Cover photograph:

Multiple Two-qubit Operations Using Semiconductor Coupled Charge Qubits
Two-qubit unitary operations such as controlled rotation (CROT), which rotates the target qubit state
conditionally on the control qubit state, and SWAP, which swaps quantum states of the two qubits, areimportant for performing quantum algorithms and correlating multiple qubits. Using coupled semiconductor
charge qubits consisting of two pairs of double quantum dots (DQD), we demonstrated CROT and SWAP,
each in a single step. (a) Scanning electron micrograph of the two-qubit device. (b) Coherent oscillationsof the first qubit representing the CROT operation. Oscillations (i) and (ii) correspond to cases where thesecond qubit is in states |1> and |0>, respectively. (c) Data showing additional slow oscillations along the
dot-dash line corresponding to correlated coherent oscillations of the first qubit. (d) Correlated coherent
oscillations of the first qubit (i). This corresponds to the data along dot-dash line in (c). Oscillation (ii)corresponds to the conditional coherent oscillations along the dot-dash line in (b). (Page 31)

Photograph of atomic force microscopy

Step-free GaN Surfaces Fabricated by Selective-area
Metalorganic Vapor Phase Epitaxy
A step-free GaN surface with the diameter of 16 µm, which was atomically flat without any monolayer
steps, was fabricated for the first time by selective area metalorganic vapor phase epitaxy. This technique can control the hetero-interfaces of nitride semiconductors in an atomic scale and realize highefficiency light emitting devices and sabband devices, such as resonant tunneling diodes and cascadelasers. In addition, we clearly observed the nucleus growth of nitride semiconductors and investigate
the mechanism in detail. (Page 16)

Liquid ordered domains on a GUV(fluorescent image).

AFM image and line profile of the domains on a supported lipid
bilayer after the GUV rupture.

Formation of Liquid-ordered Domains on a Giant Unilamellar Vesicle
Liquid-ordered (lo) domains (raft-like domains), play an important role in regards to the function andarrangement of membrane proteins. Here, we form lo domains on a giant unilamellar vesicle (GUV).
The GUV can be ruptured by increasing the salt concentration in the buffer solution and screening therepulsive electrostatic interaction between the GUV and the substrate. These micron-scale domains on
a supported lipid bilayer will help to control membrane proteins in nano-bio devices. (Page 23)－Ⅰ－Transmission electron microscope (TEM) images of free standing GaAs
nanowires(NWs). (a) single NW. (b) and (c) High-magnification images(d) HRTEM image near the NW side. (e) images for Au particles withdifferent diameters.

Photoluminescence spectra for GaAs
NWs grown using Au particles withthree nominal diameters.

Freestanding GaAs Nanowires with the Controlled Diameter and Their
Optical Properties with the Radial Quantum-confinement Effect
Semiconductor nanowires (NWs) have attracted considerable attention due to the interesting fundamental properties of such low-dimensional systems. With a view to exploring the potentially uniqueapplications of the freestanding-type nanowires, we synthesized freestanding GaAs NWs with a controlled diameter using size-selective Au particles via the Au-catalyzed vapor-liquid-solid method, andsuccessfully observed the luminescence blue shift induced by the radial quantum-confinement effect.
Our work opens the way to investigating size-related optical phenomena in bare GaAs quantum wires,and provides more opportunities for the study of one-dimensional quantum physics using freestanding
NWs. (Page 39)(a) Schematic and SEM images of bi-layer PhC (Force for symmetric mode is depicted). (b) photonic bandedge
modes in the bi-layer PhC. (c) power dependence of reflectance spectra for the symmetric mode. (d) fundamental
vibration mode with odd symmetry to modulate optical mode. (e) RF spectra of reflected light.

Ultralarge Optomechanical Coupling in a Bi-layer Photonic Crystal
We realized bi-layer photonic crystal (PhC) embedding a thin air gap and observed its optomechanical coupling phenomena. Two InP PhC slabs with thickness of 200 nm were separated by an air gap
with thickness of 200 nm. We could observe large shift of bandedge mode in reflectance spectra. Thiscan be explained by displacement of the PhC slabs by huge radiation force, resulting from strong optomechanical coupling. Such strong optomechanical coupling also allowed the tiny Brownian motionof slabs to modulate optical resonant mode, which could be observed as a peak in the RF spectra of thereflected light beam. (Page 42)－Ⅱ－Message from the Director
We are extremely grateful for your interest andsupport with respect to our research activities.
The three research areas at NTT-BRL, namely
Materials Science, Physical Science, and Optical
Science, are undertaking work designed to create
new values supporting NTT’s future business andto promote advances in science that will ultimately
benefit all mankind.
A fundamental goal of these research activities is
to improve global competitiveness. Therefore, BRL
is collaborating with many universities and research
institutes throughout the world as well as with otherNTT laboratories. BRL organizes international
conferences related to quantum physics andnanotechnology and also holds a "Science Plaza" toenhance public understanding of our activities andto ensure a frank exchange of opinions. Moreover,
one of our missions is the education of young researchers and we sponsor the biennial "BRL
School", which boasts distinguished researchers as lecturers. In November 2009, thirty-five
Ph.D. students and young researchers from universities and institutes in 9 countries participatedin the BRL School. We hope that this endeavor will encourage research and contribute to its
future growth.
It gives us immense pleasure to fulfill our mission of being an open laboratory, and todisseminate our research output worldwide. Your continued support is greatly appreciated.

Itaru Yokohama
Director
NTT Basic Research Laboratories－Ⅲ－

Contents
page◆ Cover♦ Multiple Two-qubit Operations Using Semiconductor Coupled Charge Qubits◆ Color Frontispiece ............................................................................................................Ⅰ♦ Step-free GaN Surfaces Fabricated by Selective-area Metalorganic Vapor Phase Epitaxy♦ Formation of Liquid-ordered Domains on a Giant Unilamellar Vesicle♦ Freestanding GaAs Nanowires with the Controlled Diameter and Their Optical Properties

with the Radial Quantum-confinement Effect♦ Ultralarge Optomechanical Coupling in a Bi-layer Photonic Crystal◆ 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♦ Improvement of H-terminated Diamond FETs in NO2 Atmosphere♦ Single-crystal AlN (0001)/diamond (111) Heterostructure♦ Step-free GaN films Grown by Selective-area Metalorganic Vapor Phase Epitaxy♦ Synthesis of the Parent Compound Superconductors RE2CuO4 by MBE andSpecially-designed Post-reduction♦ Growth of Graphene by Gas-source Molecular Beam Epitaxy♦ Stability-instability Transition of Reaction Fronts in Thermal Silicon Oxidation♦ Stacking Domains in Epitaxial Bilayer Graphene♦ Carbon Nanotube Synthesis from Diamond♦ Effect of Mg

2+

on Neural Activitiy♦ Fabrication of a Nano-bio Device Using Giant Unilamellar Vesicles♦ Design of an LSI Chip for a Bio-machine Interface in 0.18 µm CMOS Technology◇ Physical Science Laboratory ............................................................................................................... 25♦ Si Nanowire Ion-sensitive Field-effect Transistors with a Shared Floating Gate
♦ Tunneling Spectroscopy of Electron Subbands in Thin SOI-MOSFETs♦ Two-dimensional Patterning by Using Block Copolymer Self-assembly♦ Optical Tuning of Coupled Nanomechanical Resonators♦ Intrinsic Gap and Exciton Condensation in the νT = 1 Bilayer System♦ Fano-Kondo Effect in a Side-coupled Double Quantum Dot♦ Multiple Two-qubit Operations Using Semiconductor Coupled Charge Qubits♦ Theory of Quantum Dynamics During a Qubit Readout Process with aJosephson Bifurcation Amplifier♦ Experimentally Realizable Controlled-NOT Gate in a Flux-qubit / Resonator System♦ Kondo Effect in a Semiconductor Quantum Dot Controlled by Spin Accumulation◇ Optical Science Laboratory ................................................................................................................ 35♦ Generation of Time-bin Entangled Photon Pairs Using Cascaded Second Order

Nonlinearity in Single PPLN Waveguide♦ Numerical Analysis of Cold Fermionic Atoms in an Optical Lattice at Finite Temperatures♦ Trapping Loss Mechanism of Superconducting Atom Chips♦ Ultrafast Dynamics of Coherent Phonons in P-type Si Driven by Sub-10-fs Laser Pulses♦ Freestanding GaAs Nanowires with a Controlled Diameter and Their

Optical Properties with the Radial Quantum-confinement Effect♦ Photoluminescence Properties of Dynamic Quantum Dots

Formed by Surface Acoustic Waves♦ Sub-femtojoule All-optical Switching Using a Photonic Crystal Nanocavity♦ Strong Optomechanical Coupling in a Bi-layer Photonic Crystal♦ All-silicon Photonic Crystal Receiver for 1.55-µm Light Detection Utilizing

Two Photon Absorption

II. Data◇ Science Plaza 2009.......................................................................................................................... 45◇ 5th NTT-BRL School...................................................................................................................... 46◇ Award Winners’ List....................................................................................................................... 47◇ In-house Award Winners’ List......................................................................................................... 48◇ Research Activities in Basic Research Laboratories in 2009
◇ List of Invited Talks at International Conferences.......................................................... 49.......................................................................... 51

NTT Basic Research Laboratories Organogram

Director

Itaru Yokohama, Dr.

Nano Bio Research
Executive Manager

Keiichi Torimitsu, Dr.

Research Planning Section
Executive Manager

Toshiki Makimoto, 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. 20 (2009)Member List
As of March 31, 2010(*/ left NTT BRL in the middle of the year)

NTT Basic Research Laboratories
Director, Dr. Itaru Yokohama		

Dr. Junji Yumoto*

Nano Bio Research

Executive Manager,

Dr. Keiichi Torimitsu

Research Planning Section

Executive Research Scientist,

Dr. Toshiki Makimoto

Senior Research Scientist,
Senior Research Scientist,

Dr. Kazuhide Kumakura
Dr. Kazuaki Furukawa

NTT Research Professor
Dr. Fujio Shimizu (The University of Electro-Communications) *Prof. Shintaro Nomura (University of Tsukuba)Prof. Kyo Inoue (Osaka University)

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)Materials Science Laboratory

Executive Manager,		
Assistant Manager,

Dr. Toshiki Makimoto
Dr. Keiichi Torimitsu*
Dr. Satoru Suzuki

Thin-Film Materials Research Group:
Dr. Makoto Kasu (Group Leader)
Dr. Yasuyuki Kobayashi
Dr. Hideki Yamamoto
Dr. Tetsuya Akasaka
Dr. Yoshitaka Taniyasu
Dr. Michal Kubovic*
Dr. Kazuyuki Hirama

Dr. Hisashi Sato
Dr. Chiun-Lung Tsai*

Low-Dimensional Nanomaterials Research Group:
Dr. Hiroki Hibino (Group Leader)
Dr. Fumihiko Maeda
Dr. Hiroo Omi
Akio Tokura
Dr. Shin-ichi Tanabe

Dr. Ken-ichi Kanzaki
Dr. Daisuke Takagi

Molecular and Bio Science Research Group:
Dr. Keiichi Torimitsu (Group Leader)
Dr. Keisuke Ebata
Dr. Koji Sumitomo
Dr. Akiyoshi Shimada
Dr. Hiroshi Nakashima
Toichiro Goto
Dr. Youichi Shinozaki

Dr. Nahoko Kasai
Dr. Yoshiaki Kashimura
Dr. Aya Tanaka

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)Physical Science Laboratory

Executive Manager,

Dr. Hiroshi Yamaguchi

Assistant Manager,

Dr. Kenji Yamazaki
Takeshi Karasawa

Nanodevices Research Group:
Dr. Akira Fujiwara (Group Leader)
Dr. Yukinori Ono
Dr. Hiroyuki Kageshima Dr. Katsuhiko Nishiguchi
Dr. Jin-ichiro Noborisaka
Dr. Mohammed A. H. Khalafalla*
Nanostructure Technology Research Group:
Dr. Hiroshi Yamaguchi (Group Leader)
Dr. Masao Nagase
Toru Yamaguchi
Dr. Koji Onomitsu
Dr. Imran Mahboob
Quantum Solid State Physics Research Group:
Dr. Koji Muraki (Group Leader)
Dr. Kiyoshi Kanisawa
Dr. Kyoichi Suzuki
Dr. Takeshi Ota
Dr. Norio Kumada
Dr. Ken-ichi Hitachi
Dr. Kei Takashina*
Dr. Kasper Grove-Rasmussen* 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Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Dr. Hajime Okamoto
Junzo Hayashi

Dr. Toshiaki Hayashi
Dr.Keiko Takase
Dr. Gerardo Gamez

Dr. Shin-ichi Karimoto
Dr. Alexandre Kemp

Dr. Masumi YamaguchiOptical Science Laboratory

Executive Manager,

Dr. Yasuhiro Tokura

Assistant Manager,

Dr. Satoshi Sasaki

Quantum Optical State Control Research Group:
Dr. Yasuhiro Tokura (Group Leader)
Dr. Kaoru Shimizu
Kazuhiro Igeta
Dr. Makoto Yamashita
Dr. Hiroyuki Shibata
Dr. Hiroki Takesue
Dr. Fumiaki Morikoshi
Dr. Kiyoshi Tamaki
Daisuke Hashimoto
Dr. Kensuke Inaba
Quantum Optical Physics Research Group:
Dr. Tetsufumi Sogawa (Group Leader)Dr. Hidetoshi Nakano
Dr. Tadashi Nishikawa
Hidehiko Kamada
Dr. Kouta Tateno
Dr. Katsuya Oguri
Dr. Atsushi Ishizawa
Dr. Guoquiang Zhang
Dr. Keiko Kato
Photonic Nano-Structure Research Group:
Dr. Masaya Notomi (Group Leader)
Dr. Atsushi Yokoo
Dr. Eiichi Kuramochi
Dr. Hideaki Taniyama
Dr. Takasumi Tanabe
Dr. Kengo Nozaki
Dr. Young-Geun Roh

Masami Kumagai
Dr. Tetsuya Mukai
Dr. Toshimori Honjo
Dr. Ken-ichi Harada

Dr. Hideki Gotoh
Dr. Takehiko Tawara
Dr. Haruki Sanada

Dr. Akihiko Shinya
Dr. Hisashi Sumikura

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)Distinguished Technical Members
Masaya Notomi was born in Kumamoto, Japan on February 16, 1964. Hereceived his B.E., M.E. and Dr. Eng. degrees in applied physics from The
University of 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 semiconductor quantum
wires/dots and photonic crystal structures. He has been in NTT Basic ResearchLaboratories since 1999, and is currently working on light-propagation control
by use of various types of photonic crystals. From 1996-1997, he was with
Linköping University in Sweden as a visiting researcher. He is also a guest
associate professor of Tokyo Institute of Technology (2001-2009). He received
IEEE/LEOS Distinguished Lecturer Award in 2006, JSPS (Japan Society for the
Promotion of Science) prize in 2009, and Japan Academy Medal in 2009. He is amember of National University Corporation Evaluation Committee. He is also amember of the Japan Society of Applied Physics, IEEE, APS and OSA.

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 the Basic Research Laboratories in 1996. Since 1994, he has been
engaged in research on silicon nanostructures and their application to singleelectron devices. He was a guest researcher at the National Institute of Standards
and Technology (NIST), Gaithersburg, MD, USA during 2003-2004. He received
the SSDM Young Researcher Award in 1998, SSDM Paper Award in 1999, andJapanese Journal of Applied Physics (JJAP) Paper Awards in 2003 and 2006. He
was awarded the Young Scientist Award from the Minister of MEXT (Ministry of
Education, Culture, Sports, Science, and Technology) in 2006. He is a memberof 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., andPh.D. degrees in applied physics from The University of Tokyo, Japan, in 1989,
1991, and 1994, respectively. In 1994, he joined Basic Research Laboratories,
Nippon Telegraph and Telephone Corporation, Kanagawa, Japan. Since then,he has been engaged in the growth of high-mobility heterostructures and thestudy of highly correlated electronic states realized in such structures. He was aguest researcher at Max-Planck Institute, Stuttgart, Germany during 2001-2002.
He is a member of the Physical Society of Japan and Japan Society of Applied
Physics.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Advisory Board (2009 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. 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

Prof. Theodor W. Hänsch

Max-Planck-Institut für Festkörperforschung, Germany

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)Invited / Guest Scientists (2009 Fiscal Year)



Name

Affiliation

PeriodProf. Alexander Tzalenchuk

National Physical Laboratory, U.K.

Apr. 2009 – May 2009

Dr. Stefan Folsch

Paul-Drud-Institute, Germany

Oct. 2009 – Nov. 2009

Prof. Christos Flytzanis

Laboratoir Pierre Aigrain
Ecole Normale Supérieure, France

Sep. 2009 – Dec. 2009

Assoc. Prof. Takaaki Koga

Hokkaido University, Japan

Jan. 2007 – Dec. 2009

Dr. Hideomi Hashiba

Institute of Quantum Science,
Nihon University, Japan

Jul. 2008 – Mar. 2010

Dr. Lars Tiemann

Japan Science and Technology
Agency (JST), Japan

Apr. 2009 – Mar. 2010

Dr. Shoko Utsunomiya

National Institute of Informatics, JapanMay 2009 – Mar. 2010

Dr. Yoichi Chizaki

Advanced Industrial Science And
Technology (AIST)

Feb. 2010 – Mar. 2010

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Overseas Trainees (2009 Fiscal Year)
Name

Affiliation

PeriodChristoph Hufnagel

University of Heidelberg, Germany

Jun. 2006 – Jun. 2009

Stefano Salvatore

Technical University, Milan, Italy

Jan. 2009 – Aug. 2009

Maarten Nijland

University of Twente, the Netherlands

Jan. 2009 – Apr. 2009

Corentin Durand

University of Lille/ ISEN, France

Feb. 2009 – Jul. 2009

Pauline Renoux

INSA (Institut National des Sciences
Appliquées deToulouse), France

Feb. 2009 – Aug. 2009

Laurent-Daniel Haret

Institut d’Optique Graduate School, France

Mar. 2009 – Aug. 2009

Jelena Baranovic

University of Oxford, U.K.

May 2009 – Jun. 2009

Chia-Yuan Chang

National Chiao-Tung University, Taiwan

May 2009 – Feb. 2010

Chien-Yao Lu

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

May 2009 – Aug. 2009

Paul-Christiaan Spruijtenburg University of Twente, Enschede, the Netherlands

May 2009 – Oct. 2009

Man-Hong Yung

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

Jun. 2009 – Jul. 2009

Paul Nation

Dartmouth College, Hanover, New Hampshire
U.S.A.

Jun. 2009 – Aug. 2009

Timothee Martiel

ESPCI (Ecole Supérieure de Physiqueet de Chimie Industrielle), France

Jul. 2009 – Dec. 2009

Emmanuel Flurin

ESPCI (Ecole Supérieure de Physiqueet de Chimie Industrielle), France

Jul. 2009 – Dec. 2009

Myrtille Hunault

ESPCI (Ecole Supérieure de Physiqueet de Chimie Industrielle), France

Jul. 2009 – Dec. 2009

Stefano Pugnetti

Scuola Normale Superiore-Pisa, Italy

Aug. 2009 – Sep. 2009

Oliver Pirquet

University of Victoria, Canada

Sep. 2009 –Arianna McAllister

University of Ottawa, Canada

Sep. 2009 –Jessica Sparks

University of Waterloo, Canada

Sep. 2009 –Fabio Massimo Zennaro

Politecnico di Milano, Italy

Jan. 2010 –Gary Wolfowicz

ENS (Ecole Normale Supérieure de Cachan),FranceJan. 2010 –David Framil Carpeno

Complutense Univeristy of Madrid, Spain

Jan. 2010 –Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)



10

Name

Affiliation

PeriodJan Fiala

Czech Techinical University in Prague, Czech
Republic

Jan. 2010

Juan Manuel Agudo Carrizo UPV(Polytechnic University of Valencia), Spain

Jan. 2010

Romain Duval

INSA (Institut National des Sciences
Appliquées deToulouse), France

Feb. 2010

Raymond DavisRoyal Holloway, University of London, U.K.

Feb. 2010 – Mar. 2010

Aimée Broughton

University of Oxford, U.K.

Feb. 2010 – Mar. 2010

Laura Spencer

University of Oxford, U.K.

Feb. 2010 – Mar. 2010

Kylie Ellis

The University of Adelaide, Australia

Mar. 2010

Yuichiro Matsuzaki

University of Oxford, U.K.

Mar. 2010

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Domestic Trainees (2009 Fiscal Year)
Name

Affiliation

PeriodHiroshi Sakai

Tokyo University of Science, Japan

Apr. 2009 – Mar. 2010

Kenji Yamaya

Tokyo University of Science, Japan

Apr. 2009 – Mar. 2010

Hiroyuki Wakahara

Keio University, Japan

Apr. 2009 – Mar. 2010

Akira Wada

Tohoku University, Japan

Apr. 2009 – Mar. 2010

Kohei Morita

Kyushu University, Japan

Apr. 2009 – Mar. 2010

Satoru Miyamoto

Keio University, Japan

Apr. 2009 – Mar. 2010

Kuniaki Yamada

Keio University, Japan

Apr. 2009 – Mar. 2010

Norihito Kitajima

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Yasuhiko Oda

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Takayuki Watanabe

Tohoku University, Japan

Apr. 2009 – Mar. 2010

Takashi Kobayashi

Tohoku University, Japan

Apr. 2009 – Mar. 2010

Yuma Okazaki

Tohoku University, Japan

Apr. 2009 – Mar. 2010

Kenichiro Kusudo

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Naoyuki Masumoto

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Hiroshi Kamata

Tokyo Institute of Technology, Japan

Apr. 2009 – Mar. 2010

Tomohiro Nagase

Tokyo Institute of Technology, Japan

Apr. 2009 – Mar. 2010

Shun Takahashi

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Haruki Kiyama

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Atsufumi Inoue

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Yasushi Kanai

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Tatsuki Takakura

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Shintaro Takada

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Takafumi Fujita

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Yusuke Kondo

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Jun Yoneda

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Ryota Koibuchi

Tokyo University of Science, Japan

Apr. 2009 – Mar. 2010

Hiroki Morishita

Keio University, Japan

Apr. 2009 – Mar. 2010

Yu Morikawa

University of Tsukuba, Japan

Apr. 2009 – Mar. 2010

Hiroshi Takahashi

Tokyo Institute of Technology, Japan

Apr. 2009 – Mar. 2010

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

11

12

Name

Affiliation

PeriodTetsuya Miyawaki

Tohoku University, Japan

Apr. 2009 – Mar. 2010

Akira Oiwa

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Michihisa Yamamoto

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Monica Crasiun

The University of Tokyo, Japan

Apr. 2009 – Oct. 2009

Saverio Russo

The University of Tokyo, Japan

Apr. 2009 – Oct. 2009

Russell Deacon

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Allison Giles Daniel

The University of Tokyo, Japan

Apr. 2009 – Mar. 2010

Bäuerle Christopher

The University of Tokyo, Japan

Apr. 2009 – Jun. 2009

Tadakiyo Seki

Osaka University, JapanMay 2009 – Feb. 2010

Taiga Harada

Keio University, Japan

Aug. 2009

Keitaro Yamagami

Nagaoka University of Technology, Japan

Oct. 2009 – Feb. 2010

Motoki Tateishi

Nagaoka University of Technology, Japan

Oct. 2009 – Feb. 2010

Hiroki Shioya

The University of Tokyo, Japan

Jan. 2010 – Mar. 2010

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

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, such as
receptor proteins and lipid bilayers. The characteristic feature of MSL is the effective sharingof the unique nanofabrication and measurement techniques of each group. This enables fusionof research fields and techniques, which leads to innovative material research for the future
information technology.
We promote collaborations with domestic and international organizations, such as thecollaboration with Oxford University for bio-nano research, to develop a firm basis of basic
science.
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 architechtures,
coherent quantum control of semiconductor and superconductor systems, carrier interactions
in semiconductor hetero- and nanostructures, atom chips, spintronics manipulating bothelectron and nuclear spins. We also promote the studies of cutting-edge nanolithography
techniques, high-quality 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 realized quantum interference in two entangled photon pairs from siliconwire waveguides, lateral growth of semiconductor (InGaAs) nanowires, and an optical switch
functions at the power of sub-femto Joule by a photonic crystal nano-cavity.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)13

Improvement of H-terminated Diamond FETs in NO2 Atmosphere
Michal Kubovic and Makoto Kasu
Materials Science Laboratory
Diamond transistors are expected to provide the best performance among semiconductors
in high-frequency high-power operation because diamond has very high carrier velocity,
the highest breakdown electric field strength, and the highest thermal conductivity. We
reported the highest cut-off frequencies of fT of 45 GHz, fmax of 120 GHz, and the highest
RF output power density of 2.1 W/mm at 1 GHz [1]. However, the p-type doping mechanismof the hydrogen termination used in diamond transistors has not been clarified and the hole–2concentration has been limited at 1×1013 cm .
We have experimentally clarified that nitrogen dioxide (NO2) is the most beneficial p-type
dopant for H-terminated diamond [2-4]. As shown in Fig. 1, when NO2 gas is adsorbed onto
H-terminated diamond, the hole concentration increased greatly. With 300 ppm NO2, the–2maximum hole concentration reached 2.3×1014 cm , a value that is 20 times higher than thereported value in air. With this technology, we fabricated H-terminated diamond FETs whose
drain current is 1.8 times higher due to a decrease in source resistance [Fig. 2(a)] and whose
power-gain cut-off frequency (fmaxU) is 1.5 times higher [Fig. 2(b)] than those in air [2].
This work was partly supported by the SCOPE project of the Ministry of Internal Affairs andCommunications, Japan.
[1] M. Kasu, K. Ueda, Y. Yamauchi et al.,Diamond Relat. Mater. 16 (2007) 1010.
[2] M. Kubovic and M. Kasu, Appl. Phys.
Express 2 (2009) 086502.
[3] M. Kubovic, M. Kasu, and H. Kageshima,Appl. Phys. Lett. 96 (2010) 052101.
[4] M. Kubovic, M. Kasu, H. Kageshima, andF. Maeda, Diamond Relat. Mater. (in press).

Fig. 1. Time evolution of hole sheet concentration
during NO2 adsorption and desorption.

Fig. 2. (a) Drain current-voltage characteristics and (b) frequency dependence of power gain (unilateral gain)
before and after NO2 adsorption.

14

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Single-crystal AlN (0001)/diamond (111) Heterostructure
Kazuyuki Hirama, Yoshitaka Taniyasu, and Makoto Kasu
Materials Science Laboratory
Both aluminum nitride (AlN) and diamond have wide bandgaps: 6.0 eV for AlN and 5.5
eV for diamond. On the other hand, they have opposite doping characteristics. For AlN,
n-type doping is easier than p-type doping, while for diamond, p-type doping is easier thann-type doping. The AlN/diamond heterostructure is expected to combine the features of bothmaterials and appears promising for achieving high-efficiency deep-ultraviolet light-emitting
diodes and high-power electron devices. The key to realizing these devices is single-crystal
growth of AlN on diamond. However, to date, due to the difference in the crystal structures(hexagonal structure for AlN; cubic structure for diamond), AlN layers grown on diamondsubstrates have had multi-domain structures [1].
Here, using diamond (111) plane, we grew the AlN layer on the diamond substrate because
the atomic bonding configuration of the hexagonal AlN (0001) plane is similar to that of ―thecubic diamond (111) plane. Figure 1 shows the X-ray pole figures of AlN (0002) and (1011)
planes. In Figure 1(a), a strong diffraction peak was only observed at Ψ = 0˚. This indicatesthat the AlN [0001] direction was oriented normal to the diamond (111) surface. In Figure1(b),at Ψ = 62˚, we only observed six diffraction peaks, which are attributed to six equivalent―(1011) planes for hexagonal AlN. These results indicate single-crystal growth of the AlN (0001)
layer on the diamond (111) substrate.
In the cross-section TEM image at the heterointerface (Fig. 2), an abrupt AlN/diamondinterface was observed without any interface layer. This confirms that the single-crystal AlN(0001) layer epitaxially grows from the nucleation step just on the diamond (111) surface.
At the AlN(0001)/diamond(111) interface, there are two possible bonds, C-N or C-Al bonds.
Because the bond energy of the C-N bond (3.1 eV/bond) is stronger than that of the C-Al
bond (2.6 eV/bond), the C-N bond is preferentially formed at the AlN/diamond interface. As aresult, the AlN layer grown on diamond has Al polarity.
For
the AlN(0001)/diamond(111)heterostructure, the in-plane ―epitaxial relationshipis―――althoughthelatticemismatch
for
[101
0]AlN
||
[11
0]diamond[1010]AlN || [110]diamond,――canis larger than that for [1120]AlN || [110]diamond. The in-plane epitaxial relationship―0]AlNbe explained
in
terms
of
interfaceenergy.
Thebonddensitiesattheinterface
for
[101
―
―
―
–2
–2
0]AlN || [110]diamond are 2.7×10 14 cm and 2.2×10 14 cm ,|| [11 0]diamond and [112――|| [110]diamond
has a higher bond density and therefore
respectively. Because [1010]AlN――
lower interfacial energy, [1010]AlN || [110]diamond is energetically preferred for the singlecrystal AlN (0001) layer on diamond (111) surface.
[1] K. Hirama, Y. Taniyasu, and M. Kasu, Jpn. J. Appl. Phys. 49 (2010) 04DH01.
[2] Y. Taniyasu and M. Kasu, J. Cryst. Growth 311 (2009) 2825.
(a)

(b)

―

Fig. 1. XRD pole figures of (a) AlN (0002) and (b) AlN (1011)
planes of the AlN grown on diamond (111).

Fig. 2. TEM image at the AlN (0001)/
diamond(111) heterointerface.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)15

Step-free GaN films Grown by Selective-area Metalorganic Vapor Phase
Epitaxy
Tetsuya Akasaka, Yasuyuki Kobayashi, and Makoto Kasu
Materials Science Laboratory
Step-free surfaces of GaN-related nitride semiconductors have been strongly desired forstudying growth mechanisms and for achieving the abrupt hetero-interfaces necessary for
nitride-based devices, such as laser diodes, resonant tunneling diodes, and cascade lasers.
Previously reported surfaces of nitride semiconductors, however, showed a high density ofmonolayer steps originating from crystal defects (dislocations). Here, we report the firstsuccessful fabrication of step-free GaN surfaces, which are covered with single wide atomic
terraces without any monolayer steps. The step-free surfaces were obtained by using GaN
substrates with low dislocation densities and by optimizing growth conditions, such astemperature, growth rates, and the V/III ratio [1].
First, a SiO2 mask was deposited on a GaN (0001) substrate with low dislocation density–2(~106 cm ). Then, the SiO2 mask was patterned by photolithography so as to have many
hexagonal openings with the diameter of 16 µm. Finally, selective-area metalorganic vapor
phase epitaxy (SA-MOVPE) of GaN films was performed onto the mask-patterned GaN
substrate. Source gases were ammonia and trimethylgallium (TMG).
Figure 1 shows an atomic force microscopy (AFM) image of a GaN surface fabricated at–5940oC and at the TMG flow rate of 2.6×10 mol/min. The surface has a single wide terrace
over almost its whole area (step-free surface) except at the edges and there are no screwtype dislocations within the GaN hexagon. On the other hand, a GaN surface fabricated byconventional MOVPE exhibited a high density of monolayer steps with an average interstep
distance of ~0.1 µm (Fig. 2). In addition, a GaN surface fabricated by SA-MOVPE under nonoptimized growth conditions had several ten monolayer steps.
In conclusion, we fabricated step-free GaN surfaces with the diameter of 16 µm by SAMOVPE using GaN substrates with low dislocation density under optimized conditions.
[1] T. Akasaka, Y. Kobayashi, and M. Kasu, Appl. Phys. Express 2 (2009) 091002.

Fig. 1. AFM image of step-free GaN surface withdiameter of 16 µm grown by selective-area
metalorganic vapor phase epitaxy.
16

Fig. 2. AFM image of GaN surface grown by
conventional metalorganic vapor phase
epitaxy.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Synthesis of the Parent Compound Superconductors RE 2CuO4
by MBE and Specially-designed Post-reduction
Hideki Yamamoto, Osamu Matsumoto*, Keitaro Yamagami, and Michio Naito*
Materials Science Laboratory, *Tokyo Univ. of Agricul. & Technol.
It is commonly believed that the parent compounds of high-Tc cupratres are, universally,
Mott insulators (charge-transfer insulators). There has been, however, accumulating evidence
that indicates a series of parent compounds T’-RE2CuO4 [RE stands for rare earth element]
are superconductors with Tc even exceeding 30 K when they are optimally synthesized [1].
Most of the recent progress has been achieved by using the metal-organic decomposition(MOD) method [1]. Most likely, this originates from the necessity of removing impurity
interstitial oxygen while simultaneously preserving regular oxygen sites occupied, which
is a prerequisite for achieving superconductivity in square-coplanar CuO2 plane. It appears
that this requirement is easier to be fulfilled in the MOD films due to rather small grainsin them [2], which in turn makes it difficult to reproduce the results using other synthesis
methods. In this study, we systematically investigated the post-reduction process using MBEgrown T’-RE2CuO4 (RE=Pr, Nd) films on SrTiO3 (001) substrates for an easier reproduction
through a better understanding of the process.
Figure 1 shows several important parameters in the growth and post-reduction procedures.
To make the parent compounds superconducting, a specially-designed 2-step reduction
process was necessary, as in the case of MOD films. By optimizing oxygen partial pressure
and annealing temperature with constant duration, the MBE-grown RE2CuO4 (RE=Pr, Nd)films show superconductivity (Fig. 2) [3].
These findings are useful for synthesizing bulk specimens of the parent compoundsuperconductors, which makes evaluation of oxygen stoichiometry feasible. They are also
useful for synthesizing the thin-film specimens through an all-UHV process, with which a
direct observation of electronic structure by photoemission spectroscopy becomes possible.
Both will lead us toward the true electronic phase diagram for high-Tc cuprates.
[1] O. Matsumoto et al., Phys. Rev. B 79 (2009) 100508; Physica C 469 (2009) 924.
[2] O. Matsumoto, A. Tsukada, H. Yamamoto, T. Manabe, and M. Naito, Physica C (in press).
[3] H. Yamamoto, A. Tsukada, O. Matsumoto, and M. Naito, Physica C (in press).

Fig. 1. Parameters in MBE growth and post-reductionof RE2CuO4 thin films.

Fig. 2. ρ -T characteristics of MBE-grown
Nd 2CuO4 and Pr2CuO4 thin films.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)17

Growth of Graphene by Gas-source Molecular Beam Epitaxy
Fumihiko Maeda and Hiroki Hibino
Materials Science Laboratory
Because of the excellent electrical performance of graphene, such as a highest carrier
mobility at room temperature, it is recognized as one of the most promising candidates for the
next-generation of electronics materials. However, for its practical application, a remaining
challenge is the formation of graphene films with high quality and wafer-scale size to achieve
compatibility with a large-scale manufacturing process. To meet this challenge, we propose
a new approach for forming wafer-scale graphene, which is based on gas-source molecularbeam epitaxy (MBE). In this method, the substrate is not restricted to specific ones as it isin other promising methods, such as graphene formation by means of epitaxy on SiC [1] oron transition metals [2]. We report here a demonstration of the gas-source MBE to show thefeasibility of our new approach for the formation of graphene [3].
In this experiment, about three atomic layers of graphene, prepared by high-temperatureannealing of 6H-SiC(0001) under an ultra-high vacuum, were used as a substrate for thehomoepitaxial growth. This substrate was heated to 620oC and cracked ethanol was supplied
as a growth material. After this growth, in situ x-ray photoelectron spectroscopy (XPS)
measurements indicated that about four monolayers of graphitic material were grown. The
cross-sectional transmission electron microscope image in Fig. 1 shows that this growngraphitic material has a layered structure. These results show that graphene was grown.
Meanwhile, in the Raman spectra of the samples with and without the growth [Fig. 2], we
observed changes in the peak shape of the 2D-band and an increase in the intensity of the
G-band. This result supports the increase of graphene thickness by the growth. However,a remarkable D-band peak was also observed after the growth, indicating that the domain
size of the graphene is small. These results indicate that our new approach is feasible for theformation of wafer-scale graphene and that it would be compatible with device fabrication
processes, although improvement in the crystal quality is needed.
[1] A. J. van Bommel, J. E. Crombeen, and A. van Tooren, Surf. Science 48 (1975) 463.
[2] L. C. Isett and J. M. Blakely, Surf. Science 58 (1976) 397.
[3] F. Maeda and H. Hibino, Phys. Status Solidi B 247 (2010) 916.

Fig. 1. Cross-sectional transmission electron microscope
image after MBE growth.

18

Fig. 2. Raman spectra of the samples (a) with and(b) without the overlayer growth.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Stability-instability Transition of Reaction Fronts
in Thermal Silicon Oxidation
Hiroo Omi and Hiroyuki Kageshima*
Materials Science Laboratory, *Physical Science Laboratory
The SiO2/Si(001) has been one of the most important interfaces in silicon semiconductors
and related silicon nanotechnologies. Due to its significance, therefore, much works havebeen done to understand the roughening mechanism of silicon oxidation not only on surface[1], but also at interface [2]. In this work, morphological evolution at the interface between
the Si(001) substrate and the thermal SiO2 film grown at the oxidation temperature between
1000 and 1380oC in a dilute oxygen/Ar atmosphere were systematically studied by atomic
force microscopy (AFM) and synchrotron radiation X-ray reflectivity (XRR) measurements
as a function of oxidation temperature and time, and miscut angle of the substrates. The
AFM results show that thermal oxidation causes interface roughening with forming stepterrace structures (Region II in Fig. 1) between 1150-1250oC and then smoothened during thethermal oxidation above 1250oC (Region III in Fig. 1) independent of miscut angles below 4
deg. The interface roughening and smoothening possibly relates to the temperatures of which
determine the viscosity of the growing SiO2 film. The XRR measurements on the as-grownsilicon oxide films support the presence of the temperature dependences. As seen in Fig. 2, σ i-s
is constant in region (I), but it becomes extremely rough from Tox = 1150oC with the roughness(RMS) reaching a maximum at Tox = 1250oC in region (II). It then gradually becomes smaller
in region (III), in accordance with the AFM results in Fig. 1. The temperature dependence
of interface and surface roughening in Fig. 2 indicates that there is an apparent temperaturedependent mechanism of how the strain induced by oxidation relives at the growing interface
between Si and silicon oxide film and in the whole region of silicon oxide films.
[1] Fundamental Aspects of Silicon Oxidation, edited by Y. J. Chabal (Springer, 2001).
[2] H. Omi, H. Kageshima, and M. Uematsu, Phys. Rev. Lett. 97 (2006) 01602.
[3] H. Omi, H. Kageshima, T. Kawamura, M. Uematsu, Y.Kobayashi, S. Fujikawa, Y. Tsusaka,
Y. Kagoshima, and J. Matsui, Phys. Rev. B. 79 (2009) 245319.

Fig. 1. RMS vs oxidation temperature.

Fig. 2. Surface and interface roughness,
obtained by XRR.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)19

Stacking Domains in Epitaxial Bilayer Graphene
Hiroki Hibino1, Seigi Mizuno2, and Hiroyuki Kageshima3
Materials Science Laboratory, 2Kyushu University, and 3Physical Science Laboratory

1

Few-layer graphene (FLG) is attracting intense attention as a future electronics material
due to its superior electronic transport properties. Epitaxial FLG grown on SiC substrates
by thermal decomposition can be easily scaled up and is promising for device integration.
We have so far established a method of determining the number of graphene layers
microscopically using low-energy electron microscopy (LEEM) [1] and have succeeded in
growing bilayer graphene a few micrometers in size. In this work, we clarified the domain
structures in bilayer graphene [2].
Figure 1 shows LEEM images of FLG 1-3 layers thick grown on 4H-SiC(0001). Bilayer
graphene looks continuous in the bright-field LEEM image [Fig. 1(a)] obtained using the
specularly reflected (0,0) beam. However, the dark-field LEEM images [Figs. 1(b) and 1(c)]obtained using the diffracted (1,0) and (0,1) beams clearly show that bilayer graphene contains
two types of domains. The contrast of the two domains are reversed between the (1,0) and (0,1)
dark-field LEEM images, indicating that these domains have three-fold symmetry. Monolayer
graphene has six-fold symmetry, and two carbon atoms are located at A and B sites in a unit
cell. On the other hand, as shown in Fig. 2, bilayer graphene can have two types of stacking
orders with three-fold symmetry: AB stacking in which a B’ carbon atom is on an A carbon
atom and BA (usually called AC) stacking in which an A’ carbon atom is on a B carbon atom.
Therefore, we speculate that the two types of domains seen experimentally correspond to the
AB and AC stackings. To confirm this, we measured the energy dependence of the intensitiesof the dark-field LEEM images for the two domains and compared it to the calculated
energy dependence of the (1,0) and (0,1) low-energy electron diffraction intensities for bulk
graphite. Good agreement between these two energy dependences proves that there arestacking domains in bilayer graphene. The stacking domain structures can affect the electronictransport properties in FLG. The formation mechanism and condition for growing a single
stacking domain are the next targets.
This work was supported by KAKENHI.
[1] H. Hibino et al., Phys. Rev. B 77 (2008) 075413.
[2] H. Hibino et al., Phys. Rev. B 80 (2009) 085406.

Fig. 1. (a) Bright-field and (b)-(c) dark-field LEEM
images of epitaxial FLG. In (a), 1-3 indicate thenumber of graphene layers. Electron beam energies
were (a) about 5 eV and (b)-(c) about 58 eV.
20

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Fig. 2. Schematic illustration of AB and AC
stackings in bilayer graphene.

Carbon Nanotube Synthesis from Diamond
Daisuke Takagi and Yoshihiro Kobayashi*
Materials Science Laboratory, *Osaka University
We have succeeded in growing carbon nanotubes (CNTs) from diamond. CNTs arepromising as future base components in many industrial fields due to their various superior
properties, such as low weight, high mechanical strength, and good electrical/thermal
conductivities. So far, Fe, rare metals like Co and Ni, and noble metals like Au, Ag, and
Pt have been used as effective catalysts for CNT synthesis. However, because these metal
catalyst particles easily lose their catalytic activities due to aggregation/fusion and reaction
with substrates, they are not suitable for high-density CNT growth. Furthermore, because
these metal catalyst particles are in a liquid phase at the single-wall CNT (SWCNT) growthtemperatures, they cannot be used to precisely control the CNT structure, especially thechirality. Diamond is free from aggregation/fusion and is in a solid phase at the growthtemperatures. Therefore, we hope diamond will make it possible to grow CNTs with a
precisely controlled structure.
In this work, we clarified that the CNT syntehsis from diamond by chemical vapor
deposition (CVD) requires (1) the use of nanodiamond particles with a diameter smaller than
5 nm [1]; (2) removal of the graphite formed on the nanoparticle surface; and (3) the use ofgases that thermally decomposed easily, such as ethanol vapor and acetylene, as the carbon
feed stock [2]. Transmission electron microscopy (TEM) images [Figs. 1(a) and 1(b)] andthe Fourier transform pattern [Fig. 1(c)] obtained from Fig. 1(b) indicate that SWCNTs aregrown from nanodiamond particles. Scanning electron microscopy (SEM) image in Fig. 1(d)indicates that SWCNTs can be grown from three-dimensionally accumulated nanodiamondparticles. This means that the nanodiamond particles were in the solid phase at the CVD
ambient conditions and did not aggregate. It is known that, in metal-catalyzed CNT growth,carbon atoms are supplied to the CNT through bulk diffusion of carbon atoms in the particle.
On the other hand, CNT growth from nanodiamond particles must be promoted by surface
diffusion of carbon atoms.
Nanodiamond particles are produced at low cost and have catalyst activities as high as metal
nanoparticles. The nanodiamond particles offer the possibility of not only low-cost, highdensity growth of SWCNT but also precise control of the structure of SWCNT.
[1] E. Ōsawa, Diamond Relat. Mater. 16 (2007) 2018.
[2] D. Takagi et al., J. Am. Chem. Soc. 131 (2009) 6922.

Fig. 1. (a) TEM image of SWCNTs and (b) TEM image of a SWCNT and nanodiamond particle. (c) Fouriertransform pattern obtained from (b). (d) SEM image of SWCNTs grown from three-dimensionallyaccumulated nanodiamond particles on graphite substrate.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)21

Effect of Mg2+ on Neural Activitiy
Keiichi Torimitsu
Materials Science Laboratory
It is well known that magnesium ion (Mg2+) plays an important role in biological functions,similar to that of calcium ion (Ca2+). It would be useful to understand the effect of Mg2+ onneural functions in relation to controlling neural activity. However, the relationship between
Mg2+ and neural functions has not been well understood. Although recent studies indicatethat an Mg2+ deficient diet has significant health effects, few reports have studied the effectof Mg2+ on neural activity [1]. Here we have investigated the effect of low concentrations of
extracellular Mg2+ on membrane potential using flow cytometry, and on the intracellular Ca2+
concentration using a confocal laser microscope.
Figure 1 shows the Mg2+ dependence on the membrane potential of cortical neurons.
Oxyonol dye DiBAC4(3) was used for the measurements. The results indicate that a low
Mg2+ concentration depolarizes the membrane potential depending on the reduction in theextracelluar Mg2+ concentration below 2 mM [2, 3]. The developmental effect of Mg2+ wassignificant at 12 days in vitro (DIV), and could be observed at a concentration of less than 0.7
mM (Fig. 2) [2, 3].
The same type of Mg2+ dependence was observed in hippocampal neurons. However, theresponses of cortical and hippocampal neurons to a low Mg2+ concentration differed during
the developmental period. The results indicate that hippocampal neurons are more sensitive to
Mg2+ than cortical neurons. This may originate in the difference in the receptor distribution in
those regions [3]. Further investigation is needed to understand the mechanisms of the Mg2+
effect on neural activity.
[1] K.Torimitsu, N. Kasai, and Y. Furukawa, Clin. Calcium 14 (2004) 26.
[2] Y. Furukawa and K. Torimitsu, JJSMgR 27 (2008) 75.
[3] Y. Furukawa, N. Kasai, and K. Torimitsu, Magnes. Res. 22 (2009) 174S.

Fig. 1. Magnesium dependence of membrane potential
in cortical neurons.

22

Fig. 2. Developmental effect of magnesium on
intracellular Ca2+ concentrations.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Fabrication of a Nano-bio Device Using Giant Unilamellar Vesicles
Koji Sumitomo, Arianna McAllister, Yukihiro Tamba*, Youichi Shinozaki,
and Keiichi Torimitsu
Materials Science Laboratory, *Suzuka Nat. Coll. Tech.
To fabricate a nano-bio device that functions with membrane proteins, we are trying to form
micron-scale wells covered with a lipid bilayer on a Si substrate [1]. The membrane proteinsin the suspended membrane will be able to function as well as membrane proteins in vivo. In
this study, we used giant unilamellar vesicles (GUVs) several tens of microns in diameter toform a lipid bilayer suspended over the wells.
GUVs have been studied as a simplified cell membrane model. Figure 1 shows a functional
analysis of ion channels (gramicidin A) arranged into a GUV lipid membrane based on
an analysis of changes in fluorescent intensity. The GUVs’ internal environment includes
the fluorescent probe (pyranine), which changes its emission intensity with pH. When theenvironment outside the GUVs is changed (pH is increased), the cations pass through theion channels and cancel out the concentration gradient between the inside and outside of the
GUVs. The increase in the pH of the GUVs with time is clearly shown.
Then, the GUVs were ruptured over the wells which were fabricated on the Si substrateusing photolithography. The aperture of the wells has an overhang shape that was formedby selectively etching the Si substrate below the SiO2 layer. The wells were loaded withfluorescent probes and sealed with a lipid bilayer. Excess probes were rinsed out. Figure 2
shows that the fluorescent probes are trapped in the wells (b), although several holes aroundthe patch are unfilled (a). The overhang shape improves the probability of the confinementof the fluorescent probes in the wells because the suspended lipid bilayer is prevented
from falling into the wells. The fluorescence from the probes confined in the wells remains
unchanged for one hour or more. This indicates that the probes remain stably in the wells
without flowing out. When we changed the pH outside the wells, we could analyze thefunction of the ion channels in the suspended lipid bilayer, as in Fig. 1. We show that micronscale wells for the functional analysis of membrane proteins are formed on the Si substrate.
The transport of ions through the ion channels will be analyzed by both the fluorescentintensity change and the ion current, which will be collected by an electrode embedded in thewells. This constitutes a major step toward the fabrication of nano-bio devices.
[1] Y. Shinozaki et al., Appl. Phys. Express 3 (2010) 027002.

Fig. 1. Functional analysis of ion channels on GUVs(change of fluorescent intensity).

Fig. 2. Sealing of micron-scale wells on a
Si substrate with a lipid bilayer.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)23

Design of an LSI Chip for a Bio-machine Interface
in 0.18 µm CMOS Technology
Akiyoshi Shimada, Masaya Yamaguchi*, Nobuhiko Nakano*, and Keiichi Torimitsu
Materials Science Laboratory, *Keio University
Brain-machine interfaces that link the brain and the external world have been developedin the neuroscience and medical fields. Most of these interfaces are designed for one-way
communication; however we have developed an interface that makes two-way communication
possible through a microelectrode array (MEA)[1]. The electrical stimulation of the brain
and neural activity measurement are important in relation to this communication, as is theinterpretation of information in the brain. Furthermore, an unwired and miniaturized device isdesirable in terms of reducing the stress induced when the device is worn on the body. In thisstudy, we have developed 16-ch preamplifiers with multi-channel stimulation circuits on a 2.5mm × 1.4 mm LSI chip using a 0.18 µm CMOS process [2].
Figure 1 shows the three main components of this LSI chip: a stimulation block, ameasurement block and a mode change block. The stimulation block can produce a 16 ch
4-bit parallel arbitrary waveform by combining 10 µs-wide pluses for electrical stimulation.
The measurement block has 16 ch pre-amplifiers, and a multiplexer to combine 16 ch neuralsignals into one signal at a sampling rate of 40 kS/s. The mode change block switches
between the stimulation and measurement blocks when it receives a control signal generated
by the stimulation block. Figure 2 shows the neural activity of dissociated rat cortical neurons
on the MEA with and without stimulation. A few tens of milliseconds after applying threestimulation pulses to one electrode, neural activity was observed with a different electrode.
We will unwire the input and output between this LSI chip and the external unit to improve
the portability of the device as a brain-machine interface.
[1] A. Shimada et al., SFN 2008, Washington, D.C. U.S.A. (Nov. 2008).
[2] M. Yamaguchi et al., Jpn. J. Appl. Phys. Accepted.

Fig. 1. Circuit diagram of LSI chip designed as brainmachine interface.

24

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Fig. 2. Neural activity evoked by 3 stimulation
pulses.

Si Nanowire Ion-sensitive Field-effect Transistors
with a Shared Floating Gate
Katsuhiko Nishiguchi, Toru Yamaguchi, and Akira Fujiwara
Physical Science Laboratory
Ion-sensitive field-effect transistors (ISFETs) are one of the most powerful tools forbiotechnology and molecular engineering because they promise high integrability, goodminiaturization, and high-speed sensing. More interestingly and importantly, nanoscale
ISFETs have sensitivity high enough to detect single electrons at room temperature [1]. On
the other hand, a serious issue with ISFETs, which are usually used in ionized and/or charged
impurities distributed randomly in a liquid, is background noise. The background noise
disturbs the precise detection of small amounts of material, which hinders precise molecular
detection. In this study, in an attempt to distinguish a target signal from background noise, wefabricated nanoscale Si-based ISFETs, which are arrayed in parallel and share one floatinggate [2].
The ISFET’s channels with a constriction part were patterned on a silicon-on-insulator (SOI)
wafer (Fig. 1). A subsequent oxidation process shrunk the constriction of the channel, which
gives ISFETs high charge sensitivity with single-electron resolution [1]. Au and Ti wires wereformed simultaneously on three constrictions by a well-aligned lift-off process using electronbeam lithography. As a substance for detection, we used octadecane thiol (ODT) solved in atetrahydrofuran (THF). THF with an ODT was dripped onto the ISFETs with a dropper andthe characteristics of the current, I1, I2, I3, and I4, flowing through the four constrictions in one
device were measured.
After complete evaporation of the THF droplet, current characteristics as a function of backgate voltage shifted according to the concentration of ODT. This means that the fabricateddevices work as an ISFET to detect negatively charged ODT on the devices.
Next, we monitored I1, I2, I3, and I4 in real time when THF with an ODT was supplied (Fig.
2). Although all curves seem to change individually, I1, I2, and I3 show mutually synchronizedstep-wise changes as indicated by arrows, whereas I1 changes individually. This means that
the Au wire covering the channels for I2, I3, and I4 is covered with ODT and therefore gives
those synchronized changes due to its capacitive coupling to the channels. That is, althougheach curve individually has background noise or current caused by the THF, ODT, and FETs
themselves, real-time monitoring of I1, I2, I3, and I4 allows us to make a distinction between
such background noise and an effect caused by materials attached to the Au wire. The
presented schame is promising for a noise-robust sensor.
[1] K. Nishiguchi, Jpn. J. Appl. Phys. 47 (2008) 8305.
[2] K. Nishiguchi, Appl. Phys. Lett. 94 (2009) 163106.

Fig. 1. Device structure of the ISFETs with a shared floating gate.
(a) Scanning electron microscope. (b) schematic view.

Fig. 2. Change in current flowing through
ISFETs when the THF with ODT was
supplied.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)25

Tunneling Spectroscopy of Electron Subbands in Thin SOI-MOSFETs
Jin-ichiro Noborisaka, Katsuhiko Nishiguchi, Hiroyuki Kageshima,
Yukinori Ono, and Akira Fujiwara
Physical Science Laboratory
Complementary metal-oxide-semiconductor (CMOS) technology is now approaching thephysical limit of scaling where quantum mechanical effects manifest due to the reduction ofdevice size. On the other hand, several new devices are being explored to add functionalities
based on quantum effects to silicon devices [1, 2]. Therefore, it is important to understand andcontrol the quantum confinement effect to extend the functionality of silicon devices. Here, wereport direct observation of electron subbands in thin silicon-on-insulator (SOI) metal-oxidesemiconductor field-effect transistors (MOSFETs) by tunneling spectroscopy [3].
The observation of subbands was carried out in SOI-MOSFETs with 2-nm-thick tunnelinggate oxide [Fig. 1]. Figure 2(a) shows the tunneling current (ILG) and the derivative (dILG/dVLG)
taken at 20 K for a sample with tSOI of 25 nm. Small peaks can be seen when VLG < 0. These
characteristics are also seen for a device with a tSOI of 10 nm [Fig. 2(b)]. The appearance of
these peaks only for negative biases, which causes electron injection into the channel, andtheir tSOI dependence strongly indicate that they originate from the DOS structure of the thin
SOI channel. To understand the observed structures quantitatively, we calculated the energiesof the electron subbands in an SOI well for various electric field strengths. We found that the
VLG at which the peaks appeared in the experiments is reasonably reproduced by the subbandedge of the fourfold valley [Fig. 3(a), (b)]. This is because tunneling current is proportional to
the DOS, and the magnitude of the DOS for four-fold valleys is larger than that for two-foldones, therefore, four-fold valley subbands were clearly detected. We showed clear evidence forthe observation of a series of subband spectra in a structurally confined SiO2/Si/SiO2 quantum
well by tunneling spectroscopy.
[1] K. Uchida et al., J. Appl. Phys. 102 (2007) 074510.
[2] S. Saito et al., Jpn. J. Appl. Phys. 45 (2006) 679.
[3] J. Noborisaka et al., Appl. Phys. Lett. 96 (2010) 112102.

Fig. 1. (a) Schematic view of thedevice. (b) Transmission
electron microscope image.
26

Fig. 2. Tunneling current andconductance. (a) SOI =25 nm; (b) SOI = 10 nm.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Fig. 3. (a) Calculated subband energies.
(b) Comparison between thecalculated tunneling current andexperimental one.

Two-dimensional Patterning by Using Block Copolymer Self-assembly
Toru Yamaguchi and Hiroshi Yamaguchi
Physical Science Laboratory
Block copolymer lithography has drawn considerable attention as a combined topdown/bottom-up nanopatterning method toward 16-nm-technology nodes and beyond. The
most important challenge of its application to nanodevice fabrication is in achieving twodimensional (2D) patterning by strictly controlling the alignment of the domain interfaceof the microphase-separated domains of a block copolymer. Here, we demonstrated that aflexibly designable 2D self-assembly of the symmetric poly(styrene-b-methylmethacrylate)–1(PS-b-PMMA) (Mn: 36 kg mol , lamellar period L0=28 nm) is achieved by graphoepitaxy
using a hydrogen silsesquioxane (HSQ) resist pattern as the guide for alignment [1]. The key
to success is the combination of the neutralization of the bottom surface and the introductionof an intentionally designed 2D hydrophilic guiding pattern formed by top-down electronbeam lithography (EBL), which leads to vertical orientation and 2D alignment of lamellar
domains, respectively [Fig. 1(a)].
For rectangular confinement, vertical lamellar domains with a thickness of 4La (La: average
repeating period of the laterally aligned lamellar domains) and with a half-pitch of 16 nm
can be forced to bend using right-angled guiding patterns [Fig. 1(b)]. It is noteworthy thatthese domain structures are formed in a pure block copolymer system, which can be achieved
with high flexibility in the domain shape and period in graphoepitaxy of lamellar domainsof diblock copolymers. For hexagonal confinement, we have successfully demonstrated thatconcentric cylindrical domains are formed [Fig. 1(c)]; these domains are characterized byhigh controllability of the number of layers of the PS or PMMA rings, which is achievedby varying the width of confinement between opposite sides. This precise control of thealignment of lamellar domains can be achieved by first taking full advantage of the bottomup self-assembly of block copolymers and the top-down fabrication of the alignment guideby using high-precision EBL. We have also confirmed that these bent lamellae and concentric
cylinders were successfully transferred to a semiconductor substrate with a 16-nm half-pitch
resolution [Fig. 1(d)]. We are convinced that our method increases the applicability of block
copolymer lithography to nanodevice fabrication, as the size scale is beyond the reach of thestate-of-art top-down technology.
[1] T. Yamaguchi and H. Yamaguchi, Adv. Mater. 20 (2008) 1684.

Fig. 1. (a) Schematic diagram of the self-assembled structure in a hexagonal confinement. (b, c) Top-down
Scanning Electron Microscope (SEM) images of retained PS domains after the removal of the PMMA
domains in (b) rectangular and (c) hexagonal confinements. (d) Top-down SEM image of etched patterns.
All scale bars are 200 nm.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)27

Optical Tuning of Coupled Nanomechanical Resonators
Hajime Okamoto, Koji Onomitsu, and Hiroshi Yamaguchi
Physical Science Laboratory
Coupled nanomechanical resonators have recently become the focus of research because
they allow the study of interesting physical phenomena, such as synchronization and mode
localization[1,2]. They also enable new applications in sensors using the dynamics of thecoupled system[3]. The coupling efficiency is determined by the eigenfrequency difference inthe resonators. Therefore, frequency tuning is important and desired to control the vibrational
coupling. Here, we demonstrate the controlled coupling in nanomechanical resonators byusing photothermal stress. By this method, perfect vibrational coupling was realized[4].
The nanomechanical system has two doubly-clamped beams of 40-µm length, 10-µm
width, and 0.8-µm thickness (Fig. 1). The beams consist of top Au gates, AlGaAs/GaAs
superlattice, n-GaAs, and i-GaAs layers. The two beams are mechanically coupled throughan etching overhang. Each beam can be actuated separately by the piezoelectric effect byapplying an a.c. voltage between the gate and the n-GaAs layer. The frequency response of themechanical vibration was detected using a He:Ne laser via optical interferometry (Fig. 1). The
eigenfrequency of the beams was tuned by adjusting the laser power. These measurements
were performed in a vacuum at room temperature.
Figure 2 shows the laser power dependence of the resonance spectra of Beam 2 measured
whilst actuating Beam 1. Two coupled vibrational modes are found around the natural
frequency: the nearly symmetric and anti-symmetric vibration for the lower- and higherfrequency, respectively. The coupling efficiency between the beams can be controlled byadjusting the laser power (P). Photo-induced thermal stress modifies the eigenfrequency of thebeam with changing its spring constant. Increasing P reduces the eigenfrequency difference
between the two beams, therefore enhancing the coupling efficiency. The frequency difference
between the two coupled modes decreases with increasing P and is minimized at P = 64
µW (Fig. 2). At this laser power, the coupling is maximized and purely symmetric and antisymmetric vibration is realized. For P > 64 µW, the frequency difference again increases withP increases, i.e., the coupled beams are optically detuned. The realization of the perfectly
tunable coupled nanomechanical resonators will offer the opportunity for their high-sensitive
sensing applications and for the study of the dynamics of coupled systems.
[1] S. Shim et al., Science 316 (2007) 95.
[2] C. Pierre, J. Sound Vib. 139 (1990) 111.
[3] M. Spletzer et al., Appl. Phys. Lett. 88 (2006) 254102.
[4] H. Okamoto et al., Appl. Phys.Express 2 (2009) 062202.

Fig. 1. Microscope image of the coupled resonators
and an illustration of the measurement setup.

28

Fig. 2. Laser power dependence of the resonancespectra of the coupled modes.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)Intrinsic Gap and Exciton Condensation in the νT = 1 Bilayer System
Paula Giudici, Koji Muraki, Norio Kumada, and Toshimasa Fujisawa
Physical Science Laboratory
A system comprising two layers of two-dimensional electron systems (2DES) closely
separated at a distance of 20-30 nm, termed a bilayer electron system, exhibits unusual
properties not seen in single-layer systems. In particular, for a system where macroscopicallydegenerate discrete levels (Landau levels), formed in each layer by a magnetic field applied
perpendicular to the 2D plane, are half filled by electrons (i.e., total filling factor νT = 1) andthe interlayer distance d is small enough so that the interlayer interaction is strong, many
interesting phenomena, including dissipationless flow of electrical current oppositely directedin the two layers suggestive of excitonic superfluidity [1], have been reported. On the other
hand, when d is large enough so that the two layers behave independently, the system exhibitsa metallic behavior, which is believed to reflect the Fermi surface formed by composite
particles consisting of electrons and magnetic flux quanta.
The nature of the quantum phase transition between these largely dissimilar quantum states
has long been a subject of both theoretical and experimental interest. However, in a recent
study [2] we have shown that, in the standard experimental conditions, where a GaAs double
quantum well is subjected to a perpendicular magnetic field, the metallic phase is not fully
spin polarized and, as a result, the experimentally observed transition is governed by the
Zeeman energy, which results in a first order transition with different nature than that of aquantum phase transition expected for an ideal spinless system. In this study, by tilting themagnetic field with respect to the sample normal and thereby enhancing the Zeeman energy,
we investigated the nature of the intrinsic phase transition without any spin effects [3]. As
the Zeeman energy is increased, the energy gap of the excitonic phase saturates at a value(intrinsic gap) that depends solely on the ratio between the interlayer distance d and the inplane electron distance lB (Fig. 1) and its amplitude coincides with twice the energy difference
between the two states (Fig. 2). These results suggest that this phase transition is of second
order and the condensate is formed from the metallic state through exciton formation.
[1] M. Kellogg et al., Phys. Rev. Lett. 93 (2004) 036801.
[2] P. Giudici, K. Muraki, N. Kumada, Y. Hirayama, and T. Fujisawa, Phys. Rev. Lett. 100 (2008)
106803.
[3] P. Giudici, K. Muraki, N. Kumada, and T. Fujisawa, Phys. Rev. Lett 104 (2010) 056802.

Fig. 1. Energy gap of the excitonic phase at different d/lB
plotted as a function of the total magnetic field.

Fig. 2. Intrinsic gap vs d/lB and comparison withtwice the energy difference (solid line).

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)29

Fano-Kondo Effect in a Side-coupled Double Quantum Dot
Satoshi Sasaki and Hiroyuki Tamura
Physical Science Laboratory
Large tunability of electronic states in semiconductor quantum dot (QD) systems has
unveiled rich quantum transport phenomena such as the Kondo effect and Fano resonances.
The Kondo effect arises from spin singlet formation between the localized magnetic momentin the QD and the conduction electrons in the reservoirs, and drastically modifies the transportcharacteristics of the QD at low temperature. When a second QD (dot 2) is tunnel-coupled tothe side of the first QD (dot 1) exhibiting the Kondo effect, as schematically shown in Fig.1,
the inter-dot spin singlet formation is expected to suppress the Kondo effect. Although a large
number of theoretical studies exist on such a side-coupled double QD, very few experiments
have been reported so far. On the other hand, Fano effect arises from interference between
continuum and a resonant channel. Ratio of the transmission amplitudes via the two channels
determines the Fano resonance wave form ranging from an asymmetric peak to a dip.
In this work, we measure low temperature transport characteristics of the side-coupled
double QD fabricated from GaAs/AlGaAs two dimensional electron system, and discuss novel
Fano-Kondo interplay [1]. Figure 2 shows a grey-scale plot of the conductance as functionsof the plunger gate voltages, V1 and V2, measured with a standard lock-in method at 41 mK.
Three strong Coulomb peaks are observed when the electron number in dot 1, N1, changes
by one. Conductance between the two Coulomb peaks marked with a triangle is enhanced by
the Kondo effect where N1 is odd. Inter-dot Coulomb interaction is revealed as jumps in the
Coulomb peak positions whenever the electron number in dot 2, N2, changes by one, forming
a well-known honeycomb stability diagram. We observe conductance maxima at the upper
valley (white arrow) and minima at the lower valley (black circle) when N2 changes by one.
Detailed temperature and magnetic field dependence measurement of these features lead us toconclude that they are Fano resonances where the Kondo effect (cotunneling) in dot 1 plays arole of continuum. These features are qualitatively reproduced by theoretical calculations [2].
[1] S. Sasaki et al., Phys. Rev. Lett. 103 (2009) 266806.
[2] H. Tamura and S. Sasaki, Physca E 42 (2010) 864.

Fig. 1. Schematic diagram of the side-coupled
double quantum dot structure.

30

Fig. 2. Observed conductance as functions of theplunger gate voltages. White corresponds tohigh conductance.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)Multiple Two-qubit Operations Using Semiconductor Coupled
Charge Qubits
Takeshi Ota, Gou Shinkai*, Toshiaki Hayashi, and Toshimasa Fujisawa*
Physical Science Laboratory, *Tokyo Institute of Technology
Two-qubit unitary operations are key ingredients for performing quantum algorithms andcorrelating multiple qubits. Typical operations, such as controlled-rotation (CROT), whichrotates the target qubit state conditionally on the control qubit state, and SWAP, which swaps
quantum states of the two qubits, have been demonstrated using superconductor charge qubits
and semiconductor spin qubits[1, 2]. However usually one type of operations is realized
depending on the type of coupling (Ising, Heisenberg, etc.). Although other operations canin principle be designed in combination with some one-qubit operations, simple sequences
for shorter operation time or a smaller number of steps have been desired to maintain thecoherency of the system.
In this work, using coupled semiconductor charge qubits consisting of two sets of coupled
double quantum dots (DQD), we fabricated two-qubit device in which two spatially separated
electrons in the two qubits change their locations coherently and collectively (the correlated
coherent oscillations) and two-qubit operations such as CROT, SWAP can be performed in asingle step[3]. Figure 1 shows a scanning electron micrograph (SEM) of the two-qubit device.
The two qubits with individual source and drain electrodes are electrically isolated, and thus
independent currents can be measured simultaneously. All qubit parameters can be controlledby 11 gate voltages. By applying high-frequency voltage pulse to first qubit and measuring
the current, coherent oscillation demonstrating the superposition of the charge states |0> and|1> is observed. Here, |0> and |1> represent the location of the charge in the right and left dot,
respectively. Due to the electrostatic coupling between the two qubits, the coherent oscillationof the first qubit is strongly influenced by the charge states of the second qubit. Figure 2 shows
the demonstration of the CROT operation of the first qubit using the second qubit as a control
qubit. Figure 3(a) shows the correlated coherent oscillations in which SWAP operation is
performed.
This work was partly supported by SCOPE from the Ministry of Internal Affairs andCommunications of Japan.
[1] T. Yamamoto et al., Nature 425 (2003) 941.
[2] J. R. Petta et al., Science 309 (2005) 2180.
[3] G. Shinkai et al., Phys. Rev. Lett. 103 (2009) 056802.

Fig. 1. Two-qubit device using
coupled semiconductor
double quantum dots.

Fig. 2. Coherent oscillations of the first qubit
representing CROT operation. The
oscillations (a) and (b) correspond to thecase that the second qubit is |1>and |0>,respectively.

Fig. 3. (a) Correlated coherent oscillations of the first qubit. The
oscillations (b) correspond to
those shown in Fig. 2.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)31

Theory of Quantum Dynamics During a Qubit Readout Process with aJosephson Bifurcation Amplifier
Hayato Nakano, Kosuke Kakuyanagi, Shiro Saito, Kouichi Semba, and Hideaki Takayanagi*
Physical Science Laboratory, *Tokyo University of Science
The readout of a qubit state is a typical indirect quantum measurement that is performed
with a probe. We report here our successful theoretical analysis of a superconducting qubit
readout with a Josephson bifurcation amplifier (JBA) as the probe. We also use this readout
method in our experiments.
JBA is a non-linear oscillator, which has two resonance modes (high-amplitude mode E
state, and low-amplitude mode G state). Small changes in operational parameters (driving
frequency, driving amplitude, etc.) determine which mode is realized. When we make a JBA
interact with a qubit, the resulting JBA state reflects a small change in the effective operational
conditions depending on the qubit state. So, we can readout the qubit state (microscopic
information) as the realized JBA state (macroscopic information) [1]. This constitutes a formof quantum signal amplification. The JBA readout method is suitable for quantum processing
because it has almost no detrimental effect on the post-measurement qubit state. The readout
process is certainly the quantum time-evolution (quantum dynamics) of a qubit-JBA coupledsystem. We have clarified the process theoretically. In particular, we have shown how asuperposed qubit is projected into one of the measurement basis states probabilistically during
this readout process [2].
As the driving force is increased, the interaction between the qubit and the JBA gradually
increases, and the unitary evolution makes the coupled system become an entangled state
consisting of two qubit-JBA correlated states (0<t<τ1: see figures below). In one of themthe qubit is in the excited (e) state, and the JBA is in the G state. In the other, the qubit isin the ground (g) state, and the JBA is in the G’. As the driving force is further increased,
the g-G’ pair starts to transit to g-E. At this point, the decoherence in the JBA destroys theentanglement (t~τ2). In due cource, the coupled system becomes a mixture consisting of ane-G and g-E pair. This means that the coupled system is now (t~τ3) one of the two possible
states although we do not know which is realized until we perform a measurement. By judging
whether the JBA state is G or E with a usual classical measurement, we can know into whichstate (g or e) the qubit is projected.
[1] I. Siddiqi et al., Phys. Rev. Lett. 93 (2004) 207002.
[2] H. Nakano, S. Saito, K. Semba, and H. Takayanagi, Phys. Rev. Lett. 102 (2009) 257003.

Fig. 1. Time-evolution of JBA (a) → (b) → (c) → (d)(Q-representation).
32

Fig. 2. Time variation of entanglement strength
between qubit and JBA.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)Experimentally Realizable Controlled-NOT Gate in a Flux-qubit /Resonator System
Shiro Saito, Todd Tilma*, Simon J. Devitt*, Kae Nemoto*, and Kouichi Semba
Physical Science Laboratory, *National Institute of Informatics
Superconducting qubits have attracted increasing interest in the context of quantum
computing and quantum information processing [1]. We are focusing on a superconducting
flux qubit/resonator system [see Fig. 1(a)] where the resonator works as a quantum bus (qubus).
Using the qubus concept we can perform any two-qubit operation between any two qubitsthat are coupled to the quantum bus without using multiple swap gates, which are required inother systems that use direct qubit-qubit coupling. We present an experimentally realizablemicrowave pulse sequence that effects the controlled-NOT (C-NOT) gate operation in a qubit/
resonator system [2]. From numerical simulations, we obtained a process fidelity FP [3] of
98.8 % (98.0 %) for a two-(three-)qubit/resonator system under ideal conditions.
Figure 1(a) is a schematic of our system. Each qubit couples to the resonator through amutual inductance M. Because of the fixed coupling, the qubit transition frequency depends
slightly on the resonator state. We utilize this frequency difference to realize the C-NOT
gate in cooperation with a two-photon blue side band (BSB) transition, which can create
an entanglement between the control qubit and the resonator. Figure 1(b) shows a basic
operational sequence of pulses on our two-qubit/resonator system. The pulse characteristics
are represented by a frequency (C: carrier frequency, BSB: BSB frequency), a length(π/2, π) and a phase (0, π, ϕ ) from the top to the bottom. We obtained an FP of 98.8 % by
optimizing the free evolution time T and the phase of the second BSB pulse ϕ . Here we set thefrequencies of the control, target qubit and resonator at 6, 5 and 10 GHz, respectively, and thecoupling between the qubit and the resonator at 0.1 GHz. Moreover, we obtained a high FP of
98.0 % even when we added a third qubit with a frequency of 7 GHz, which means that our
proposal is scalable. The total gate time is 200 ns, which is much shorter than the coherencetime of a flux qubit (4 µs). We estimated FP under decoherence (see Fig. 2). We obtained an
FP of 90.3 % under the best conditions yet achieved experimentally: Q=106 and Γ1=Γ2=0.25
MHz. Even with this realistic decoherence model, FP still exceeds 90 %, showing that our gate
remains robust against this type of loss.
This work was supported by KAKENHI.
[1] J. Clarke and F. K. Wilhelm, Nature 453 (2008) 1031.
[2] S. Saito, T. Tilma, S. J. Devitt, K. Nemoto, and K. Semba, Phys. Rev. B 80 (2009) 224509.
[3] I. L. Chuang and M. A. Nielsen, J. Mod. Opt. 44 (1997) 2455.

Fig. 1. (a) Superconducting flux-qubit/resonator system.
(b) Pulse sequence of C-NOT gate.

Fig. 2. Process fidelity under decoherence.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)33

Kondo Effect in a Semiconductor Quantum Dot
Controlled by Spin Accumulation
Toshiyuki Kobayashi1, Shoei Tsuruta1,2, Satoshi Sasaki1, Toshimasa Fujisawa1,
Yasuhiro Tokura3, and Tatsushi Akazaki1,2
1
Physical Science Laboratory, 2Tokyo University of Science, 3Optical Science Laboratory
The spin of a localized electron embedded in a semiconductor quantum dot interacts with thespins of surrounding conduction electrons to form a spin-singlet coherent quantum many-bodystate. The state is known as the Kondo effect, which changes the state by temperature, electricfield, and magnetic field. Since both the localized and conduction electrons play importantroles in forming the Kondo state, the Kondo effect should be suppressed if the conduction
electrons are spin-polarized. However, any experimental investigation of the Kondo effectwith spin-accumulated conduction electrons had been a challenge owing to the difficulty ofgenerating a 100 % spin-polarized state. We have succeeded in measuring the continuous
modulation of the Kondo effect by accumulating only spin-up electrons near a quantum dot
using a spin filter of a quantum wire under a high magnetic field whose spin selectivity ismore than 90 % [1].
The Kondo effect accompanies the formation of the Kondo density of states (KDOS) at thechemical potential µ of a lead, because the conduction electrons at the Fermi energy interact
resonantly with the localized electron (Fig. 1). Since the KDOS moves with µ , changing theµ of just the spin-up electrons by injecting only spin-up electrons from a quantum wire to aquantum dot shifts only the spin-up KDOS and modulates the spin-splitting of the KDOS.
The position of the KDOS can be measured as a peak in the differential conductance gD of aquantum dot (Fig. 2).
[1] T. Kobayashi et al., Phys. Rev. Lett. 104 (2010) 036804.

Fig. 1. (a) Scanning electron micrograph of thedevice and the measurement setup. (b)-(d)Chemical potentials µ and KDOS ρ when
the conductance g E of a quantum wire isfixed at 0, e2/h, and 2e2/h and VE is applied.

34

Fig. 2. Conductance peak attributed to the KDOS
shifts with VE. When the conductance g E of aquantum wire is e2/h, the µ of a spin-up electron
shifts with VE, which is measured as a shift in
the conductance peak.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)Generation of Time-bin Entangled Photon Pairs Using Cascaded
Second Order Nonlinearity in Single PPLN Waveguide
Myrtille Hunault, Hiroki Takesue, Osamu Tadanaga*, Yoshiki Nishida*, Masaki Asobe*
Optical Science Laboratory, *NTT Photonics Laboratories
Cascaded second-order nonlinearity (χ(2): χ(2)) process in a single periodically poled lithium
niobate (PPLN) waveguide is a well known technique for wavelength conversion in the
1.5-µm band [1]. Recently, this technique has been used in a quantum optics experiment, inwhich squeezed vacuum pulses were generated [2]. Here, we report the generation of time-bin
entangled photon pairs using the χ(2): χ(2) process in a single PPLN waveguide.
Figure 1 shows the setup. A 1551.1 nm continuous lightwave was modulated into a pulse
train with a 100 ps width and a 500 MHz repetition frequency using an intensity modulator(IM). The pulses were amplified by an erbium-doped fiber amplifier (EDFA), filtered toeliminate amplified spontaneous emission noise from the EDFA, and then launched into a
PPLN waveguide. In the PPLN waveguide, the 1.5-µm pump pulse train was converted to a
780-nm pulse train via SHG (second harmonic generation), and simultaneously, the generated
780-nm pulse train worked as a pump for spontaneous parametric down conversion. As aresult, we generated sequential time-bin photon pairs [3], whose state is approximately givenby. Here,denotes the state of a photon in the temporal position k and themode z (=s: signal, or i: idler), and N is the number of pulses for which the phase coherence ofthe pump is preserved. The output light from the PPLN waveguide was introduced into opticalfilters, which separated the signal and idler photons. The signal and idler photons were theninput into 1-bit delayed interferometers. We can observe a two-photon interference fringe bymeasuring the coincidence counts between the signal and idler channels while changing thephase of the interferometers.
As shown in the inset of Fig. 1, we observed two-photon interference fringes with visibilities
up to as high as 97 % . Thus, we successfully confirmed the generation of high-purity
entanglement based on the proposed scheme.
[1] M. H. Chou et al., IEEE Photon. Technol. Lett. 11 (1999) 653.
[2] K. Hirosawa et al., Phys. Rev. A 80 (2009) 043832.
[3] H. de Riedmatten et al., Phys. Rev. A 69 (2004) 050304(R).

Fig. 1. Experimental setup (inset: two-photon interference fringes).
Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)35

Numerical Analysis of Cold Fermionic Atoms in an Optical Lattice at
Finite Temperatures
Kensuke Inaba and Makoto Yamashita
Optical Science Laboratory
Cold atoms trapped in optical lattices are ideal model systems for investigating the manybody problems which have been studied for many years in condensed matter physics. These
controllable systems are thus considered as a quantum simulator. In fact, the quantum phasetransition from a metallic state to a Mott insulating state has been successfully realized using
fermionic 40K atoms in optical lattices [1]. The antiferro-magnetic (AF) transition in the
optical lattice system is a major current concern for condensed matter physicists, because
it could provide ways to elucidate the nature of high Tc superconductors. According to therecent rapid progress in cold atom experiments, one can expect the AF phase in optical latticesystems to be observed at lower temperatures in the near future. This naturally motivates us
to undertake a detailed theoretical study of the properties of the AF transition in this system.
However, there was no reliable theoretical method to investigate this issue, because thetrapping potential, which is a characteristic of optical lattice systems, makes the analysis much
more complex.
We have investigated the two-component fermionic atoms trapped in a two-dimensional(2D) optical lattice [2]. We extended the self-energy functional approach (SFA), which is
known as a powerful numerical tool to analyze strongly correlated electron systems at finite
temperatures. However, due to the trapping potential, it has been difficult to investigate
realistic optical lattice systems using a conventional SFA algorithm. We solved this difficulty
and confirmed that the extended-SFA can be successfully applied to the 2D optical latticesystem. The calculated results showed reasonable agreements with the previous experimental
and theoretical results [1]. Furthermore, we studied the AF transition in this 2D optical latticesystem systematically. As shown in Fig. 1, below the AF transition temperature, the AFordered region develops from the bottom of the trapping potential where the Mott insulating
region appears at certain higher temperatures. Finally, we estimated the AF transition
temperature (Fig. 2), and proposed a suitable parameter region for observing the AF orderedphase experimentally.
This work was partly supported by CREST of the Japan Science Technology Agency.
[1] U. Schneider et al., Science 322 (2008) 1520; R. Jordens et al., Nature 455 (2008) 204.
[2] K. Inaba and M. Yamashita, submitted to Phys. Rev. A.

Fig. 1. (a) Schematic diagram of the AF ordered phaseof two-component fermions trapped in a 2D
optical lattice. (b) Numerical result: Spatial
distribution of magnetization below the AF
transition temperature.
36

Fig. 2. AF transition temperatures Tc as afunction of characteristic energy scaleof trapping potential Et for different
interaction strengths U, where energy unit
W is the bandwidth.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Trapping Loss Mechanism of Superconducting Atom Chips
Tetsuya Mukai, Christoph Hufnagel, and Fujio Shimizu*
Optical Physics Laboratory,*The University of Electro-Communications
A stable confinement of neutral atoms in quantum regime is an indispensable techniquefor realizing quantum gate operations over an atomic system. Trapping atoms with a fieldof micro-fabricated circuit on chip "atom chip" enables strong trapping confinement withpractical resources and it is expected to be a key technology for quantum manipulation of
atoms. The first step for developing the atom chip quantum device is overcoming a serious
loss problem that is significant in the vicinity of a chip surface. Our approach is employing a
superconducting circuit, which is expected to reduce the spin-flip loss rate in many orders ofmagnitude. So far we have succeeded in trapping atoms with a superconducting circuit withpersistent current [1] and demonstrated an order improvement in trapping stability. However,
our experimental results also suggested that the trapping loss mechanism of superconducting
atom chip is not the same as that of conventional atom chips. In this year we studied andclarified the trapping loss mechanism of superconducting atom chip [2].
At first we investigated the current distribution in a superconducting wire by measuring thetrap height over applied bias field (Fig. 1). By comparing with the calculated trap height withand without magnetic fluxes, the experimental result clearly suggested that magnetic fluxes
were penetrating into the superconducting wire.
Secondly we analyzed the experimentally obtained trapping loss rate as a function of trap
heights (Fig. 2). The trapping loss rate shows specific curve when the data was taken with thesame persistent current, but after washing out the current and re-introducing the persistentcurrent, the loss rate shows a different curve. With these experimental results, we came tounderstand that the penetrated magnetic fluxes with dendritic pattern locally modified thetrapping potential and introduced a spin flip transition at zero field point. The existenceof dendritic magnetic fluxes was also proved by an experiment with a novel trap with asuperconducting disc [3].
This research was partly supported by CREST of Japan Science and Technology Agency and
KAKENHI.
[1] T. Mukai, C. Hufnagel et al., Phys. Rev. Lett. 98 (2007) 260407.
[2] C. Hufnagel, T. Mukai, and F. Shimizu, Phys. Rev. A 79 (2009) 053641.
[3] F. Shimizu, C. Hufnagel, and T. Mukai, Phys. Rev. Lett. 103 (2009) 253002.

Fig. 1. Trap height over applied bias magnetic field. The
filled squares represent the experimental dataand solid (dotted) curve represents a calculation
with (without) magnetic flux penetration.

Fig. 2. Decay rate over several trap heights.
Different marks represent the data taken on
the different days. Persistent current was
introduced several times on each day.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)37

Ultrafast Dynamics of Coherent Phonons in P-type Si Driven by
Sub-10-fs Laser Pulses
Keiko Kato, Atsushi Ishizawa, Katsuya Oguri, Hideki Gotoh, and Hidetoshi Nakano
Optical Science Laboratory
Coherent phonons are the in-phase lattice vibrations driven by the ultrashort laser pulses
whose duration is shorter than the oscillatory period. In contrast to frequency-domain
approaches, such as Raman spectroscopy or infrared-active spectroscopy, the observation ofcoherent phonons provides time-domain information about the lattice vibrations.
For Si, which is the fundamental semiconductor, the Raman spectrum is modified by p-type
doping, reflecting the asymmetric shape of the valence band in k-space [1]. To study theelectron-phonon dynamics dominated by the asymmetry in the carrier distribution, we haveobserved coherent phonons in p-type Si [2].
We performed time-resolved reflectivity measurements with a sub-10-fs Ti:sapphireoscillator at a center wavelength of 780 nm. Samples were non-doped Si and p-type Si. The
carrier concentration in the p-type Si was 3×1019–1.5×1020 /cm3.
The time-resolved reflectivity changes for non-doped Si and the p-type Si are shown in
Figs. 1(a) and (b), respectively. The oscillatory signal, originating from coherent phonons in
Si, is observed after an overlap between the pump and probe pulses at t=0. In the p-type Si,
the decay from the photo-generated carriers, which distribute anisotropically in k-space (i.e.,
anisotropic state-filling), is observed as shown by the dotted line in Fig. 1(b). In the p-type
Si, the Fermi level is lowered in the valence band with the non-parabolic structure, whichcauses the anisotropic hole distribution [2]. When the oscillatory signal is fitted with cos(ω 0t+ φ ), where ω 0 and φ correspond to the frequency and initial phase of the coherent phonons,
respectively, the initial phase in the p-type Si is shifted to the cosine phase with the anisotropy
in the hole distribution.
This research was supported by KAKENHI.
[1] F. Cerdeira, T. A. Fjeldly, and M. Cardona, Phys. Rev. B 8 (1973) 4734.
[2] K. Kato, A. Ishizawa, K. Oguri, K. Tateno, T. Tawara, H. Gotoh, and H. Nakano,Jpn. J. Appl. Phys. 48 (2009) 100205.

Fig. 1. Time-resolved reflectivity for (a) non-doped Si and (b) the p-type Si. Insets show enlarged graphs aroundt=0. Black dots are the experimental results. The gray line is the fitting result, the black solid line is thecomponent of coherent phonons, and the black dotted line is the decay of anisotropic state-filling.

38

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Freestanding GaAs Nanowires with a Controlled Diameter and Their
Optical Properties with the Radial Quantum-confinement EffectGuoquiang Zhang, Kouta Tateno, Haruki Sanada, and Hideki Gotoh
Optical Science Laboratory
Semiconductor nanowires (NWs) have attracted considerable attention owing to theinteresting fundamental properties of such low-dimensional systems and the exciting prospects
of utilizing these materials in nanotechnology-enabled electronic and photonic applications.
NWs are expected to provide the building blocks with which to form new nanostructures andrealize novel 1-dimensional structures. To explore the potentially unique applications of thesefreestanding NW building blocks, we synthesized freestanding GaAs NWs with a controlled
diameter and studied their optical properties with the radial quantum-confinement effect.
The NW growth was undertaken in a metalorganic vapor phase epitaxy system and Au
nanoparticles were used to catalyze the NW growth via the vapor-liquid-solid (VLS) mode [1].
We controlled the diameter of the GaAs NWs by using size-selective Au colloidal particles
with nominal diameters of 5, 10, 20, 40, and 60 nm [2]. We characterized the structure anddiameter of the NWs using transmission electron microscopy (see Fig. 1). We successfully
controlled the NWs with very few stacking faults by growing them at a very low temperature.
We studied their optical properties by employing micro-photoluminescence (PL) at 3.6 K[3]. Figure 2(a) shows PL spectra from individual NWs of different Au particle sizes. PL
peak energies clearly exhibit the blue shift with decreasing Au particle size due to the radialquantum-confinement effect [2]. We analyzed the absorption and emission polarization
characteristics of these NWs and found large anisotropies between polarization resolved
PL spectra (see Fig. 2(b)). These results suggest that both the dielectric constant contrast
and the quantum-confinement effect have to be considered [2]. This work opens the way toinvestigating size-related optical phenomena in bare GaAs quantum wires, and provides more
opportunities for the study of one-dimensional quantum physics using freestanding NWs.
[1] G. Zhang et al., J. Appl. Phys. 103 (2008) 014301.
[2] G. Zhang et al., Appl. Phys. Lett. 95 (2009) 123104.
[3] G. Zhang et al., Jpn. J. Appl. Phys. 49 (2010) 015001.

Fig. 1. TEM images of free standing GaAs NWs. (a) Single
NW. (b) and (c) high-magnification images of thesegments near the middle and tip in (a). The inset in(b) is the corresponding diffraction pattern, whichindicates a zinc-blende structure. (d) HRTEM image
near the NW side. (e) Images for Au particles withdifferent diameters.

Fig. 2. (a) PL spectra of single GaAs NWs grownusing Au particles with three nominal
diameters. (b) Polarization resolved PL
spectra. The red broken line indicates thefree excitonic PL energy in bulk GaAs.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)39

Photoluminescence Properties of Dynamic Quantum Dots
Formed by Surface Acoustic Waves
Tetsuomi Sogawa, Haruki Sanada, and Hideki Gotoh
Optical Science Laboratory
Surface acoustic waves (SAWs) provide a dynamic one- or two-dimensional lateralmodulation of the band structure of quantum wells (QWs) [1, 2]. In this study, we investigate
the dynamic optical properties of excitons in GaAs/AlAs moving dots (dynamic quantum
dots, DQDs) formed by the interference of orthogonally propagating SAW beams. The SAWs
induce a strain as well as a piezoelectric modulation of the materials properties. Due to theD4d symmetry of the underlying GaAs crystal, the interference of the two orthogonal SAW
beams leads to the formation of two interpenetrating square arrays of DQDs [3], as shownin Fig. 1(a), where the in-plane components of the particle displacement field are shown
schematically. One of the arrays (black and gray circles) consists of potential dynamic dots
(p-DDs) created by the modulation of the piezoelectric potential. The second array (blackand gray squares) is composed of strain dynamic dots (s-DDs), where the band gap becomesminimum or maximum due to the modulation of the hydrostatic strain.
Spatially resolved photoluminescence (PL) measurement at 4 K was carried out by using
a synchronized excitation method [1]. Figure 1(b) shows the PL mapping for a 6.3-nm QW
recorded at a photon energy of 1.623 eV, which is located in the lower-energy side of the
PL peak (centered at 1.630 eV in the absence of a SAW). In the PL polarization studies, wedefine the degree of polarization anisotropy ρ as the relative difference ρ = (PL[1-10] – PL[110]) / (PL[1-10] + PL[110]) between the PL intensity emitted along the [1-10] (PL[1-10]) and [110] (PL[110])propagation directions of the individual SAW beam. Figures 1 (b) and (c) clearly demonstrate
the formation of the two DQD arrays. The strong and weak PL positions in Fig. 1(b)correspond to the tensile (black squares in Fig. 1(a)) and compressive (gray squares in Fig.
1(a)) s-DD positions, respectively. In contrast, the positive (negative) ρ areas in Fig. 1 (c) arelocated at the saddle point of the tensile s-DDs along the [1-10] ([110]) direction, denoted bya black (gray) circle in Figs. 1 (b) and (c). The positions with strong PL anisotropy correspondto the array of the p-DDs.
[1] T. Sogawa et al., Phys. Rev. B 80 (2009) 075304.
[2] T. Sogawa et al., Appl. Phys. Lett. 91 (2007) 141917.
[3] F. Alsina et al., Solid State Commun. 129 (2004) 453.

Fig. 1. (a) Schematic illustration of the in-plane components of the particle displacement field. (b) PL mapping forthe 6.3-nm QW recorded at a photon energy of 1.623 eV, which is located in the lower-energy side of the
PL peak. (c) Spatial distribution of the PL anisotropy for 6.3-nm QW.

40

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Sub-femtojoule All-optical Switching Using a Photonic Crystal Nanocavity
Kengo Nozaki, Takasumi Tanabe, Akihiko Shinya, Shinji Matsuo*, Tomonari Sato*,
Hideaki Taniyama, and Masaya Notomi
Optical Science Laboratory, *NTT Photonics Laboratory
Photonic crystal (PhC) nanocavities, which exhibit a high cavity Q and an ultrasmall modal
volume V, allow a strong light-matter interaction. As a result we can expect them to provide
the basis for very low power active devices. In particular, the energy needed for all-opticalswitching based on the carrier-induced resonance shift should be effectively reduced, because
the required control energy should be proportional to V/Q. In this study, we successfully
achieved an extremely low switching energy and a fast switching time by combining InGaAsP,
which exhibits a strong carrier-based nonlinearity, and an ultrasmall PhC nanocavity.
Figure 1(a) and (b) are a top-view image of the PhC structure and the transmission
spectrum, respectively. The H0 nanocavity is formed by shifting two adjacent air holes in
opposite directions. A computational calculation produced a modal volume V of only 0.025µm3. Figure 2 shows the switching dynamics measured with a pump-probe technique. Whenthe probe pulse wavelength matches the modal peak, the probe pulse transmission is abruptly
switched off when the pump pulse temporally overlaps the probe pulse. In contrast, the probetransmission is switched on at shorter probe wavelengths. This is because carrier nonlinearity
induces a resonant blueshift. The minimum switching time window of 20 ps is attributed to
localized carrier generation and a fast carrier escaping from the cavity. The switching energy
with a contrast of 3 dB is only 0.42 fJ, which is more than two orders of magnitude lower thanthat of previously reported all-optical switches.
We showed that an InGaAsP-PhC nanocavity offers the possibility of realizing an alloptical switch operating with ultrasmall energy, a fast response time, and ultrasmall footprint
integratability on a single chip. Other PhC-based optical devices, such as optical memories,
photo-detectors, and modulators can also be achieved for chip-scale electronics-photonics
interconnection.
This work was partly supported by CREST of Japan Science and Technology Agency.
[1] T. Tanabe et al., Appl. Phys. Lett. 87 (2005) 151112.
[2] K. Nozaki et al., Nature Photon. (in press).

Fig. 1. (a) Top-view image and calculated mode
profile of H0 nanocavity. (b) Transmission
spectrum with calculated fitting curve.

Fig. 2. Switching dynamics. The upper and lower plots
are for switch-off and switch-on operations,
respectively. ∆λdet denotes the detuning of a probe
wavelength from the modal peak.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)41

Strong Optomechanical Coupling in a Bi-layer Photonic Crystal
Young-Geun Roh, Takasumi Tanabe, Akihiko Shinya, Hideaki Taniyama,
Eiichi Kuramochi, Shinji Matsuo*, Tomonari Sato*, and Masaya Notomi
Optical Science Laboratory, *NTT Photonics Laboratories
Mechanical interaction between light and matter is one of the most fundamental problems
in physics. Recently, coupling phenomena between optical and mechanical resonant modes inphotonic structures has attracted strong interests. In 2006, our group theoretically predictedthat a bi-layer photonic crystal (PhC) with a thin air gap can generate strong radiation force [1].
In this work, we have realized a bi-layer PhC for the first time and have demonstrated strong
optomechanical coupling in it [2].
A periodic hole pattern arranged in a square lattice was fabricated in two vertically separated
slabs using electron beam lithography, dry-wet etching, and CO2 supercritical drying (Fig. 1).
The period, hole diameter, slab thickness, and gap thickness are 750 nm, 540 nm, 200 nm,
and 200 nm, respectively. We performed reflectance spectrum measurements of the bi-layer
PhC formed in the lateral area of 30×20 µm, which revealed photonic bandedge resonantmodes around 1567 nm and 1457 nm. These modes exhibit opposite mode symmetry along
the vertical direction. Figure 2 shows reflectance spectra obtained by wavelength scan aroundsymmetric mode (1567 nm), which exhibit input power dependence and optical bistability. We
concluded that the observed redshift is explained by a slab displacement (i.e. gap decrease)induced by attractive radiation force for the symmetric resonant mode. The thermo-opticallyinduced shift is excluded because we observed opposite blueshift for the antisymmetricmode (1457 nm). We estimated that each slab was displaced by 0.9 nm at Pin=13 mW when
the redshift was 1.8 nm. This corresponds to attractive force of 10.8 nN, and thus F/U (i.e.
generated force per unit energy in cavity) can be estimated 0.4 µN/pJ, which is a very large
value among various optomechanical systems. Thanks to this large optomechanical coupling,
we have successfully observed tiny Brownian motion of mechanical modes of bi-layer PhCs
[shown in Fig. 3(a)] in RF spectra of the reflected light beam [Fig. 3(b)].
[1] M. Notomi et al., Phys. Rev. Lett. 97 (2006) 023903.
[2] Y. Roh et al., Phys. Rev. B 81 (2010) 121101(R).

Fig. 1. SEM image of fabricated bi-layer PhC.

Fig. 2. (a) Power dependence of reflectance spectra.
(b),(c) Simultaneous scan of each resonant mode

42

Fig. 3. (a) Fundamental vibration mode of bi-layer
PhC. (b) RF spectrra of reflected beam

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)All-silicon Photonic Crystal Receiver for 1.55-µm Light Detection Utilizing
Two Photon Absorption
Takasumi Tanabe, Hisashi Sumikura, Hideaki Taniyama, Akihiko Shinya,
and Masaya Notomi
Optical Science Laboratory
Silicon (Si) is widely used to constitute electrical circuits, but it is also a good material for
constructing optical integrated circuits. Indeed, optical waveguides and nanocavities havebeen fabricated on Si chips. However, Si cannot be used to detect 1.5-µm light because it istransparent in this wavelength region. Therefore, germanium (Ge) on Si detectors have been
fabricated, but these detectors exhibit a relatively large dark current because of the 4 % latticemismatch between Ge and Si [1]. In addition, ion-implanted Si detectors have been studied,but they also suffer from a large dark current because of the presence of defects [2]. If we
can fabricate an all-Si detector, we should benefit from a low dark current because of thegood crystal quality of Si. For this purpose, we need to employ two-photon absorption (TPA)
whose coefficient is usually very small. In this study, we used a very high-Q photonic crystal(PhC) nanocavity to compensate for the low TPA coefficient and to enable us to detect very
weak optical light in an all-Si device [3].
Figure 1 is an illustration of our pin integrated PhC nanocavity. The Q of the fabricateddevice was 4.3×105 and the transmittance was 24 % [Fig. 2(a) inset]. The dark current was
just –15 pA when we applied a –3 V bias. Figure 2(a) shows photocurrent versus input
power. Due to the strong light confinement of the nanocavity, the TPA current is visible at–8an extremely low input power of 10 W. The QE at an input power of 1.17 µW was very
high at ~10 % (we define QE as 100 % when one photon generates one electron). Thisvalue corresponds to 44 % of the cavity-coupled light being sufficiently absorbed. Such ahigh detection efficiency with 1.55 µm light is obtained because of the high Q of the PhC
nanocavity.
We also demonstrated 0.1-Gb/s photo receiver operation using the same device [Fig. 2(b)].
Only light that can resonate with the cavity was detected electrically. This demonstrationshows that our Si-chip integrated device can be used for telecom light detection.
[1] S. Assefa, F. Xia, and Y. Vlasov, Nature 262 (2010) 80.
[2] M. Geis et al., Opt. Express 17 (2009) 5193.
[3] T. Tanabe et al., Appl. Phys. Lett. 96 (2010) 101103.

Fig. 1. Schematic illustration of pin integrated photonic
crystal nanocavity.

Fig. 2. (a) Input power versus photocurrent. Inset
is the transmittance spectrum. (b) 0.1-Gb/sphoto receiver demonstration.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)43

Ⅱ．DataScience Plaza 2009
"Science Plaza 2009," an open-house event of NTT Basic Research Laboratories (BRL),
was held at NTT Atsugi R&D Center on Friday, November 27th, 2009. Under the banner"Nanoscience Opens Up the Quantum World", Science Plaza aimed to disseminate our latest
research accomplishments through various sections of people inside and outside of NTT andto gather diverse opinions.
Following an opening address from Dr. Itaru Yokohama, the director of BRL, one of
distinguished technical members of NTT BRL, Dr. Koji Muraki gave a lecture on "Electron
correlation in semiconductor nanostructures ― deriving natural team play from electrons-".
In the afternoon session, Prof. Hideo Hosono, Tokyo Institute of Technology, gave a special
lecture entitled "Real joy of material research ― Toward discovery of treasure trove ―". Eachlecture was well-attended and followed by heated question-and-answer sessions.
As regards the poster exhibits, 44 posters, including 13 from Microsystem Integration
Laboratories and Photonics Laboratories, presented our latest research accomplishments.
While explaining the originality and impact ― as well as the future prospects ― of ourresearch accomplishments, these posters were intensively discussed, and many meaningful
opinions were heard. This year’s "Lab. Tour" ― a guided tour of research facilities at NTT
BRL that has been receiving high reputation from visitors over the years ― took place at fivedifferent labs, so that as many people as possible could join the tour. This time we also openeda booth to show the NTT R&D recruitment system for job-seeking researchers and students.
After all lectures, presentations, and exhibitions, a banquet was held in Center’s dining room,
where lively conversation among participants deepened their amity.
More than 220 people from research institutes, universities, and general industries, as well
as from NTT Group, attended Science Plaza 2009. Thanks to the efforts of all participants, theconference ended on a high note. We would thus like sincerely to express our gratitude to allof the participants.

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)45

5th NTT-BRL School
The fifth NTT Basic Research Laboratories (BRL) school was held from November 24-27,
2009 at the NTT Atsugi R&D Center. The aim of the NTT-BRL school is to foster young
researchers in physics and applied physics field and to promote the international visibility of
NTT BRL. This year the theme was "Current Research on Cutting-edge Materials", which is
closely related to the intensive research based on the materials that NTT BRL is conducting.
Prestigious professors and researchers were invited to the school as lecturers. There werethirty-five participants, who were mainly Ph. D students, from nine countries.
On the first day, after the director of NTT BRL had provided an overview of NTT BRL,
Prof. Klaus Ploog (Former Director of Paul-Drude-Institute, Germany) presented lectures
entitled "Advanced materials for information storage". He also gave lectures every day during
the school that covered sustainable energy based on the materials science from the ecologicalpoint of view. Prof. Takao Someya (The University of Tokyo, Japan) gave a talk on "Organic
materials for electronics, displays, LEDs" on the afternoon of the first day. In this school,
there were several lectures by researchers working at NTT BRL. Dr. Toshiki Makimotogave a lecture on "State-of-the-art Devices using Group-III Nitride Semiconductors". Dr.
Hiroshi Yamaguchi talked about the "Micro/nanomechanical Devices using Compound
Semiconductor". Dr. Masaya Notomi gave a talk entitled "Perspective on artificial dielectrics".
A poster session was held in the evening of the second day, where each student gave apresentation about his/her research at the university. All the students, lecturers, and NTT BRL
researchers had a good time exchanging information on current research topics in various
fields. On the second and third days we provided an overview of NTT BRL. A laboratory tour
was conducted so that the students could see the research facilities. Managers of NTT BRL
gave talks on recent activities at each laboratory. On the final day, all the participants attended
NTT BRL Science Plaza 2009, which is an exhibition of recent research achievements andactivities. They enjoyed detailed discussions with researchers about on-going research topics.
At the farewell party, best poster prizes were awarded to the students who gave noteworthy
presentations. The students were able to network and build friendships and exchange contact
addresses. NTT BRL will continue to provide these kinds of occasions to support young
researchers and help establish human networks in the fields of physics and applied physics.

46

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

Award Winners’ List (Fiscal 2009)
Poster award inInternational symposium on
purinergic signalling in new
strategy of drug discovery(Fukuoka Purine 2009)

Y. Shinozaki

Localization of P2X4 receptors inlipid raft-like structure of in vitro
model of cell membrane

July. 25,
2009

Japanese Journal ofApplied Physics Research
Paper Presentation Awards

K. Kakuyanagi

High visibility measurement ofsuperconducting flux qubit using
Josephson bifurcation amplifierSep. 8,2009

Certificate of appreciationfrom The surface science
society of Japan

Basic
Research
Laboratories

Certificate of appreciation

Oct. 28,
2009

3rd International
Symposium on
Nanomedicine
The Best Poster Award

Y. Shinozaki

Direct Visualization of Single
Receptor Dynamics: the Relationshipbetween Molecular Scturcture andPhysiology/Pathology

Nov. 5,2009

MNC 2008 Outstanding
paper Award

K. Tamaru
K. Nonaka
M. Nagase
H. Yamaguchi
S. Warisawa
S. Ishihara

Direct actuation of GaAs membraneusing microprobe of SPM

Nov. 16,2009

MNC 2008 Young Authors
Award

K. Tamaru

Direct actuation of GaAs membraneusing microprobe of SPM

Nov. 16,2009

Japan Electronic Materials
Society, outstanding
performance award

H. Wakahara

Observation of exciton and free career
electroluminescnece from a carbon
nanotube by simultaneous optical andelectric measurements

Nov. 20,
2009

Award from Commitiee ofsemiconductor interface
control

Basic
Research
Laboratories

Award

Nov. 20,
2009

Iijima Award

D. Takagi

Carbon Nanotube Growth from
Diamond Nanoparticles

Mar. 3,2010

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)47

In-house Award Winners’ List (Fiscal 2009)

48

NTT R&D Award

I. Mahboob
H. Okamoto
K. Onomitsu
H. Yamaguchi"Realization of new functional
devices based on semiconductor
mechanical resonators"

Dec. 9,2009

NTT R&D Award

M. Yamaguchi
K. Suzuki
Y. Ono"Great improvement of recovery rateof liquid helium and reduction in
fixed costs by introduction of a new
management system"

Dec. 9,2009

Award for Achievements
by Director of Basic
Research Laboratories

T. Fujisawa
G. Shinkai
T. Hayashi
T. Ota"Development of multi-functional
quantum information processing
devices using two-qubit structures"Mar. 26,
2010

Award for Achievements
by Director of Basic
Research Laboratories

Y. Shinozaki
N. Kasai
K. Sumitomo
K. Torimitsu

AFM study of structure and dynamics
in a membrane receptor protein

Mar. 26,
2010

Award for Achievements
by Director of Basic
Research Laboratories

D. Takagi
Y. Kobayashi"Development of new catalysts forcarbon nanotube growth"Mar. 26,
2010

Award for Excellent papers
by Director of Basic
Research Laboratories

T. Tanabe
M. Notomi
H. Taniyama
E. Kuramochi"Dynamic Release of Trapped Light
from an Ultrahigh-Q Nanocavity via
Adiabatic Frequency Tuning", Phys.
Rev. Lett. 102 (2009) 043907.

Mar. 26,
2010

Award for Excellent papers
by Director of Basic
Research Laboratories

H. Hibino
H. Kageshima
M. Nagase
Y. Kobayashi
H. Yamaguchi"Microscopic thickness determinationof thin graphite films formed on
SiC from quantized oscillation inreflectivity of low-energy electrons",
Phys. Rev. B 77 (2008) 075413.

Mar. 26,
2010

Award for Excellent papers
by Director of Basic
Research Laboratories

K. Tamaki"Unconditional security of theBennett 1992 quantum-keydistribution scheme with a strong
reference pulse", Phys. Rev. A 80
(2009) 032302.

Mar. 26,
2010

Award for encouragement
by Director of Basic
Research Laboratories

H. Okamoto"Optical control of mechanicalvibration in nanomechanicalresonators"

Mar. 26,
2010

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)Research Activities in Basic Research Laboratories in 2009
The numbers of papers published in international journals, presentations at international
conferences and applied patents in year 2009 amounted to 129, 276, and 40, respectively. The
numbers for each research area are as follows;
Papers Published in International Journals(Jan. - Dec. 2009)Materials Science37

Physical Science

44

Optical Science

48
0

10

20

30

40

50

Number of Papers

Presentations at International Conferences(Jan. - Dec. 2009)Materials Science62

Physical Science

123

Optical Science

91

0

20

40

60

80

100

120

140

Number of Presentations

Applied Patents (Jan. - Dec. 2009)Materials Science

13

Physical Science

11

Optical Science

16

0

5

10

15

20

Number of Applied Patents

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)49

The numbers of research papers published in the major journals are shown below.
Journals
Applied Physics Letters
Physical Review B
Applied Physics Express
Japanese Journal of Applied Physics
Optics Express
Physical Review Letters
Physical Review A
International Journal of Modern Physics B
Nanotechnology
Journal of the American Chemical Society
The Journal of Physical Chemistry B
Nature Physics
PLoS Biology
Reports on Progress in Physics
Small*IF2008: Impact Factor 2008 (Journal Citation Reports,2008)(IF2008*)
3.726
3.322
1.309
3.88
7.18
2.908
0.558
3.446
8.091
4.189
16.821
12.683
12.09
6.525

Numbers
11
11
9
9
9
8
7
5
4
1
1
1
1
1
1

The average IF2008 for all research papers from NTT Basic Research laboratories is 3.58.

The numbers of presentations in the major conferences are shown below.
Conferences
Numbers
International Symposium on. Nanoscale Transport and Technology 200942
The 18th International Conference on Electronic Properties of Two-Dimensional Systems
242009 International Conference on Solid State Devices and Materials
17
29th Conference on Lasers and Electro Optics and the 27th International Quantum Electronics
9
Conference
The 12th International Superconductive Electronics Conference
7
International Symposium on Advanced Nanodevices and Nanotechnology
6
14th Narrow Gap Semiconductor and Systems
6
14th International Conference on Modulated Semiconductor Structures
6
22nd International Microprocesses and Nanotechnology Conference
6
Materials Research Society Meeting
5
The European Conference on Lasers and Electro-Optics and the XIth European Quantum
4
Electronics Conference
2009 American Physical Society March Meeting
4
Neuroscience 20094
13th International Conference on Silicon Carbide and Related Materials
4
Silicon Nanoelectronics Workshop
4International Symposium on Nanomedicine
4
17th International Colloquium on Scanning Probe Microscopy
4Asia-Pacific Workshop on Fundamental and Application of Advanced Semiconductor Devices
3
8th International Conference on Nitride Semiconductor
3
The 22nd Annual Meeting of the IEEE Photonics Society
3International Union of Physiological Science 2009
3
SPIE Photonics West 2009
3
International Symposium on Nanoscience and Quantum Physics 20093
The 9th International Conference on Materials and Mechanisms of Superconductivity
3
Emergent Phenomena in Quantum Hall Systems 3
3
The 9th European Conference on Applied Superconductivity
3
The 36th International Symposium on Compound Semiconductors
350

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

List of Invited Talks at International Conferences (2009)
I. Materials Science Laboratory(1)

H. Omi, H. Kageshima, S. Uematsu, T. Kawamura, Y. Kobayashi, S. Fujikawa, Y. Tsusaka, Y.
Kagoshima, and J. Matsui, "Stability-instability transition of reaction fronts in thermal silicon oxidation",
Symposium on Surface and Nano Science 2009, Shizukuishi, Japan (Jan. 2009).

(2)

Y. Taniyasu and M. Kasu, "Recent progress in AlN deep-UV light-emitting diodes: physics and device
structure", SPIE Photonics West, San Jose, U.S.A. (Jan. 2009).

(3)

M. Kasu, "Nitride semiconductors and diamond", Ambient GCOE Research Exchange Seminar, "WideGap Semiconductor; the presence and its future" Waseda Univ, Japan. (Mar. 2009).

(4)

M. Kasu, K. Ueda, Y. Taniyasu, and K. Michal, "Progress of diamond semiconductor technologies:
doping and heterostructures", 3rd Industrial Diamond Conference, Paris, France (Apr. 2009).

(5)

H. Omi, T. Kawamura, and Y. Kobayashi, "Advanced SOI interface characterization using grazing
incidence X-ray diffraction", 215th The Electrochemical Society Meeting, San Francisco, U.S.A. (May2009).

(6)

D. Takagi, Y. Kobayashi, and Y. Homma, "Single-walled carbon nanotube growth from nanosized
diamond particles by chemical vapor deposition", New Diamond and Nano Carbons Conference 2009,
Traverse City, Michigan, U.S.A. (June 2009)(7)

S. Suzuki and Y. Kobayashi, "Defect engineering in single-walled carbon nanotubes", 25th International
Conference on Defects in Semiconductors, St.Petersburg, Russia (July 2009).

(8)

K. Torimitsu, "Effect of Mg2+ on rat neural activity in vitro", 12th International Magnesium Symposium,Lasi, Romania (Sep. 2009).

(9)

H. Hibino, H. Kageshima, and M. Nagase, "Structure and electronic properties of epitaxial graphenegrown on SiC studied by surface electron microscopy", 22nd International Microprocesses andNanotechnology Conference, Sapporo, Japan (Nov. 2009).

(10)

K. Furukawa, "Supported lipid bilayer formation at interface", International Symposium on
Nanomedicine, Okazaki, Japan (Nov. 2009).

(11)

M. Kasu, "Ultimate widegap semiconductors: diamond and aluminum nitride", Joint NTUU "KPI" andNTT seminar, Kiev, Ukraine (Nov. 2009).

(12)

K. Torimitsu, "Understanding receptor protein structure and functions for biomimetic device", 3rdInternational Symposium on Nanomedicine, Okazaki, Japan (Nov. 2009).

(13)

H. Hibino, H. Kageshima, and M. Nagase, "Microscopic evaluations of structure and electronic
properties of epitaxial graphene", 7th International Symposium on Atomic Level Characterizations for New
Materials and Devices, Hawaii, U.S.A. (Dec. 2009).

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)51

II. Physical Science Laboratory

52

(1)

K. Muraki, "Spin-dependent phase diagram in bilayer 2D electron systems", APS March Meeting 2010,
Oregon, U.S.A. (Mar. 2009).

(2)

M. Nagase, H. Hibino, H. Kageshima, and H. Yamaguchi, "Novel microscopies for graphene on SiC",
2009 RCIQE (Research Center for Integrated Quantum Electronics) International Seminar, Sapporo, Japan(Mar. 2009).

(3)

H. Yamaguchi, "Micro/Nanomechanical systems based on compound semiconductor heterostructures",
Frontiers in Nanoscale Science and Technology 2009 (FNST 2009), Boston, U.S.A (May 2009).

(4)

K. Muraki, "New lights on the ground-state phase diagrams of bilayer electron systems", Emergent
Phenomena in Quantum Hall Systems 3 (EPQHS-3), Capannori (Lucca), Italy (Jun. 2009).

(5)

M. Nagase, H. Hibino, H. Kageshima, and H. Yamaguchi, "Metrology of microscopic propertiesof graphene on SiC", 2009 Asia-Pacific Workshop on Fundamentals and Applications of Advanced
Semiconductor Devices, Busan, Korea (Jun. 2009).

(6)

H. Yamaguchi,"Heterostructure-based micro/nanomechanical systems", The 18th International
Conference on Electronic Properties of Two-Dimensional Systems (EP2DS), Kobe, Japan (Jul. 2009).

(7)

K. Semba, J. Johansson, K. Kakuyanagi, H. Nakano, S. Saito, H. Tanaka, and H. Takayanagi, "Quantum
state control, entanglement, and readout of the Josephson persistent current qubit", Solid State Based
Quantum Information Processing 2009 (QIP 2009), München, Germany, (Jul. 2009).

(8)

H. Yamaguchi, "Compound semiconductor micro/nanomechanical systems", 8th Topical Workshop on
Heterostructure Microelectronics (TWHM2009), Nagano, Japan (Aug. 2009).

(9)

A. Fujiwara, K. Nishiguchi, and Y. Ono, "Single-electron devices based on silicon nanowire MOSFETs",
10th Trends in Nanotechnology International Conference (TNT 2009), Barcelona, Spain, (Sep. 2009).

(10)

A. Fujiwara, K. Nishiguchi, and Y. Ono, "Silicon nanowire MOSFETs and their application to singleelectron device", International Conference on Nanoscience and Technology, China 2009 (ChinaNANO
2009), Beijing, China (Sep. 2009).

(11)

Y. Ono, M. Khalafalla, S. Horiguchi, K. Nishiguchi, and A. Fujiwara, "Identification of single boron
acceptors in nanowire MOSFETs", 2009 International Conference on Solid State Devices and Materials(SSDM 2009), Sendai, Japan (Oct. 2009).

(12)

I. Mahboob and H. Yamaguchi, "Electromechanical systems for memory and logic devices", 2009
International Conference on. Solid State Devices and Materials (SSDM 2009). Sendai, Japan, (Oct. 2009).

(13)

H. Kageshima, H. Hibino, and M. Nagase, "Epitaxial graphene growth using LEEM and first-principles",13th International Conference on Silicon Carbide and Related Materials (ICSCRM 2009), Nürnberg,
Germany, (Oct. 2009).

(14)

K. Semba, "Control of entanglement and quantum superposition of superconducting persistent current
qubit few photon system", 22nd International Symposium on Superconductivity 2009 (ISS 2009), Tsukuba,
Japan, (Nov. 2009).

(15)

K. Semba, "Superconducting qubit as an entanglement generator", Quantum Technologies: Information
and Communication (QTIC 2009), Tokyo, Japan (Dec. 2009).

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

(16)M. Nagase, H. Hibino, H. Kageshima, and H. Yamaguchi, "Microscopic characterization of few-layer
graphene on SiC", International Symposium on Advanced Nanodevices and Nanotechnology (ISANN
2009), Hawaii, U.S.A. (Dec. 2009).

(17)

M. Nagase, H. Hibino, H. Kageshima, and H. Yamaguchi, "Microscopic characterization of few-layer
graphene on SiC using an integrated nanogap probe", 17th International Colloquium on Scanning Probe
Microscopy (ICSPM 17), Izu, Japan (Dec. 2009).

III. Optical Science Laboratory(1)

M. Notomi, "Manipulating light by ultrahigh-Q nanocavities", Nanomata 2009, Tirol, Austria (Jan. 2009).

(2)

T. Tanabe, A. Shinya, E. Kuramochi, H. Taniyama, and M. Notomi, "All-optical switches and bistabledevices using high-Q photonic crystal nanocavities", SPIE Photonics West 2009, San Jose, U.S.A. (Jan.
2009).

(3)

M. Notomi, "Evolution of modulated mode-gap cavities", SPIE Photonics West 2009, San Jose, U.S.A.
(Jan. 2009).

(4)

K. Tateno, Q. Zhang, and H. Nakano, "Heterostructures in GaP-based free-atanding nanowires on Si
substrates", SPIE Photonics West 2009, San Jose, U.S.A. (Jan. 2009).

(5)

H. Nakano, A. Ishizawa, and K. Oguri, "Dependence of harmonics generation properties on carrierenvelope phase of few-cycle laser field", COAST/CORAL Symposium on Ultrafast Intense Laser Science,
Karuizawa, Japan (Mar. 2009).

(6)

H. Takesue, "Telecom-band entanglement swapping using high-speed singlephoton detectors based on
sinusoidally-gated InGaAs/InP avalanche photodiodes", SPIE Defence, Security + Sensing 2009, Advanced
Photon Counting Techniques III, Orland, U.S.A. (Apr. 2009).

(7)

M. Notomi, "Strong light confinement with and without periodicity", The 8th International Photonic andElectromagnetic Crystal Structures Meeting (PECS-VIII), Sydney, Australia (Apr. 2009).

(8)

H. Takesue, K. Harada, H. Fukuda, T. Tsuchizawa, T. Watanabe, K. Yamada, Y. Tokura, and S. Itabashi,"Silicon photonics in quantum communications", The Conference on Lasers and Electro-Optics and The
Quantum Electronics and Laser Science Conference (CLEO/QELS), Baltimore, U.S.A. (May 2009).

(9)

M. Notomi, "Adiabatic frequency tuning of ultrahigh-Q nanocavities", The 8th International Symposium
on Electrical Transport and Optical Properties of Inhomogeneous Media, Crete, Greek (Jun. 2009).

(10)

T. Honjo, A. Uchida, K. Amano, K. Hirano, H. Someya, H. Okumura, K. Yoshimura, P. Davis, and Y.
Tokura, "Differential-phase-shift quantum key distribution experiment using fast physical random bit
generator with chaotic semiconductor lasers", 18th International Laser Physica Workshop, Barcelona, Spain(Jul. 2009).

(11)

T. Tanabe, M. Notomi, H. Taniyama, and E. Kuramochi, "Recent progress of dynamically tuned photonic
crystal nanocavities", 18th International Laser Physics Workshop, Barcelona, Spain (Jul. 2009).

(12)

M. Yamashita, M. W. Jack, K. Inaba, K. Igeta, and Y. Tokura, "Gutzwiller study of Bose-Fermi mixtures
trapped in three-dimensional optical lattices", 18th International Laser Physics Workshop, Barcelona, Spain(Jul. 2009).

(13)

M. Notomi, E. Kuramochi, and T. Tanabe, "Manipulating slow light by ultrahigh-Q nanocavites and theircoupled arrays", OSA Topical Meeting on Slow and Fast Light 2009, Honolulu, U.S.A. (Jul. 2009).

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)

53

54

(14)

K. Tawara, S. Hughes, and H. Kamata, "Cavity mode emission in weakly coupled quantum-dot-cavity
system:Photon statistics and mode attraction", Photons and Spins in Nanostructures, Sapporo, Japan (Jul.
2009).

(15)

M. Yamashita, A. Yamamoto, and N. Kawakami, "DMRG study of ultracold fermionic atoms in opticallattices", Workshop on Matrix Product State Formulation and Density Matrix Renormalization Group
Simulations, Kobe, Japan (Aug. 2009).

(16)

H. Taniyama, E. Kuramochi, and T. Tanabe, Y-G. Roh, M. Notomi, "High-Q air-slot photonic crystal
cavities", 9th International Conference on Numerical Simulation of Optoelectronic Devices, Gwangju,
Korea (Sep. 2009).

(17)

A. Shinya, S. Matsuo, K. Nozaki, T. Tanabe, E. Kuramochi, T. Satou, T. Kakitsuka, and M. Notomi, "Alloptical memories based on photonic crystal nanocavities", Photonics in Switching 2009, Pisa, Italy (Sep.
2009).

(18)

M. Notomi, E. Kuramochi, T. Tanabe, and H. Taniyama, "Manipulating slow light by ultrahigh-Q
nanocavites and their coupled arrays", Frontiers in Optics 2009, San Jose, U.S.A. (Oct. 2009).

(19)

H. Nakano, K. Oguri, Y. Okano, and T. Nishikawa, "Dynamics of femtosecond-laser-ablated liquidalminium nanoparticles probed by means of spatiotemporally resolved X-ray-absorpion fine-structure
spectroxcopy", 10th International Conference on Laser Ablation, Singapore, Singapore (Nov. 2009).

(20)

H. Takesue, "Quantum communication experiments using telecom-band entangled photons",
International Conference on Quantum Information and Technology (ICQIT), Tokyo, Japan (Dec. 2009).

(21)

H. Nakano, K. Oguri, and A. Ishizawa, "High-order harmonics of carrier-envelope phase controlled fewcycle laser pulse for time-resolved spectroscopy", 5th Asian Symposium on Intense Laser Science, Hanoi,
Vietnam (Dec. 2009).

(22)

M. Notomi, "Manipulation of light by photonic crystals", International Conference on Quantum
Information and Technologies, Tokyo, Japan (Dec. 2009).

Research Activities in NTT Basic Research Laboratories Vol. 20 (2009)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/