Yb), with an ionic radius of 0.99 Å in Yb3+,
has been incorporated in silicates and oxides. The incorporation of Yb effectively promotes
the energy transfer from the Yb ions to Er ions, which results in high efﬁciency of the Er ion
luminescence when pumped at a wavelength of 980 nm. In order for these materials to be
used as gain media for optical ampliﬁers, they have to fulﬁll the requirement of broadband
luminescence at the region of the C-band telecommunication transmission wavelengths (15301565 nm). Flat regions and broad peaks in the photoluminescence spectrum are required forbroadband amplification. In this work, we grow ErxYb2–xSi2O7 and ErxYb2–xO3 crystalline
mixtures on Si(111) substrates by RF-sputtering of Er2O3, Yb2O3 on Si and subsequentannealing in Ar atmosphere, and characterize their optical properties [1].
Thin films composed of polycrystalline ErxYb2–xO3 grains and crystalline ErxYb2–xSi2O7
layers were formed on a Si(111) substrate by RF-sputtering and subsequent thermal annealingin Ar gas ambient up to 1100oC. The films were characterized by synchrotron radiation
grazing incidence X-ray diffraction (Fig. 1), cross-sectional transmission microscopy, energy
dispersive X-ray spectrometry and micro photoluminescence measurements. In the annealed
ﬁlm of 950oC it is observed that the I15/2 - I13/2 Er3+ photoluminescence exhibits simultaneously
maximum intensity and peak width at room temperature (Fig. 2). This effect satisfies therequirements for broadening the C-band of an optical ampliﬁer on Si.
[1] H. Omi, Y. Abe, M. Anagnosti, and T. Tawara, AIP Adv. 3 (2013) 042107.

Fig. 1. θ–2θ X-ray powder diffraction patternobtained at the incidence angle of 1.0o from thesamples (a) as-grown at room temperature andannealed at (b) 900 (c) 1000 and (d) 1100oC
in an Ar ambient. The X-ray wavelength was
0.124 nm.

Fig. 2. Photoluminescence spectra from samples
annealed at Ta = 900, 950, 1000, and1100oC, obtained at 300 K with excitation
wavelength at 980 nm.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)23

Synthesis of Ultrathin Hexagonal Boron Nitride for Tunneling Applications
Carlo M. Orofeo, Satoru Suzuki, Hiroyuki Kageshima*, and Hiroki Hibino
Materials Science Laboratory, *Physical Science Laboratory
Production of atomically thin hexagonal boron nitride (h-BN) has considerably advancedin the past years given especially their synthesis is so much similar to the more populargraphene. Like graphene, the ability to control the number of layers is of fundamental interestas thin BN layers have the potential for several new applications such as a transport barrier
for tunneling transistors and spintronics. Here, we report the growth of large-area, monolayerh-BN ﬁlm on hetero-epitaxial Co ﬁlm supported by a sapphire substrate.
The synthesis was done using low-pressure chemical vapor deposition (LPCVD) methodwith ammonia-borane (NH3–BH3) or borazane used as BN precursors [1]. Our ﬁndings fromgrowth evolution studies reveal that the growth of the monolayer h-BN film proceeds intriangular, oppositely oriented domains that are commensurate (1×1) to the underlying Co
lattice (Fig. 1(b)). It is also inferred that these triangles are N-terminated and that the merging
of the BN islands create defects at the domain boundary. The growth of h-BN appears to be
self-limiting at a monolayer, with thicker domains only appearing in patches, presumably
initiated between domain boundaries. Further, an alternative method for determining thenumber of layers of the synthesized h-BN film was developed by employing low-energy
electron energy microscopy (LEEM). The measurement was taken directly after growth, andthe number of layers can be determined from the reﬂectivity curve of the LEEM measurement(Fig. 1(a)), thus, information on the number of layers can be taken fast without the need forcross-section. Reﬂectivity measurements of the thicker h-BN ﬁlms show oscillations resulting
from the resonant electron transmission through quantized electronic states of the h-BNﬁlms, with the number of minima scaling up with the number of h-BN layers (Fig. 1(a)). First
principles density functional theory calculations explain that the positions of oscillations are
related to the electronic band structure of h-BN.
We also investigate the tunneling properties of the h-BN by fabricating metal/BN/metal
devices on rigid and flexible substrates and compare the properties to exfoliated h-BN
(Fig. 1(c), inset) [2]. The measured current of the tunneling devices sandwiched by metalelectrodes is linear around zero bias and increases exponentially at higher biases, a behavior
consistent with direct tunneling (Fig. 1(c)). Further, from tunneling theory, we estimate thebarrier height for tunneling to be ~2.5 eV, and the dielectric strength to be 3.78 ± 0.83 GVm–1,
which are comparable to those of exfoliated monolayer BN. Our results demonstrate that
CVD-grown BN can be a perfect alternative to exfoliated BN for tunneling applications, suchas vertical transistors and spintronics, with an advantage of being available in a large area.
[1] C. M. Orofeo, S. Suzuki, H. Kageshima, and H. Hibino, Nano Res. 6 (2013) 335.
[2] C. M. Orofeo, S. Suzuki, and H. Hibino, J. Phys. Chem. C 118 (2014) 3340.

Fig. 1. (a) Reﬂectivity and LEEM image (inset) of the grown h-BN showing different signatures corresponding
to the number of layers. The number "0" means 0 layer or the substrate. (b) AFM image of the growthevolution of h-BN showing two, oppositely oriented triangles. (c) I-V curves of the metal/BN/metal devices
with different effective area. Inset shows the tunnel device fabricated on a ﬂexible substrate (PEN).
24

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Thermal Instability of Graphene on a Substrate
Satoru Suzuki
Materials Science Laboratory
Graphene is a one-atom-thick thin film consists of the honeycomb lattice of carbon.
Graphene is generally considered to be thermally and chemically stable because of its robust
sp2 bonding with no dangling bonds. In a practical graphene sample, however, the situationis complex. Graphene often contacts a substrate, metal electrodes, gas molecules in theenvironment, and residue of PMMA which is commonly used as a protective layer in thetransfer process. We show that a practical graphene sample obtained by the commonly used
growth and transfer techniques is not stable against heating in a high vacuum [1]. The originof the heating-induced structural instability is also studied.
In this study, we only used very common techniques for both CVD growth and transfer.
Single-layer graphene was grown on Cu foil by the low-pressure CVD method. A protective
PMMA layer was formed on the graphene ﬁlm on the Cu foil by spin-coating. The PMMA/
graphene film was isolated by dissolving the Cu foil in an FeCl3 solution and the film wastransferred to a substrate in deionized water. Finally, the PMMA film was removed withacetone. Raman spectra of graphene transferred to a SiO2 substrate before and after heating
in a high vacuum are shown in Fig. 1. A broad spectrum appears with heating. The spectral
broadenings mean that the Raman selection rule is relaxed due to disorder induced by heating.
Figure 2 shows O 1s XPS of a graphene/Au sample before and after heating at several
temperatures. The integrated intensity almost stays constant at 400oC and higher temperatures.
The binding energy values are close to those of physisorbed H2O and O2 molecules. These
results show that the oxygen-containing molecules are inserted between the graphene and thesubstrate and that the molecules cannot be easily eliminated even in an ultrahigh vacuum andat a high temperature. The structural instability is likely due to defect formation caused byreactions with H2O and O2 molecules underneath graphene.
[1] S. Suzuki, C. M. Orofeo, S. Wang, F. Maeda, M. Takamura, and H. Hibino, J. Phys. Chem. C 117 (2013)
22123.

Fig. 1. Raman spectra of graphene transferred to a
SiO2 substrate before and after heating in a highvacuum at several temperatures.

Fig. 2. O 1s XPS of graphene transferred to a Au
substrate before and after heating in a highvacuum at several temperatures.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)25

Sensing Fabric "hitoe" to Continuously Monitor Bioelectrical Signals
Shingo Tsukada, Nahoko Kasai, Hiroshi Koizumi1, and Koji Fujii2
Materials Science Laboratory, 1NTT Microsystem Integration Laboratries
2
NTT Science and Core Technology Laboratries GroupWe fabricated flexible and highly biocompatible electrodes consisting of a conductive
polymer PEDOT-PSS combined with textiles or threads in order to detect biomedical signals[1]. In this paper, we describe the new sensing fabric "hitoe", which has been developed
jointly by Toray Industries, Inc. and NTT.
By coating PEDOT-PSS on an advanced nanofiber textile (diameter 700 nm), we havesuccessfully fabricated "hitoe", which is an extremely durable sensing fabric that is sensitive
enough to detect weak bioelectrical signals. Figure 1 shows the difference between this andthe previous technique. A thin layer of PEDOT-PSS coated on the textile provides electricalconductivity while retaining the characteristics of the fiber itself, namely air permeability,
ﬂexibility, and a feeling of softness. The nanoﬁber textile, whose diameter is more than 20
times less than conventional PET fibers, provides better electrical conductivity and greater
durability against washing, because the surface area for coating is increased. Furthermore,since the points of contact with the skin are also increased, which allows the material to ﬁt
the body more closely, contact resistance between the skin and the electrodes is reduced.
The bioelectrical signals can be monitored without using any electrolyte paste, which isindispensable with conventional medical electrodes. When "hitoe" is mounted on a shirt, theheart rate and electrocardiograms can be recorded simply by wearing it (Fig. 2).
Using our sensing fabric " hitoe " , we will attempt to commercialize a clothing-typebioelectrical sensor and introduce new services that utilize "hitoe" incorporated in a clothingtype bioelectrical sensor and a smartphone.
[1] S. Tsukada, H. Nakashima, and K. Torimitsu, PLoS ONE 7 (4) (2012) e33689.

Fig. 1. Differences in skin contact between
conventional PET ﬁber and the nanoﬁber.

26

Fig. 2. A shirt made with "hitoe" for ECG
monitoring (Joint development with Toray).

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Stable Sealing of Microcavities with a Lipid Membrane for
Nanobiodevices
Aya Tanaka, Hiroshi Nakashima, Yoshiaki Kashimura, and Koji Sumitomo
Materials Science Laboratory
The integration of biological substances in electronic devices has great potential for various
applications such as biosensing and drug discovery. We have developed nanobiodevices forthe optical and electrophysiological analysis of biomaterials, especially membrane peptides
and proteins, by using microwells on a silicon substrate covered with lipid bilayers [1].
However, a lipid membrane suspended over a microwell is unstable, so it is difficult tomeasure the membrane protein function over a long period. It is known that the cell membrane
in living cells is stabilized by proteins anchored to the cell membrane and the cytoskeleton.
The fabrication of a cytoskeleton-mimetic structure in microwells promises the mechanicalimprovement of the device. Here, we describe a hydrogel conﬁned in a microwell array as apotential cytoskeleton candidate for the mechanical support of lipid bilayers (Fig. 1(a)) [2].
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. The hydrogel was prepared from an aqueous
solution of hydrogel precursors including calcein, which yields a green ﬂuorescence on thesubstrate. Before the polymerization was complete, the microwells were sealed with lipid
bilayers by rupturing giant unilamellar vesicles including rhodamine with red fluorescentemission on the substrate. The hydrogel formed out of the wells was removed by pushing it ina direction horizontal to the substrate.
The formation of lipid bilayers on the hydrogel-confined microwells was observed withfluorescence microscopy and atomic force microscopy (AFM). Fluorescence images areshown in Fig. 1(b) and (c). Red florescence from the rhodamine in the lipid bilayers wasobserved at the microwells where calcein ﬂuorescence was observed in the hydrogel solution.
Microwells filled with hydrogel were observed by AFM (Fig. 1(d)). These observations
indicate that the lipid bilayer confines the hydrogel precursors in the microwells and thehydrogel supports the formation of a lipid bilayer for at least 2 weeks.
Since the chemical composition of a hydrogel is easily modiﬁed, we can obtain hydrogels
with desirable properties such as mechanical strength, an electric charge, and responsivenessto a stimulus. The array has potential applications to the functional reconstitution of living
cells in microwells.
[1] K. Sumitomo et al., Biosensors and Bioelectronics 31 (2012) 445.
[2] A. Tanaka, H. Nakashima, Y. Kashimura et al., Jpn. J. Appl. Phys., 53 (2014) 01AF02.

Fig. 1. (a) Schematic illustration of cytoskeleton-mimetic structure on the substrate. Fluorescence images of
microwells (b) lipid bilayer and (c) lipid bilayer + hydrogel. (d) AFM image of microwells. Arrows indicate
the same microwell in each image.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)27

Ligand-Induced Structural Changes in a Single Ion Channel Receptor
Youichi Shinozaki*, Aya Tanaka, and Nahoko Kasai
Materials Science Laboratory, *University of Yamanashi
We have attempted to fabricate "nano-biodevices" for detecting and regulating biological
functions. In this study we investigated ligand-induced structural changes in ion channels
reconstituted into a supported membrane on a mica substrate using fast-scanning atomic
force microscopy (AFM) [1]. Fast-scanning AFM enables us to visualize the structure of asingle protein with sub-nanometer scale resolution at up to 80 ms/frame, which is ideal for the
structural examination of biological molecules such as proteins.
We employed an N-methyl-D-aspartate type ligand-gated ionotropic glutamate receptor(GluNR) obtained from rat cortical neurons and used an electrophysiological method to revealthat native GluNRs in the suspended membrane exhibited ion channel activity.
On the basis of recent studies of GluNRs, it is suggested that ligand binding domains (LBDs)
and N-terminal domains (NTDs) have two-fold symmetry and a dimer-of-dimers structure(Fig. 1(a)). When we imaged membrane-unreconstituted GluNRs, they exhibited acharacteristic structure with two saddle-shaped particles (corresponding to dimeric NTDs) anda circular particle (corresponding to a transmembrane domain (TMD)) (Fig. 1(b)). Long-term
imaging of a single GluNR channel has shown the structural ﬂexibility of NTDs (Fig. 1(c)).
We then investigated ligand-induced structural changes in the extracellular part of GluNRs
reconstituted in supported membranes quantitatively (Fig. 2). Without ligands, the tetramericparticles of NTDs exhibited various conformations including a circular structure without
subunits, structures with two- and four-fold symmetry, and a dimer-of-dimers structure. Afterbeing treated with an agonist, the NTDs appeared to be less ﬂexible, and many of them werein the dimer-of-dimers conformation. After a prolonged agonist treatment (> 30 minutes), a
large gap was formed between the two NTD dimers, which were suppressed by pre-treatment
with GluNR antagonists.
These results suggested that the extracellular parts of the ion channel receptors werehighly ﬂexible and dynamic, and demonstrated that their structure can be controlled by using
exogenously applied small compounds even after they have been reconstituted into supported
lipid bilayers on a Si substrate.
[1] Y. Shinozaki, A. Tanaka, N. Kasai, et al., Appl. Phys. Express 7 (2014) 027001.

Fig. 1. Structure of membrane-unreconstituted GluNRs.
(a) Predicted structure of tetrameric GluNR. (b) Two
saddle-shaped particles of NTDs (asterisks). (c) Longterm imaging of a single GluNR. Arrows: LBDs.

28

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Fig. 2. Pharmacological effect on the
structure of reconstituted GluNR.

Fast and High-Sensitivity Charge Sensor Combinedwith a Resonance Circuit
Katsuhiko Nishiguchi, Hiroshi Yamaguchi, Akira Fujiwara,
Herre S. J. Zant*, and Gary A. Steele*
Physical Science Laboratory, *Delft University of Technology
A ﬁeld-effect transistor (FET), a device that ampliﬁes a signal applied to a gate terminal,
can be used as a sensor with a high charge sensitivity [1]. In particular, a FET with a tennanometer-scale channel (Fig. 1(a)) allows single-electron detection at room temperature [2].
With this capability, the FET can transmit data using one electron as one bit [3] and can detecta tiny signal in micro-electro-mechanical systems [4]. However, such a small channel makes
its resistance higher, which leads to a limitation of FET operation speed (10~100 kHz). In thiswork, we demonstrate high-speed charge detection with single-electron resolution using aradio-frequency FET (RF-FET) [5].
In the RF-FET, an inductor L is connected to the FET and the combination of L with a stray
capacitor Cs of the FET functions as an LC resonance circuit as shown in Figure 1(b). Whena carrier signal Scarrier, whose frequency fcarrier is close to the resonance frequency [=1/(2πLCs)],
is applied to the circuit, some part of the signal is reﬂected (hereafter referred to as Sref). By
modulating channel resistance with gate signal Sgate whose frequency fgate is 10 MHz, thereﬂection characteristics of the circuit are also modulated. As a result, a side peak originatingfrom Sgate appears on both side of the main peak from fcarrier in a Sref spectrum as shown in Fig. 2.
Since Sgate power corresponds to a single-electron signal, the appearance of the two side peaksmeans single-electron detection at 10 MHz. This fast detection is possible because the LC
circuit matches the low impendence of the circuits to the high-impedance of the small FET
channel. On the other hand, a Si FET enables us to use high-power Scarrier, which leads to anincrease in side-peak amplitude. And the frequencies of the side peaks, fcarrier ± fgate, are highenough to almost completely avoid 1/f noise, which typically occurs at low frequency. As aresult, the RF-FET allows signal detection with a charge sensitivity of ~10–4 e/Hz0.5 up to 20
MHz. By applying Sref and Scarrier to a mixer, frequencies of the side peaks are down-converted
from fcarrier ± fgate to fgate, which allows detection of Sgate with arbitrary waveforms. Such signal
detection at room temperature with a combination of high charge sensitivity and fast operation
enables us to use the RF-FET in a range of applications. This work was partly supported by
the Funding Program for Next Generation World-Leading Researchers of JSPS.
[1] M. H. Devoret and R. J. Schoelkopf, Nature 406 (2000) 1039.
[2] K. Nishiguchi et al. Jpn. J. Appl. Phys. 47 (2008) 8305.
[3] K. Nishiguchi et al. Appl. Phys. Lett. 88 (2006) 183101.
[4] I. Mahboob et al. Appl. Phys. Lett. 95 (2009) 233102.
[5] K. Nishiguchi et al. Appl. Phys. Lett. 103 (2013) 143102.

Fig. 1. (a) Scanning electron microscope image of an FET.
(b) Equivalent circuit of an RF-FET.

Fig. 2. Single-electron detection
using an RF-FET.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)29

Accuracy Evaluation of Si Single-Electron Transfer Devices
at Extremely Low Temperature
Gento Yamahata, Katsuhiko Nishiguchi, and Akira Fujiwara
Physical Science Laboratory
One electron can be accurately manipulated by means of single-electron (SE) transfer. This
technique can be applied to ultralow-power-consumption devices and current standards inmetrology. For these applications, a transfer error rate of below 10-8 is necessary. Although
we have reported an absolute accuracy evaluation of Si SE transfer devices, the transfer
error rate has been about 10–2 due to thermal ﬂuctuation at T = 17 K [1]. Here we report anabsolute accuracy evaluation at T = 30 mK, where the error rate is about 10–4. In addition, wetheoretically show that the error rate can be reduced to a value on the order of 10–8 [2].
Figure 1 shows a schematic of the device. On an Si-on-insulator substrate, we fabricated an
SE transfer device, which comprises three nanowire transistors (LG1, LG2, and LG3 are gateelectrodes), and a charge sensor, which comprises a nanowire transistor (UG is gate electrode).
When we apply a positive voltage to LG3 and pulse voltages to LG1 and LG2, a transfer
current via a charge island between LG1 and LG2 is generated between the source and drain.
In addition, when a node is formed by applying a negative voltage to LG3, an SE is shuttled
by applying one more pulse voltage to the source. During the shuttle SE transfer, we detectedchanges in the number of electrons in the node by measuring current Is passing through the
charge sensor to evaluate the transfer errors.
In the experiment, we evaluated the transfer error during the transfer of two SEs. Figure 2(a)shows changes in Is during the shuttle transfer of two SEs, where the abrupt increase anddecrease in Is correspond to the ejection and injection of the two SEs, respectively. In thismeasurement, we observed one error. By counting the number of such errors, we obtained
the error rate of about 10–4, which is two orders magnitude better than the previous result.
The error originates from an effective device-temperature (Teff) increase caused by the pulse
voltage. In addition, we estimated the lower bound of the error rate from a theoretical ﬁt to thetransfer current (Fig. 2(b)). When Teff was decreased by decreasing the amplitude of the pulse
voltage, the transfer mechanism changed and the lower bound of the error rate decreased. At
minimum Teff (~ 5 K), the lower bound of the error rate is on the order of 10–8.
This work was partly supported by the Funding Program for Next Generation WorldLeading Researchers of JSPS.
[1] G. Yamahata, K. Nishiguchi, and A. Fujiwara, Appl. Phys. Lett. 98 (2011) 222104.
[2] G. Yamahata, K. Nishiguchi, and A. Fujiwara, Phys. Rev. B 89 (2014) 165302.

Fig. 1. Schematic of the device.

30

Fig. 2. (a) Typical result of counting thenumber of SEs. (b) Typical transfer
current (circles) and ﬁt (line).

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Coherent Phonon Manipulation in Coupled Mechanical Resonators
Hajime Okamoto, Imran Mahboob, Koji Onomitsu*, and Hiroshi Yamaguchi
Physical Science Laboratory, *Materials Science Laboratory
Semiconductor nanomechanical resonators enable the pursuit of new physical phenomenon
than can only be observed through the tiny mechanical displacement as well as enabling thedevelopment of nanoscience and nanotechnology. Coupling such nanomechanical resonators
has recently emerged as a subject of interest, because the sympathetic oscillation dynamics
in the coupled system expand the potential applications of nanomechanical objects suchas highly precise sensors, signal amplifier, and logic gates. However, an obstacle to thefurther development of this architecture arises from the usually weak coupling between thenanomechanical components. This limits the ability to coherently transfer the vibration energy
between the resonators within the ring-down time.
We have realized the strong coupling and coherent energy transfer between two GaAs
doubly-clamped beam resonators (Fig. 1(a)) by the parametric mode mixing technique [1, 2].
The piezoelectric modulation of the spring constant of one beam at the frequency difference
between the two beams leads to the dynamic coupling of the two beams, enabling the cyclic(Rabi) oscillations of phonons between the two vibrational states (Fig. 1(b), (c)). The Rabi cycle
period, i.e., the coupling strength, is adjustable by changing the gate voltage (Fig. 1(d)). As aresult, the vibration energy can be quickly transferred from one beam to the other enabling thevibration of the original beam to be switched off on a time-scale orders of magnitude shorter
than its ring-down time [3]. This quick energy transfer opens up the prospect of high-speed
repetitive operations for sensors and logics using nanomechanical systems.
This work was supported by KAKENHI.
[1] I. Mahboob, K. Nishiguchi, H. Okamoto, and H. Yamaguchi, Nature Phys. 8 (2012) 387.
[2] H. Okamoto et al., Nature Phys. 9 (2013) 480.
[3] H. Yamaguchi, H. Okamoto, and I. Mahboob, Appl. Phys. Express 5 (2012) 014001.

Fig. 1. (a) Schematic drawing of the sample and the piezoelectric effect. The beams consist of 400-nm-thick
i-GaAs, 100-nm-thick n-GaAs, 300-nm-thick AlGaAs, and 60-nm-thick Au electrodes. The piezoelectriceffect enables harmonic driving, pumping and detection of the mechanical motion via gate voltage. (b)Schematic drawing of the mechanical resonance for beams L,R and the phonon reaction picture during thepumping. The frequency of beam R is higher than that of beam L (293.93 kHz) by 440 Hz. The coherent
energy exchange between the two beams is achieved by applying the pump voltage to beam L with thefrequency difference between the two beams. (c) Schematic of the pumping protocol in a mass and springmodel. (d) Pump voltage dependence of the coherent oscillations measured via the time response of beam
R at ωR.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)31

An Electromechanical Phonon Laser
Imran Mahboob, Katsuhiko Nishiguchi, Akira Fujiwara, and Hiroshi Yamaguchi
Physical Science Laboratory
A phonon-laser has been a tantalising prospect since the inception of a laser. Although an
optical transition in an atom can be easily selected and amplified by a photon-cavity in alaser, the lack of discrete phonon transitions makes their selection and amplification by anequivalent phonon-cavity a formidable challenge.
To address this, we have developed an electromechanical resonator, shown in Fig. 1(a),which harbours an atom-like spectrum of discrete mechanical vibrations namely localised
phonon modes. An analysis of this spectrum reveals the electromechanical atom can host a
3-mode system, which mimics a 3-level laser scheme, where the energy difference of 2 higher(ω H and ω M) modes is resonant with a long-lived lower mode (ω L) as schematically depicted
in Fig. 1(b).
In this configuration pumping the higher mode, via the piezoelectric transducers
incorporated into the mechanical element, results in an output signal i.e. spontaneous phononemission or a mechanical vibration in both the lower and middle modes from just a single
input into the higher mode. An analysis of the phonon emission observed in the lower mode
reveals that it exhibits all the hallmarks of a laser including (i) an onset to the emission (ii)a spectrally sharp line width of 80 mHz as shown in Fig. 1(c) (iii) and gain narrowing. Even
more remarkably, when the higher mode is pumped with broadband incoherent noise, it still
results in spectrally pure thus coherent emission, i.e. lasing in the lowest mode [1].
These observations confirm that all-mechanical phonon-lasing can occur in a process
resembling stimulated Brillouin scattering and it suggests that concepts from photonics can bereadily applied to phononics in the electromechanical resonator platform. This in turn paves
the way towards a new class of technology utilising ultra-pure mechanical vibrations [2].
[1] I. Mahboob et al., Phys. Rev. Lett. 110 (2013) 127202.
[2] Viewpoint: Lasers of Pure Sound, J. T. Mendonça, Physics 6 (2013) 32.

Fig. 1. (a) An SEM image of the phonon laser which is executed in an electromechanical resonator integrated
with piezoelectric transducers at both clamping points via the gate electrodes. The mechanically compliant
element of the electromechanical resonator is the bridge like structure which sustains multiple modes. (b)A schematic of the 3-mode scheme used to execute the phonon laser. (c) Phonon lasing is observed in thelowest mode with a line width of only 0.08 Hz when ωH is pumped with noise of 70 Hz bandwidth.

32

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Storage and Retrieval of Quantum States in a Hybrid Quantum System
Shiro Saito1, Xiaobo Zhu1, Robert Amsüss1,3, Yuichiro Matsuzaki1,
Kosuke Kakuyanagi1, Takaaki Shimo-Oka4, Norikazu Mizuochi4, Kae Nemoto5,
William J. Munro2, and Kouichi Semba1,51
Physical Science Laboratory, 2Optical Science Laboratory,
3
TU Wien, 4Osaka University, 5NII
Superconducting quantum bits (qubits) are one of the most promising candidates for a future
large-scale quantum processor because of their controllability and scalability. However thecurrently reported coherence times of these has not yet reached the levels associated withthose of microscopic systems such as electron spins, nuclear spins etc. On the other hand, it
is hard to control and scale up such systems as they are well isolated from their environment.
In this context, a superconductor-spin ensemble hybrid system has attracted considerable
attention. We have utilized a nitrogen vacancy (NV) spin ensemble in diamond to act as aquantum memory for a superconducting ﬂux qubit. By bonding the diamond crystal on topof a gap tunable flux qubit [1], we had realized strong coupling between the qubit & spin
ensemble and further observed vacuum Rabi oscillations between them [2]. However we
couldn’t store quantum information in the spin ensemble because its coherence time wastoo short. To overcome this we applied an in-plane magnetic ﬁeld of 2.6 mT to the diamond
crystal to reduce strain effects on decoherence and thus succeeded in performing quantum
memory operations [3].
The inset of Fig. 1(a) shows a pulse sequence for storage of a single excitation present in
the ﬂus qubit. First we detuned the qubit from the spin ensemble and applied a microwave πpulse to prepare the qubit in the excited state |1>qb|0>ens. Next to transfer the excitation to thespin ensemble |0>qb|1>ens, we applied an iSWAP pulse making the qubit on resonance withthe spin ensemble for 30 ns. Then we keep the excitation in the spin ensemble for a storage
time T and retrieved it by applying the iSWAP pulse again. Finally we measured the state of
the qubit. From this experiment, a decay time of the excitation was determined as 20.8 ns(Fig. 1(a)). In a similar manner, we can store a superposition state in the spin ensemble byusing two microwave π/2 pulses instead of the π pulse (Inset of Fig. 1(b)). From this Ramseyinterference experiment on the spin ensemble, we could evaluate the decay time of thesuperposition state at 33.6 ns (Fig. 1(b)). These results show that we can store information of
a population and a phase, namely an arbitrary quantum state in the spin ensemble. Our results
are a signiﬁcant ﬁrst step to realize the long lived quantum memory and we will improve thediamond property and a coupling scheme to realize it.
This work was supported by FIRST and NICT.
[1] X. Zhu, et al., Appl. Phys. Lett. 97 (2010) 102503.
[2] X. Zhu, et al., Nature 478 (2011) 221.
[3] S. Saito, et al., Phys. Rev. Lett. 111 (2013) 107008.

Fig. 1. Quantum memory operations. (a) storage of a single excitation. (b) storage of a superposition state.
Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)33

Quantum State Projection with Various Measurement Strengths
Kosuke Kakuyanagi, Hayato Nakano, Kouichi Semba*, and Shiro Saito
Physical Science Laboratory, *NIIA superconducting loop, which has Josephson junctions, exhibits discrete energy levels.
In particular, in an external magnetic field of around Φ = 0.5Φ 0, we can ignore the higher
energy levels of this superconducting circuit, and so the circuit works as a two-level
quantum system called a superconducting ﬂux qubit. These quantum systems can represent
both an excited state and a ground state, which correspond to "1" and "0", respectively,
and the superposition of two states. When we measure a quantum superposition state, thequantum state is probabilistically projected to an excited state or a ground state. By using a
superconducting qubit, we can generate a superposition state and measure a quantum state on
the superconducting circuit.
We measure a superconducting flux qubit state using the Josephson bifurcation readout
method, which employs the bistable state of a non-linear resonator. With this readout method,
we can detect convergent states of a nonlinear resonator that depend on the qubit state byachieving coupling between a superconducting qubit and a non-linear resonator. This readout
method has advantages including a fast and low measurement back-action. To understand how
the projection occurs, we performed an experiment in which we undertook a readout strength
dependent measurement [1].
First, we generate an arbitrary superposition state by operating a rotation gate. Next, weapply various amplitude readout pulses to the qubit. At that time, if state projection occurs,a mixed state consisting of an excited state and a ground state appears. On the other hand, if
projection does not occur, the quantum state maintains a pure state. To distinguish between
these two states, we measure the ﬁnal state of the qubit after employing a rotation operation.
The experiment was performed at a few 10 mK to avoid the effect of thermal excitation.
Figure 1 shows the readout pulse amplitude dependence of the dephasing indicator α using
the usual readout pulse amplitude as a standard. When the pulse amplitude reaches h = 0.9,
the α value suddenly decreases. This result means the projection suddenly occurs when we
increase the measurement strength. This experimental result supports a theoretical analysis of
the Josephson bifurcation readout method [2].
[1] K. Kakuyanagi, S. Kagei, R. Koibuchi, S. Saito, A Lupaşcu, K. Semba, and H. Nakano, New J. Phys. 15(2013) 043028.
[2] H. Nakano, S. Saito, K. Semba, and H. Takayanagi, Phys. Rev. Lett. 102 (2009) 257003.

Fig. 1. Measurement strength dependence of α.
34

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Realizing Topological Insulating Phase in the Heterostructure Composedof Direct Transition Band Gap Semiconductors
Kyoichi Suzuki, Yuichi Harada, Koji Onomitsu*, and Koji Muraki
Physical Science Laboratory, *Material Science Laboratory
Topological insulators (TIs) have received substantial attention as a new state of matter,
which cannot be classiﬁed into traditional materials such as metals, insulators, semiconductors,
etc. TIs are characterized by distinct surface channels for three-dimensional (3D) TIs or
distinct edge channels for two-dimensional (2D) TI composed of counterpropagating electron
flows with opposite spin directions. In the channels, back scattering with spin reversal isprohibited. Therefore, TIs are promising for spintronic devices and low-power consumption
devices.
In contrast with TIs confirmed so far, which have a conduction-valence band inversion
in the material itself, we have succeeded in realizing a topological insulating phase arisingfrom the heterojunction between InAs and GaSb, which both are III-V semiconductors withdirect transition band gap [1]. Taking advantage of industrially developed semiconductor
technologies, device application of TIs will be promoted. In addition, in the wake of our
success, various combinations of materials will be investigated toward the development of
new TIs.
Figure 1 shows the schematic diagram of 2D-TI in the InAs/GaSb heterostructure. At theheterointerface, the conduction band bottom of InAs is lower in energy than the valence band
top of GaSb as if conventional TI materials. By spin-orbit interaction, 2D-TI band structure is
generated.
[1] K. Suzuki, Y. Harada, K. Onomitsu, and K. Muraki, Phys. Rev. B 87 (2013) 235311.

Fig. 1. Schematic diagram of 2D-TI generated from the InAs/GaSb heterostructure.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)35

Encapsulated Gate-All-Around InAs Nanowire Field-Effect Transistors
Satoshi Sasaki, Guoqiang Zhang*, Kouta Tateno*, Yuichi Harada,
Shiro Saito, Akira Fujiwara, Tetsuomi Sogawa*, and Koji Muraki
Physical Science Laboratory, *Optical Science Laboratory
Semiconductor nanowires (NWs) are attracting growing interest as promising building
blocks for the next generation of nanoelectronic devices. InAs NWs are of particularimportance in view of application to high-speed, low-power-consumption field-effecttransistors (FETs) due to their high intrinsic electron mobility. We fabricated InAs NW FETs
with a gate-all-around (GAA) structure, which enables improved electrostatic control, by
employing a novel two-step gate electrode formation method. The gate electrode overlaps thesource/drain electrodes, leading to a dramatic increase in driving current as a result of reduced
series resistance [1].
InAs NWs are grown via the Au-catalyzed vapor-liquid-solid (VLS) mode in a MOVPE
system. The as-grown NWs are conformally coated with 6 nm of Al2O3, used as high-k gate
dielectric, via atomic layer deposition (ALD). The NWs are then transferred to another Si/SiO2
substrate with a prepatterned Ti/Au lower gate electrode (Fig. 1). Source and drain Ohmic
contact regions are deﬁned by electron-beam lithography at both ends of the NW, followed
by Ar plasma etching to remove the surface oxides, and deposition of Al without breaking
vacuum. This way, Ohmic contacts with low resistance are obtained. The Al surface is thenoxidized to form an Al2O3 insulator in order to ensure electrical isolation between the uppergate and the source/drain electrodes. Finally, the Ti/Au upper gate is deposited overlapping thesource/drain electrodes, thus encapsulating the NW and realizing GAA structure.
Figure 2 shows drain current Id vs. drain voltage Vd characteristics for various gate voltages
Vg, for a FET device with gate length Lg = 220 nm and NW diameter d = 70 nm. The device
exhibits n-type FET operation with a threshold voltage of 0.39 V. Drain current normalized by
the NW circumference, w = πd, is also shown. Normalized transconductance, gm/w, is 0.55 S/
mm at Vd = 0.5 V, which outperforms existing FETs with homogeneous InAs NW channels.
These superb on-state properties are ascribed to improved electrostatic control by GAA
structure and to the reduction in series resistance by the gate-overlap geometry.
[1] S. Sasaki，G. Zhang, K. Tateno, H. Suominen, Y. Harada，S. Saito，A. Fujiwara, T. Sogawa, and K.
Muraki, Appl. Phys. Lett. 103 (2013) 213502.

Fig. 1. Schematic device structure (left) and scanningelectron microscope image (right) of the InAs
NW FET.

36

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Fig. 2. Output characteristics of the InAs NW
FET at room temperature.

AC Admittance of DNTT-Based MIS Capacitors
Toshiaki Hayashi
Physical Science Laboratory
Frequency-dependent carrier dynamics in dinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene(DNTT)-based metal-insulator-semiconductor (MIS capacitor) were studied by using
admittance measurements [1]. The device structure is Al (50 nm) /AlOx (4 nm) /DNTT(30 nm) /Au (90 nm). Figure 1 shows an optical microscope image of the sample. AC
admittance Y (= G + jωC) was measured using a Solatron Impedance Analyzer. A small AC
voltage VAC (=30 mV) superimposed on a DC voltage VDC was applied between the bottom
gate and the top contact. Figure 2 shows the frequency dependence of the imaginary andreal parts of the admittance divided by ω measured at VDC = –2.5 V. As the data show, thefrequency dependences of C and G/ω are mutually correlated with each other. Two steps
corresponding to the peaks in G/ω can be seen in C.
On the basis of an experimental study of devices with different contact geometries, peaks
observed in the conductance spectra corresponding to slopes in the capacitance spectra wereclassiﬁed into two groups. The high-frequency peak PH was proportional to the top contact
size and attributed to the carrier injection from the top contact to the DNTT/insulator interface
just underneath the contact while the low-frequency peak PL was only observed when thedevice had DNTT region that was not covered by the top contact. The low-frequency peak
was attributed to the drift current from the covered DNTT to the uncovered DNTT. The model
calculation of carrier diffusion reproduces the low-frequency peaks very well. It is shown thatthe field-effect mobility from the accumulation region (–2.5 V) to the subthreshold region(–1.1 V) can be estimated by ﬁtting the data for each VDC.
[1] T. Hayashi, N. Take, H. Tamura, T. Sekitani, and T. Someya, J. Appl. Phys. 115 (2014) 093702.

Fig. 1. Optical microscope image of the DNTT-base
MIS capacitor used in this work.

Fig. 2. C-f (a) and G/ω-f (b) characteristics
measured at VDC = –2.5 V.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)37

Cluster State Generation for Ultracold Atoms in an Optical LatticeKensuke Inaba, Yuuki Tokunaga*, Kiyoshi Tamaki, Kazuhiro Igeta, and Makoto Yamashita
Optical Science Laboratory, *NTT Secure Platform Laboratories
An optical lattice is the artiﬁcial crystal created by the laser interference, and a million ofultracold atoms can be trapped in each lattice site. Using (pseudo-) spin states of each atom asa qubit, we might realize million-bit-size quantum computer. For this ﬁnal goal, it is required
to establish the high-ﬁdelity entanglement generation. In this study, we theoretically propose
an entanglement generation implemented with a combination of some simple experimental
techniques, such as, irradiating lasers and tuning their intensities [1]. Precise numericalsimulation conﬁrms that our method can create a high-ﬁdelity multipartite entanglement, thatis, the cluster state, in a short operation time with scalability.
In what follows, we detail a part of our method. Here, we use a hyperﬁne state of a fermion
as a qubit. By utilizing quantum phase transition of fermions, such as, the band insulatingtransition, we can prepare the required initial state in which a single atom occupies eachlattice site. However, in this state, there is no entanglement between atomic spins at different
sites (Fig. 1(a)). By performing some operations on this state, e.g., adding laser lights, we
can design the Hamiltonian of the atoms, which allows us to control the spin-spin correlationand then yields spin entanglement (Fig. 1(b)). However, the Hamiltonian describing theatomic quantum states includes the extra quantum states, such as, orbital states and multiplesite occupancies, in addition to the (qubit) spin states. Existence of the extra states is thesource of the error that greatly decreases ﬁdelity of entanglement generation. The previous
proposals avoid such an error by creating entanglement slowly (Fig. 2(a)), which is, however,a weak point for practical implementations. We thus propose to utilize a resonant interorbital transition, which can be induced by only modulating an optical lattice potential withan additional laser. The resonant tunneling allows us to fast create entanglement, while it also
causes an error due to the appearance of an excited orbital state (Fig. 2(b)). We clarify themechanism of this error and further propose to synchronize an oscillation caused by the error
with that of the entanglement generation [dotted and solid lines in Fig. 2(b), respectively]. We
can thus create a very high-ﬁdelity entangled cluster state within a short time.
[1] K. Inaba, et al, Phys. Rev. Lett. 112 (2014) 110501.

Fig. 1. (a) An optical lattice trapping a single atomin each site. (b) Entangled cluster state.
Generating entanglement can be achieved bydesigning the atomic Hamiltonian with some
operations, such as adding lasers, tuning
their intensities, and etc.
38

Fig. 2. Numerical simulation results for previous (a) andpresent (b) methods. Solid lines represent ﬁdelity
between the cluster and the generated states.
Dashed lines are the existing probability of extra
states, which causes an error. Arrows show a time
when the cluster state is created.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

An On-Chip Single Photon Buffer
Based on Coupled Resonator Optical Waveguide
Hiroki Takesue, Nobuyuki Matsuda*, Eiichi Kuramochi*,
William John Munro, and Masaya Notomi*
Optical Science Laboratory, *NTT Nanophotonics Center
Integrated quantum optical circuits are now drawing attention as a way to realize advanced
quantum information processing using photons. Several core elements such as entanglement
sources, gates, and detectors have been already realized. In addition to these functions, single
photon buffers on a chip will help us to realize reconfigurable integrated quantum opticalcircuits. Here, we report a single photon buffer experiment using a coupled resonator opticalwaveguide (CROW) based on silicon photonic crystal cavities [1].
Figure 1 shows the experimental setup. 1551.1-nm, 20-ps pump pulses were injected intoa dispersion shifted fiber (DSF) to generate correlated photon pairs via spontaneous fourwave mixing. The signal photon from a pair at a wavelength of 1546.70 nm was coupled to
the CROW with a lensed ﬁber, and then received by a superconducting single photon detector(SSPD), while the idler photon (1555.53 nm) was directly received by another SSPD. The
detection signals from the SSPDs were input into a time interval analyzer for coincidence
measurements. A schematic of the CROW used in the experiments is shown in the inset of
Fig. 1 [2]. We used a CROW whose lattice constant and inter-cavity distance were 420 nm
and 2.1 µm, respectively. The number of cavities was 400, which means that the total length
was 840 µm. The silicon chip that included the CROW was equipped with another waveguideof the same length, where the CROW section was replaced with a line defect waveguide. This
waveguide was used as a reference for the temporal delay.
Figure 2 shows the coincidence histograms when the signal photons transmitted through the
CROW (□) and the reference waveguide (○). We observed a clear shift of the coincidence
peak by 151.1±0.5 ps when the signal photon passed through the CROW. This result suggeststhat the speed of the pulsed photons were slowed to 1/59 of the light speed in a vacuum. We
also observed the cross correlation between the signal and idler photons and found to be 3.25
±0.06, which indicates that a non-classical intensity correlation was preserved after the photon
buffering in the CROW. In addition to this experiment, we successfully tuned the delay timeby 50 ps using the temperature dependence of the CROW dispersion characteristics. Finally,
we experimentally conﬁrmed that a time-bin entangled state could be preserved in the CROW.
[1] H. Takesue, N. Matsuda, E. Kuramochi, W. J. Munro, and M. Notomi, Nature Commun. 4 (2013) 2725.
[2] M. Notomi, E. Kuramochi, and T. Tanabe, Nature Photon. 2 (2008) 741.

Fig. 1. Experimental setup.

Fig. 2. Time-interval histogramsaround coincidence peaks.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)39

Long-Term Performance of Quantum Key Distribution over 90-km Optical
Links Installed in a Field Environment of Tokyo Metropolitan Area
Kaoru Shimizu, Kiyoshi Tamaki, and Toshimori Honjo*
Optical Science Laboratory, *NTT Secure Platform Laboratories
The long-term operation performance, robustness and feasibility, of a differential phase shift(DPS) quantum key distribution (QKD) system to provide a long-distance key distribution
service over optical ﬁber networks was examined by a series of ﬁeld experiments that werecarried out using a test-bed optical network in the Tokyo metropolitan area: Tokyo QKD
network (Fig. 1) [1]. In spite of a 30-dB transmission loss and 90-km propagation alongan optical link installed in a field environment, the stable generation of a secure key wasdemonstrated for 25 days in a completely free-run operation with a 1-GHz clock DPS-QKD
system employing a weak coherent light pulse and superconducting single photon detectors(SSPDs) [2]. The average sifted key generation rate and the quantum bit error rate (QBER)
were 11 kbps and 2.6 % (Fig. 2(a)), respectively. The average generation rate of secure key
after error correction and privacy ampliﬁcation was 1.1 kbps with a ﬂuctuation of ±0.5 kbps
(Fig. 2(b)). Here, we deﬁned the secure key as the ﬁnal key which was proven to be secureagainst general individual attacks.
A comparison with meteorological data revealed the way in which the ﬁeld environment
influenced the key distribution performance. The secure key generation was considerably
stable unless a strong wind disturbed the optical link which was composed of both aerial andunderground regions with the approximately same total length. With the current system, someimperfections in photonic devices still limited the achievable performance levels, for example,
the temporal bit error deterioration and the ﬁnite operation period. Some technical solutions
were also provided to cope with these remaining problems.
This work was carried out in fruitful collaboration with the National Institute of Information
and Communications Technology (NICT).
[1] M. Sasaki et.al., Opt. Express 19 (2011) 10387.
[2] K. Shimizu, T. Honjo, M. Fujiwara, T. Ito, K. Tamaki, S. Miki, T. Yamashita, H. Terai, Z. Wang, and M.
Sasaki, J. Lightwave Technol. 32 (2014) 141.

Fig. 1. Experimental conﬁguration, (a) Setup
of 90-km optical link and (b) Setup of
DPS-QKD system.
40

Fig. 2. Experimental (a) QBER and (b) secure
key generation rate for 25 days / 1 hour
average.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Growth of InP Nanowires on Graphene-Covered Fe
Kouta Tateno, Guoqiang Zhang, and Hideki Gotoh
Optical Science Laboratory
Recently, the large-scale growth of single-layer and few-layer graphene has been
demonstrated by the roll-to-roll fabrication method, and the advanced technique oftransferring graphene sheets to ﬂexible plastic substrates has led to stretchable, foldable, andtransparent electronics and optoelectronics [1]. Graphene layers can be formed on many kindsof substrates. Here, we report on InP nanowires (NWs) on graphene/SiC(0001) and graphenecovered Fe. The vapor-liquid-solid (VLS) method is widely used to make freestanding NWs.
The growth is driven catalytically in a nano-area by nanometer-scale metal particles. Thisfeature is very useful for fabricating nanodevices because of the feasibility of forming p-njunctions and various heterostructures like quantum dots and core-shell structures.
The VLS growth was carried out in a low-pressure metalorganic vapor phase
epitaxy (MOVPE) reactor [2]. Trimethyl indium (TMIn) was the group-III source, andtertiarybutylphosphine (TBP) was the group-V source. We used Au particles as catalysts. The
structures were observed by scanning electron microscopy (SEM) and transmission electron
microscopy (TEM). III-V NWs tend to grow in the [111]B direction. Figure 1 shows a InP NW
and an In ball grown on graphene/SiC(0001). Vertical NWs indicate that the (111)B face was
likely to form initially on the 2D graphene surface. However, the low decomposition rate of
TBP caused some In balls on the graphene surface. Some Au particles where the phosphorous
supply was not enough could not form crystalline InP. This is due to less active sites ongraphene to decompose TBP and also weak bonding characteristics of graphene surface. We
have also tried to grow InP NWs on graphene/metal for flexible device application. Aftersearching for proper metal among Cu, Ni and Fe, we could grow the NWs only on graphene/
Fe. For Cu and Ni, the phosphorous reaction was so strong that it changed the surface
morphology, which made the NW growth impossible. Fe forms various alloy compounds withcarbon, and by adding carbon, Fe becomes harder, which is known as steel. The formation ofsteel would be important for the success of the subsequent InP NW growth. Figure 2 shows
the demonstrated InP NWs grown on a micron Fe wire like spines of cacti. We also conﬁrmed
the cathodoluminescence (CL) from InP NWs. This system is very promising for a future NW
application using ﬂexible substrates.
[1] S. Bae et al., Nature Nanotech. 5 (2010) 574.
[2] K. Tateno et al., Jpn. J. Appl. Phys. 53 (2014) 015504.

Fig. 1. Bright-ﬁeld (BF) TEM image for a InP NW
and a ball on graphene/SiC(0001).

Fig. 2. SEM images and panchromatic CL image for InP
NWs on a micron Fe wire covered by graphene.
The lower images were obtained at 14 K.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)41

Topological Raman Band in the Carbon Nanohorn
Ken-ichi Sasaki, Yoshiaki Sekine*, Kouta Tateno, and Hideki Gotoh
Optical Science Laboratory, *Materials Science Laboratory
Five-membered rings (pentagons) are found throughout the honeycomb network ofcarbon. For example, pentagons appear in fullerenes, at the apexes of carbon nanohorns,
at the junctions of carbon nanotubes, and in a ﬂat sheet of graphene as a constituent of theStone-Wales defect [1]. A pentagon is a topological defect, which is represented as the ﬂux
of a pseudomagnetic field that is perpendicular with respect to the graphene layer [2]. Aninteresting consequence of such a flux in quantum mechanics is the Aharonov-Bohm (AB)effect. However, the AB effect is usually observed at very low temperature and/or for samples
essentially devoid of defects so that they maintain coherence, which prevents us from utilizing
the AB effect in practical applications.
We show that a topological defect causes a special band (peak) in the Raman spectrum of acarbon nanohorn, which we call a topological Raman band [3]. A topological Raman band is
excited through the AB effect for pentagons, and can be observed even at room temperature.
A photo-excited "relativistic" carrier with a non-zero winding number is the key to activatinga topological D Raman band (Fig. 1). A topological D band can be distinguished from theconventional D band excited at the graphene edge by its non-dispersive nature, because theselection rules for electron-phonon matrix elements are altered in an essential way by thepresence of the pentagon.
[1] H. W. Kroto et al., Nature 318 (1985) 162; S. Iijima et al., Nature 356 (1992) 776; S. Iijima et al., Chem.
Phys. Lett. 309 (1999) 165; A. Hashimoto et al., Nature 430 (2004) 870.
[2] J. González et al., Phys. Rev. Lett., 69 (1992) 172; P. E. Lammert et al., Phys. Rev. Lett., 85 (2000) 5190; K.
Sasaki et al., Prog. Theor. Phys. 113 (2005) 463.
[3] K. Sasaki et al., Phys. Rev. Lett., 111 (2013) 116801.

Fig. 1. (Left) Process exciting a topological D band in a nanohorn. (Right) A path with a zero winding number
does not contribute to the D band.

42

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Generation of Isolated Attosecond Pulse in Carbon K-Edge (284 eV)
Region with Double Optical Gating
Hiroki Mashiko, Tomohiko Yamaguchi, Katsuya Oguri, and Hideki Gotoh
Optical Science Laboratory
As is well known, carbon is important fundamental element of inorganic compounds(graphene, nanotube, etc.) and organic compounds (hydrocarbon, bio cell, etc.). The K-shellabsorption edge in carbon [284 eV photon energy (4.4 nm wavelength)] has capability for
optical imaging the element. Meanwhile, attosecond (10–18 s: as) pulse is shortest laser pulsein the world. The laser with ultrashort pulse width would be useful for visualizing of living
cell structure. In order to generate the attosecond pulse with 284 eV photon energy, the peakintensity of the driving laser should be >1.4×1015 W/cm2 [1]. Here, we report attosecond
pulse generation with only 247 µJ pulse energy using a double optical gating (DOG) [2]. The
technique is combined with elliptically dependent polarization gating and two-color gating.
The temporal gate effect can emphasize the cut-off spectrum component in the pulse.
In this experiment, we used the Ti:Sapphire laser with 247 µJ pulse energy with 7 fs
duration. The temporal gate width with DOG was fixed to ~1.3 fs. The driving laser was
focused on a cell filled with helium gas (backing pressure: ~1.2 bar, interaction length:
300 µm). The spectrum of generated attosecond pulse was monitored with a soft x-ray
spectrometer (resolution: 3.8 eV in the 284 eV region). Figure 1 shows the spectral
distribution with (a) the carbon filter and (b) carbon and boron filters. The boron K-edge(188 eV) and carbon K-edge (284 eV) were clearly observed. Consequently, 284 eV pulse
were successfully generated from the driving laser with only 247 µJ pulse energy, which pulse
energy is lowest value ever reported. In addition, the spectral bandwidth is larger than 140 eV.
The Fourier-transform-limited pulse, assuming a ﬂat phase, was 20 as duration as shown in
Fig. 2. The value is much shorter than previous reported value of 80 as in the world record [3].
The characteristic time scale for electron motion is atomic unit of time, which is 24 as. The
attosecond pulse will have a profound impact on the study of various electron dynamics in the
carbon K-edge region.
[1] Z. Chang et al., Phys. Rev. Lett. 79 (1997) 2967.
[2] H. Mashiko et al., Appl. Phys. Lett. 102 (2013) 171111.
[3] E. Goulielmakis et al., Science 320 (2008) 1614.

Fig. 1. Spectral distribution of attosecond pulse with(a) carbon ﬁlter and (b) carbon and boron ﬁlters.

Fig. 2. Fourier-transform-limited pulse.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)43

Modification of Exciton Optical Properties with Coherent Phonons in
Quantum Dots
Hideki Gotoh, Haruki Sanada, Hiroshi Yamaguchi*, and Tetsuomi Sogawa
Optical Science Laboratory, *Physical Science Laboratory
Optically active semiconductor quantum dots (QDs) have been extensively studied because
they are good candidates for quantum devices. Quantum devices rely on the optical propertiesof the excitons in QDs, which exist more stably than in other semiconductors. Excitons
should be coherently manipulated without any decoherence processes for quantum device
applications. Previously, optical, electric, and magnetic ﬁelds have been employed as sources
for the manipulation. In this report, we show that coherent phonons induced by ultrafast
optical pulses will provide a good new approach to QD manipulation [1].
The QD sample used in the measurement was based on GaAs/AlGaAs quantum wells (QWs)
fabricated on an undoped (001) GaAs substrate. The QDs were formed in a thin (4.2 nm
thick) GaAs layer sandwiched between AlGaAs barriers. The QD sample had a 100 nmthick titanium ﬁlm on its surface and the QDs were located 100 nm below the surface. In themeasurement, we used a pulse laser (duration: 150 fs, repetition: 80 MHz, energy: 1.653 eV)as the excitation source. Optical pulses from the source were divided into two paths: one(Laser PL) was for creating excitons in QDs and the other (Laser Metal) was for illuminating
the metal ﬁlm as in Fig. 1. Figure 2 shows the PL spectra for different laser metal intensities
with the laser PL power constant. Fine well-separated PL peaks were seen in the PL spectrum
for laser PL (Laser Metal = 0 mW). The PL peaks originated from single excitons conﬁned
in the QDs. The spectra changed greatly with increases in Laser Metal intensity. Thesephenomena cannot be explained simply in terms of the heating effects induced by the laser
metal. As an alternative way of evaluating the effects of illuminating metal, we also measured
the reflectance properties using an optical interferometric method. Clear time-oscillatinginterferometric signals were observed that responded to the intensity of Laser Metal. The
oscillating signals conﬁrmed that coherent phonons were created in the QD sample. In QDs,
coherent phonons form time- and space-oscillating strain waves leading to a change in the PL
properties. The coherent phonons will constitute a new manipulation source whose responsetime is much shorter than that of previous methods employing ultrafast optical sources.
[1] H. Gotoh, H. Sanada, H. Yamaguchi, and T. Sogawa, Appl. Phys. Lett. 103 (2013) 112104.

Fig. 1. GaAs quantum dots (QD) and experimental
conﬁguration around QD sample.

44

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Fig. 2. Laser metal power dependence ofphotoluminescence spectra for QD.

Optical Nanocavity Formed by a Semiconductor Nanowire
and a Si Photonic Crystal
Atsushi Yokoo1,2, Muhammad Danang Birowosuto1,2, Guoquiang Zhang2, Kouta Tateno2,
Masato Takiguchi1,2, Eiichi Kuramochi1,2, Hideaki Taniyama1,2, Masaya Notomi1,2
1
NTT Nanophotonics Center, 2Optical Science Laboratory
Semiconductor nanowires are attractive for their small diameters of less than 100 nm. In
particular, III-V semiconductor nanowires can be used in a variety of structures, such as coreshell and multilayer heterostructures and p-i-n junctions, by arranging growth sequencesin epitaxial growth, which may enable us to realize small optical devices with low energy
consumption. However, a nanowire itself can not provide sufficient optical confinement toachieve the desired device performance because it is too small to match the wavelength oflight. On the other hand, Si photonic crystal provides optical conﬁnement with the dimensionof the wavelength of light; however, it requires a regrowth process in order to incorporate
optically active material. Therefore, the types of materials we can use with Si photonic crystal
are limited.
Here, we demonstrate that a nanocavity can be created in a photonic crystal by placing ananowire in a trench in a line defect of Si photonic crystal. We move the nanowire by meansof AFM manipulation, in which a nanoprobe can be used to drag a small object. In addition,
the position of the nanocavity can be shifted by moving the nanowire in the trench (Fig. 1) [1].
The nanocavity is a mode-gap cavity generated by partially changing the effective refractive
index in the line defect [2, 3]. We obtained the highest Q-factor of 9500 (resonant wavelength:
1.5 µm) for a sample with a InAsP/InP heterostructure nanowire (2620-nm length, 85-nm
diameter) installed into a trench in a line defect (lattice constant of 416 nm, trench width of
150 nm, depth of 75 nm) of a photonic crystal. As the the Q-factor for the movable cavity canvary at each nanowire position, we can evaluate the Q-factor dependence of cavity photon
lifetime by evaluating each photon lifetime in the nanowire-induced cavities with an identicalnanowire placed at different positions. We conﬁrmed that the photon lifetime decreases withincreasing Q-factor, which can be attributed to the Purcell effect. We obtained a photon
lifetime of 91 ps for a nanowire-induced photonic crystal cavity with a Q-factor of 5200, whichis the shortest lifetime ever achieved for a III-V semiconductor nanowire.
This demonstration indicates thepossibility of realizing photonic
integrated circuits on demand, where
optically active material is installed
into a universal photonic crystal
substrate to provide a nanocavity
with the desired functionality.
[1] M. D. Birowosuto, A. Yokoo, G. Zhang,
K. Tateno, E. Kuramochi, H. Taniyama,
M. Takiguchi, and M. Notomi, Nature
Mater. 13 (2014) 279.
[2] M. Notomi and H. Taniyama, Optics
Express 16 (2008) 18657.
[3] M. D. Birowosuto, A. Yokoo, H.
Taniyama, E. Kuramochi, M. Takiguchi,
and M. Notomi, J. Appl. Phys. 112 (2012)
113106.

Fig. 1. Diagram of cavity creation by installing a nanowire
into a trench in a line defect of photonic crystal by AFM
manipulation. The nanowire is moved in the trench torealize a movable cavity. Spectra show an emission fromthe nanowire-induced cavity located at different positions.
Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)45

InGaAs Photodetectors Based on Photonic Crystal Waveguide Including
Ultrasmall Buried Heterostructure
Kengo Nozaki, Shinji Matsuo*, Koji Takeda*, Tomonari Sato*, Eiichi Kuramochi,
and Masaya Notomi
Optical Science Laboratory, *NTT Photonics Laboratories
Low-power optical link between CMOS chips and photonic network on chip have been
extensively studied. One of the challenges with photodetectors (PDs) is to realize a small
junction capacitance to use as a receiver in such short-range optical links. If the capacitancecan be greatly reduced by reducing the size of the PDs, the RC constant could be kept at alow level even during connection with a high load resistor. The result would be a low thermal
noise and an enhanced output voltage while maintaining a fast response. This would lead tothe reduction of electrical amplification or even its elimination (referred as a receiver-less
PD). There would then be a strong demand for nano-PDs with a small junction capacitanceand high absorption efﬁciency.
Semiconductor photonic crystal (PhC) can conﬁne light in a small core waveguide, whichmeans that high responsivity can still be expected for a few-µm-long PD. This also enables us
to reduce the length of the p-i-n junction and subsequently reduce the junction capacitance.
Figure 1 is a schematic and SEM image of our PD based on a PhC waveguide [1]. An InGaAsbulk absorption layer with a length of only 3.4 µm was embedded in the waveguide, and Zn
and Si ion were doped to form the lateral p-i-n junction. The photocurrent for input of CW
light is shown in Fig. 2(a). We estimated a sufficiently large responsivity of ~1 A/W at abias voltage of –1 V. This means that there was no apparent non-radiative recombination or
carrier trapping at the hetero interface, which is unique and signiﬁcant for our BH structure.
Figure 2(b) shows an eye pattern for modulated light with 231–1 pseudo-random bit sequence,indicating a good response for a bit rate of 10 Gb/s. We can expect faster response speed by
reduction of RC time constant, and the on-chip light-to-voltage conversion would be possible
if the PD is connected with load resistance. They would make us to expect a great potential for
use as an integrable low-power photoreceivers in future intra-chip optical networks.
[1] K. Nozaki, S. Matsuo, K. Takeda, T. Sato, E. Kuramochi, and M. Notomi, Opt. Express 21 (2013) 19022.

Fig. 1. Device structure (a) Schematic of PhC-based
pin-PD. (b) SEM image of fabricated sample.
46

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Fig. 2. Device characteristics (a) Photocurrent
versus optical input power characteristics.
(b) Eye pattern for 10 Gb/s optical signal.

Enhanced and Suppressed Spontaneous Emission from a Buried
Heterostructure Photonic Crystal Cavity
Masato Takiguchi1,2, Hisashi Sumikura1,2, Muhammad Danang Birowosuto1,2,
Eiichi Kuramochi1,2, Tomonari Sato1,3, Koji Takeda1,3, Shinji Matsuo1,3, and Masaya Notomi1,2
1
NTT Nanophotonics Center, 2Optical Science Laboratory, 3NTT Photonics Laboratories
Chip-scale optical interconnection and photonic network-on-chip architecture are being
widely studied. Among various candidates, a photonic crystal (PhC) cavity device ispromising because its ultra-small mode volume and high quality factor (Q) will enable highspeed modulation devices, such as lasers and light emitting diodes (LEDs). To realize efﬁcientand ultrafast light-emitting nanophotonic devices, we study spontaneous emission control
in a buried-heterostructure (BH) photonic crystal cavity in which InGaAsP quantum wells(QW) are embedded in an InP PhC (Fig. 1). Spontaneous emission from conventional QWPhC cavities have been extensively investigated, but they suffer from poor carrier conﬁnement
and surface non-radiative recombination. Therefore, the spontaneous emission control has
been only observed in quantum dots PhC cavities. The present study shows that BH-QW-PhC
cavities can exhibit distinctive spontaneous emission control in QW-PhCs because of strong
carrier conﬁnement and low surface non-radiative recombination.
In this experiment [1], we examined the emission enhancement and suppression in our
samples with different lattice constants at 4K. Figure 2(a) shows the PL decay for the L2
cavity at 1406 nm in an off-resonant condition, at 1430 nm in an on-resonant condition and areference QW emission, measured at excitation powers of 100 nW, which is 10 times lower
than the lasing threshold. Here we used the L2 cavity with a quality factor of 4200 (Fig. 2 (b)).
As seen in Fig. 2(a), the on-resonant emission apparently becomes faster, and the emission
rate obtained by a single exponential ﬁtting was 4.9×109 s–1 (tPL = 0.2 ns) which is 3.8 times
faster than the same-size BH-QW without the PhC structure. The off-resonant emission rate
was 1.7×108 s–1 (tPL = 6.0 ns) and 7.5 times slower than the BH-QW emission without a PhC
structure. This means that we can control the spontaneous emission rate by a factor of 30
between on-resonant and off-resonant conditions. This is the largest ratio observed in QWPhCs, and comparable to the best QD-PhCs. The result implies our devices may have highspontaneous emission coupling efficiency, BH-QW-PhC cavities should be promising for
devices light emitting based on cavity QED effects, and that they have great potential for
realizing very efﬁcient and ultra-fast light-emitting nanophotonic devices.
[1] M. Takiguchi, H. Sumikura, M. D. Birowosuto, E. Kuramochi, T. Sato, K. Takeda, S. Matsuo, and M.
Notomi, Appl. Phys. Lett. 103 (2013) 091113.

Fig. 1. (a) Schematic of L2 PhC cavity structure. An
active region is embedded inside an L2 photonic
crystal cavity. (b) Cross-section of BH-QW-PhC
structure.

Fig. 2. (a). Emission lifetimes from L2 cavity onresonant, L2 cavity off-resonant and BH-QW
without PhC (0.80×0.30×0.15 μm3). (b) L2
cavity spectrum at 4 K.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)47

Low Energy Consumption Direct Modulation of Lambda-Scale Embedded
Active-Region Photonic-Crystal Lasers
Koji Takeda1,2, Tomonari Sato1,2, Akihiko Shinya1,3, Eiichi Kuramochi1,3,
Masaya Notomi1,3, Koichi Hasebe1,2, Takaaki Kakitsuka1,2, and Shinji Matsuo1,2
1
NTT Photonics Laboratory 2Optical Science Laboratory, 3NTT Nanophotonics Center
There have been many attempts to form optical interconnects on CMOS chips with adistance ranging from core-to-core and chip-to-chip level. Light sources used in such shortdistance optical interconnects have to be driven with ultra-low energy consumptions, e.g.
10 fJ/bit [1]. We have developed lambda-scale embedded active-region photonic-crystal(LEAP) lasers to use them as light sources for on- and off-chip optical interconnect [2]. In thispaper, we report how much energy the LEAP lasers consumed under direct modulations.
Device fabrication procedures were similar to that we have reported elsewhere [3]. Ion
implantations and thermal diffusions of dopants formed lateral p-i-n junction. Photoniccrystals were formed by electron-beam lithography and dry etching, followed by wet etching.
We measured a light output and an applied voltage versus an injected current, and theresult is shown in Fig. 1. We obtained a threshold current of 32 µA, and the maximum output
power was 39.3 µW at a current injection of 300 µA. There was an optical coupling loss ofapproximately 8 dB, and the plot shows calibrated output power at the waveguides. We thendrove the LEAP lasers with a pseudo-random bit sequence of 231 – 1 at a bit rate of 10 Gb/s.
Output light was monitored by a digital sampling oscilloscope via an optical amplifier thatwas used to compensate an optical coupling loss. Figure 2 shows the eye diagram of the
LEAP lasers. We needed only 80-µA current injection to achieve a clear eye opening with an
extinction ratio of 10 dB. We achieved the energy consumption of smaller than 10 fJ/bit under
this operating condition.
Part of this work was supported by the New Energy and Industrial Technology Development
Organization (NEDO).
[1] D. A. B. Miller, proc. IEEE 97 (2009) 1166.
[2] K. Takeda et al., Nature Photon. 7 (2013) 569.
[3] S. Matsuo et al., JSTQE 19 (2013) 4900311.

Fig. 1. L-I-V characteristic of the LEAP laser.

48

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Fig. 2. 10-Gb/s eye diagram.

Significant L-Band Responsivity Improvement of Germanium Waveguide
Photodiode by Franz-Keldysh Effect
Kotaro Takeda, Tatsurou Hiraki, Tai Tsuchizawa, Hidetaka Nishi, Rai Kou, Hiroshi Fukuda1,
Tsuyoshi Yamamoto1, Yasuhiko Ishikawa2, Kazumi Wada2, and Koji Yamada
NTT Nanophotonics center, 1NTT Microsystem Integration Laboratories, 2The University of Tokyo
The responsivity of germanium photodiode (GePD) for L-band (1565 – 1625 nm) decreases
because of a decrease in the absorption coefﬁcient of germanium around 1580-nm wavelength[1]. Hence, increase in the responsivity is required to apply a GePD as a photodetector for
the L-band. Under a high-bias condition, the Franz-Keldysh (FK) effect might increase
responsivity in the L-band. An increase of absorption coefﬁcients under high bias voltage wasrecently observed in the band around 1580 nm [2]. Moreover, the avalanche effect also might
increase responsivity in the L-band. The avalanche multiplication gain should be observedin the L-band because it does not depend on wavelength. In this study, we investigate theresponsivity of a GePD driven with a high bias field to give rise to the FK and avalanche
effects in the L-band. And we separate the contribution of each to the responsivity by
calculating the inﬂuences of them.
We employed a waveguide coupled GePD to measure the responsivity in the L-band underhigh bias voltage. The width, length, and thickness of the Ge mesa are 10, 50, and 1 μm,
respectively. The dark currents are about 117 nA and 111 μA at 2- and 15-V bias voltage.
Figure 1 shows the responsivity of the GePD for various bias voltages. The responsivity at
15 V bias reaches over 1.14 A/W in the whole L-band. At bias voltage above 11 V, it increases
with bias voltage owing to the avalanche effect. In order to exclude the inﬂuence of avalanche
effect, the responsivity was normalized by the avalanche multiplication factor (Mav) as shownin Fig. 2. In the band from 1550 to 1640 nm, the responsivity increases for all bias voltages.
This behavior agrees well with the calculation result of FK effect described as solid line in
Fig. 2. Thus, we conclude that the high responsivity in the L-band of GePD is derived fromthe FK and the avalanche effect. Figure 3 (a) shows the minimum detection limit of GePD ata wavelength of 1640 nm. The minimum detection limits decrease because of the responsivity
increase due to the FK effect as the bias voltage increases. However, they increase rapidly
at bias voltage of over 11 V. This is because huge noise from dark current due to avalanche
multiplication. Figure 3 (b) shows the minimum detection limit when the dark current issuppressed to 1/50 of the experimental values in this work. The avalanche effect is effective inthis case. Thus, Optimized reduction of dark current and control of the bias ﬁeld applied to Ge
are necessary to obtain effective multiplication due to both effects.
To the best of our knowledge, this study is the ﬁrst observation of responsivity increase in
GePD for the L-band. And it opens up a possibility of GePD as L-band detector.
[1] C. T. DeRose, et al., Opt. Express 19 (2011) 24897.
[2] T. Y. Liow, et al., in Proc. OFC, no OM3K. 2 (2013).

Fig. 1. The responsivity of the GePD
for various bias voltages.

Fig. 2. Normalized responsivity of the
GePD for various bias voltages.

Fig. 3. The minimum detection
limit of GePD at awavelength of 1640 nm.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)49

Ⅱ．Data

6th NTT-BRL School
The sixth NTT Basic Research Laboratories (BRL) School was held on November 24-26,
2013 at our NTT Atsugi R&D Center. The aim of the school was to foster young researchers in
the nano and quantum science ﬁelds and to promote the international visibility of NTT BRL.
This year the theme of the school was "Nano and Quantum Science: Driving Tomorrow’s
Technology", closely related to ongoing research within NTT BRL. Prestigious professors andresearchers were invited as the school lecturers. We accepted thirty-ﬁve students, mainly Ph.
D students, from fourteen countries.
On the first day, Prof. John Clarke (University of California, Berkeley, U.S.A.) presented
lectures entitled "Theory, practice and applications of Superconducting Quantum Interference
Devices (SQUIDs)". He also gave lectures on the second day that covered applications
ranging from cosmology to medicine using SQUID femtoscience. On the afternoon of theﬁrst day, after the director of NTT BRL, Dr. Tetsuomi Sogawa, provided an introduction of
NTT Laboratories, while the three senior distinguished researchers of NTT BRL gave lectures
on "Micro/nanomechanical systems using compound semiconductor heterostructures" by
Dr. Hiroshi Yamaguchi, "Topologically protected quantum effects in solid state" by Dr. Koji
Muraki, and "Nanophotonics toward the smallest energy consumption" by Dr. Masaya Notomi.
On the second and third day, Prof. Oliver Schmidt (Institute Director, IFW Dresden, Germany)gave two lectures entitled "Quantum dots: From growth to quantum device" and "Shaping
nanomembranes into a new nanoworld". After the lecture of the second day, we conducted alab tour to show our research facilities and introduce recent research activities at NTT BRL.
Then we went on an excursion to Mt. Ohyama belonging to Tanzawa mountain range which is
close to the NTT Atsugi R&D Center. The participants enjoyed foliage that was lighting up andtofu dishes at a Japanese traditional restaurant. On the third day, Prof. Jonathan Finley (Walter
Schottky Institute, Germany) gave a lecture on "Optically probing charge and spin dynamics
in single and coupled quantum dots". After the lecture, all participants attended ISNTT (aninternational conference on nanoscale transport and technology) hosted by NTT BRL. As partof this, the students gave poster presentations regarding their university research. All students,
lecturers, and NTT BRL researchers had excellent time exchanging information on current
research topics in various fields. In the joint party of BRL School and ISNTT, "Best Poster
Prizes" were awarded to three students who gave noteworthy poster presentations. The students
got the opportunity to discuss high-quality research and build human network and friendships
within this school. NTT BRL will continue to provide these occasions to support young
researchers and to establish research collaborations in the ﬁelds of nano and quantum science.

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)51

International Symposium on
Nanoscale Transport and Technology (ISNTT2013)
International Symposium on Nanoscale Transport and Technology (ISNTT2013) was heldat the NTT Atsugi R&D Center from November 26 to 29, 2013, and brought together 208
participants from 16 countries. The participants enjoyed oral and poster presentations at the
symposium, exchanging their views and ideas on nanotechnology and quantum devices.
Since 1998, NTT Basic Research Laboratories (BRL) has been holding a lot of international
conferences on various topics and technologies. ISNTT was ﬁrst organized in 2009 to promotemutual exchange between different device and material technologies on semiconductors,
superconductors, and new materials, and since then it has been held about every two years.
ISNTT2013 of which the logo represents hybrid system was co-chaired by Drs. Akira
Fujiwara, Hiroshi Yamaguchi, and Koji Muraki of NTT BRL, and it was aimed at further
enhancing interaction among different research ﬁelds to develop new idea and technology.
On the 26th, 27th, and 29th, respectively, the session started with keynote lectures entitled"The UC Santa Barbara quantum computing effort" by Prof. Andrew Cleland (University ofCalifornia), "Quantum anomalous Hall effect in magnetic topological insulators" by Prof. QiKun Xue (Tsinghua University), and Flying qubits and quantum electron optics with surface
acoustic wave by Prof. Seigo Tarucha (The University of Tokyo). Throughout the symposium
we had 13 oral sessions with 48 oral presentations including 17 invited talks by world
leading researchers, on nanodevices, topological insulators, nanomechanics, quantum bits
and computers, single-electron devices, graphene, quantum spin Hall effect, optical devices,and so on. In addition there were 71 presentations at the poster session on the 26th and 27th.
Since a part of the poster sessions was held jointly with the 6th
NTT-BRL school, many young researchers and students had
enthusiastic discussions in front of the posters. The symposium
was stimulating and successful, strengthening worldwide
network among researchers based on the open-laboratory policyof NTT BRL.

52

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

List of BRL Seminars (Fiscal 2013)
Date

SpeakerAfﬁliation
Title

May-10Dr. Rin Okuyama

Keio University, Japan
Lasing of optical phonons in semiconductor double quantum
dots

May-21

Prof. Andrea Fiore

Eindhoven University of Technology, the Netherlands
Towards fully integrated quantum photonic circuits

May-24

Mr. Kiyoshi Kanazawa

Kyoto University, Japan
Energy transport driven by a thermal non-Gaussian
ﬂuctuations

Jun-12

Prof. Mark Sanquer

CEA-INAC-SPSMS, France
The coupled atom transistor: a ﬁrst realization with shallow
donors implanted in a trigate silicon nanowire

Prof. Nobuhisa Ishii

The University of Tokyo, Japan
Generation of few-cycle, intense IR pulses from a
BIBO-based optical parametric chirped pulse ampliﬁer andtheir use in the generation of waveform-dependent highharmonics in the water window

Dr. Alex S. Clark

University of Sydney, Australia
Nonlinear quantum photonics: generating and manipulating
single photons

Jul-10Prof. Marko Loncar

Harvard University, U.S.A.
Group IV Photonics: From Silicon to Diamond "Sioptomechanics and Diamond nanophotonics"

Jul-11

Mr. Takuro Ideguchi
Mr. Simon Holzner

Max-Planck-Institute of Quantum Optics, Germany
Adaptive dual-comb spectroscopy

Sep-3

Dr. Michael Jack

Scion, New Zealand
From cold atoms to warm molecules

Sep-6

Akira Saito Ph. D.

National Institute of Informatics (NII), Japan
Impracticality of coherent computing and annealing machinemodelsSep-11

Prof. Igor Aharonovich

University of Technology, Sydney (UTS), Australia
Wide bandgap semiconductors for Nanophotonics

Sep-11

Prof. Benoit Hackens
Dr. Sébastien Faniel
Dr. Frederico Martins

Université catholique de Louvain, Belgium
Imaging and manipulating quantum transport at the nanometer
scale

Jun-19

Jul-5

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

53

Date

SpeakerAfﬁliation
Title

Sep-13

Dr. Hari Dahal

American Physical Society, U.S.A.
APS publications and peer-review in PRB

Sep-26

Dr. Shota Kita

Harvard University, U.S.A.
Optomechanical Nanobeam Transducers towards Ultrahigh
Resolution Mass SpectrometryOct-24

Prof. Hiroyuki Hirayama

Tokyo Institute of Technology, Japan
Silicene formed by epitaxial growthOct-31

Prof. Gerard J. Milburn

The University of Queensland, Australia
Single photon opto-mechanics

Nov-5

Prof. Peide Ye

Purdue University, U.S.A.
2D Materials and Devices beyond Graphene

Prof. Andrew WhiteThe University of Queensland, Australia
Intriguing chemists and upsetting computer scientists using
light and mirrors

Dr. Kenji Yoshii

Japan Atomic Energy Agency (JAEA) / Okayama University,
Japan
Novel multiferroic materials RFe2O4 (R: rare-earth element)–Their discovery and subsequent development

Dr. Nicolas ClémentCNRS, France
Emergence of 0D Ion-Sensitive Field Effect Transistors-A new tool for energy harvesting and electrical study ofsingle biomolecules ?-Nov-13

Prof. Pawel Hawrylak

National Research Council of Canada, Canada
Electron-electron interactions, topology and transport andoptical spin blockade in semiconductor and graphene quantumdots

Nov-21

Dr. Neill Lambert

RIKEN, Japan
Non-equilibrium QED: from nano-mechanics to hybrid
devices

Dec-5

Dr. Yasuhiro Yamada

The University of Tokyo, Japan
Resolution Effects on Current Measurement in Nanoscale
Systems

Dec-10Dr. Ed Gerstner

Executive editor of Nature Communications, U.K.
Nature open access journals seminar

Nov-5

Nov-7

Nov-1154

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

Date

SpeakerAfﬁliation
Title

Dec-16

Dr. Kazuyuki Nakayama

Fukuoka University, Japan
Manipulation of Spontaneous Emission with Quasi-periodic
Metamaterials

Dec-19Dr. Gregor Koblmüller

Technical University Munich, Germany
Progress in arsenide-based nanowires and their devices

Jan-16

Dr. Daryl Beggs

The University of Bristol, U.K.
Optical delay in silicon photonic crystal waveguides:
accelerating slow-lightJan-23

Prof. Jing Kong

Massachusetts Institute of Technology, U.S.A.
Synthesis and applications of graphene and related
nanomaterials

Feb-5

Prof. Michael Trupke

The Vienna University of Technology, Austria
Diamond defects for sensing and quantum applications

Feb-21

Dr. Kei Sawada

RIKEN, Japan
Berry-phase theory with analogy among optics, dynamics,
and electric circuits

Mar-3

Prof. Isabelle Zaquine

Telecom Paris Tech, France
Multi-user entanglement distribution at telecom wavelengthMar-10Dr. Michael R. Vanner

The University of Queensland, Australia
Experimental non-linear optomechanical measurement of
mechanical motion

Mar-12

Dr. Erwann Bocquillon

Ecole Normale Supérieure, FranceElectron quantum optics in quantum Hall edge channels

Mar-26

Dr. Mandar Deshmukh

Tata Institute of Fundamental Research, India
Probing phase transitions in nanoscale correlated systems
showing MIT and CDW physics using nanomechanics

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

55

Award Winners’ List (Fiscal 2013)
The Commendation for
Science and Technology by
the Minister of Education,
Culture, Sports, Scienceand Technology, Research
Category Prize

H. Yamaguchi

Optoelectromechanical hybrid
devices using compound
semiconductor heterostructures

Apr. 16,
2013

The Commendation for
Science and Technology by
the Minister of Education,
Culture, Sports, Scienceand Technology, The Young
Scientists’ Prize

K. Nishiguchi

Nanometer-scale semiconductor
devices with high functionality

Apr. 16,2013

JSAP Fellow

H. Yamaguchi

Pioneering Contributions to
the Application of Compound
Semiconductor Heterostructures to
Mechanical Devices

Sep. 16,2013

JSAP Outstanding Paper
Award

K. Nishiguchi
A. Fujiwara

Single-Electron Stochastic
Resonance Using Si Nanowire
Transistors

Sep. 16,2013

M. Yamaguchi

A case study of the communication
between families living at remotelocation
Report of the communication styleusing "Denwa-channel" for ﬁve years

Dec. 19,2013

6th International Symposium
on Advanced Plasma Scienceand its Applications for
Nitrides and Nanomaterials,
Best Presentation Award

C.-H. LinN-face GaN (000-1) ﬁlms grwon
by group-III source ﬂow-rate
modulation epitaxy

Mar. 6,2014

JSAP Young Scientist Oral
Presentation Award

S. Tanabe

Damage-free transfer of graphenegrown on SiC

Mar. 17,2014

JSAP Poster Awards

T. GotoA. Ishizawa
H. NishiN. Matsuda
R. KouK. Hitachi
T. Nishikawa
K. YamadaT. Sogawa
H. Gotoh

On-chip supercontinuum generationfrom a dispersion-controlled silicon
waveguide

Mar. 18,
2014

Human communication
award

56

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

In-house Award Winners’ List (Fiscal 2013)
NTT Science and CoreTechnology Laboratory
Group Director Award

H. Sanada
Y. Kunihashi
K. Onomitsu
H. Gotoh

Magnetic-ﬁeld-free mobile
spin resonance in high-purity
semiconductor heterostructures

Dec. 20,
2013

BRL Director Award
Award for Achievements

K. Nishiguchi
A. Fujiwara

New applications using silicon
nanometer-scale devices at room
temperature

Mar. 27,
2014

BRL Director Award
Award for Achievements

A. Yokoo
D. Birowosuto
G. Zhang
K. Tateno
E. Kuramochi
M. Takiguchi
M. Notomi

Inventive approach for integration of
nanowire into nanophotonics by using
nanomanipulation

Mar. 27,
2014

BRL Director Award
Award for Excellent Papers

Y. Krockenberger
H. IrieO. Matsumoto
K. Yamagami
M. Mitsuhashi
A. Tsukada
M. Naito
H. Yamamoto"Emerging superconductivity hidden
beneath charge-transfer insulators"
Scientiﬁc Reports 3, 2235 (2013)

Mar. 27,
2014

BRL Director Award
Award for Excellent Papers

I. Mahboob
K. Nishiguchi
A. Fujiwara
H. Yamaguchi"Phonon Lasing in an Electromechanical Resonator"
Physical Review Letters 110, 127202(2013)

Mar. 27,
2014

BRL Director Award
Award for Excellent Papers

K. Sasaki
Y. Sekine
K. Tateno
H. Gotoh"Topological Raman Band in the
Carbon Nanohorn"
Physical Review Letters 111, 116801(2013)

Mar. 27,
2014

BRL Director Award
Award for Performance

K. Onomitsu
T. Hayashi
K. Suzuki

Contribution for signiﬁcantenhancement in durability, safety,
and cost reduction of liquid nitrogen
supply system

Mar. 27,
2014

BRL Director Award
Award for Encouragement

D. Hatanaka

Novel structural mechanicalsystems using semiconductor based
mechanical resonators

Mar. 27,
2014

BRL Director Award
Award for Encouragement

K. Hitachi

Nonlinear optics for frequency
stabilized optical frequency comb

Mar. 27,
2014

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)57

Numbers of Papers, Presentations and Patents (2013)
The numbers of papers published in international journals, presentations at international
conferences and applied patents in year 2013 amounted to 115, 282, and 70, respectively. The
numbers for each research area are as follows;
Papers Published in International Journals(Jan. – Dec. 2013)
Materials Science36

Physical Science

36

Optical Science33

Nanophotonics Center

10
0

10

20

30

40

50

60

Number of Papers

Presentations at International Conferences(Jan. – Dec. 2013)
Materials Science

65

Physical Science

113

Optical Science64

Nanophotonics Center

40
0

20

40

60

80

100

120

Number of Presentations

Applied Patents (Jan. – Dec. 2013)
Materials Science23

Physical Science

16

Optical Science

14

Nanophotonics Center

17
0

5

10

15

20

Number of Applied Patents

58

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

25

30

The numbers of research papers published in the major journals are shown below.
(IF2012)*

Numbers

Applied Physics Letters

3.794

16

Physical Review B

3.767

16

Japanese Journal of Applied Physics

1.067

8

Optics Express

3.546

7

Applied Physics Express

2.731

6

Nature Communiation

10.015

5

Journal of Crystal Growth

1.552

5

Physical Review A

3.042

4

Physical Review Letters

7.943

3

New Journal of Physics

4.063

3

AIP Advances

1.349

3

Nature Physics

19.352

2

Scientiﬁc Reports

2.927

2

Journal of Applied Physics

2.21

2

Nature Nanotechnology

31.17

1

Nature Photonics

27.254

1

Reports on Progress in Physics

13.232

1

Nano Letters13.025

1

ACS Nano

12.062

1

Nano Research

7.392

1

Chemical Communications

6.378

1

Journal of Physical Chemistry C

4.814

1

Journal of Biological Chemistry

4.651

1

Optics Letters

3.385

1

Ultramicroscopy

2.47

1

Journals*IF2012:Impact Factor 2012

The average IF2012 for all research papers from NTT Basic Research laboratories is 4.40.

The numbers of presentations in the major conferences are shown below.
Conferences

Numbers

International Symposium on Nanoscale Transport and Technology 2013（ISNTT2013）31

40th International Symposium on Compound Semiconductors & 25th International Conferenceon Indium Phosphide and Related Materials (ISCS & IPRM 2013)18

20th International Conference on Electronic Properties of TWO-Dimensional Systems(EP2DS-20)

17

The 10th Conference on Lasers and Electro-Optics Paciﬁc Rim, and The 18th OptoElectronics
and Communications Conference / Photonics in Switching 2013 (CLEO-PR & OECC/PS 2013)15

The Conference on Lasers and Electro-Optics (CLEO/QELS 2013)13

JSAP-MRS Joint Symposia 201310

APS March Meeting 20138

Recent Progress in Graphene Research 20138

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

59

List of Invited Talks at International Conferences (2013)
I. Materials Science Laboratory

60

(1)

H. Yamamoto, Y. Krockenberger, and M. Naito, "Development of New Superconductors Tailored by
MBE", Electronic Materials and Applications 2013 (EMA2013), Orlando, U.S.A. (Jan. 2013).

(2)

Y. Taniyasu, J. -F. Carlin, A. Castiglia, R. Butté, and N. Grandjean, "Lattice-Matched AlInN/GaN
Heterostructures: n- and p-type Doping and UV-LEDs", SPIE Photonics West 2013, San Francisco, U.S.A.
(Feb. 2013).

(3)

Y. Taniyasu "AlN-Based UV/Visible Light-Emitting Devices", 5th GCOE International Symposium on
Photonics and Electronics Science and Engineering, Kyoto, Japan (Mar. 2013).

(4)

Y. Krockenberger, H. Irie, B. Eleazer, and H. Yamamoto, "Superconductivity Research Advanced by New
Materials and Spectroscopies", ICC-IMR International Workshop Superconductivity Research Advanced by
New Materials and Spectroscopies, Sendai, Japan (July 2013).

(5)

Y. Krockenberger, H. Irie, B. Eleazer, and H. Yamamoto "Competing Electronic Interactions Driven by
Oxygen Coordination in Two-Dimensional Cuprates", International Symposium on Science Explored by
Ultra Slow Muon 2013 (USM2013), Shimane, Japan (Aug. 2013).

(6)

F. Maeda, "Graphene Growth on Graphene by Molecular Beam Epitaxy", Crystal & Graphene Science
Symposium-2013 on 'Crystal Engineering to Graphenes, Fullerenes, Carbon Nanotubes & Semiconductors',
Boston, U.S.A. (Sep. 2013).

(7)

H. Hibino, S. Tanabe, M. Takamura, and Y. Murata "Electronic Transport Properties and Nanostructure
Self-Organization of Quasi-Freestanding Graphene on SiC", 5th International Conference on Recent
Progress in Graphene Research (RPGR 2013), Tokyo, Japan (Sep. 2013).

(8)

H. Omi "Real Time Grazing Incidence X-ray Diffraction from Erbium Doped Material Growing on Si
Substrate", JSAP-MRS Joint Symposia 2013, Kyoto, Japan (Sep. 2013).

(9)

F. Maeda and H. Hibino "Growth of Graphene by Molecular Beam Epitaxy Using Cracked Ethanol andEthylene", Topical Workshop on MBE-grown graphene, Berlin, Germany (Sep. 2013).

(10)

H. Hibino, C. M. Orofeo, and S. Suzuki "Fabrication and Characterization of BN/Graphene
Heterostructures", 9th International Symposium on Atomic Level Characterizations for New Materials andDevices '13 (ALC'13), Hawaii, U.S.A. (Dec. 2013).

(11)

K. Sumitomo, N. Kasai, A. Tanaka, Y. Kashimura, T. Goto, A. Oshima, and S. Tsukada, "Nanobiodevice
that Consists of Membrane Proteins and an Artificial Lipid Bilayer", 2013 EMN Fall Meeting, Orlando,
U.S.A. (Dec. 2013).

(12)

K. Kumakura, Y. Kobayashi, M. Hiroki, T. Makimoto, T. Akasaka, and H. Yamamoto "MechanicallyTransferred GaN-Based Optical and Electronic Devices", The International Semiconductor Device
Research Symposium (ISDRS2013), Maryland, U.S.A. (Dec. 2013).

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

II. Physical Science Laboratory(1)

H. Yamaguchi, H. Okamoto, and I. Mahboob, "Strong Coupling and Time-Domain Control inElectromechanical Parametric Resonators", Tohoku-Harvard Joint Workshop New Directions in Materials
for Nanoelectronics, Spintronics and Photonics (10th RIEC International Workshop on Spintronics), Sendai,
Japan (Jan. 2013).

(2)

I. Mahboob, "Phonon-Cavity Electromechanics in the Strong Coupling Regime", Interdisciplinary
Workshop on Quantum Device, Tokyo Japan (Jan. 2013).

(3)

H. Yamaguchi, I. Mahboob, and H. Okamoto, "Strong Modal-Coupling and Parametric Control inElectromechanical Resonators", The 8th ASRC international workshop on "Spin Mechanics", Tokai, Japan(Feb. 2013).

(4)

N. Kumada, S. Tanabe, H. Hibino, H. Kamata, M. Hashisaka, K. Muraki, and T. Fujisawa, "Transport ofEdge Magnetoplasmons in Graphene", Korea-Japan joint workshop, Daejeon, Republic of Korea (Apr.
2013).

(5)

S. Saito, X. Zhu, R. Amsuss, Y. Matsuzaki, K. Kakuyanagi, T. Shimooka, N. Mizuochi, K. Nemoto, W. J.
Munro, and K. Semba, "Superconducting Qubit Spin Ensemble Hybrid System", Asia Paciﬁc workshop on
Quantum Information Science (APWQIS 2013), Tokyo, Japan (May 2013).

(6)

K. Muraki, "NMR Spectroscopy of FQH Liquid and Solid Phases in the First", Symposium on Quantum
Hall Effects and Related Topics, Stuttgart, Germany (June 2013).

(7)

K. Muraki, "NMR Probing of Fractional Quantum Hall Liquid and Wigner Solid Phases", 20th
International Conference on Electronic Properties of TWO-Dimensional Systems (EP2DS-20), Wroclaw,
Poland (July 2013).

(8)

I. Mahboob, "An Electromechanical Phonon Laser", The 18th International Conference on Electron.
Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON18), Matsue, Japan (July 2013).

(9)

I. Mahboob, "Phonon-Lasing in an Electromechanical 3-Mode System", Tsukuba Nanotechnology
Symposium 2013 (TNS'13), Tsukuba, Japan (July 2013).

(10)

K. Kanisawa, "Electronic Processes in Adatom Dynamics at Epitaxial Semiconductor Surfaces Studied
Using MBE-STM Combined System", 17th International Conference on Crystal Growth and Epitaxy（ICCGE-17), Warsaw, Poland (Aug. 2013).

(11)

H. Yamaguchi, I. Mahboob, and H. Okamoto, "Nonlinear Phonon Dynamics in GaAs/AlGaAs
Electromechanical Resonators", 10th Topical Workshop on Heterostructure Microelectronics (TWHM
2013), Hakodate, Japan (Sep. 2013).

(12)

H. Yamaguchi, I. Mahboob, and H. Okamoto, "Coherent Manipulation and Phonon Lasing inElectromechanical Resonators", International Centre for Theoretical Physics Workshop "Frontiers ofNanomechanics", Trieste, Italy (Sep. 2013).

(13)

A. Fujiwara, "Silicon-Based Nanodevices for Diverse Applications", 39th International Conference on
Micro and Nano Engineering (MNE 2013), London, United Kingdom (Sep. 2013).

(14)

H. Yamaguchi, H. Okamoto, T. Watanabe, and Y. Okazaki, "Mechanical Systems Coupled to
Semiconductor Quantum Structures", CeNS Workshop 2013, Nanosciences: Great Adventures on Small
Scales, Venice, Italy (Sep. 2013).

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

61

(15)

S. Saito, X. Zhu, R. Amsuss, Y. Matsuzaki, K. Kakuyanagi, T. Shimooka, N. Mizuochi, K. Nemoto,
W. J. Munro, and K. Semba, "Quantum Hybrid System of Superconducting Flux Qubit and Diamond Spin
Ensemble", JSAP-MRS Joint Symposia 2013, Kyoto, Japan (Sep. 2013).

(16)

K. Muraki, "Resistively Detected NMR Study of Correlated Electrons in a GaAs Quantum Well:
Fractional Quantum Hall States and More", 2013 International Conference on Solid State Devices andMaterials (SSDM2013), Fukuoka, Japan (Sep. 2013).

(17)

Y. Takahashi, H. Takenaka, T. Uchida, M. Arita, A. Fujiwara, and H. Inokawa, "High-Speed Operation of
Si Single-Electron Transistor", The Electrochemical Society Meeting (224th ECS Meeting), San Francisco,
U.S.A. (Oct. 2013).

(18)

T. Fujisawa, H. Kamata, M. Hashisaka, N. kumada, K. Muraki, and H. Hibino, "Plasmon Wavepacket
in Edge Channels of GaAs and Graphene", Quantum Science Symposium Asia-2013, Tokyo, Japan (Nov.
2013).

(19)

H. Yamaguchi, I. Mahboob, H. Okamoto, and Y. Okazaki, "Coherent Manipulation and Lasing
Operation in Micromechanical Phonon Cavities", International Symposium on Advanced Nanodevices andNanotechnology (ISANN2013), Hawaii, U.S.A. (Dec. 2013).

III. Optical Science Laboratory

62

(1)

W. J. Munro, X. Zhu, R. Amsüss, Y. Matsuzaki, K. Kakuyanagi, T. Shimooka, N. Mizuochi, K. Semba,
S. J. Devitt, K. Nemoto, and S. Saito, "Quantum Computation, Communication and Interfaces Using NV
Centers: Hybridisation of Superconducting Flux Qubits with Diamond Ensembles", Workshop on Diamond- Spintoronics, Photonics, Bio-applications, Hong Kong, People's Republic of China (Apr. 2013).

(2)

N. Matsuda, "Ultra-Narrowband Nonlinear Wavelength Conversion Using Coupled Photonic Crystal
Nanocavities", Conference on Lasers and Electro-Optics - International Quantum Electronics Conference(CLEO / EUROPE - IQEC 2013), Munich, Germany (May 2013).

(3)

N. Matsuda, "Monolithic Source of Telecom-Band Polarization Entanglement on a Silicon Photonic
Chip", The 10th Conference on Lasers and Electro-Optics Paciﬁc Rim, and The 18th OptoElectronics andCommunications Conference / Photonics in Switching 2013 (CLEO-PR & OECC/PS 2013), Kyoto, Japan(June 2013).

(4)

T. Sogawa, and H. Sanada, "Spin Transport and Manipulation by Surface Acoustic Waves", 12th
conference of Asia-Paciﬁc Physics Conference (APPC12), Makuhari, Japan (July 2013).

(5)

M. Yamashita, K. Inaba, and H. Tsuchiura, "Collapse and Revival Dynamics of Spin-1 Bosons in Optical
Lattices", 22nd International Laser Physics Workshop (LPHYS '13), Prague, Czech Republic (July 2013).

(6)

W. J. Munro, X. Zhu, R. Amsüss, Y. Matsuzaki, K. Kakuyanagi, T. Shimooka, N. Mizuochi, K. Semba,
K. Nemoto, and S. Saito, "Hybrid Quantum Systems: A Route Forward for Distributed Information
Processing", 5th biennial Conference on Quantum Information and Quantum Control (CQIQC-V), Toronto,
Canada (Aug. 2013).

(7)

W. J. Munro, X. Zhu, Y. Matsuzaki, A. M. Stephens, K. Nemoto, and S. Saito, "Hybridization ofSuperconducting Flux Qubits and Diamond Ensembles: A Route to Local Gates for Quantum Repeaters",
SPIE Optics + Photonics 2013, San Diego, U.S.A. (Aug. 2013).

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

(8)H. Shibata, "MBE Growth of MgB2 for Superconducting Single-Photon Detector", 2013 Energy Material& Nanotechnology Meeting (2013 EMN FALL), Beijing, People's Republic of China (Sep. 2013).

(9)

K. Azuma, "What is Really Required in Quantum Repeaters?", Quantum Science Symposium Asia-2013,
Tokyo, Japan (Nov. 2013).

(10)

H. Shibata, "Quantum Key Distribution over 70dB Channel Loss Using SSPD with Ultralow Dark Count
Rate", Quantum Science Symposium Asia-2013, Tokyo, Japan (Nov. 2013).

(11)

H. Sanada, Y. Kunihashi, H. Gotoh, K. Onomitsu, M. Kohda, J. Nitta, P. V. Santos, and T. Sogawa,"Manipulation of Electron Spin Coherence Using Acoustically Induced Moving Dots in Semiconductors",
International Symposium on Advanced Nanodevices and Nanotechnology (ISANN2013), Hawaii, U.S.A.
(Dec. 2013).

(12)

K. Tamaki, "Research Activities in Tokyo QKD Network ~From Field Test to Security Proof~" Quantum
Information Technologies Madrid Consortium, Madrid, Spain (Dec. 2013).

IV. Nanophotonics Center(1)

H. Fukuda, T. Tsuchizawa, H. Nishi, R. Kou, T. Hiraki, K. Takeda, K. Wada, Y. Ishikawa, and K.
Yamada, "Silicon, Silica, and Germanium Photonic Integration for Electronic and Photonic Convergence",
SPIE Photonics West 2013, San Francisco, U.S.A. (Feb. 2013).

(2)

S. Matsuo, "Monolithically Integrated Optical Link Using Photonic Crystal Laser and Photodetector",
25th International Conference on Indium Phosphide and Related Materials (IPRM 2013), Kobe, Japan(May 2013).

(3)

M. Notomi, "Towards Femtojoule-per-bit Optical Communication in a Chip", 15th International
Conference on Transparent Optical Networks (ICTON 2013), Cartagena, Spain (June 2013).

(4)

K. Yamada, "Silicon Photonics for Optical Interconnects and Telecom Applications", 2013 Vail Computer
Elements Workshop, Denver, U.S.A. (June 2013).

(5)

K. Yamada, T. Tsuchizawa, H. Nishi, R. Takahashi, T. Hiraki, K. Takeda, H. Fukuda, Y. Ishikawa,
K. Wada, and T. Yamamoto, "High-Performance Photonic Integrated Circuits Based on Si-Ge-silica
Monolithic Photonic Platform", The 10th Conference on Lasers and Electro-Optics Paciﬁc Rim, and The
18th OptoElectronics and Communications Conference / Photonics in Switching 2013 (CLEO-PR & OECC/
PS 2013), Kyoto, Japan (June 2013).

(6)

T. Sato, K. Takeda, A. Shinya, K. Nozaki, H. Taniyama, K. Hasebe, T. Kakitsuka, M. Notomi, and S.
Matsuo, "Ultralow-Threshold Electrically Driven Photonic-Crystal Nanocavity Laser", The 10th Conferenceon Lasers and Electro-Optics Paciﬁc Rim, and The 18th OptoElectronics and Communications Conference /Photonics in Switching 2013 (CLEO-PR & OECC/PS 2013), Kyoto, Japan (June 2013).

(7)

T. Sato, K. Takeda, A. Shinya, K. Nozaki, H. Taniyama, K. Hasebe, T. Kakitsuka, M. Notomi, and S.
Matsuo, "Electrically Driven Photonic-Crystal Lasers Using an Ultra-Compact Embedded Active Region",
IEEE Photonics Society Summer Topical Meeting Series 2013, Hawaii, U.S.A. (July 2013).

(8)

T. Kakitsuka, "Current-Injection Photonic-Crystal Lasers with Ultra-Low Power Consumption", 12th
Chitose International Forum on Photonics Science and Technology (CIF12), Chitose, Japan (July 2013).

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)

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(9)

M. Notomi, "Enhanced Light-Matter Interactions in Photonic Crystal Nanocavities for Ultralow-Power
Photonics", SPIE Optics + Photonics 2013, San Diego, U.S.A. (Aug. 2013).

(10)

H. Fukuda, K. Takeda, T. Hiraki, T. Tsuchizawa, H. Nishi, R. Kou, Y. Ishikawa, K. Wada, T. Yamamoto,and K. Yamada, "Large-Scale Silicon Photonics Integrated Circuits for Interconnect and Telecom
Applications", The 10th International Conference on Group IV Photonics (GFP 2013), Seoul, Republic ofKorea (Aug. 2013).

(11)

M. D. Birowosuto, H. Sumikura, A. Yokoo, M. Takiguchi, and M. Notomi, "Light-Matter Interaction of
Quantum Dots and Nanowires in Novel High-Q Photonic Crystal Cavities at Telecom Wavelength", 34th
Progress in Electromagnetics Research Symposium (PIERS 2013), Stockholm, Sweden (Aug. 2013).

(12)

H. Sumikura, M. D. Birowosuto, and M. Notomi, "Quantum Optical Devices Based on Photonic Crystal
Nanocavities", 34th Progress in Electromagnetics Research Symposium (PIERS 2013), Stockholm, Sweden(Aug. 2013).

(13)

T. Sato, K. Takeda, A. Shinya, K. Nozaki, H. Taniyama, K. Hasebe, T. Kakitsuka, M. Notomi, and
S. Matsuo, "High Temperature Operation of Lambda-Scale Embedded Active-Region Photonic-Crystal
Lasers", IEEE Photonics Conference 2013 (IPC 2013), Washington, U.S.A. (Sep. 2013).

(14)

S. Matsuo, T. Sato, and K. Takeda, "Photonic Crystal Laser for Optical Interconnects", Frontiers in
Optics/Optical Society of America 2013 (FiO/OSA 2013), Orland, U.S.A. (Oct. 2013).

(15)

M. Notomi, "Toward fJ/bit Optical Communication in a Photonic Crystal Chip", Frontiers in Optics/Laser
Science (FiO/LS 2013), Florida, U.S.A. (Oct. 2013).

(16)

K. Yamada, "Si-Ge-Silica Monolithic Photonics Integration Platform for Telecommunications
Applications", Silicon Photonics Forum, Kaohsiung, Taiwan (Nov. 2013).

(17)

M. Notomi, "Enhanced Spontaneous Emission from Nanocavities, Nanowires, and Nano-Emitters", SPIE
Micro+Nano Materials, Devices, and Applications 2013, Melbourne, Australia (Dec. 2013).

Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)