Schematic illustration of the vertical-typetransferred LED.

Photograph of the transferred AlGaN/GaN
structure on the foreign sapphire substrate.

Cover photograph:

Optical Image of the Blue-Light Electroluminescence from theTransferred Vertical-Type Light-Emitting DiodeWe demonstrate that hexagonal boron nitride can form a release layer that enables the mechanical transfer
of gallium nitride-based devices structures onto foreign substrates. For the vertical-type transferred lightemitting diode (LED), after the LED structure had been released, the electrodes were deposited on the backside of the LED. Then, we mounted it onto the indium sheet. An AlGaN/GaN heterostructure, an InGaN/
GaN multiple-quantum-well (MQW) structure, and the MQW LED, in area from five millimeters squareto two centimeters square, are then mechanically released from the sapphire substrates and successfullytransferred onto other substrates. (Page 14)

PEDOT-PSS silk (left) andnaive silk (right) thread

Macroscopic image

Skin surface electrodes

Conductive Polymer Combined with Silk Fibers
for Biomedical Electrodes
We developed and characterized bio-interface material with a conductive polymer combined silk fibers
for biomedical signal recordings, such as electroencephalography. Biocompatible, soft and hydrophilic
electrode offers long-term stable communication to living tissues for biomedical and information andcommunication technology without stress to the subjects. (Page 23)

Cleavage in ultra- high vacuum

Manipulation with scanningtunneling microscope“N”made by 11 In atoms

In Atom Manipulation on Cleaved InAs(110) Surface
We have succeeded in manipulating In atoms vertically and horizontally on an InAs(110) surface
obtained by cleaving in ultra-high vacuum using scanning tunneling microscope (STM). Atomic-scale
devices made by this atom manipulation technique are expected in future. (Page 30)－Ⅰ－(a) Superconductor-diamond hybrid system. (b) Microwave spectrum of a superconducting flux quibt.
(c) Vacuum Rabi oscillation between a flux qubit and a spin ensemble.

Coherent Coupling of a Gap-Tunable flux Qubit to an Electron Spin
Ensemble in Diamond
A superconductor-diamond hybrid system has attracted considerable interest as the electron spin
trapped at a nitrogen-vacancy (NV) center in diamond has the potential to be a quantum memory fora superconducting qubit. In this research we have achieved strong coupling between a gap-tunable
flux qubit and an NV spin ensemble. Furthermore we also observed the coherent exchange of a single
quantum of energy between them. This is the first step towards the realization of a long-lived quantum
memory and hybrid devices coupling microwave and optical systems. (Page 33)(a) Ultracold atoms in a vacuum chamber. (b) Schematic diagram of Bose-Fermi mixtures in an optical latticethat is a periodic potential created by the laser interference. (c) Pair occupancies obtained by both experiments
and numerical calculations considering ambiguity of experimental parameters.

Exploring Novel Quantum Phases of Bose-Fermi Mixtures
Trapped in an Optical Lattice
Collaborating with the group at Kyoto University, we investigated the Bose-Fermi mixtures trapped in
an optical lattice, and observed novel quantum phases induced by the interaction between bosons andfermions. We developed a numerical method for efficiently analyzing this system, and quantitatively
reproduced the experimental observations done by the Kyoto University group. We further analyzed
quantities that are difficult to be measured by the current experimental techniques. Based on theseresults, we determined what kind of quantum phases appear in this system, and finally clarified theappearance of the novel quantum phases. (Page 35)－Ⅱ－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's missions are to promote progress in scienceand innovations in leading-edge technology toadvance NTT's business. To achieve these missions,researchers in fields including physics, chemistry,
biology, mathematics, electronics, informatics, andmedicine, conduct basic research on materials science,physical science and optical science.
Our management principle is based on an "opendoor" policy. For example, we are collaboratingwith many universities and research institutes
in Japan, US, Europe, and Asia as well as otherNTT laboratories. We co-organize international
conferences relating to quantum information andatom manipulation with other research institutions
to disseminate our research output and to give NTT researchers including the younger ones theopportunity to share ideas with the foremost authorities and to learn from them.
These activities enable us to realize our "open door" policy and our missions with respect tothe promotion of advances in science and the development of groundbreaking technology forNTT's business. Your continued support will be greatly appreciated.
July, 2012

Toshiki Makimoto
Director
NTT Basic Research Laboratories－Ⅲ－

Contents
page◆ Cover♦ Optical Image of the Blue-Light Electroluminescence from the Transferred Vertical-Type

Light-Emitting Diode◆ Color Frontispiece ............................................................................................................Ⅰ♦ Conductive Polymer Combined with Silk Fibers for Biomedical Electrodes♦ In Atom Manipulation on Cleaved InAs(110) Surface♦ Coherent Coupling of a Gap-Tunable Flux Qubit to an Electron Spin Ensemble in Diamond♦ Exploring Novel Quantum Phases of Bose-Fermi Mixtures Trapped in an Optical Lattice◆ Message from the Director ................................................................................................Ⅲ◆ NTT Basic Research Laboratories Organogram ................................................................ 1◆ Member List ....................................................................................................................... 2
I. Research Topics◇ Overview of Research in Laboratories ............................................................................................... 13◇ Materials Science Laboratory ............................................................................................................ 14♦ Layered Boron Nitride as a Release Layer for Mechanical Transfer of GaN-Based Devices♦ Deep-UV Light Emission from AlN/GaN Short-Period Superlattices♦ Molecular Beam Epitaxy of High Quality Thin Films of Infinite Layer Cuprate

Superconductor (Sr, La)CuO2♦ Thermally Stable Operation of Hydrogen-Terminated Diamond FETs by Al2O3 Passivation♦ Molecular Beam Epitaxal Growth of Graphene and Nanofin Networks♦ Erbium Silicates as Advanced Optical Materials for Light Emission at

Telecommunicatios Wavelength in Silicon Photonics♦ Peculiar Temperature Dependence of Resistance in Epitaxial Monolayer Graphene♦ Functional Analysis of Membrane Proteins Using Microwell Array♦ Multifunctional Stimulation Electrode for Optical, Electrical and Chemical Stimulation♦ Conductive Polymer Combined with Silk Fibers for Biomedical Electrodes◇ Physical Science Laboratory ............................................................................................................... 24♦ Single-Electron Stochastic Resonance Using Nanowire Transistors♦ Absolute Accuracy Evaluation of Si Single-Electron Transfer Devices♦ A New Charge Sensing Scheme Using the Anti-Symmetric Vibration of Coupled MechanicalResonators

♦ Remote Actuation of an Electromechanical Resonator♦ Unraveling the Spin Polarization of the ν = 5/2 Fractional Quantum Hall State♦ Gate Operation of InAs/AlGaSb Heterostructures with an Atomic-Layer-Deposited

Insulating Layer♦ Indium Atom Manipulation on a Cleaved InAs Surface♦ Observation of Hysteretic Transport due to Dynamic Nuclear Spin Polarization in a

GaAs Lateral Double Quantum Dot♦ Mediation of Entanglement between a Microscopic Two Level System and a Macroscopic

Resonator Using a Superconducting Flux Qubit♦ Coherent Coupling of a Gap-Tunable Flux Qubit to an Electron Spin Ensemble in Diamond♦ In0.75Ga0.25As Quantum Point Contact Utilizing Wrap-Gate Geometry◇ Optical Science Laboratory ................................................................................................................ 35♦ Exploring Novel Quantum Phases of Bose-Fermi Mixtures Trapped in an Optical Lattice♦ Enhanced Optical Nonlinearity in a Silicon Photonic Crystal Slow-Light Waveguide♦ Generation of Femtosecond Laser Pulses at 1-GHz Repetition Rate Derived from Continuous

Wave Laser Diode♦ Transport and Manipulation of Electron Spins Using Surface Acoustic Waves♦ Bonding and Anti-Bonding Orbitals in Raman Spectroscopy for Graphene Edge
♦ Ultrahigh-Q Nanocavities Written with a Nanoprobe♦ Ultralow-Power All-Optical RAM Chip Based on Nanocavities

II. Data◇ Award Winners’ List (Fiscal 2011)................................................................................................. 43◇ In-house Award Winners’ List (Fiscal 2011).................................................................................. 44◇ Numbers of Papers, Presentations and Patents (2011).................................................................... 45◇ List of Invited Talks at International Conferences (2011).............................................................. 47

NTT Basic Research Laboratories Organogram
As of March 31, 2012

Director

Toshiki Makimoto, Dr.

Nano Bio Research
Executive Manager

Keiichi Torimitsu, Dr.

Research Planning Section
Executive Manager

Tetsuomi Sogawa, Dr.

Materials Science Laboratory
Executive Manager

Toshiki Makimoto, Dr.

Physical Science Laboratory
Executive Manager

Hiroshi Yamaguchi, Dr.

Optical Science Laboratory
Executive Manager

Yasuhiro Tokura, Dr.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)1

Member List
As of March 31, 2012(*/ left NTT BRL during the year)

NTT Basic Research Laboratories
Director, Dr. Toshiki Makimoto

Nano Bio Research

Executive Manager,

Dr. Keiichi Torimitsu

Research Planning Section

2

Executive Research Scientist,

Dr. Tetsuomi Sogawa

Senior Research Scientist,

Dr. Hiroki Takesue

Senior Research Scientist,

Dr. Akihiko Shinya

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Materials Science Laboratory

Executive Manager,

Dr. Toshiki Makimoto
Dr. Nahoko Kasai

Thin-Film Materials Research Group:
Dr. Hideki Yamamoto (Group Leader)
Dr. Makoto Kasu*
Dr. Yasuyuki Kobayashi
Dr. Tetsuya Akasaka
Dr. Kazuhide Kumakura
Dr. Yoshiharu Krockenberger Dr. Kazuyuki Hirama
Low-Dimensional Nanomaterials Research Group:
Dr. Hiroki Hibino (Group Leader)
Dr. Fumihiko Maeda
Dr. Kazuaki Furukawa
Dr. Satoru Suzuki
Dr. Ken-ichi Kanzaki
Dr. Makoto Takamura
Dr. Yuya Murata
Molecular and Bio Science Research Group:
Dr. Koji Sumitomo (Group Leader)Dr. Hiroshi Nakashima
Dr. Akiyoshi Shimada
Dr. Touichiro Goto
Dr. Aya Tanaka

Dr. Hisashi Sato
Dr. Yoshitaka Taniyasu

Dr. Hiroo Omi
Shin-ichi Tanabe

Dr. Yoshiaki Kashimura
Dr. Shingo Tsukada

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)3

Physical Science Laboratory

Executive Manager,

Dr. Hiroshi Yamaguchi
Toru Yamaguchi
Takeshi Karasawa

Nanodevices Research Group:
Dr. Akira Fujiwara (Group Leader)
Dr. Yukinori Ono
Dr. Hiroyuki Kageshima
Dr. Jin-ichiro Noborisaka
Dr. Gento Yamahata

Dr. Katsuhiko Nishiguchi
Dr. Gabriel Lansbergen

Nanostructure Technology Research Group:
Dr. Hiroshi Yamaguchi (Group Leader)
Dr. Kenji Yamazaki
Dr. Koji Onomitsu
Daiki Hatanaka
Dr. Imran Mahboob

Dr. Hajime Okamoto
Junzo Hayashi

Quantum Solid State Physics Research Group:
Dr. Koji Muraki (Group Leader)
Dr. Kiyoshi Kanisawa
Dr. Satoshi Sasaki
Dr. Toshiaki Hayashi
Dr. Takeshi Ohta
Dr. Ken-ichi Hitachi
Dr. Keiko Takase
Tadashi Saku*
Superconducting Quantum Physics Research Group:
Dr. Kouichi Semba (Group Leader)Dr. Hayato Nakano
Dr. Shiro Saito
Hirotaka Tanaka
Dr. Kousuke Kakuyanagi
Dr. Xiaobo Zhu
Spintronics Research Group:
Dr. Tatsushi Akazaki (Group Leader)
Dr. Yuichi Harada
Dr. Hiroyuki Tamura
Dr. Yoshiaki Sekine
Dr. Hiroshi Irie

4

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Dr. Kyoichi Suzuki
Dr. Norio Kumada
Dr. Takashi Kobayashi

Dr. Shin-ichi Karimoto
Dr. Yuichiro Matsuzaki

Dr. Masumi YamaguchiOptical Science Laboratory

Executive Manager,

Dr. Yasuhiro Tokura
Dr. Takehiko Tawara

Quantum Optical State Control Research Group:
Dr. Yasuhiro Tokura (Group Leader)
Dr. Kaoru Shimizu
Kazuhiro Igeta
Dr. Makoto Yamashita
Dr. Hiroyuki Shibata
Dr. Fumiaki Morikoshi
Dr. Kiyoshi Tamaki
Dr. Kensuke Inaba
Dr. Koji Azuma
Dr. Hiromitsu Imai
Dr. William John Munro
Dr. Haruka Tanji
Quantum Optical Physics Research Group:
Dr. Tetsuomi Sogawa (Group Leader)Dr. Hideki Gotoh
Dr. Tadashi Nishikawa
Dr. Katsuya Oguri
Dr. Atsushi Ishizawa
Dr. Guoquiang Zhang
Dr. Keiko Kato
Dr. Ken-ichi Sasaki
Photonic Nano-Structure Research Group:
Dr. Masaya Notomi (Group Leader)
Dr. Atsushi Yokoo
Dr. Eiichi Kuramochi
Dr. Hisashi Sumikura
Dr. Kengo Nozaki
Dr. Masaaki Ono
Dr. Jimyung Kim
Dr. Xu, Hao

Dr. Masami Kumagai
Dr. Tetsuya Mukai
Daisuke Hashimoto
Dr. Nobuyuki Matsuda
Dr. Toshihiro Kubo

Dr. Kouta Tateno
Dr. Haruki Sanada
Dr. Ken-ichi Hitachi

Dr. Hideaki Taniyama
Dr. Masato Takiguchi
Dr. Danang Birowosuto

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

5

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 a group leaderof Photonic Nanostructure Research Group since 2004. He is also entitled as
Senior Distinguished Scientist of NTT. From 1996-1997, he was with Linköping
University in Sweden as a visiting researcher. He was a guest associate professorof Department of Applied Electronics in Tokyo Institute of Technology (20032009), and is currently a guest professor of Department of Physics in Tokyo
Institute of Technology. He received IEEE/LEOS Distinguished Lecturer Awardin 2006, JSPS (Japan Society for the Promotion of Science) prize in 2009, Japan
Academy Medal in 2009, and 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. He is serving as a memberof 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 on October 30, 1961. He received 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 tunneling microscopy. His current interests
are micro/nanomechanical devices using semiconductor heterostructures. He
was a visiting research fellow in Imperial College, University of London, U.K.
during 1995-1996 and a visiting research staff in Paul Drude Institute, Germany
in 2003. He is a guest professor in Tohoku University from 2006 and a directorof the Japanese Society of Applied Physics in 2008 and 2009. He served as morethan 40 committee members of academic societies and international conferences.
He received Inoue Prize for Science (2012), Institute of Physics 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 Physical Science Laboratory anda group leader of Nanostructure Technology Research Group. He is a member of
the Japan Society of Applied Physics, the Physical Society of Japan, Institute ofPhysics (UK), and IEEE.

6

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Distinguished Researchers
Akira Fujiwara was born in Tokyo, Japan on March 9, 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 was a guest researcher at the National Institute ofStandards and Technology (NIST), Gaithersburg, MD, USA during 2003-2004.
He received the SSDM Young Researcher Award in 1998, SSDM Paper Award in
1999, and Japanese Journal of Applied Physics (JJAP) Paper Awards in 2003 and2006. He was awarded the Young Scientist Award from the Minister of MEXT
(Ministry of Education, Culture, Sports, Science, and Technology) in 2006. He
was a director of the Japanese Society of Applied Physics in 2010 and 2011. He
is a member of the Japan Society of Applied Physics and the IEEE.

Koji Muraki was born in Tokyo, Japan in 1965. 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 Basic ResearchLaboratories, Kanagawa, Japan. Since then, he has been engaged in the growthof high-mobility heterostructures and the study of highly correlated electronic
states realized in such structures. He was a guest researcher at Max-Planck
Institute, Stuttgart, Germany during 2001-2002. He is a member of the PhysicalSociety of Japan and Japan Society of Applied Physics.

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, Japan in 1996, 1998, and 2001, respectively. He joined NTT
Basic Research Laboratories in 2001. He has been engaged in wide bandgap
semiconductor research. His current interests are epitaxial growth and device
application of nitride semiconductors, especially aluminum nitride (AlN). He
is a visiting researcher at Ecole Polytechnique Fédérale de Lausanne (EPFL)
during 2011-2012. He received the Young Scientist Award for the Presentationof 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 (SIMC-XIV) in 2007, and the Young Scientists’Prize from the
Minister of Education, Culture, Sports, Science and Technology in 2011, theYoung Scientist Award at the 38th International Symposium on Compound
Semiconductors (ISCS2011) in 2011. He is a member of the JSAP.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)7

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. He is amember of the Physical Society of Japan.

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. He received IUPAP Young Author Best Paper Award at the International
Conference on Physics of Semiconductors 2000, Graduate Student Award Silverat the Materials Research Society 2000 Fall Meeting, and Young Scientist Awardat the Japan Society of Applied Physics Spring Meeting in 2000. He is a memberof the Japan Society of Applied Physics.

8

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Advisory Board (2011 Fiscal Year)
Name

Affiliation

Prof. Gerhard Abstreiter

Walter Schottky Institute, Germany

Prof. Boris L. Altshuler

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

Prof. Serge Haroche

Département de Physique,
De l‘Ecole Normale Supérieure, France

Prof. Theodor W. Hänsch

Max-Planck-Institut für Quantenoptik, Germany

Prof. Mats Jonson

Department of Physics, Göteborg University, Sweden

Prof. Anthony J. Leggett

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

Prof. Johan E. Mooij

Kavli Institute of Nanoscience,
Delft University of Technology, The Netherlands

Prof. John F. Ryan

Clarendon Laboratory, University of Oxford, U.K.

Prof. Klaus von Klitzing

Max-Planck-Institut für Festkörperforschung, Germany

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)9Invited / Guest Scientists (2011 Fiscal Year)

10

Name

Affiliation

PeriodDr. Lars Tiemann

Japan Science and Technology
Agency (JST), Japan

Apr. 2009 – Feb. 2012

Dr. Takasumi Tanabe

Keio University, Japan

Jul. 2010 – Mar. 2012

Dr. Kenichiro Kusudo

National Institute ofInformatics (NII), Japan

Apr. 2011 – Mar. 2012

Dr. Mao-Chuang Yeh

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

May 2010 – Jun. 2011

Dr. Stefan Fölsch

Paul-Drud-Institute, Germany

Oct. 2011 – Nov. 2011

Dr. Trevor David Rhone

Japan Science and Technology
Agency (JST), Japan

Feb. 2012 – Jan. 2013

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Overseas Trainees (2011 Fiscal Year)
Name

Affiliation

PeriodRoberto Lo Nardo

Palermo University, Italy

Jan. 2011 – Aug. 2011

Diego Sabbagh

University of Studies "Roma Tre", Italy

Jan. 2011 – Aug. 2011

Yibo Fu

University of Toulouse, France

Feb. 2011 – Sep. 2011

Yasir Makhdoom

University of British Columbia, Canada

May 2011 – Aug. 2011

Mohamed Oudah

University of Ottawa, Canada

May 2011 – Aug. 2011

Rahul S. Deshpande

Indian Institute of Technology Guwahati, India

Jun. 2011 – Jul. 2011

Gregory Webber

University of Victoria, Canada

Jul. 2011 – Dec. 2011

Hanna Le Jeannic

ESPCI ParisTech (École supérieure de physique et Jul. 2011 – Dec. 2011de chimie industrielles de la ville de Paris), France

Melanie Marcel

ESPCI ParisTech (École supérieure de physique et Jul. 2011 – Dec. 2011de chimie industrielles de la ville de Paris), France

Amaury Badon

ESPCI ParisTech (École supérieure de physique et Jul. 2011 – Dec. 2011de chimie industrielles de la ville de Paris), France

Henri J. Suominen

The University of Edinburgh, Switzerland

Vincent NierESPCI ParisTech (École supérieure de physique et Aug.2011 – Dec. 2011de chimie industrielles de la ville de Paris), France

Adrien Gourgout

ESPCI ParisTech (École supérieure de physique et Sep. 2011 – Dec. 2011de chimie industrielles de la ville de Paris), France

Benjamin Pingault

ESPCI ParisTech (École supérieure de physique et Sep. 2011 – Jan. 2012de chimie industrielles de la ville de Paris), France

Andy Berry

University of Victoria, Canada

Sep. 2011 –Michael Firka

University of Victoria, Canada

Sep. 2011 –Jingjing Huang

California Institute of Technology, U.S.A.

Sep. 2011 – Dec. 2011

Elan Grossman

Georgia Institute of Technology, U.S.A.

Jan. 2012 –Bennett Eleazer

Georgia Institute of Technology, U.S.A.

Jan. 2012 –Yong Fan Jiang

The University of British Columbia, Canada

Jan. 2012 –Gediminas Dauderis

Vilnius University, Lithuania

Jan. 2012 –Maria Anagosti

University of Gent, Belgium

Jan. 2012 –Roger Molto Pallares

Chemical Institute of Sarria (IQS), Spain

Jan. 2012 –Aug.2011 –Sanna Maria Rauhamäki University of Jyväskylä, FinlandJan. 2012 –Alex Yang

The University of British Columbia, Canada

Jan. 2012 –Shibin Thomas

Mahatma Gandhi University, India

Mar. 2012

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)11

Domestic Trainees (2011 Fiscal Year)

12

Name

Affiliation

PeriodTakayuki Watanabe

Tohoku University

Apr. 2011 – Mar. 2012

Shogo Aihara

Keio University

Apr. 2011 – Mar. 2012

Hiroshi Kamata

Tokyo Institute of Technology

Apr. 2011 – Mar. 2012

Shun Dai

University of Tokyo

Apr. 2011 – Mar. 2012

Naoyuki Masumoto

University of Tokyo

Apr. 2011 – Mar. 2012

Yuma Okazaki

Tohoku University

Apr. 2011 – Mar. 2012

Yoji Kunihashi

Tohoku University

Apr. 2011 – Mar. 2012

Rento Osugi

Tohoku University

Apr. 2011 – Mar. 2012

Tatsuya Baba

Tokyo University of Science

Apr. 2011 – Mar. 2012

Shunichi Matsumoto

Tokyo University of Science

May 2011 – Mar. 2012

Hajime Suzuki

Tokyo University of Science

May 2011 – Mar. 2012

Mohammed Fauzi

Tohoku University

Jun. 2011

Takanobu Tsunoi

Yokohama National University

Jun. 2011 – Mar. 2012

Atsushi Iwamoto

The University of Tokushima

Aug. 2011– Sep. 2011

Rui Asaoka

Tohoku University

Sep. 2011 – Oct. 2011

Masato Inoue

Kyushu University

Sep. 2011 – Dec. 2011

Atsushi Hagiwara

The University of Electro- Communications

Sep. 2011

Takayuki Tanaka

Hokkaido University

Sep. 2011

Yuta Noguchi

Nagaoka University of Technology

Oct. 2011 – Feb. 2012

Yamato Munataka

Nagaoka University of Technology

Oct. 2011 – Feb. 2012

Keita Sakuma

Nagoya University

Oct. 2011 – Dec. 2011

Hiroto Oomae

Nagaoka University of Technology

Oct. 2011 – Dec. 2011

Yoshiyuki Abe

Toyohashi University of Technology

Oct. 2011 – Feb. 2012

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Ⅰ．Research Topics

Overview of Research in Laboratories
Materials Science Laboratory
Toshiki Makimoto
The Materials Science Laboratory (MSL) aims at producing new functional materials anddesigning of advanced device based on novel materials and biological function. Controllingthe configuration and coupling of atoms and molecules is our approach to accomplish thesegoals. We have three research groups covering from thin film materials, such as nitride
semiconductors, diamond, graphene, and superconductors, to biological molecules, suchas receptor proteins and lipid bilayers. The distinctive characteristic of MSL is its effective
sharing of the unique nanofabrication and measurement techniques of each group. This
enables fusion of research fields and techniques, which leads to innovative material research
for the future information technology.
This year, we successfully obtained research results on the mechanical transfer of largesize GaN devices using layered BN (Mechanical Transfer using a Release-layer : "METRE"
method), the unique transport characteristics of the monolayer epitaxial graphene, and thebiomedical electrodes using conductive polymer and silk.

Physical Science Laboratory
Hiroshi Yamaguchi
We are studying semiconductor and superconductor-based solid-state devices, which will
have a revolutionary impact on communication and information technologies in the 21st
century. In particular, we promote research of nanoscale devices fabricated using high-quality
crystal growth and fine lithographic techniques.
The five groups in our laboratory are working in the following areas: precise and dynamical
control of single electrons, nanodevices operating with ultra low power consumption, novel
nanomechanical systems utilizing mechanical degrees of freedom in solid-state architectures,
coherent quantum control of semiconductor and superconductor systems, carrier interactions
in semiconductor hetero- and nanostructures, spintronics manipulating both electron andnuclear spins. We also promote the studies of cutting-edge nanolithography techniques, highquality crystal growth, and theoretical studies including first-principle calculations.

Optical Science Laboratory
Yasuhiro Tokura
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 verysmall optical integrated circuits using two-dimensional photonic crystals, based on the opticalproperties of semiconductor nanostructures like a quantum dot.
In this year, we demonstrated a highly efficient optical non-linearity with a coupledresonator optical waveguide and established a comprehensive theoretical description for
quantum mechanical properties of cooled atoms trapped in an optical lattice made withlightwaves. We also demonstrated spin transport and manipulation in semiconductors by
surface acoustic waves, and developed an ultralow-power all-optical RAM based on photonic
crystal nanocavities.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)13

Layered Boron Nitride as a Release Layer for Mechanical Transfer of
GaN-Based Devices
Yasuyuki Kobayashi, Kazuhide Kumakura, Tetsuya Akasaka, and Toshiki Makimoto
Materials Science Laboratory
Nitride semiconductors are the materials of choice for a variety of device applications. One
important practical goal is to realize such devices on large, flexible and affordable substrates,on which direct growth of nitride semiconductors of sufficient quality is problematic. Several
techniques have been investigated to enable the transfer of nitride devices from one substrate
to another, but existing methods still have some important disadvantage. Here we demonstratethat hexagonal boron nitride (h-BN) can form a release layer that enables the mechanicaltransfer of GaN-based device structures onto foreign substrates [1].
Photograph in Figure 1 shows the transferred AlGaN/GaN heterostructure, approximately
2 cm square, on an adhesive sheet (an indium sheet in this case) attached to a foreign sapphire
substrate. We can see the surface of the indium sheet because the AlGaN is transparent. The
size of the transferred area can be controlled by the adhesive sheet size. Some protrusions fromthe indium sheet are clearly visible, indicating the AlGaN/GaN heterostructure is mechanicallyreleased from the native sapphire substrate. No cracks were observed in the transparent
AlGaN/GaN heterostructure up to maximum size of about 1 cm square, suggesting thatmechanical release process using the h-BN layer ensures minimal crack formation. Next, we
describe the electroluminescence emitted from the transferred multiple quantum well (MQW)
light-emitting diode (LED) at room temperature. For comparison, the same MQW LED
structure was grown on a typical low-temperature AlN buffer layer on a sapphire substrate andthe conventional MQW LED was fabricated without lift-off. Current-voltage characteristicsof the transferred LED show clear rectification. The electroluminescence intensities fromthe transferred LED were comparable to or higher than the intensities from the conventional
LED on the low-temperature AlN buffer layer at the same current. The comparable intensitiesof the electroluminescence of the conventional and transferred LED indicate that the MQWpreserves its original quality after the transfer. We further succeeded in transferring a verticaltype LED. This vertical-type LED emits blue light at room temperature (Figure 2).
The process we report here opens the way to releasing and transferring a wide range of
nitride semiconductor devices to large-area, flexible and affordable substrates.
[1] Y. Kobayashi, K. Kumakura, T. Akasaka, and T. Makimoto, Nature 484 (2012) 223.

Fig. 1. Photograph of the transferred AlGaN/GaN
structure on the foreign sapphire substrate.

14

Fig. 2. Optical image of the blue-light EL fromthe transferred vertical-type LED.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Deep-UV Light Emission from AlN/GaN Short-Period Superlattices
Yoshitaka Taniyasu and Makoto Kasu
Materials Science Laboratory
AlGaN alloys are promising materials for ultraviolet (UV) light-emitting diodes (LEDs)
with emission wavelengths ranging from 210 nm (AlN) in deep-UV to 365 nm (GaN) in nearUV regions. At present, the emission efficiency of deep-UV LEDs is much lower than thatof near-UV LEDs. One intrinsic reason for the lower emission efficiency is attributed to thevalence band structure [1]. For GaN the topmost valence band is the heavy hole (HH) band.
The transition between the conduction band (CB) and HH band is allowed for electric field
perpendicular to the c-axis (E⊥c), and the emission intensity is therefore strong along thec-axis (from C-plane). On the contrary, for AlN the topmost valence band is the crystal-field
split-off (CH) band. The transition between the CB and CH band is allowed for electric fieldparallel to the c-axis (E||c), and the emission intensity is therefore weak along the c-axis (fromC-plane). Because the LEDs are fabricated with the C-plane orientation, which is suitable forhigh-quality growth, the emission intensity is intrinsically low for deep-UV LEDs using highAl-content AlGaN. Recently, we demonstrated that AlN/GaN short-period superlattices (SLs)show stronger deep-UV light emission from the C-plane than the AlGaN alloys [2].
Transmission electron microscopy (TEM) images of AlN/GaN short-period SLs are shownin Fig. 1. The GaN well thickness was 0.48 nm (1.8 monolayesr) and the AlN barrier thickness
was 1.82 nm (7.3 monolayers). The growth of the SL structure with abrupt interfaces between
AlN and GaN was confirmed. The emission properties of the AlN/GaN short-period SLs werecharacterized by photoluminescence (PL). As the GaN well thickness decreased from 2.5 to 0.9
monolayers, the emission wavelength decreased from 275.8 to 236.9 nm due to the quantum
size effect. To investigate the polarization property, angle-dependent PL was carried out(Fig. 2). For an AlGaN alloy, the emission along the c-axis (θ = 0°) was weak because of the
E||c polarization. On the contrary, for the AlN/GaN short-period SLs, the emission along thec-axis was strong. This is because the quantized energy level for holes originates from the
HH band of GaN and therefore the transition between the electron and hole quantized energy
levels is allowed for E⊥c. Due to the different polarization properties, the AlN/GaN shortperiod SL shows four times higher emission intensity than the AlGaN alloy. We also fabricateda deep-UV LED with AlN/GaN short-period SLs as an emission layer and confirmed strong
deep-UV light emission from C-plane.
[1] Y. Taniyasu and M. Kasu, Appl. Phys. Lett. 90 (2007) 261911.
[2] Y. Taniyasu and M. Kasu, Appl. Phys. Lett. 99 (2011) 251112.

Fig. 1. (a) Cross-sectional TEM image of the AlN/GaN
short-period SLs and (b) its higher magnification.

Fig. 2. PL of (a) the AlN/GaN short-period
SLs and (b) the AlGaN alloy.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)15

Molecular Beam Epitaxy of High Quality Thin Films of Infinite Layer
Cuprate Superconductor (Sr, La)CuO2
Yoshiharu Krockenberger, Keita Sakuma, and Hideki Yamamoto
Materials Science Laboratory
Infinite layer cuprate superconductors are built up only by CuO2 planes spaced by Sr or La.
Consequently, their crystal structure is the simplest among all of the cuprate superconductors.
However, the synthesis of the infinite layer phase remains arduously as the tetragonal crystal
structure (P4/mmm, S.G. 221) is stabilized only under high pressure synthesis conditions [1].
Nonetheless, early studies have shown that Sr1–xLaxCuO2 thin films can be grown by molecularbeam epitaxy (MBE) [2]. In contrast to bulk samples synthesized under high pressure, single
phase thin films readily allow electronic transport measurements. We have synthesized highquality infinite layer cuprate superconductors by MBE [3]. Crucial growth parameters are astringent stoichiometry control which was done by electron impact emission spectroscopy.
Beside the stoichiometry of the cations, the oxidizing conditions during the growth play asignificant role for the appearance of superconductivity. Infinite layer cuprate films grown by
MBE have been analyzed by high resolution transmission electron microscopy. Over large
areas (>1000 nm2) crystalline imperfections are not observed, in contrast to films synthesizedby other methods. Those films are grown coherently on DyScO3(110) as shown in Fig. 1.
Notably Laue oscillations are also observed the reciprocal space map (Fig. 1). In Fig. 2, weshow the temperature dependence of the resistivity. Metallic conduction as well as an RRR
value of >4 are observed. Also shown in Fig. 2 are the magneto resistivity curves, where
the magnetic field is applied perpendicular to the CuO2 planes. In addition to the resistivetransition into the superconducting phase, we also observed a clear Meissner shielding by a
SQUID magnetometer. The residual resistivity of those films is estimated to be approximately
10 μΩcm, thus small enough for further investigations on the Fermi surface of infinite layer
cuprate superconductors from Shubnikov - de Haas oscillations.
[1] M. G. Smith et al., Nature 351 (1991) 549.
[2] S. Karimoto et al., Appl. Phys. Lett. 79 (2001) 2767.
[3] Y. Krockenberger et al. Appl. Phys. Exp. 5 (2012) 043101.

Fig. 1. Reciprocal space map of a Sr0.90La0.10CuO2
film grown on a DyScO3(110) substrate.

16

Fig. 2. Temperature dependence of the electrical resistivityof a Sr0.90La0.10CuO2 film grown on a DyScO3(110)substrate for magnetic fields applied perpendicular
to the CuO2 planes.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Thermally Stable Operation of Hydrogen-Terminated Diamond FETs
by Al2O3 Passivation
Kazuyuki Hirama1, Hisashi Sato1, Yuichi Harada2, and Makoto Kasu1, 3
1Materials Science Laboratory, 2Physical Science Laboratory, 3Saga University
High-frequency (>100 GHz) operations have been demonstrated for hydrogen-terminated(H-terminated) diamond field effect transistors (FETs) with a hole accumulation layer channel[1]. Recently, we revealed that the hole carriers are mainly generated by nitrogen-dioxide(NO2) adsorpted on the H-terminated surface. However, there still remains a thermal stability
problem: With increasing temperature in a vacuum, the hole carrier density decreases, most
likely due to desorption of the adsorbates. In this work, to solve the problem, we passivatedthe H-terminated diamond surface with Al2O3.
After highly concentrated NO2 adsorption (2% in N2) to the H-terminated diamond surface,a 10-nm-thick Al2O3 passivation layer was deposited by the atomic layer deposition (ALD)
method. Figure 1 shows the temperature dependence of sheet hole concentration (ps) and holemobility (μ) of the hole accumulation layer on the passivated diamond surface. Both ps and μwere the same values in the repeated measurements. This confirms that the hole accumulation
layer on the passivated diamond surface is thermally stable. In a temperature range > 30°C,
the ionization energy was estimated to be as low as 6.2 meV. On the other hand, μ changes in–1–1
proportion to 1/T (the T rule) for T > 100°C. The T rule indicates the degeneration of thehole carriers at higher temperatures [2].
Next, we applied the Al2O3 passivation technique to diamond FETs. Figure 2 shows thedrain current-voltage (IDS-VDS) characteristics of the passivated diamond FET at 200°C and
RT before and after the 200°C heating in a vacuum. Before the 200°C heating, the maximum
IDS (IDSmax) at RT was –200 mA/mm. At 200°C, the IDSmax decreased to –180 mA/mm. After the
200°C heating, the IDSmax increased to the initial value of –200 mA/mm at RT. Before and after
the heating, IDS at every VGS clearly agree well with each other. The threshold voltage (Vth)remained constant (+1 V), which implies that the hole density under the gate electrode stayedexactly the same value after the heating cycle below 200°C. Therefore, the IDS decrease at
200°C is attributed to the temperature dependence of hole mobility, as observed in Fig. 1(b).
These results reveal that the Al2O3 passivated diamond FETs can be operated without thermal
degradation at least up to 200°C.
[1] M. Kasu et al., Electronics Lett. 41 (2005) 1249.
[2] M. Kasu, H. Sato, and K. Hirama, Appl. Phys. Express 5 (2012) 025701.

(a)

(b)

Fig. 1. Temperature dependence of (a) sheet hole density and(b) mobility.

Fig. 2. IDS-VDS characteristics of apassivated diamond FET.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)17

Molecular Beam Epitaxal Growth of Graphene and Nanofin Networks
Fumihiko Maeda and Hiroki Hibino
Materials Science Laboratory
For graphene, which is a material of great interest for the future electronics, establishinga method for its wafer-scale fabrication remains a challenge for its application to largescale integration. We have proposed a new approach to fabricate graphene based on gassource molecular beam epitaxy (MBE) and have shown its feasibility [1]. Then, we observed
an interesting nanostructure, which forms a network. Here, we report an investigation of its
structural details [2].
As a substrate, we used graphene, from one to two layers, formed on n-type SiC(0001)
by annealing at 1800°C in Ar ambient at about 100 Torr. For the MBE growth, the substrate
was heated under the flow of ethanol cracked by a W filament set at 2000°C. By atomic
force microscopy (AFM), the topographic image of a sample grown at 915°C was obtained[Fig. 1(a)]. In this image, the network structure can be seen on the substrate surface. Crosssectional transmission electron microscopy (TEM) images of this sample in Fig. 2 reveal thatthese networks consist of one or two layers of graphene, which stick out from the surface likea fin whose height is about 5 nm. (Here, we call this ridge-structure a “graphene nanofin”.) We
speculate that the nanofins would be formed by collisions between incommensurate domainsof the laterally growing graphene at their boundary, which means that a single domain ofgraphene islands is surrounded by the nanofins. Thus, the domain size of the laterally growngraphene is estimated to be less than 100 nm using the average distance between the nanofinsfrom the section analysis of Fig. 1(b). This fin structure of atomic layer thickness with an open
end has not been reported previously and is observed here for the first time. We expect that thegraphene nanofin could be applied for interconnection and devices as the thinnest material of
one atomic layer.
This work was supported by KAKENHI.
[1] F. Maeda and H. Hibino, Phys. Status Solidi B 247 (2010) 916.
[2] F. Maeda and H. Hibino, J. Phys. D: Appl. Phys. 44 (2011) 435305.

Fig. 1. (a) Topographic AFM image and (b) AFM section
analysis along the dotted line in the image.

18

Fig. 2. Cross-sectional TEM images after MBE growth.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Erbium Silicates as Advanced Optical Materials for Light Emission at
Telecommunicatios Wavelength in Silicon Photonics
Hiroo Omi and Takehiko Tawara*
Materials Science Laboratory, *Optical Science Laboratory
Erbium silicates and erbium oxide, such as Er2SiO5 and Er2Si2O7, are promising materials
as light emitters at the telecommunications wavelength and as optical amplifiers in the fieldof silicon photonics. In the erbium compounds, the density of erbium ions is 1022 atoms/
cm3, which is orders of magnitude greater than that typically obtained by Er ion implantationin silicon substrate, allowing access to a large number of emitting centers. In this work, we
combined real-time synchrotron radiation grazing incidence X-ray diffraction (GIXD) andPL experiments to optimize the structures and optical properties of erbium silicates on silicon
substrate. We firstly studied the formation of the erbium silicates during annealing in Ar gas
and O2/Ar mixture gases in real time. We determined the crystallographic structures and thetemperature of crystallization, and assessed the possible reactions for the silicate formation.
We secondly measured the photoluminescence (PL) from a sample annealed at 1060°C [1].
The 100-nm-thick erbium oxides were deposited on 100-nm-thick silicon oxide filmgrown on Si(001) substrates by reactive sputtering at room temperature. The samples arethen annealed at up to 1300°C in Ar and O2/Ar mixture gases. In micro-PL experiments, thesamples were pumped by CW laser at the wavelength of 532 nm.
The GIXD measurements show that erbium silicates and erbium oxide are formed byinterface reactions between silicon oxide and erbium oxides deposited on silicon oxide byreactive sputtering in Ar gas and O2/Ar mixture gas ambiences. The erbium silicates areformed above 1060°C in Ar gas ambience and above 1010°C in O2/Ar gas ambience, anderbium silicides are dominantly formed above 1250°C. The I15/2-I13/2 Er3+ PL from the erbium
silicate exhibits abnormal temperature dependence (see Fig. 1). The PL intensity from theEr2SiO5 silicate exhibits abnormal temperature dependence of 1.529-μm Er3+ PL; the PL
intensity decreases from 4 to 70 K and increases from 70 to 300 K. The increase of the PL
intensity with increasing temperature observed at off-resonant excitation conditions can be
explained by the phonon-assisted resonant absorption of the 532-nm excitation photons at the2
H11/2 levels of Er3+ ions in the erbium silicate films.
[1] H. Omi, T. Tawara, and M. Tateishi, AIP Advances 2 (2012) 012141.

Fig. 1. Photoluminescence from erbium silicates grown on Si substrate (a), Temperature dependence of
the PL intensity (b).

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)19

Peculiar Temperature Dependence of Resistance in
Epitaxial Monolayer Graphene
Shinichi Tanabe1, Yoshiaki Sekine2, Hiroyuki Kageshima2,
Masao Nagase3, and Hiroki Hibino1
1
Materials Science Laboratory, 2Physical Science Laboratory, 3The University of Tokushima
Monolayer graphene is expected to have high mobility due to its unique electronic structure,and it is an attractive material for electronics applications. Although its properties are being
investigated in monolayer graphene flakes obtained by mechanical exfoliation of graphite,mechanical exfoliation is not suitable for obtaining large-area monolayer graphene. Thus,
establishing a method for its mass production is needed. Monolayer graphene on SiC can begrown on a large scale by thermal decomposition of SiC(0001) in an Ar environment [1]. In
top-gated Hall bar devices using monolayer graphene on SiC as the channel, promising results,
such as ambipolar characteristics and the quantum Hall effect, were obtained at 2 K [2]. As afurther step towards utilizing monolayer graphene on SiC for devices at room temperature, weinvestigated its electronic transport characteristics up to 200 K.
Figure 1 shows the gate-voltage (VG) dependence of four-terminal resistance from 2 to 200 K.
When VG is at the charge neutrality point (VCNP), the resistance decreases as temperature(T) increases. However, when VG is away from the VCNP, for example VG – VCNP = 30 V, theresistance increases as T increases. The T dependence of resistance at the VCNP is due to theincrease of thermally activated carriers. The T dependence of resistance at VG away from the
VCNP originates from decrease in mobility as shown in Fig. 2. The T dependence of mobility
is determined by temperature-independent scatterings (A), acoustic phonon scatteringin graphene (B), and phonon scattering from extrinsic sources (C). From the analysis in
Fig. 2, the phonon scattering from extrinsic sources, which is thought to be from the substrate,strongly affects the T dependence of mobility [3]. The mobility decrease with increasing T is
expected to be suppressed by controlling the phonon scattering from the substrate.
This work was supported by KAKENHI.
[1] K. Emstev et al., Nature Mater. 8 (2009) 203.
[2] S. Tanabe et al., Appl. Phys. Express 3 (2010) 075102.
[3] S. Tanabe et al., Phys. Rev. B 84 (2011) 115458.

Fig. 1. Gate-voltage dependence of resistance from
2 to 200 K.

20

Fig. 2. Temperature dependence of mobility at–2electron density of 6×1011 cm .

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Functional Analysis of Membrane Proteins Using Microwell Array
Koji Sumitomo, Yukihiro Tamba*, Yoshiaki Kashimura, and Aya Tanaka
Materials Science Laboratory, *Suzuka Nat. Coll. Tech.
For the functional analysis of ion channel activity, an artificial lipid bilayer suspended
over microwells was formed that ruptured giant unilamellar vesicles on a Si substrate. Ca2+ion indicators (fluo-4) were confined in the microwells by sealing the microwells with alipid bilayer as shown in Fig. 1. An overhang formed at the microwells prevented the lipid
membrane from falling into them and allowed the stable confinement of the fluorescentprobes. The transport of Ca2+ ions through channels formed by α-hemolysin inserted in alipid membrane was analyzed by employing the fluorescence intensity change of fluo-4 inthe microwells [1]. The insertion of α-hemolysin into a suspended lipid membrane and theformation of nanopores induce the transport of Ca2+ ions, and the fluorescence intensity of
fluo-4 increased as a result. When the α-hemolysin concentration is higher, the fluorescenceintensity should reach its maximum value earlier as shown in Fig. 2.
The microwell volume was very small (1~100 femtoliters), so a highly sensitive monitor
could be realized. The detection limit is several tens of ions/sec/μm 2, and this is much smaller
than the ion current in a standard electrophysiological measurement. Smaller microwells will
make it possible to mimic a local ion concentration change in the cells, although the signal
to noise ratio must be further improved for the functional analysis of a single channel. We
demonstrated that a microwell array with confined fluorescent probes sealed by a lipid bilayer
could constitute a basic component of a highly sensitive biosensor array that works withfunctional membrane proteins. This array will allow us to realize parallel testing devices witha high throughput.
[1] K. Sumitomo et al., Biosensors and Bioelectronics 31 (2012) 445.

Fig. 1. Microwell sealed with lipid bilayer. (a) Schematic
illustration of the model. Fluorescent images of lipid
patch (b) and microwells before (c) and after (d) Ca2+ ion
transport.

Fig. 2. Change in fluorescence intensity
induced by the addition of various
concentrations of α-hemolysin.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)21

Multifunctional Stimulation Electrode for Optical, Electrical andChemical Stimulation
Akiyoshi Shimada1, Shuichiro Asakawa2, and Kazuhide Nakajima3
1
Materials Science Laboratory, 2Photonics Laboratories, and 3Access Network Service System
Laboratories
We have developed a new method for delivering water-soluble chemicals, broadband lightand electrical stimulation using one optical fiber. This constitutes a new tool in photoreleasetechnology for controlling cellular chemistry and physiology [1].
First we injected caged glutamate (4-Methoxy-7-nitroindolinyl-caged-L-glutamate) into a
culture consisting of dissociated cortical neurons of an embryonic day 18 rat using a holeassisted optical fiber (HAF)[2]. The HAF has a Ge-doped silica core and six equally spaced
holes with a diameter of 14 μm in the cladding surrounding the core (Fig. 1). The end of
the HAF was located just above the neurons. 250 μM of caged glutamate was injected into
these holes with a syringe pump via a microfluidic device (Fig. 2). To photorelease caged
glutamate, 365 nm ultraviolet (UV) light from an LED was coupled into the HAF through themicrofluidic device. The cortical neurons were preloaded with the Ca2+ sensitive fluorescentdye, fluo-4. When the UV light released the glutamate, we observed an increase in theintracellular Ca 2+ concentration using fluorescent microscopy [Fig. 3(a)]. We then applied
electrical stimulation from this HAF by utilizing these holes filled with electrolyte solution
and observed an increase in the intracellular Ca2+ concentration [Fig. 3(b)].
The HAF has an outer diameter of 125 μm and an extremely low bending loss characteristiccompared with conventional optical fiber. This HAF provides the possibility of achieving aless invasive approach to surgery.
[1] A. Shimada et al., Neuroscience2011, 204.27, Washington DC, 2011.
[2] K. Nakajima et al., Photonics Technology Letters, IEEE 15 (2003) 1737.

Fig. 1. Hole-assisted optical fiber.

Fig. 2. Multifunctional stimulation fiber.

22

Fig. 3. Dissociated rat cortical neurons labeledwith calcium florescent dye. Neural activity
evoked by opt-chemical stimulation (a) andelectrical stmulation (b).

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Conductive Polymer Combined with Silk Fibers for Biomedical Electrodes
Shingo Tsukada, Hiroshi Nakashima, and Keiichi Torimitsu
Materials Science Laboratory
A bio-electrode is an essential tool for nano-bio research as an interface between livingorgans and electrical devices (circuits). Electrode materials for biomedical signal recordings,
such as electrocardiograms (ECG) and electroencephalography (EEG) are expected to be
soft, hydrophilic and electro-conductive to minimize the stress imposed on living tissue,
especially for long-term monitoring. We have developed and characterized string shaped
electrodes consisting of a conductive polymer combined with silk fibers, which provide a new
biocompatible interface with living tissue under both dry and wet conditions [1].
An electro-conductive polyelectrolyte, Poly (3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT-PSS) was electrochemically combined with silk fibers from
Bombyx mori (Fig. 1). The polymer composite 280 μm fiber bundle exhibited a conductivityof 0.0018 S/cm (260 Kohm/mm) and a tensile strength of 1,000 CN in dry and wet states. The
chemical addition of glycerol to the PEDOT-PSS silk fiber improved the conductivity to 0.23
S/cm (2 Kohm/mm). Glycerol also controls the wettability of PEDOT-PSS thus improving its
durability in water and washing cycles. Without using any electrolytes, pastes or solutions,the electroconductive string directly collects electrical signals from living tissue and transmits
them to metal cables (Fig. 2). This PEDOT-PSS silk glycerol fiber composite offers a newclass of biocompatible electrodes for biomedical, information and communication technology
without imposing any stress on the subjects.
[1] S. Tsukada et al., PLoS ONE 7(4) (2012) e33689.

Fig. 1. a. PEDOT-PSS silk thread (right), baresilk thread (left). b. Macroscopic imageof PEDOT-PSS silk thread (right) andbare silk (left). c. SEM image of PEDOTPSS silk thread (Scale bar 20 μm).

Fig. 2. a. Structure of skin surface electrode made of PEDOTPSS silk thread. b. Electrocardiogram simultaneously
recorded by PEDOT-PSS silk electrode (1), conventional
medical electrodes (2) and textile electrode (Scale bar
1 sec 50 mV). c. EEG recordings from rat brain (Scalebar 1 sec 50 μV, F3, F4: Frontal head left & right, C3,
C4: Central left & right).

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)23

Single-Electron Stochastic Resonance Using Nanowire Transistors
Katsuhiko Nishiguchi and Akira Fujiwara
Physical Science Laboratory
Stochastic resonance (SR) is a unique phenomenon that takes advantage of noise to enhance
the response of a system to a weak signal [1]. SR is known to be beneficial in geographic
and biological systems and has motivated studies seeking to implement an SR function into
electronic devices. However, since noise is artificially superimposed on the devices, total
system becomes complicated and operation speed for SR is limited by the bandwidth of theartificial noise spectrum. In this work, we demonstrate fast SR operation utilizing shot noise
originating from single-electron (SE) transfer in nanowire transistors [2].
The device is composed of two transistors fabricated on a silicon-on-insulator wafer(Fig. 1). The first transistor (T-FET) transfers single electrons. An upper gate (UG) and lower
gate (LG2) are used to induce an electron source (ES) and electron-storage node. LG1 controls
SE transfer from the ES to the node in the same manner as that in the subthreshold regime ofa transistor, i.e., non-linear characteristics. The SEs transferred to the MN are detected by theother transistor (D-FET) as shown in Fig. 2 [3]. An analysis of individual SE transports, inwhich the histogram of interval δ t between each SE transport shows exponential decay (inset
of Fig. 2), reveals that SEs are transferred randomly to the node, which means shot noise in
the transistor. Since such non-linear characteristics and random transport are fundamental in atransistor, they are available when δ t is on the order of nanoseconds or shorter, which allows
fast SR.
When square waveforms as input signal Sin are applied to the ES and the differential of
current flowing through the D-FET is monitored as output signal Sout, the similarity (orcorrelation coefficient) between Sin and Sout becomes the maximum at the particular voltage
applied to LG1. This means that shot noise originating from SE transport activates SR. On theother hand, when the number of electrons transferred to the node within the particular interval
is also used as Sout, SR characteristics are confirmed even at the interval of 10 ns because shotnoise guarantees complete randomness of SE transport. SR utilizing these features allows
fast pattern perception: an input image with low contrast is converted to an image with higher
contrast (Fig. 3). Here, Sin is extremely small so that Sout is represented by a few hundred
electrons and the interval of each signal input is 10 ns. Therefore, SR using SE-based shotnoise is useful for single-shot sensing of quickly moving targets.
[1] L. Gammaitoni et al., Rev. Mod. Phys. 70 (1998) 223.
[2] K. Nishiguchi and A. Fujiwara, Jpn J. Appl. Phys. 50 (2011) 06GF04.
[3] K. Nishiguchi et al., Jpn J. Appl. Phys. 47 (2008) 8305.

Fig. 1. Device structure.

24

Fig. 2. SE detection. The inset is ahistogram of δ t.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Fig. 3. Pattern perception using SR.

Absolute Accuracy Evaluation of Si Single-Electron Transfer Devices
Gento Yamahata, Katsuhiko Nishiguchi, and Akira Fujiwara
Physical Science Laboratory
Single-electron (SE) transfer is expected to be used in ultralow power consumption circuits
and current standards in metrology. Accuracy of the SE transfer is crucial for determining bit
errors or uncertainty in the current standards. A sufficiently low error rate, typically an error
per transferred electron of about 1 part in 108, is necessary for the current standards. Here
we demonstrate an absolute accuracy evaluation of the SE transfer [1] in high-speed transfer
devices constructed by using Si nanowire metal-oxide-semiconductor field-effect transistors(MOSFETs) [2].
Figures 1 and 2 show a schematic diagram and a scanning electron microscope image of thedevice, respectively. The SE transfer device comprises three Si nanowire MOSFETs (FET1, 2,
and 3) on a silicon-on-insulator wafer. A high-sensitivity charge sensor is composed of anotherSi nanowire MOSFET (S-FET). For the absolute evaluation of accuracy of the SE transfer,a node is first formed by turning FET3 off. Then, pulse voltages are applied to FET1, FET2,
and the source (S) to shuttle an SE between the source and the node. Finally, we evaluate thetransfer error by detecting the number of electrons in the node during the SE shuttle transfer.
The merit of this scheme is that the error of the high-speed transfer is evaluated by detecting
the average number of electrons in the node with a low-speed sensor. As a first step, we carriedout single-shot measurement and thereby separated SE captures into the node and SE ejections
from the node to investigate the transfer mechanism.
Figure 3 shows a typical result of the detection during the SE shuttle transfer at atemperature of 17 K. The abrupt changes of the detection current (IS-D) indicate the captureand ejection of an SE. Here, two capture errors are observed. From longer measurements,
the best error rates of the capture and ejection are estimated to be about 2.1 % and 0.25 %,respectively. The former can be explained by thermal fluctuations, indicating the possibility ofachieving high-accuracy transfer by reducing temperature or scaling down the device size. The
latter can not be explained by thermal fluctuations. From the dependence of the pulse voltage
amplitude, we attribute it to transfer mediated by a trap level. Since the trap-mediated transfer
shows low error, it could be possible to achieve high-accuracy SE transfer.
[1] G. Yamahata et al., Appl. Phys. Lett. 98 (2011) 222104.
[2] A. Fujiwara et al., Appl. Phys. Lett. 92 (2008) 042102.

Fig. 2. Scanning electron microscope image of thedevice.

Fig. 1. Schematic of the SE transfer device for
accuracy evaluation.

Fig. 3. Charge detection during SE shuttle transfer.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)25

A New Charge Sensing Scheme Using the Anti-Symmetric Vibration of
Coupled Mechanical Resonators
Hajime Okamoto, Koji Onomitsu, and Hiroshi Yamaguchi
Physical Science Laboratory
High-sensitive charge detection using a micromechanical resonator has recently attracted
great attention [1]. There is however a drawback in such mechanical sensing in that thevibration of the resonator itself causes backaction on the object to be measured. In thisstudy, we propose a new mechanical sensing protocol that suppresses the vibrational
backaction based on the unexcited anti-symmetric vibration mode in two GaAs based coupledmicromechanical resonators [Figs. 1(a) and 1(b)]. When the two resonators are perfectly
coupled and simultaneously driven, the anti-symmetric vibration mode is not excited because
the out-of-phase vibration is cancelled by the in-phase actuation [Fig. 1(c)]. However, once
the frequency of one of the resonators is detuned by added charges via the piezoelectric effectin GaAs, the perfect coupling is broken and the anti-symmetric mode is excited [Fig. 1(c)].
Therefore, by monitoring the change in the amplitude of the anti-symmetric mode one candetect charges that are added to the resonator.
The two elastically coupled doubly-clamped beams consist of i-GaAs, n-GaAs, and GaAs/
AlGaAs superlattice layers and Au gates [Figs. 1(a) and 1(b)]. The frequency of beam B ismatched to that of beam A by using the photothermal frequency shift induced by HeNe laser
irradiation [2]. The two beams are simultaneously actuated by a piezo-actuator set beneaththe resonators in a vacuum at room temperature, while the mechanical motion of beam B isdetected with the reflected laser via optical interferometry. Highly-sensitive charge detection
is demonstrated by applying a low-frequency (313 Hz) gate voltage to beam A. This gate
modulation induces an electric field between the top gate and the n-GaAs layer, resulting inpiezoelectric stress in the longitudinal ([110]) direction. This causes the frequency detuning
and therefore breaking the symmetry of the anti-symmetric vibration mode. The change in thevibrational amplitude is detected with a spectrum analyzer via lock-in detection of the output
signal from the interferometer. The charge sensitivity is derived from the corresponding noise
spectrum and the highest sensitivity of 147 e/Hz0.5 is obtained at room temperature [Fig. 1(d)][3]. Because this sensing scheme is based on the unexcited initial state, the vibration backaction
can be minimized. This sensing scheme can also be extended for mass sensing.
[1] A. N. Cleland and M. L. Roukes, Nature 392 (1998) 160.
[2] H. Okamoto et al., Appl. Phys. Express 2 (2009) 062202.
[3] H. Okamoto et al., Appl. Phys. Lett. 98 (2011) 014103.

Fig. 1. (a) A schematic drawing of the coupled resonators. (b) Optical micrograph of the sample. (c) Change in
the anti-symmetric mode by DC detuning. (d) Charge noise spectrum for the actuation frequency of 753.5
kHz.
26

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Remote Actuation of an Electromechanical Resonator
Daiki Hatanaka, Imran Mahboob, and Hiroshi Yamaguchi
Physical Science Laboratory
Electromechanical resonators with small mass and high quality-factor have attracted
intensive attention due to their potential applications as sensors [1], signal processors [2] andto study macroscopic quantum phenomena [3]. Actuation of the electromechanical resonator
is essential in order to access the various mechanical functions. In the actuation methods
reported so far, mechanical oscillations were induced by directly applying a voltage to anelectrode on the mechanical resonator. The presence of the electrode for these direct electricalactuations not only loads the resonator but can also yield Joule heating which increases
the mechanical energy dissipation and thus degrades the resonator performance. In orderto overcome these obstacles, a contact free driving technique that does not need the directelectrical actuation was developed [4].
A GaAs/AlGaAs-based mechanical resonator containing a two dimensional electron gas(2DEG) and gold top-gates (TGs) was fabricated, which was placed inside a coil operatingin the radio-frequency (RF) range as shown in Fig. 1. The mechanical resonator reveals thefundamental mode fres = 172990.5 Hz at less than 200 mK as shown in the inset of Fig. 1. The
coil shows a number of LC resonances (the upper panel in Fig. 2) and it emits RF waves tothe mechanical resonator when the coil transmission is maximized. To demonstrate remote
actuation using the RF waves, the mechanical response as function of the coil frequency
fcoil ranging from 10 to 130 MHz was measured (the lower panel in Fig. 2). The RF wave’s
amplitude was modulated at frequency fAM and when fAM = fres, the mechanical oscillator
resonated at frequencies that corresponded to the LC resonances in the coil. The RF waves
generated from the coil could drive the mechanical oscillator to resonance. This driving
scheme enables the mechanical oscillations to be remotely induced and paves the way towards
new applications for electromechanical resonators.
[1] A. N. Cleland and M. L. Roukes, Nature 392 (1998) 160.
[2] I. Mahboob and H. Yamaguchi, Nature Nanotech. 3 (2008) 275.
[3] A. D. O’Connell et al., Nature 464 (2010) 697.
[4] D. Hatanaka et al., Appl. Phys. Lett. 99 (2011) 103105.

Fig. 1. A schematic of the micron-sized mechanical resonatorinside a coil and the experimental set-up. The inset
shows piezoelectrically driven and detected mechanicalresponse at an actuation voltage of 12 mVrms.

Fig. 2. The coil and the mechanical resonatorresponse when excited by AM RF
waves whilst sweeping the coilfrequency with a power of –25 dBm.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)27

Unraveling the Spin Polarization of the ν = 5/2 Fractional
Quantum Hall State
Lars Tiemann1, 2, Gerardo Gamez1, Norio Kumada1, and Koji Muraki1, 2
1
Physical Science Laboratory, 2Japan Science and Technology Agency
Fundamental particles in nature are classified as either fermions or bosons according to how
the wave function changes sign with interchange of two particles. Remarkably, behavior ofparticles in a correlated state is often described in terms of quasiparticles possessing properties
different from those of the original particles. In two dimensions, a quasiparticle behaving
differently from fermions or bosons is theoretically possible. In particular, theory predicts
the existence of quasiparticles with exceedingly unusual properties. These quasiparticles,
known as non-Abelian quasiparticles, whose interchange takes the system from one of its
many ground states to another, have attracted strong interest from both theory and experiment
as it would establish the foundation for topological quantum computing—an entirely novel
architecture for error free quantum computation [1].
Fractional quantum Hall states that emerge in a two-dimensional electron system confined
to a heterointerface of pristine semiconductor crystals, such as GaAs/AlGaAs, are expected
to host such exotic quasiparticles that are neither fermions or bosons. Of particular interest is
the one at Landau level filling factor ν = 5/2 [2], which is predicted to support non-Abelianquasiparticles. However, unlike other states, the exact origin of the ν = 5/2 state remains
unknown. The likely candidates for its wave function that emerged through experiment [3]include one that does not support non-Abelian quasiparticles. Exploiting the fact that thesewave functions have different spin states, we have demonstrated for the first time that all theelectrons in the ν = 5/2 state have their spins fully polarized along the applied field using
resistively detected nuclear magnetic resonance (NMR) (Fig. 1) [4]. With our results, possible
theoretical models are narrowed down to only those supporting non-Abelian quasiparticles.
[1] C. Nayak et al., Rev. Mod. Phys. 80 (2008) 1083.
[2] R. L. Willet et al., Phys. Rev. Lett. 59 (1987) 1779.
[3] I. P. Radu et al., Science 320 (2008) 899.
[4] L. Tiemann, G. Gamez, N. Kumada, and K. Muraki, Science 335 (2012) 828.

Fig. 1. (a) Longitudinal resistance (R xx) versus gate
voltage. (b) Resistively detected NMR spectraof 75As measured at 6.4 T at ν = 2, 5/2 and 5/3.
Insets show the measurement set up (left) andthe spin configuration at each ν (right).

28

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Gate Operation of InAs/AlGaSb Heterostructures with an Atomic-LayerDeposited Insulating Layer
Kyoichi Suzuki, Yuichi Harada, Fumihiko Maeda*,
Koji Onomitsu, Toru Yamaguchi, and Koji Muraki
Physical Science Laboratory, *Materials Science Laboratory
InAs/AlGaSb heterostructures are promising for applications to high-speed electronic
devices, such as high-frequency field-effect transistors, because of their large electron
concentration and high room-temperature electron mobility. There remains a serious
impediment to achieving the expected device characteristics, however, posed by the largegate leakage through the AlGaSb barrier and GaSb cap layers. To circumvent this difficulty,
various methods of fabricating a gate insulator have been examined. In particular, atomic layer
deposition (ALD), which makes it possible to deposit a thin and uniform insulating layer withhigh dielectric constant, is considered to be an up-and-coming technique [1,2].
It is well known in the InAs/AlGaSb system that, without any surface treatment, nativeoxides of the GaSb cap layer and/or defects at the cap/insulator interface induce electron
trap states. Accumulation and release of electrons in and out of these trap states partiallycompensate the gate electric field and thus impede the gate operation. We have investigatedthe effects of the surface treatments before forming an Al2O3 insulating layer by ALD (Fig. 1)[3]. We find that dilute HCl treatment for only 10 s effectively removes the electron trap statesand greatly improves the gate operation (Fig. 2).
[1] J. E. Crowell, J. Vac. Sci. Technol. A 21 (2003) S88.
[2] I. J. Gelfand, S. Amasha, D. M. Zumbuhl, M. A. Kastner, C. Kadow, and A. C. Gossard,
Appl. Phys. Lett. 88 (2006) 252105.
[3] K. Suzuki, Y. Harada, F. Maeda, K. Onomitsu, T. Yamaguchi, and K. Muraki, Appl. Phys.
Express 4 (2011) 125702.

Fig. 1. InAs/AlGaSb heterostructure with an
Al2O3 insulating layer by ALD.

Fig. 2. Electron concentration (n2d) as a function of gate
voltage (VG). (a)No-treatment. (b)HCl-treatment

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)29

Indium Atom Manipulation on a Cleaved InAs Surface
Kyoichi Suzuki, Stefan Fölsch*, and Kiyoshi Kanisawa
Physical Science Laboratory, *Paul-Drude-Institut
As semiconductor devices become more advanced and more highly integrated, further
miniaturization and further reduction of power consumption are desired. Atomic-scale
devices are the ultimate ones for meeting these demands. A promising way to construct thesedevices is to use a scanning probe microscope system. Up to now, we have achieved verticalmanipulation of In atoms on an InAs(111)A surface by means of reversible tip-surface
transfer [1]. Here we have succeeded manipulation of In atoms in not only vertical but also
horizontal directions on an InAs(110) surface obtained by cleaving in ultra-high vacuum [2].
On the InAs(111)A surface, the manipulated In atom is bound to the potential pocket
originating from the surface reconstruction resulting in difficulty for the lateral manipulation.
In contrast, on the InAs(110) surface, the surface reconstruction effect is small and thepotential pockets are not very deep. Taking advantage of inelastic tunneling excitation andinversion asymmetry of the surface, the In atoms can be manipulated in the specific horizontal
direction ([001]) (Fig. 1).
Many compound semiconductors have same zinc-blend crystal structure as InAs. Wideand flat (110) surface can be obtained easily by cleaving. On the basis of our achievement,
progress of the atom manipulation on other semiconductor (110) surfaces and on crosssectional surfaces of heterostructures is expected.
This work was partly supported by a subsidy from the Strategic Japanese-German
International Cooperative Program on Nanoelectronics supported by the Japan Science andTechnology Agency (JST) and the German Research Foundation (DFG).
[1] S. Fölsch, J. Yang, C. Nacci, and K. Kanisawa, Phys. Rev. Lett. 103 (2009) 096104.
[2] K. Suzuki, S. Flösch, and K. Kanisawa, Appl. Phys. Express 4 (2011) 085002.

Fig. 1. STM images of In atoms on an InAs(110) surface. (a) and (b): In atoms are shown as black dots. When
the STM tip approaches to the surface with the negative sample voltage (–1.0 V), an atom transfers fromthe tip to the surface. (c) and (d): In atoms are shown as white dots. When the tip approaches to a target
atom with the positive sample voltage (+1.0 V), the atom transfers from the surface to the tip. (e)-(g): Whenthe sample voltage is swept above a target atom, the atom hops horizontally in [001] direction by an In-As
zigzag row.

30

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Observation of Hysteretic Transport due to Dynamic Nuclear Spin
Polarization in a GaAs Lateral Double Quantum Dot
Takashi Kobayashi1,2, Kenichi Hitachi1, Satoshi Sasaki1,2, and Koji Muraki1
1
Physical Science Laboratory, 2Tohoku University
Electron spin dynamics in a semiconductor quantum dot (QD) is affected by the nuclear
spin ensemble of the host material. This makes nuclear spin (NS) manipulation importantin view of quantum information processing using physical qubits based on electron spins
in QDs. Recently, we have observed a hysteretic transport signaling dynamic nuclear spinpolarization (DNP) in a GaAs lateral double QD (DQD) regarded as a promising candidate forthe physical implementation of the spin qubit because of its high controllability [1]. Magneticfield dependence of this signal suggests strongly unbalanced DNP between two dots, which isapplicable to a rapid manipulation of a spin qubit.
Figure 1 shows the DQD sample [(a)] and the dot current Idot measured in the few-electron
regime [(b)]. Idot is clearly suppressed in the trapezoid region owing to the spin blockade (SB),where transport is blocked whenever parallel-spin electrons singly occupy both two dots.
In the SB region, electron spin relaxation results in leak current reflecting the spin relaxation
mechanism [2]. To investigate this mechanism, we measured Idot as a function of ε definedby the arrow in Fig. 1(b) and in-plane magnetic field B||. While the Idot spectrum obtainedby ε sweeps at each value of B|| [Fig. 2(a)] does not show any feature at ε < 0, clear Idot
enhancement appears over a wide range of ε and B|| in that obtained by up sweeps of B|| ateach value of ε [Fig. 2(b)]. Figure 2(c), which displays Idot measured by round sweeps of B||,reveals that this Idot enhancement is hysteretic with respect to the sweep direction of B||. This
result indicates DNP occurring for up sweeps of B||, similarly to previous reports on DQDs ofdifferent materials and/or shapes [3]. Furthermore, the gradually escalating current level ofthis DNP signal with B|| suggests strongly unbalanced DNP between the two dots, where NSs
are polarized preferentially in one of the two dots.
[1] T. Kobayashi et al., Phys. Rev. Lett. 107 (2011) 216802.
[2] F. H. L. Koppens et al., Science 309 (2005) 1346.
[3] K. Ono and S. Tarucha, Phys. Rev. Lett. 92 (2004) 256803; A. Pfund et al., Phys. Rev. Lett.
99 (2007) 036801; H. O. H. Churchill et al., Nature Phys. 5 (2009) 321.

Fig. 1. (a) SEM image of the DQD sample.
(b) Idot spectrum in the few-electron
regime. (n,m) denotes the occupationof the left and right dots.

Fig. 2. ε and B|| dependence of Idot around the SB regime. (a) is
obtained by ε sweeps at each value of B||. (b) is obtained by
up sweeps of B|| at each value of ε . (c) Idot obtained by roundsweeps of B||.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)31

Mediation of Entanglement between a Microscopic Two Level System
and a Macroscopic Resonator Using a Superconducting Flux Qubit
Alexander Kemp, Shiro Saito, William John Munro*, and Kouichi Semba
Physical Science Laboratory, *Optical Science Laboratory
Circuit quantum electrodynamics in superconducting circuits has demonstrated the couplingof superconducting qubits to microwave photons in a superconducting resonator, paving a way
for scaling up the qubit system [1]. During these experiments, microscopic two level systems(TLS) coupled to the qubit were observed [2]. Here we report on the study of an entangledstate of a microscopic TLS and a macroscopic resonator by way of a superconducting flux
qubit [3].
A spectrum of the flux qubit depicted in fig. 1(a) shows two anti-crossings at 6.17 GHz and8.95 GHz. These represent the coupling of the qubit to the TLS and the resonator, respectively.
The coupling strengths were 55 MHz and 154 MHz. The qubit energy can be controlled by an
external magnetic flux through the qubit. Using a flux shift pulse, we can bring the qubit on
resonance with the TLS (or resonator) and create any entangled state between the qubit andthe TLS (or resonator). Utilizing such pulses we realized an entangled state between the TLS
and the resonator.
Figure 1(b) shows a pulse sequence to make this entangled state. First, a microwave π-pulse
prepares the qubit in the excited state |100> (where the state is represented by |qubit, TLS,
resonator>). Next a SWAP pulse brings the qubit on resonance with the TLS creating theentangled state (|100>+|010>) / 2 . Then a SWAP pulse between the qubit and the resonatorrealizes the entangled state (|001>+|010>) / 2 . The state then acquires a relative phase φ = ∆Eτ /ħ during a period of free evolution of a time τ . Here ∆E is the energy difference between
the |001> and |010> levels. To observe this phase evolution we reverse our pulse sequence, weapply the SWAP pulse and then the SWAP pulse followed by the readout of the populationof the qubits excited state Pex. Figure 2 shows that Pex as a function of τ oscillates with thefrequency of ∆E/h. This indicates an entangled state between the TLS and the resonator isrealized during the free evolution.
In the future we will replace the TLS by a controllable quantum memory and scale up our
superconducting qubits with long-lived quantum memories.
This work was supported by KAKENHI.
[1] L. DiCarlo et al., Nature 467 (2010) 574.
[2] R. W. Simmond et al., Phys. Rev. Lett. 93 (2004) 077003.
[3] A. Kem et al., Phys. Rev. B 84 (2011) 104505.

Left: Fig. 1. (a) Spectrum of a flux qubit. (b) Pulse
sequence for the experiment.
Right: Fig. 2. (a) Switching probability Pex as a function of τ .
(b) Fourier spectrum of Pex.
32

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Coherent Coupling of a Gap-Tunable Flux Qubit to an Electron Spin
Ensemble in Diamond
Xiaobo Zhu1, Shiro Saito1, Alexander Kemp1, Kosuke Kakuyanagi1, Shinichi Karimoto1,
Hayato Nakano1, William J. Munro2, Yasuhiro Tokura1, Mark S. Everitt3, Kae Nemoto3,
Makoto Kasu4, Norikazu Mizuochi5,6, and Kouichi Semba1
1
Physical Science Laboratory, 2Optical Science Laboratory, 3National Institute of Informatics,
4
Materials Science Laboratory, 5Osaka University, 6PREST-JST
During the last several years, significant effort into superconducting quantum bits (qubits)
based on Josephson junctions have been made. However, the experimentally reported
coherence times are likely to be insufficient for future large-scale quantum computing. A
natural solution is an engineered quantum memory based on atomic and molecular systems.
–
An electron spin trapped at a nitrogen-vacancy (NV ) center in diamond is known to havea very long coherent time and can be coupled via mutual inductance to a flux qubit. It istherefore an ideal candidate to acts as a quantum memory for our flux qubit.
We have designed and fabricated an upgraded flux qubit, whose gap can be tuned in situ by
two high bandwidth control lines [1], giving two fundamental improvements: "gap control"and "σx coupling". Based on these fundamental improvements many new applications can berealized. For example, it opens up the possibility to realize a high fidelity coupling to otherquantum systems and so demonstrate a quantum memory operation.
–
We glued an NV diamond sample on top of our superconducting circuit. We for the
first time observed an anti-crossing structure at 2.88 GHz which clearly shows a ~70 MHz–
coupling between the NV spin ensemble and the gap-tunable flux qubit (Fig. 1). Furthermore
we also observed the coherent exchange of a single quantum of energy between the flux qubit–
and a macroscopic ensemble consisting of about 6×107 NV centers (Fig. 2). This is the firststep towards the realization of a long-lived quantum memory and hybrid devices coupling
microwave and optical systems [2].
This work was supported by KAKENHI.
[1] X. Zhu et al., Appl. Phys. Lett. 97 (2010) 102503.
[2] X. Zhu et al., Nature 478 (2011) 221.

Fig. 1. Energy spectrum of the flux qubit coupled–
to an NV center ensemble.

Fig. 2. Coherent oscillations of the flux qubit / NV
center ensemble coupled system.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)–33

In0.75Ga0.25As Quantum Point Contact Utilizing Wrap-Gate Geometry
Hiroshi Irie, Yuichi Harada, Hiroki Sugiyama*, and Tatsushi Akazaki
Physical Science Laboratory, *NTT Photonics Laboratories
Quantum nanostructures, such as quantum point contacts (QPCs) or quantum dots, in highIn-content InxGa1–xAs offer unique functionalities originated from its material properties.
Firstly, by exploiting the strong spin-orbit interaction (SOI) in InGaAs, the electronic spin canbe manipulated through the SOI. As an example, electrons moving through QPC experience
the selective spin-flipping caused by SOI induced spin-splitting, which implies that the
InGaAs QPC works as a spin-polarizer without the need of magnetic field [1]. Secondarily,
InGaAs nanostructures are promising for the development of semiconductor/superconductor
hybrid devices. Since high-In-content InxGa1–xAs forms low Schottky barriers (or no barrier
for x > 0.77) against most metals, superconducting Cooper pairs can be effectively injected
into InGaAs. Superconducting quantum point contact, a counterpart of the semiconducting
QPC, has been intensively investigated to realize a quantum bit using Andreev boundstates or to observe Majorana fermions that are induced at the interface between an s-wave
superconducting electrode and one-dimensional channel with strong SOI.
In this study, we improved fabrication technique to realize QPCs in an In0.75Ga0.25As/InAlAs
two-dimensional electron gas heterostructure [2]. The key challenge in realizing a wellbehaved QPC is efficient electrostatic control of a one-dimensional channel using the gateelectrode. The fabricated QPCs employ a 100-nm-wide mesa constriction and a gate electrode
that wraps around the constriction for three-dimensional electric-field gating. Conformal
aluminum-oxide growth by means of atomic layer deposition is employed to suppress gateleakage while minimizing the interface state density. Figure 1 shows an SEM image of thefabricated QPC and a schematic drawing of the cross-section. The wrap-gate QPCs show clear
conductance steps, demonstrating the formation of one-dimensional channels with quantizedtransverse modes, as shown in Fig. 2. This technique can be easily extended to the fabricationof quantum dots and superconductor/QPC/superconductor junctions, which opens up a novel
approach for the studies of spin-related phenomena in InGaAs-based quantum nanostructures.
This work was supported by KAKENHI.
[1] M. Eto et al., J. Phys. Soc. Jpn. 74 (2005) 1934.
[2] H. Irie et al., Appl. Phys. Express 5 (2012) 024001.

Fig. 1. SEM image and cross-sectional drawing of QPC.

34

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Fig. 2. Conductance vs. gate voltage.

Exploring Novel Quantum Phases of Bose-Fermi Mixtures Trapped in an
Optical LatticeKensuke Inaba and Makoto Yamashita
Optical Science Laboratory
Recently, atomic gases trapped in a vacuum chamber can be cooled down to several nanoKelvins regime, where the quantum effects govern physical properties of the system. The
high controllability of atoms provides us with sophisticated tools for measuring the quantum
phenomena. Thus, this system can be regarded as a quantum simulator [1], which attracts
much interest of many researchers in various fields, such as condensed matter physics,
elementary particle physics, quantum chemistry, and so on. In particular, the atoms trappedin an optical lattice, which is the artificially created periodic potential by laser interference,are expected to make great progress in condensed matter physics, because such fermionic
atoms mimic electrons in a metallic crystal [2]. We can explore the pure quantum many-bodyeffects by using this system without any lattice distortions and impurities. Interestingly, thiscontrollable system allows us to expand the current knowledge in the electron systems.
Collaborating with the group at Kyoto University, we investigated the Bose-Fermi mixtures
trapped in an optical lattice both theoretically and experimentally, and clarified appearance ofnovel quantum phases not observed in condensed matters [3]. Here, we introduce a part of ourresults on the attractively interacting Bose-Fermi mixtures. Kyoto University group measured
the pair occupancies with photo-association spectroscopy by changing the number of
fermionic atoms. We developed the numerical method for analyzing this system and applied it
to the experiments. We show our results in Fig. 1(a) and (b), and briefly explain the proceedingof the measurements in Fig. 1(c). Our calculations show good quantitative agreements withexperiments. We further analyzed the quantities that are difficult to be directly measured
by the current experimental techniques. Based on these results, we clarified that the nonmonotonic behavior of Bose-Bose pair occupancy seen in Fig. 1(b) results from the crossover
among novel quantum phases. We also investigated the repulsively interacting system andfound a different type of crossover.
[1] I. Bloch, Nature Phys. 1 (2005) 23.
[2] M. Greiner and S. Fölling, Nature 453 (2008) 736.
[3] S. Sugawa, K. Inaba et al., Nature Phys. 7 (2011) 642.

Fig. 1. (a) Bose-Fermi pair and (b) Bose-Bose pair occupancies observed by photo-association spectroscopy.
The number of bosons is fixed at 5000. Numerical calculations consider the experimental ambiguityof estimated temperatures. (c) Schematic diagrams of the Bose-Fermi pair occupancy measurements.
Irradiated laser induces photo-associated transition from a pair of atoms to a molecular state at each site,
and the molecule immediately moves outside of the optical lattice. By counting the lost atoms, we canthus determine the Bose-Fermi pair occupancies. Another excitation laser is used for the Bose-Bose pairoccupancy.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)35

Enhanced Optical Nonlinearity in a Silicon Photonic Crystal
Slow-Light WaveguideNobuyuki Matsuda, Ken-ichi Harada, Hiroki Takesue,
Eiichi Kuramochi, Hideaki Taniyama, and Masaya Notomi
Optical Science Laboratory
Slow light (SL) in an optical chip provides an enhanced light-matter interaction, thanks to
the longitudinally compressed optical field and the prolonged interaction time between themedium and the slowly-propagating light within. We have already fabricated high-bandwidth
SL waveguides using a 1-D chain of silicon photonic-crystal ultrahigh-Q (~ 1 million)
nanocavities and demonstrated v g less than c/100 in the telecom band [1]. This time wedemonstrated SL enhancement of all-optical wavelength-conversion efficiency in our device
via the four-wave-mixing (FWM) experiment [2].
Schematic of our SL waveguide (vg = c/36, 0.42-mm long) is shown in Fig. 1. We input
telecom-band pump and signal beam into the device and observed a new idler field that was
created by the stimulated FWM, which arises from the third-order optical nonlinearity in thecore material (Si). We plotted measured signal-to-idler wavelength conversion efficiency as afunction of input pump power as shown in Fig. 2. The conversion efficiency was proportional
to the the square of the pump power because the FWM is a two-photon absorption process.
From the result, we obtained the value of nonlinear constant γ , which is the degree ofwaveguide nonlinearity, as 18,600 /W/m. The value is 107 times larger than that of standard
single-mode fibers and even larger than 300 /W/m of a silicon wire waveguide (vg = c/4.2) [3]and 2,930 /W/m of a photonic crystal SL waveguide that employed a line defect mode (vg =c/30) [4]. The extremely high nonlinearity of our device is originating from SL enhancement((1/vg)2 dependence of γ ) and a strong spatial confinement of the SL mode due to wavelengthsized photonic crystal cavities. This value is the highest yet reported for silicon-core nonlinear
waveguides with an integrated structure, indicating a potential to provide a new stage for
integrated waveguide photonic devices with ultralow power consumption.
This work was supported by KAKENHI.
[1] M. Notomi, E. Kuramochi, and T. Tanabe, Nature Photon. 2 (2008) 741.
[2] N. Matsuda et al., Opt. Express 19 (2011) 19861.
[3] K. Harada et al., IEEE J. Sel. Top. Quantum Electron. 16 (2010) 325.
[4] C. Monat et al., IEEE. J. Sel. Top. Quantum Electron. 16 (2010) 344.

Fig. 1. Silicon photonic-crystal coupled-resonator opticalwaveguide.

36

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Fig. 2. Signal-to-idler wavelength conversion
efficiency via the FWM.

Generation of Femtosecond Laser Pulses at 1-GHz Repetition Rate
Derived from Continuous Wave Laser Diode
Tadashi Nishikawa and Atsushi Ishizawa
Optical Science Laboratory
Femtosecond pulse lasers with a gigahertz repetition rate are attractive for a variety of
applications, including the analysis of nanomechanical and optomechanical systems, as amultiphoton tool for nanomedicine and nanobiotechnology, for high-speed asynchronous
optical sampling, and as a carrier-envelope-offset-locked frequency comb with a wide mode
spacing [1]. Conventional methods for generating a femtosecond pulse train are based on apassive mode-locking technique. However, since the cavity length must correspond to therepetition rate, it is difficult to obtain femtosecond pulses with a high repetition rate exceeding
1GHz. Moreover, the repetition rate and wavelength have limited tunability. We propose
a simple method to generate GHz repetition rate optical pulses with a widely selectable
repetition rate and wavelength by using commercial optical phase-modulators (PMs), a
commercial intensity-modulator (IM), and a standard single-mode fiber (SMF).
The phase of the light from a CW laser diode (LD) with a center wavelength of 1552 nm
are modulated with PMs driven by an external RF synthesizer at modulation frequency of 25
GHz. This process causes repetitive up- and down-chirping at 25 GHz. The linear part of thedown-chirping is selectively gated with the IM, resulting in a flat optical frequency comb witha 24-nm bandwidth. After chirping compensation with a SMF, we obtained a 230-fs pulse at
25 GHz. After an optical gate, which reduces the repetition rate from 25 GHz to 1 GHz (or250 MHz), the optical pulse train is amplified up to an average power of 1 W in an erbiumdoped fiber amplifier (EDFA). Since the laser peak intensity is estimated to be more thanseveral kilowatts in the EDFA, spectral broadening occurs by self-phase modulation. Then,the chirped pulse is compressed by 1-m-long glass block. We succeeded in the generation of
a 1-W, 120-fs optical pulse at 1 GHz and a 1-W, 80-fs optical pulse at 250 MHz [2]. Figure
1 shows the spectrum and autocorrelation trace for the latter case. As far as we know, these
are the shortest pulses ever achieved for these repetition rates using a CW LD as a seed lightsource. Our scheme could provide a sub-100-fs laser with widely tunable repetition rate andwavelength by changing the modulation frequency of the RF synthesizer and the wavelengthof a tunable laser diode. These features mean that our proposed laser system has the potential
to become a powerful tool for a variety of applications.
[1] A. Ishizawa, T. Nishikawa et al., Electron. Lett. 46 (2010) 1343.
[2] A. Ishizawa, T. Nishikawa et al., Optics Express 23 (2011) 22402.

Fig. 1. (a) Spectrum and (b) autocorrelation trace obtained using the optical gate at 250 MHz.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)37

Transport and Manipulation of Electron Spins
Using Surface Acoustic Waves
Haruki Sanada, Hideki Gotoh, Koji Onomitsu*, and Tetsuomi Sogawa
Optical Science Laboratory, *Physical Science Laboratory
Transporting electron spins in semiconductors will be a crucial technique both for
fundamental research on spin-orbit interactions [1] and for the spintronics applications thatneed spin information transfer [2]. We have investigated the spin dynamics of electrons
traveling with moving wires and dots formed by surface acoustic waves (SAWs) [3].
The moving wires and dots are generated in a 20-nm-thick GaAs/AlGaAs(001) quantum well
(QW) grown by molecular beam epitaxy. Interdigital transducers (IDTs) designed for operation
at a SAW wavelength of 2.55 μm were processed on the sample. Depending on the IDT's
direction, Rayleigh SAWs propagate along [–110] or [110] with a velocity vSAW = 3 km/s. The
single SAW beams produce moving wires, which are formed by the one-dimensional lateralconfinement of the SAW-induced piezoelectric potential. The interference between the two
orthogonal SAW beams forms moving dots traveling along [010] with a velocity of 2 vSAW.
To measure the spin dynamics during transport, we employed Kerr microscopy with apump-probe technique. A circularly polarized pump light generated spin-polarized electrons
at a fixed position on the sample; and a linearly polarized probe light, which can be scanned in
the QW plane, was used to detect the magneto-optic Kerr effect. Since the Kerr rotation angle
θK is proportional to the spin density at the probe position, we can obtain two-dimensional
images of spin distribution under SAWs.
Figure 1 shows the two-dimensional images of the spin transport measured in the absenceof an external magnetic field. For both moving wires and dots, we successfully extracted
the precession behavior induced by the spin-orbit interaction. We also found that the spin
precession frequency for the moving dots depends on the SAW intensity (Fig. 2). The
theoretical analysis of the data revealed the existence of SAW-induced spin-orbit interactions,indicating that the spin precession angle is acoustically tunable. These techniques will provide
the versatility needed for spin manipulation in future spintronics applications.
This work was partly supported by KAKENHI.
[1] Y. Kato et al., Nature 427 (2004) 50.
[2] S. A. Wolf et al., Science 294 (2001) 1488.
[3] H. Sanada et al., Phys. Rev. Lett. 106 (2011) 216602.

Fig. 1. Two-dimensional images of spin densities for moving
wires traveling along [–110] (a), [110] (c), and for moving
dots traveling along [010] (b).

38

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Fig. 2. SAW intensity dependence of theprecession frequency for moving
dots. The line is a theoretical fit.

Bonding and Anti-Bonding Orbitals in Raman Spectroscopy for
Graphene Edge
Ken-ichi Sasaki, Keiko Kato, Yasuhiro Tokura, and Satoru Suzuki*
Optical Science Laboratory, *Materials Science Laboratory
Graphene has several notable properties not seen in the conventional semiconductor. For
example, there is a degree of freedom known as pseudospin. It is a general idea regarding
the superposition of bonding and antibonding orbitals. Normally bonding orbital is morestable than antibonding orbital in energy, however, graphene is a special material in whichbonding and antibonding orbitals are degenerate. As a result, various types of superposition
are realizing at an energy contour surface. The direction of pseudospin is defined by thesuperposition of bonding and antibonding orbitals in the same manner as the direction of spinis determined by the superposition of up and down spins. We are pursuing the possibility ofpseudospintronics of graphene.
As it is the first stage of spintronics to distinguish between up and down spins, it is an
important stage of pseudospintronics to distinguish between up and down pseudospins. Whilespin direction is changed by a magnetic field, pseudospin direction is changed by a stress.
In material, there exists an internal strain called phonon, and the pseudospin direction isgoverned by the interaction between electron and phonon. Raman spectroscopy is suitablefor investigating the pseudospin. Here, we report on our study, in which the two pseudospinsthat correspond to bonding and antibonding orbitals are automatically selected in the Raman
spectroscopy for graphene edge.
In the Raman spectrum taken at a graphene edge, it is commonly observed that the D band
appears as a prominent peak [1]. A notable feature of the D band is that there is a strong
dependence on the polarization of light: when the polarization is parallel to the edge, theintensity is the maximum, and it is suppressed for perpendicular polarization. We clarified that
this polarization dependence originates from the pseudospin dependence of electron-phonon
interaction. Namely, because the D band is a special (strain) phonon mode that consists onlyof the bond stretching motion, the bonding and antibonding orbitals couple selectively to the Dband [2]. This means that exciting the D band at graphene edge is the same as selecting the up
and down pseudospins (bonding and antibonding orbitals) among all directions of pseudospins[Fig. 1(a)].
In addition, we predict that the D band splits into two peaks [Fig. 1(b)]. The higher (lower)
frequency peak originates from up (down) pseudospin. By this splitting, it is possible todistinguish between up and down pseudospins. Although there is no report on the splitting of
the D band at graphene edge yet, the splitting of the D band has been observed in defective
carbon nanotubes [3].
[1] C. Cashiragi et al., Nano Lett. 9 (2009) 1433.
[2] K. Sasaki et al., Phys. Rev. B 85 (2012) 075437.
[3] S. Suzuki and H. Hibino, Carbon 49 (2011) 2264.
Fig. 1. (a) The energy dispersion of graphene (Diraccone). The solid and empty circles represent
the electronic states (with bonding andantibonding orbitals) that can selectively excite
the D band phonon. The arrows correspond totheir pseudospin directions. (b) The splittingof the D Raman band.

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)39

Ultrahigh-Q Nanocavities Written with a Nanoprobe
Atsushi Yokoo, Takasumi Tanabe, Eiichi Kuramochi, and Masaya Notomi
Optical Science Laboratory
High-Q nanocavities have been extensively studied recently because they are considered key
elements in low-power photonic devices and integrated circuits. These high-Q nanocavities
in photonic crystals were fabricated by a combination of high-resolution electron-beamlithography and dry etching techniques. However, this means that the photonic crystal device
components should be incorporated in the CAD data before the fabrication process begins. It
is difficult to add other components to photonic crystals once they have been fabricated.
We propose employing the selective oxidation of silicon photonic crystals by using thescanning nanoprobe of an atomic force microscope (AFM) to form an ultrahigh-Q nanocavity
in a line defect of a 2D Si photonic crystal slab as shown in Fig. 1 [1]. Selective anodic
oxidation produces an ultrasmall oxide pattern on a Si surface if we apply a voltage between
the probe's conductive tip and the target, which leads to local modification of the thickness andeffective refractive index of a Si slab. This process is sometimes referred to as scanning-probe
lithography (SPL) or AFM lithography. In this strategy, we utilize the fact that a very small
spatial index modulation (∆n/n < 0.1 % ) changes the mode-gap edge frequency of themodified area to create barrier regions, while the unmodified area retains its original modegap edge frequency [2]. We evaluate peak width of cavity resonance of a photonic crystal
sample post-modulated by SPL and HF wet etching. As a result, an ultrahigh-Q (>1 million)
nanocavities with a mode volume of 0.2 μm 3 can be formed by employing scanning probe
lithography on a pre-patterned line defect in a silicon photonic crystal as shown in Fig. 2. We
confirmed that a photon lifetime of the cavity is around 1.25 ns. This is the first realizationof ultrahigh-Q nanocavities by the post-process modification of photonic crystals. With thismethod, we can form an ultrahigh-Q nanocavity with controllable cavity parameters at anarbitrary position along a line defect. Furthermore, the fabricated nanocavity achieves ultralow power all-optical bistable operation owing to its large cavity enhancement effect. The
threshold power for the bistable operation is close to the values obtained for conventional
photonic crystal nanocavity devices. This demonstration indicates the possibility of realizing
photonic integrated circuits on demand, where various circuit patterns are written with ananoprobe on a universal photonic crystal substrate.
[1] A. Yokoo, T. Tanabe, E. Kuramochi, and M. Notomi, Nano Lett. 11 (2011) 3634.
[2] M. Notomi and H. Taniyama, Optics Express 16 (2008) 18657.

Fig. 1. Schematic of nanocavity formation by SPL
applied to a line defect in photonic crystal.

40

Fig. 2. Cavity resonance of a photonic crystal sample
post-modulated by SPL and HF wet etching.
(Q-factor : 1.3 x 106)

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Ultralow-Power All-Optical RAM Chip Based on Nanocavities
Kengo Nozaki, Akihiko Shinya, Shinji Matsuo*, Yasumasa Suzaki*, Toru Segawa*,
Tomonari Sato*, Ryo Takahashi*, and Masaya Notomi
Optical Science Laboratory, *NTT Photonics Laboratories
An optical random-access memory (o-RAM) will enable us to develop various high-speed
logic elements with a small power consumption [1], and is expected to play a key role infuture optical routers in which high-bit-rate optical packets are processed without E-O/O-E
conversion. A PhC nanocavity is a possible candidate for an o-RAM because of its ultrasmall
size, ultralow power consumption, and large-scale integrability on a chip.
We achieved a novel buried heterostructure (BH) with which to form a PhC nanocavity, as
shown in Fig. 1(a), where an ultra-compact InGaAsP is buried in an InP-PhC waveguide [2].
This structure allowed us to strongly confine both photons and carriers, enabling a bistablebehavior with very small optical power, as shown in Fig. 1(b). Thus memory state switching
between the "on" and "off" states can be successfully obtained with a combination of CW
bias light and optical pulse input. Operation power was only 30 nW, which is several orders ofmagnitude lower than of the power required by previously reported o-RAMs.
To demonstrate the feasibility for integration, we fabricated a four-bit memory array
integrated in the same chip and demonstrated a four-bit RAM operation as shown in Fig. 1(c).
The 40-Gb/s data ("1101" or "1010") were first spatially demultiplexed by an all-optical serialto-parallel converter, and then stored in four different cavities. Finally, the stored four-bit data
were successfully read by injecting read pulses after a buffering time of 500 ns. There has
been no previous report of integrated nanophotonics and our work is the first demonstration of"Integrated o-RAM chip".
This work was supported by the National Institute of Information and Communications
Technology (NICT).
[1] M. Notomi et al., IET Circuits Devices & Systems 5 (2011) 84.
[2] K. Nozaki et al., Nature Photon. 6 (2012) 248.

Fig. 1. (a) Optical RAM element based on photonic crystal nanocavity having compact buried heterostructure. (b)Optical bistability on optical input/output characteristic. (c) Integrated optical RAM operation for 40-Gb/s,
4-bit signal train by parallely-integrated nanocavities on a chip.
Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)41

Ⅱ．Data

Award Winners’ List (Fiscal 2011)
The Commendation for
Science and Technology by
the Minister of Education,
Culture, Sports, Scienceand Technology, The Young
Scientists’ Prize

Y. Taniyasu

Research on the crystal growth of
AlN and its application to the deepultraviolet light-emitting devices

Apr. 20,
2011

H. Yamaguchi

For personal contribution to theadvancement of physics as adiscipline and a profession

May 18,2011

Y. Taniyasu

Seminal Contributions to the Growthof AlN and its Application to the
Shortest Wavelength Light Emitting
DiodesMay 25,2011

JSAP Outstanding Paper
Award ― 2011

K. Kakuyanagi

Generation of Non-ClassicalMicrowave Photon States in an
Inductor; Capacitor Resonator
Coupled to a Superconducting Flux
Qubit

Aug. 30,
2011

An MOC Paper Award, the
7th Micropotics Conference

N. Ishikura,
T. Baba,
E. Kuramochi,
M. Notomi

Ultrahigh-resolution tunable delay
and its application to fast opticalcorrelator

Nov. 2,
2011

The 28th Inoue Prize for
Science

H. Yamaguchi

Pioneering Contributions to the
Study of Quantum MechanicalBehavior
in Minute Mechanical Structures

Feb. 3,
2012

JSAP Outstanding
Presentation Award ― 2011

D. Hatanaka

Highly efficient remote actuation ofa mechanical oscillator by 2DEGcarrier control

Mar. 15,2012

The Institute of Physics (IOP)
Fellow

The Young Scientist
Award of the International
Symposium on Compound
Semiconductors 2011

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)43

In-house Award Winners’ List (Fiscal 2011)

44

NTT Corporation President
Award

H. Yokoyama
T. Kobayashi
N. Watanabe
K. Kumakura
M. Hiroki
Y. OdaCommercialization of high quality
nitride semiconductor epitaxial wafers
for high power applications

Oct. 21,2011

NTT Science and CoreTechnology Laboratory
Group Director Award

S. Saito
K. Kakuyanagi
X. ZhuH. NakanoS. Karimoto
H. Tanaka
W. J. Munro
K. Semba

Pioneering new research fields inquantum information processing
with Josephson quantum circuits

Dec. 21,2011

BRL Director Award
Award for Achievements

X. ZhuS. Saito
A. Kemp
K. Kakuyanagi
S. Karimoto
H. NakanoW. J. Munro
Y. Tokura
M. Kasu
K. Semba

For proof-of-principle experiment of
quantum memory using superconducting
flux qubit and NV centers in diamondMar. 28,
2012

BRL Director Award
Award for Achievements

M. Yamashita
K. Inaba
M. W. Jack

The development of the theoreticalmethod for cold atom analysis and thediscovery of the novel quantum phases
in optical lattice systems

Mar. 28,
2012

BRL Director Award
Award for Achievements

H. Sanada
H. GotoK. Onomitsu
T. SogawaControl of optical and spin propertiesof semiconductors by surface acoustic
waves

Mar. 28,
2012

BRL Director Award
Award for Achievements

K. Nozaki
A. Shinya
M. Notomi
Y. Suzaki
T. SegawaT. SatoS. Matsuo
R. Takahashi

Realization of ultralow-power 4-bit
optical RAM subsystem based on
integrated photonic crystal nanocavities

Mar. 28,
2012

BRL Director Award
Award for Excellent Papers

X. ZhuS. Saito
A. Kemp
K. Kakuyanagi
S. Karimoto
H. NakanoW. J. Munro
Y. Tokura
M. Kasu
K. Semba"Coherent coupling of a superconducting
flux qubit to an electron spin ensemble
in diamond," Nature 478, 221-224(2011).

Mar. 28,
2012

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Numbers of Papers, Presentations and Patents (2011)
The numbers of papers published in international journals, presentations at international
conferences and applied patents in year 2011 amounted to 132, 217, and 51, respectively. The
numbers for each research area are as follows;

Papers Published in International Journals(Jan. – Dec. 2011)23

Materials Science

Physical Science

54

Optical Science

55
0

10

20

30

40

50

60

Number of Papers

Presentations at International Conferences(Jan. – Dec. 2011)Materials Science57

Physical Science

97

Optical Science

63

0

20

40

60

80

100

Number of Presentations

Applied Patents (Jan. – Dec. 2011)Materials Science26

Physical Science

11

Optical Science

14

0

5

10

15

20

25

30

Number of Applied Patents

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)45

The numbers of research papers published in the major journals are shown below.
(IF2010*)

Numbers

Physical Review B

3.774

18

Applied Physics Letters

3.841

16

Japanese Journal of Applied Physics

1.024

13

Physical Review Letters

7.622

12

Optics Express

3.753

11

Applied Physics Express

2.778

5

Physical Review A

2.861

4

Nature Physics

18.43

3

Nano Letters12.2193

New Journal of Physics

3.849

3

Nature36.104

2

Nanotechnology

3.652

2

Nature Nanotechnology

30.324

1

ACS Nano

9.865

1

Journal of the American Chemical Society

9.023

1

Small

7.336

1

Proceedings of the IEEE

5.151

1

Carbon

4.896

1

Journal of Physical Chemistry C

4.524

1

Langmuir

4.269

1

-

1

JournalsNature Communications*IF2010: Impact Factor 2010 (Journal Citation Reports, 2010)

The average IF2010 for all research papers from NTT Basic Research Laboratories is 4.78.

The numbers of presentations in the major conferences are shown below.
Conferences46

Numbers

International Symposium on Nanoscale Transport and Technology

372011 International Conference on Solid State Devices and Materials

19

Electronic Properties of Two-Dimensional Systems 19

1224th International Microprocesses and Nanotechnology Conference

5

38th International Symposium on Compound Semiconductors

5

Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science
Conference

5International Symposium on Surface Science

5

22nd European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes andNitrides4

24th International Symposium on Superconductivity

4

Biophysical Society 55th Annual Meeting

4

ERATO Macroscopic Quantum Control Conference on Ultracold Atoms and Molecules

4

Frontiers in Nanoscale Science and Technology

4

Quantum Nanostructure and Nanoelectronics 20114

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

List of Invited Talks at International Conferences (2011)
I. Materials Science Laboratory(1)

H. Hibino, S. Tanabe, and H. Kageshima, "Growth and characterization of graphene on SiC", Graphene
Workshop in Tsukuba 2011, Tsukuba, Japan (Jan. 2011).

(2)

H. Hibino, S. Tanabe, and H. Kageshima, "Growth, structure, and transport properties of epitaxial
graphene on SiC " 8th International Symposium on Atomic Level Characterizations for New Materials andDevices '11 (ALC'11) Seoul, Korea (May 2011).

(3)

M. Kasu, K. Hirama, and Y. Taniyasu "High-thermal-efficiency AlGaN/GaN HEMTs on diamond", AsiaPacific Workshop on Fundamentals and Applications of Advanced Semiconductor Devices, Daejeon, Korea(June 2011).

(4)

H. Hibino, S. Tanabe, and H. Kageshima, "Growth and electronic transport properties of monolayer
and bilayer graphene on SiC", XX International Material Research Congress 2011 (IMRC 2011), Cancun,
Mexico (Aug. 2011).

(5)

M. Kasu, K. Hirama, and Y. Taniyasu, "Nitride/diamond heterostructures -from growth to devices-", 22nd
European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes and Nitrides (Diamond2011), Garmisch-Partenkirchen, Germany (Sep. 2011).

(6)

A. Shimada, T. Iwata, N. Nakano, and K. Torimitsu, "CMOS LSI for excitation and measurement ofneural activity with microelectrode array", 2011 International Conference on Solid State Devices andMaterials, Nagoya, Japan (Sep. 2011).

(7)

M. Kasu and K. Hirama, "Diamond-based Electronic Device Technologies", International Conference on
Carbon-based Nano-Materials and Devices, Suzhou, China (Oct. 2011).

(8)

H. Hibino, S. Tanabe, and H. Kageshima, "Carrier transport in epitaxial graphene grown on SiC(0001)",
3rd International Symposium on the Science and Technology of Epitaxial Graphene (STEG3), Saint
Augustine, U.S.A. (Oct. 2011).

(9)

H. Omi, "Surface plasmon of gold nanorods in solutions", BIT's 1st Annual World Congress of NanoS&T, Dalian, China (Oct. 2011).

(10)

Y. Krockenberger, "Sr2RuO4 thin films: What's next?", International Workshop for Young Researchers on
Topological Quantum Phenomena in Condensed Matter with Broken Symmetries, Shiga, Japan (Nov. 2011).

(11)

K. Furukawa and J. Durao, "Donor-to-Acceptor Distance Dependent Fluorescence Resonance Energy
Transfer Efficiency for Multiple Donors and Acceptors System Confined within 2-Dimensional Fluid of
Supported Lipid Bilayer", International Symposium on Surface Science (ISSS-6), Funabori, Japan (Dec.
2011).

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)47

II. Physical Science Laboratory

48

(1)

H. Okamoto, D. Ito, K. Onomitsu, H. Sanada, H. Gotoh, T. Sogawa, and H. Yamaguchi, "Carriermediated opto-mechanical coupling in GaAs cantilevers", Frontiers in Nanoscale Science and Technology
Workshop (FNST2011), Saitama, Japan (Jan. 2011).

(2)

H. Nakano, "Time-evolution during superconducting qubit measurement process", International
Symposium "Nanoscience and Quantum Physics 2011" (nanoPHYS'11), Tokyo, Japan (Jan. 2011).

(3)

S. Saito, "Entanglement between macroscopic resonator and microscopic two level system througha flux qubit", The Third International Workshop on Dynamics and Manipulation of Quantum Systems(DMQS2010), Tokyo, Japan (Feb. 2011).

(4)

H. Nakano, "Energy flow and information flow in qubit measurement process", International Conferencein Quantum Bio-Informatics Center (QBIC2011), Chiba Japan (Mar. 2011).

(5)

Y. Ono, M.A.H. Khalafalla, J. Noborisaka, G.P. Lansburgen, and A. Fujiwara, "Dopants in silicontransistors: transport and photoemission", CMOS Emerging Technologies Workshop, Whistler, BC, Canada(June 2011).

(6)

T. Shinada, M. Hori, Y. Ono, A. Komatsubara, K. Kumagai, T. Tanii, T. Endoh, and I. Ohdomari,"Control of dopant distribution by dingle-ion implantation and its impact on transconductance of FETs",
2011 Asia-Pacific Workshop on Fundametals and Applications of advanced Semiconductor Devices(AWAD2011), Daejeon, Korea (June 2011).

(7)

T. Koga, T. Matsuura, S. Faniel, S. Souma, S. Mineshige, Y. Sekine, and H. Sugiyama, "Determinationof spin-orbit coefficients and application to the spin-filter devices using InGaAs/InAlAs heterostructures",2011 Asia-Pacific Workshop on Fundamentals and Applications of Advanced Semiconductor Devices(AWAD2011), Daejeon, Korea (June 2011).

(8)

H. Yamaguchi, I. Mahboob, H. Okamoto, and K. Onomitsu, "Heterostructure-based parametric resonatorand its applications", The Second International Seminar on Nano-Electro-Mechanical Systems (NEMS2011),
Toulouse, France (July 2011).

(9)

L. Tiemann, G. Gamez, N. Kumada, and K. Muraki, "The spin polarization of the ν = 5/2 fractional
quantum Hall state", The 19th international Conference on Electronic Properties of Two-Dimensional
Electron Systems (EP2DS19), Tallahassee, Florida, U.S.A. (July 2011).

(10)

H. Okamoto, D. Ito, T. Watanabe, K. Onomitsu, H. Sanada, H. Gotoh, T. Sogawa, and H. Yamaguchi,"Carrier-mediated opto-mechanical coupling in GaAs micromechanical resonators", 17th International
Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON 17),
Santa Barbara, CA, U.S.A. (Aug. 2011).

(11)

L. Tiemann, G. Gamez, N. Kumada, and K. Muraki, "The spin polarization of the ν = 5/2 fractional
quantum Hall state", 26th International Conference on Low Temperature Physics (LT26), Beijing, China(Aug. 2011).

(12)

X. Zhu, S. Saito, A. Kemp, K. Kakuyanagi, S. Karimoto, H. Nakano, W. J. Munro, Y. Tokura, M. S.
Everitt, K. Nemoto, M. Kasu, N. Mizuochi, and K. Semba, "Coupling an ensemble to a superconducting
qubit", 26th International Conference on Low Temperature Physics (LT26), Beijing, China (Aug. 2011).

(13)

K. Semba, "Toward hybrid quantum systems ~ A quest for a quantum memory ~", Shonan Workshop
Report on "Hybrid Quantum Devices", Kanagawa, Japan (Nov. 2011).

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

(14)K. Semba, "Coherent coupling of a superconducting f lux qubit to an ensemble of NV-centers indiamond", Quantum Technologies: Information, Communication and Computation, Tokyo, Japan (Nov.
2011).

(15)

T. Yamaguchi, H. Yamaguchi, and T. Iyoda,"Directed self-assembly of block copolymers toward singledigit nanolithography", 24th International Microprocesses and Nanotechnology Conference (MNC2011),
Kyoto, Japan (Oct. 2011).

(16)

K. Muraki, "NMR measurement of the spin polarization in the ν = 5/2 fractional quantum Hall state andin the N = 1 Landau level", Microsoft Station Q Fall Meeting, Santa Barbara, CA, U.S.A. (Dec. 2011).

III. Optical Science Laboratory(1)

K. Tateno, G. Zhang, H. Gotoh, and T. Sogawa," Characterization of InP-related Nanowires", Frontiers in
Nanoscale Science & Technology (FNST2011), Saitama, Japan (Jan. 2011).

(2)

M. Notomi, "Bi-layer Photonic Crystals for Optomechanics", SPIE Photonics West 2011, California,
U.S.A. (Jan. 2011).

(3)

W.J. Munro, "Universal Continuous variable quantum computation: what is needed?", Royal SocietyInternational Scientific Seminar on Continuous Variable Quantum Computation: Prospects and Challenges(CVQC), Milton Keynes, U.K. (Feb. 2011).

(4)

M. Notomi, "fJ/bit nanophotonics for future ICT", International Conference of Nanophotonics, Shanghai,
China (May 2011).

(5)

M. Notomi, "fJ/bit nanophotonics for future ICT", The 10th Japan-Sweden QNANO Workshop, Visby,
Sweden (June 2011).

(6)

H. Takesue, "Entanglement generation using silicon wire waveguide", IEEE Summer Topicals, Montreal,
Canada (July 2011).

(7)

K. Nozaki, T. Tanabe, A. Shinya, S. Matsuo, G. Sato, E. Kawaguchi, H. Taniyama, and M. Notomi,"Photonic crystal nanocavities toward on-chip low-power nanophotonic devices", IQEC/CLEO PR, Sydney,
Australia (Aug. 2011).

(8)

S.J. Devitt, A.M. Stephens, W.J. Munro, and K. Nemoto, "The Optical Quantum Computer", SPIE, San
Diego, U.S.A. (Aug. 2011).

(9)

W.J. Munro, S.J. Devitt, and K. Nemoto, "Designing quantum repeaters and networks", SPIE, San Diego,
U.S.A. (Aug. 2011).

(10)

M. Notomi, "fJ/bit photonics platoform based on photonic crystals", SPIE, San Diego, U.S.A. (Aug. 2011).

(11)

K. Azuma, "Quantum repeaters and computation built on a single module", Quantum Science
Symposium 2011, Massachusetts, U.S.A. (Sep. 2011).

(12)

M. Notomi, K. Nozaki, S. Matsuo, A. Shinya, G. Sato, and H. Taniyama, "fJ/bit Integrated Nanophotonics
based on photonic Crystals", ECOC, Geneva, Switzerland (Sep. 2011).

(13)

Y. Tokura, "Spin orbit interaction and spin accumulation in quantum dot systems", PIERS2011, Suzhou,
China (Sep. 2011).

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

49

50

(14)

H. Takesue, "Quantum communication experiments using superconducting single-photon detectors",
International Workshop on Nanowire Superconducting Single-Photon Detectors (NSSPD), Eindhoven,
Netherlands (Sep. 2011).

(15)

T. Kubo, "Measurement Induced Backaction by Coupling with an Environment Containing a Quantum
Dot as a Nanosensor", BIT's 1st Annual world Congress of Nano-S&T, Dalian, China (Oct. 2011).

(16)

M. Notomi, E. Kuramochi, H. Taniyama, T. Tanabe, K. Nozaki, A. Shinya, S. Matsuo, G. Sato, and E.
Kawaguchi, "Modulated mode-gap cavities in various forms", IEEE Photonics Conference, Arlington,
U.S.A. (Oct. 2011).

(17)

M. Notomi, "Integrated Nanophotonics for Green ICT", 12th RIES International Symposium, Hokkaido,
Japan (Nov. 2011).

(18)

A. Yokoo, T. Tanabe, E. Kuramochi, and M. Notomi, "Nano-fabrication for photonic crystal functional
device", 11th International Symposium on Advanced Orgainc Photonics, Seoul, Korea (Nov. 2011).

(19)

M. Notomi, K. Nozaki, S. Matsuo, A. Shinya, T. Sato, and H. Taniyama, "fJ/bit Integrated Nanophotonics
Based on Nanocavities", SPIE Asia Communications and Optics Conference (ACP 2011), Shanghai, China(Nov. 2011).

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Ⅱ．DataAward Winners’ List (Fiscal 2011)
The Commendation for
Science and Technology by
the Minister of Education,
Culture, Sports, Scienceand Technology, The Young
Scientists’ Prize

Y. Taniyasu

Research on the crystal growth of
AlN and its application to the deepultraviolet light-emitting devices

Apr. 20,
2011

H. Yamaguchi

For personal contribution to theadvancement of physics as adiscipline and a profession

May 18,2011

Y. Taniyasu

Seminal Contributions to the Growthof AlN and its Application to the
Shortest Wavelength Light Emitting
DiodesMay 25,2011

JSAP Outstanding Paper
Award ― 2011

K. Kakuyanagi

Generation of Non-ClassicalMicrowave Photon States in an
Inductor; Capacitor Resonator
Coupled to a Superconducting Flux
Qubit

Aug. 30,
2011

An MOC Paper Award, the
7th Micropotics Conference

N. Ishikura,
T. Baba,
E. Kuramochi,
M. Notomi

Ultrahigh-resolution tunable delay
and its application to fast opticalcorrelator

Nov. 2,
2011

The 28th Inoue Prize for
Science

H. Yamaguchi

Pioneering Contributions to the
Study of Quantum MechanicalBehavior
in Minute Mechanical Structures

Feb. 3,
2012

JSAP Outstanding
Presentation Award ― 2011

D. Hatanaka

Highly efficient remote actuation ofa mechanical oscillator by 2DEGcarrier control

Mar. 15,2012

The Institute of Physics (IOP)
Fellow

The Young Scientist
Award of the International
Symposium on Compound
Semiconductors 2011

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)43

In-house Award Winners’ List (Fiscal 2011)

44

NTT Corporation President
Award

H. Yokoyama
T. Kobayashi
N. Watanabe
K. Kumakura
M. Hiroki
Y. OdaCommercialization of high quality
nitride semiconductor epitaxial wafers
for high power applications

Oct. 21,2011

NTT Science and CoreTechnology Laboratory
Group Director Award

S. Saito
K. Kakuyanagi
X. ZhuH. NakanoS. Karimoto
H. Tanaka
W. J. Munro
K. Semba

Pioneering new research fields inquantum information processing
with Josephson quantum circuits

Dec. 21,2011

BRL Director Award
Award for Achievements

X. ZhuS. Saito
A. Kemp
K. Kakuyanagi
S. Karimoto
H. NakanoW. J. Munro
Y. Tokura
M. Kasu
K. Semba

For proof-of-principle experiment of
quantum memory using superconducting
flux qubit and NV centers in diamondMar. 28,
2012

BRL Director Award
Award for Achievements

M. Yamashita
K. Inaba
M. W. Jack

The development of the theoreticalmethod for cold atom analysis and thediscovery of the novel quantum phases
in optical lattice systems

Mar. 28,
2012

BRL Director Award
Award for Achievements

H. Sanada
H. GotoK. Onomitsu
T. SogawaControl of optical and spin propertiesof semiconductors by surface acoustic
waves

Mar. 28,
2012

BRL Director Award
Award for Achievements

K. Nozaki
A. Shinya
M. Notomi
Y. Suzaki
T. SegawaT. SatoS. Matsuo
R. Takahashi

Realization of ultralow-power 4-bit
optical RAM subsystem based on
integrated photonic crystal nanocavities

Mar. 28,
2012

BRL Director Award
Award for Excellent Papers

X. ZhuS. Saito
A. Kemp
K. Kakuyanagi
S. Karimoto
H. NakanoW. J. Munro
Y. Tokura
M. Kasu
K. Semba"Coherent coupling of a superconducting
flux qubit to an electron spin ensemble
in diamond," Nature 478, 221-224(2011).

Mar. 28,
2012

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

Numbers of Papers, Presentations and Patents (2011)
The numbers of papers published in international journals, presentations at international
conferences and applied patents in year 2011 amounted to 132, 217, and 51, respectively. The
numbers for each research area are as follows;

Papers Published in International Journals(Jan. – Dec. 2011)23

Materials Science

Physical Science

54

Optical Science

55
0

10

20

30

40

50

60

Number of Papers

Presentations at International Conferences(Jan. – Dec. 2011)Materials Science57

Physical Science

97

Optical Science

63

0

20

40

60

80

100

Number of Presentations

Applied Patents (Jan. – Dec. 2011)Materials Science26

Physical Science

11

Optical Science

14

0

5

10

15

20

25

30

Number of Applied Patents

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)45

The numbers of research papers published in the major journals are shown below.
(IF2010*)

Numbers

Physical Review B

3.774

18

Applied Physics Letters

3.841

16

Japanese Journal of Applied Physics

1.024

13

Physical Review Letters

7.622

12

Optics Express

3.753

11

Applied Physics Express

2.778

5

Physical Review A

2.861

4

Nature Physics

18.43

3

Nano Letters12.2193

New Journal of Physics

3.849

3

Nature36.104

2

Nanotechnology

3.652

2

Nature Nanotechnology

30.324

1

ACS Nano

9.865

1

Journal of the American Chemical Society

9.023

1

Small

7.336

1

Proceedings of the IEEE

5.151

1

Carbon

4.896

1

Journal of Physical Chemistry C

4.524

1

Langmuir

4.269

1

-

1

JournalsNature Communications*IF2010: Impact Factor 2010 (Journal Citation Reports, 2010)

The average IF2010 for all research papers from NTT Basic Research Laboratories is 4.78.

The numbers of presentations in the major conferences are shown below.
Conferences46

Numbers

International Symposium on Nanoscale Transport and Technology

372011 International Conference on Solid State Devices and Materials

19

Electronic Properties of Two-Dimensional Systems 19

1224th International Microprocesses and Nanotechnology Conference

5

38th International Symposium on Compound Semiconductors

5

Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science
Conference

5International Symposium on Surface Science

5

22nd European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes andNitrides4

24th International Symposium on Superconductivity

4

Biophysical Society 55th Annual Meeting

4

ERATO Macroscopic Quantum Control Conference on Ultracold Atoms and Molecules

4

Frontiers in Nanoscale Science and Technology

4

Quantum Nanostructure and Nanoelectronics 20114

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

List of Invited Talks at International Conferences (2011)
I. Materials Science Laboratory(1)

H. Hibino, S. Tanabe, and H. Kageshima, "Growth and characterization of graphene on SiC", Graphene
Workshop in Tsukuba 2011, Tsukuba, Japan (Jan. 2011).

(2)

H. Hibino, S. Tanabe, and H. Kageshima, "Growth, structure, and transport properties of epitaxial
graphene on SiC " 8th International Symposium on Atomic Level Characterizations for New Materials andDevices '11 (ALC'11) Seoul, Korea (May 2011).

(3)

M. Kasu, K. Hirama, and Y. Taniyasu "High-thermal-efficiency AlGaN/GaN HEMTs on diamond", AsiaPacific Workshop on Fundamentals and Applications of Advanced Semiconductor Devices, Daejeon, Korea(June 2011).

(4)

H. Hibino, S. Tanabe, and H. Kageshima, "Growth and electronic transport properties of monolayer
and bilayer graphene on SiC", XX International Material Research Congress 2011 (IMRC 2011), Cancun,
Mexico (Aug. 2011).

(5)

M. Kasu, K. Hirama, and Y. Taniyasu, "Nitride/diamond heterostructures -from growth to devices-", 22nd
European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes and Nitrides (Diamond2011), Garmisch-Partenkirchen, Germany (Sep. 2011).

(6)

A. Shimada, T. Iwata, N. Nakano, and K. Torimitsu, "CMOS LSI for excitation and measurement ofneural activity with microelectrode array", 2011 International Conference on Solid State Devices andMaterials, Nagoya, Japan (Sep. 2011).

(7)

M. Kasu and K. Hirama, "Diamond-based Electronic Device Technologies", International Conference on
Carbon-based Nano-Materials and Devices, Suzhou, China (Oct. 2011).

(8)

H. Hibino, S. Tanabe, and H. Kageshima, "Carrier transport in epitaxial graphene grown on SiC(0001)",
3rd International Symposium on the Science and Technology of Epitaxial Graphene (STEG3), Saint
Augustine, U.S.A. (Oct. 2011).

(9)

H. Omi, "Surface plasmon of gold nanorods in solutions", BIT's 1st Annual World Congress of NanoS&T, Dalian, China (Oct. 2011).

(10)

Y. Krockenberger, "Sr2RuO4 thin films: What's next?", International Workshop for Young Researchers on
Topological Quantum Phenomena in Condensed Matter with Broken Symmetries, Shiga, Japan (Nov. 2011).

(11)

K. Furukawa and J. Durao, "Donor-to-Acceptor Distance Dependent Fluorescence Resonance Energy
Transfer Efficiency for Multiple Donors and Acceptors System Confined within 2-Dimensional Fluid of
Supported Lipid Bilayer", International Symposium on Surface Science (ISSS-6), Funabori, Japan (Dec.
2011).

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)47

II. Physical Science Laboratory

48

(1)

H. Okamoto, D. Ito, K. Onomitsu, H. Sanada, H. Gotoh, T. Sogawa, and H. Yamaguchi, "Carriermediated opto-mechanical coupling in GaAs cantilevers", Frontiers in Nanoscale Science and Technology
Workshop (FNST2011), Saitama, Japan (Jan. 2011).

(2)

H. Nakano, "Time-evolution during superconducting qubit measurement process", International
Symposium "Nanoscience and Quantum Physics 2011" (nanoPHYS'11), Tokyo, Japan (Jan. 2011).

(3)

S. Saito, "Entanglement between macroscopic resonator and microscopic two level system througha flux qubit", The Third International Workshop on Dynamics and Manipulation of Quantum Systems(DMQS2010), Tokyo, Japan (Feb. 2011).

(4)

H. Nakano, "Energy flow and information flow in qubit measurement process", International Conferencein Quantum Bio-Informatics Center (QBIC2011), Chiba Japan (Mar. 2011).

(5)

Y. Ono, M.A.H. Khalafalla, J. Noborisaka, G.P. Lansburgen, and A. Fujiwara, "Dopants in silicontransistors: transport and photoemission", CMOS Emerging Technologies Workshop, Whistler, BC, Canada(June 2011).

(6)

T. Shinada, M. Hori, Y. Ono, A. Komatsubara, K. Kumagai, T. Tanii, T. Endoh, and I. Ohdomari,"Control of dopant distribution by dingle-ion implantation and its impact on transconductance of FETs",
2011 Asia-Pacific Workshop on Fundametals and Applications of advanced Semiconductor Devices(AWAD2011), Daejeon, Korea (June 2011).

(7)

T. Koga, T. Matsuura, S. Faniel, S. Souma, S. Mineshige, Y. Sekine, and H. Sugiyama, "Determinationof spin-orbit coefficients and application to the spin-filter devices using InGaAs/InAlAs heterostructures",2011 Asia-Pacific Workshop on Fundamentals and Applications of Advanced Semiconductor Devices(AWAD2011), Daejeon, Korea (June 2011).

(8)

H. Yamaguchi, I. Mahboob, H. Okamoto, and K. Onomitsu, "Heterostructure-based parametric resonatorand its applications", The Second International Seminar on Nano-Electro-Mechanical Systems (NEMS2011),
Toulouse, France (July 2011).

(9)

L. Tiemann, G. Gamez, N. Kumada, and K. Muraki, "The spin polarization of the ν = 5/2 fractional
quantum Hall state", The 19th international Conference on Electronic Properties of Two-Dimensional
Electron Systems (EP2DS19), Tallahassee, Florida, U.S.A. (July 2011).

(10)

H. Okamoto, D. Ito, T. Watanabe, K. Onomitsu, H. Sanada, H. Gotoh, T. Sogawa, and H. Yamaguchi,"Carrier-mediated opto-mechanical coupling in GaAs micromechanical resonators", 17th International
Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON 17),
Santa Barbara, CA, U.S.A. (Aug. 2011).

(11)

L. Tiemann, G. Gamez, N. Kumada, and K. Muraki, "The spin polarization of the ν = 5/2 fractional
quantum Hall state", 26th International Conference on Low Temperature Physics (LT26), Beijing, China(Aug. 2011).

(12)

X. Zhu, S. Saito, A. Kemp, K. Kakuyanagi, S. Karimoto, H. Nakano, W. J. Munro, Y. Tokura, M. S.
Everitt, K. Nemoto, M. Kasu, N. Mizuochi, and K. Semba, "Coupling an ensemble to a superconducting
qubit", 26th International Conference on Low Temperature Physics (LT26), Beijing, China (Aug. 2011).

(13)

K. Semba, "Toward hybrid quantum systems ~ A quest for a quantum memory ~", Shonan Workshop
Report on "Hybrid Quantum Devices", Kanagawa, Japan (Nov. 2011).

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

(14)K. Semba, "Coherent coupling of a superconducting f lux qubit to an ensemble of NV-centers indiamond", Quantum Technologies: Information, Communication and Computation, Tokyo, Japan (Nov.
2011).

(15)

T. Yamaguchi, H. Yamaguchi, and T. Iyoda,"Directed self-assembly of block copolymers toward singledigit nanolithography", 24th International Microprocesses and Nanotechnology Conference (MNC2011),
Kyoto, Japan (Oct. 2011).

(16)

K. Muraki, "NMR measurement of the spin polarization in the ν = 5/2 fractional quantum Hall state andin the N = 1 Landau level", Microsoft Station Q Fall Meeting, Santa Barbara, CA, U.S.A. (Dec. 2011).

III. Optical Science Laboratory(1)

K. Tateno, G. Zhang, H. Gotoh, and T. Sogawa," Characterization of InP-related Nanowires", Frontiers in
Nanoscale Science & Technology (FNST2011), Saitama, Japan (Jan. 2011).

(2)

M. Notomi, "Bi-layer Photonic Crystals for Optomechanics", SPIE Photonics West 2011, California,
U.S.A. (Jan. 2011).

(3)

W.J. Munro, "Universal Continuous variable quantum computation: what is needed?", Royal SocietyInternational Scientific Seminar on Continuous Variable Quantum Computation: Prospects and Challenges(CVQC), Milton Keynes, U.K. (Feb. 2011).

(4)

M. Notomi, "fJ/bit nanophotonics for future ICT", International Conference of Nanophotonics, Shanghai,
China (May 2011).

(5)

M. Notomi, "fJ/bit nanophotonics for future ICT", The 10th Japan-Sweden QNANO Workshop, Visby,
Sweden (June 2011).

(6)

H. Takesue, "Entanglement generation using silicon wire waveguide", IEEE Summer Topicals, Montreal,
Canada (July 2011).

(7)

K. Nozaki, T. Tanabe, A. Shinya, S. Matsuo, G. Sato, E. Kawaguchi, H. Taniyama, and M. Notomi,"Photonic crystal nanocavities toward on-chip low-power nanophotonic devices", IQEC/CLEO PR, Sydney,
Australia (Aug. 2011).

(8)

S.J. Devitt, A.M. Stephens, W.J. Munro, and K. Nemoto, "The Optical Quantum Computer", SPIE, San
Diego, U.S.A. (Aug. 2011).

(9)

W.J. Munro, S.J. Devitt, and K. Nemoto, "Designing quantum repeaters and networks", SPIE, San Diego,
U.S.A. (Aug. 2011).

(10)

M. Notomi, "fJ/bit photonics platoform based on photonic crystals", SPIE, San Diego, U.S.A. (Aug. 2011).

(11)

K. Azuma, "Quantum repeaters and computation built on a single module", Quantum Science
Symposium 2011, Massachusetts, U.S.A. (Sep. 2011).

(12)

M. Notomi, K. Nozaki, S. Matsuo, A. Shinya, G. Sato, and H. Taniyama, "fJ/bit Integrated Nanophotonics
based on photonic Crystals", ECOC, Geneva, Switzerland (Sep. 2011).

(13)

Y. Tokura, "Spin orbit interaction and spin accumulation in quantum dot systems", PIERS2011, Suzhou,
China (Sep. 2011).

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

49

50

(14)

H. Takesue, "Quantum communication experiments using superconducting single-photon detectors",
International Workshop on Nanowire Superconducting Single-Photon Detectors (NSSPD), Eindhoven,
Netherlands (Sep. 2011).

(15)

T. Kubo, "Measurement Induced Backaction by Coupling with an Environment Containing a Quantum
Dot as a Nanosensor", BIT's 1st Annual world Congress of Nano-S&T, Dalian, China (Oct. 2011).

(16)

M. Notomi, E. Kuramochi, H. Taniyama, T. Tanabe, K. Nozaki, A. Shinya, S. Matsuo, G. Sato, and E.
Kawaguchi, "Modulated mode-gap cavities in various forms", IEEE Photonics Conference, Arlington,
U.S.A. (Oct. 2011).

(17)

M. Notomi, "Integrated Nanophotonics for Green ICT", 12th RIES International Symposium, Hokkaido,
Japan (Nov. 2011).

(18)

A. Yokoo, T. Tanabe, E. Kuramochi, and M. Notomi, "Nano-fabrication for photonic crystal functional
device", 11th International Symposium on Advanced Orgainc Photonics, Seoul, Korea (Nov. 2011).

(19)

M. Notomi, K. Nozaki, S. Matsuo, A. Shinya, T. Sato, and H. Taniyama, "fJ/bit Integrated Nanophotonics
Based on Nanocavities", SPIE Asia Communications and Optics Conference (ACP 2011), Shanghai, China(Nov. 2011).

Research Activities in NTT Basic Research Laboratories Vol. 22 (2011)

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