Research Activities
in
NTT Basic Research Laboratories
Volume 19
Fiscal 2008

July 2009
NTT Basic Research Laboratories,
Nippon Telegraph and Telephone Corporation (NTT)http://www.brl.ntt.co.jp/

Cover photograph:Self-Assembled Gold Nanorod Arrays
Designed array structures of gold nanorods (diameter: 10 nm, length: 40 nm). The surface of gold
nanorod is modified by lipid molecules or polymers etc. A variety of building blocks of gold nanorods
are successfully fabricated via self-assembly of the surface anchored molecules. The gold nanorod arrays
are applicable for nano plasmonic materials or highly sensitive biochips that can detect intermolecularinteractions on a single molecular scale.

Schematics and AFM imagesof ATP receptor

Conformational changes in
ATP receptor

Observation of Ligand-Induced Conformational Changes in Single ATP
Receptors with Fast-Scanning Atomic Force Microscopy
Proteins, known as "receptors" that exist in cells, exhibit their functions via binding with small compounds such as hormones. When the receptor is a type of ion channel, it opens its pore after binding
with compounds thereby flowing ions through it and resulting in exhibiting its function. We observed
the topology and stimulation-induced conformational changes in adenosine triphosphate (ATP) receptor, an important receptor in pain sensation, with atomic force microscopy (AFM). (Page 20)(a) STM topography of a single donor (bright spot). (b) Distance r dependence of LDOS from a single donor.
Energy positions ε1～ε3 give bound state levels. (c) Spatial LDOS maps at ε1～ε3. (d) LDOS intensity of the lowest
energy level ε1 as a function of distance r. By measuring this dependence, the Bohr radius (aB1) is determined.

Direct Measurement of the Binding Energy and Bohr Radiusof a Single Hydrogenic Defect in a Semiconductor Quantum Well
It is well known that the behavior of donor impurities, which are very important for semiconductor
devices, can be approximately understood by the hydrogenic model. The two fundamental properties
are the binding energy and the Bohr radius. However, These values have not been characterized for asingle donor before. By measuring the local density of states (LDOS) in the vicinity of the defect at thesemiconductor quantum well surface using low-temperature scanning tunneling microscopy (STM),
we have succeeded in determining both the binding energy and the Bohr radius. (Page 28)－Ⅰ－3D nanostructure in positive resist [(a), (b)] and another structure in negative resist [(c), (d)]. As each pairconstitutes a stereogram, 3D images can be seen with parallel viewing.

Fabrication of Three-Dimensional Nanostructures
by Electron Beam Lithography
New methods in three-dimensional nanofabrication technique using electron beam (EB) lithography
have been devised, promising nanotechnology applications. The accuracy of 3D positioning (i.e., 3Dalignment) has been improved up to the order of 10 nm. Moreover, effective suppression of the proximity effect due to electron scattering has been achieved, enabling us to freely fabricate various 3D
nanostructures. (Page 27)(a) Scanning electron microscope image of a fabricated width-modulated line-defect photonic crystal nanocavity.
The air holes in the nanocavity are shifted slightly outside the line defect. The 3D plots shown in (b) and (c)are measured spectrograms of the output light at a waveguide after it had been trapped in the photonic crystal
nanocavity. The graphs behind the 3D plots are spectrally convoluted temporal waveforms. (b) Output without
modulation. (c) Output when the cavity is modulated at t=0 ps. The wavelength of the trapped light shifts
towards a shorter wavelength as a result of adiabatic wavelength conversion, and the light is immediately output
into the waveguides and generates a short pulse.

Short Pulse Generation by Adiabatic Wavelength Shifting
Photonic crystal nanocavities have a long photon lifetime, which enables us to manipulate photons
while they are trapped. For example, we can adiabatically change the wavelength of the trapped lightby changing the refractive index of the cavity, which is analogous to a vibrating string of a guitar. As aresult of the adiabatic wavelength shifting of light, we can demonstrate the Q switching of a very small
cavity integrated on a silicon chip. We demonstrate short pulse generation from a very high Q cavity
with arbitrary timing by adiabatic wavelength shifting. This demonstration paves the way to the development of an on-chip photon memory. (Page 41)－Ⅱ－Message from the Director
We are deeply grateful for your interest andsupport with respect to our research activities.
Our mission is to overcome technological obstacles
such as providing high-capacity transmission anddelivering absolutely safe telecommunication. To
achieve these goals, we are focusing on 1. Iconoclastic
Science and Technology, 2. Innovative technologies,
3. Incubating new ideas and strengthening ourcompetences. This will allow us to contribute to thesuccess of NTT＇ s business and promote advancesin science that we hope will ultimately benefit all
mankind.
As we proceed with our research, there are somevery high barriers to overcome and we are also
facing the demand to make speedy progress. If weare to achieve our goals, it is important that we
adopt a global perspective in relation to our research
activities, and to this end we are actively collaborating with many universities and research
institutes throughout the world as well as with other NTT laboratories. To help promote apublic understanding of our activities and frank exchanges of opinion, BRL holds a "Science
Plaza" every year. We also host international conferences at NTT Atsugi R&D Center. The
International Symposium on Nanoscale Transport and Technology (ISNTT2009) was heldin January 2009, and more than 200 people attended. Moreover, one of our missions is theeducation of young researchers and we have sponsored four "BRL Schools" since 2002. The
BRL School boasts distinguished researchers as lecturers, and on each occasion more than 30
graduate students from both at home and abroad have felt its benefit. 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 in this way, andto disseminate our research output worldwide. Your continued support is greatly appreciated.

Junji Yumoto
Director
NTT Basic Research Laboratories－Ⅲ－

Contents
page◆ Color Frontispiece .............................................................................................................Ⅰ♦ Observation of Ligand-Induced Conformational Changes in Single ATP Receptors with Fast-

Scanning Atomic Force Microscopy♦ Direct Measurement of the Binding Energy and Bohr Radius of a Single Hydrogenic Defectin a Semiconductor Quantum Well
♦ Fabrication of Three-Dimensional Nanostructures by Electron Beam Lithography♦ Short Pulse Generation by Adiabatic Wavelength Shifting◆ Message from the Director ................................................................................................Ⅲ◆ Member List ........................................................................................................................1
I. Research Topics◇ Overview of Research in Laboratories ............................................................................................... 11◇ Materials Science Laboratory ............................................................................................................ 12♦ Boron-Implanted Diamond FETs Formed by Ion-Implantation andHigh-Pressure and High-Temperature Annealing♦ High Performance Nitride-Based Heterojunction Bipolar Transistors on GaN Substrates―♦ Anisotropic In-Plane Strains in Non-Polar Al1-xGaxN (1120) Films (x<0.2)♦ Molecular Beam Epitaxial Growth of Hexagonal Boron Nitride on Ni(111) Substrate♦ Simultaneous Optical and Electrical Characterization at Nanoscale with Scanning Probe

Microscope♦ Diameter Dependence of Hydrogen Adsorption on Single-Walled Carbon Nanotubes♦ Number-of-Layers Dependence of Electronic Properties of Epitaxial Few-Layer Graphene♦ Precise Control of Gold Nanorod Arrays♦ Observation of Ligand-Induced Conformational Changes in Single ATP Receptors with

Fast-Scanning Atomic Force Microscopy♦ The Preferential Reconstitution of Receptor Proteins into Model Lipid Domains Studied

by Atomic Force Microscopy♦ Effect of Nanogap on Dynamics of Lipid Bilayer◇ Physical Science Laboratory ............................................................................................................... 23♦ Stochastic Data Processing Based on Single Electrons Using Nano Field-Effect Transistors♦ Identification of Single Dopant Position in Silicon Nanotransistor♦ Bit Operation in a Parametrically Pumped Electromechanical Resonator♦ In-plane Conductance Measurements of Few-Layer Graphene on SiC Substrate♦ Fabrication of Three-Dimensional Nanostructures by Electron Beam Lithography♦ Direct Measurement of the Binding Energy and Bohr Radius of a Single Hydrogenic Defectin a Semiconductor Quantum Well
♦ Electrons and Holes in a Single Silicon Slab
♦ New Readout Method for Josephson Persistent-Current Qubits Using a Josephson

Bifurcation Amplifier♦ Evidence of Noise-Suppression with Superconductive Atom Chip
♦ Single-Shot Readout of a Josephson Persistent Current Quantum Bit♦ Photoluminescence Spectroscopy of Nonlinear- and Linear-Screening Regimes in a

Low-Density Two-Dimensional Electron System♦ Negative Photoconductivity in In0.52Al0.48As/In0.7Ga0.3As Heterostructures◇ Optical Science Laboratory ................................................................................................................ 35♦ Numerical Simulation of Ultracold Atoms Trapped in Optical Lattices♦ Single Photon Detection Using MgB2 Superconductor♦ Generation of High-Purity Entangled Photon Pairs Using Silicon Wire Waveguide♦ Efficient Carrier Envelope Offset Locking for a Frequency Comb by Modifying a Collinear

f-to-2f Interferometer♦ Cavity Emission and Photon Statistics in Exciton-Cavity Coupled Systems♦ Magneto-Optical Spectroscopy of Charge-Tunable Quantum Dots
♦ Short Pulse Generation by Adiabatic Wavelength Shifting♦ Ultrahigh-Q Photonic Crystal Slab Nanocavities in Very Thin Barriers♦ Dynamic High-Q Cavity Formation and Photon Pinning by Index Modulation

II. Data◇ Science Plaza 2008 ............................................................................................................................. 45◇ ISNTT2009 ......................................................................................................................................... 46◇ The 5th Advisory Board ..................................................................................................................... 47◇ Award Winners’ List .......................................................................................................................... 48◇ In-house Award Winners’ List ............................................................................................................ 49◇ List of Visitors’ Talks ......................................................................................................................... 50◇ Research Activities in Basic Research Laboratories in 2008 ............................................................. 54◇ List of Invited Talks at International Conferences ............................................................................. 56

Member List
As of March 31, 2009(* moved to another position within a year)

NTT Basic Research Laboratories

Director,Dr. Junji YumotoResearch Planning Section

Executive Research Scientist,

Dr. Toshiki Makimoto

Senior Research Scientist,

Dr. Kazuhide Kumakura
Dr. Hideki Gotoh*

Senior Research Scientist,

Dr. Kazuaki Furukawa
Dr. Koji Muraki*

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

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)Materials Science Laboratory

Executive Manager,

Dr. Keiichi Torimitsu

Assistant Manager,

Dr. Satoru Suzuki
Dr. Hiroo Omi*

Thin-Film Materials Research Group:
Dr. Makoto Kasu (Group Leader)
Dr. Yasuyuki Kobayashi
Dr. Hideki Yamamoto
Dr. Tetsuya Akasaka
Dr. Kazuhide Kumakura*
Dr. Kenji Ueda
Dr. Atsushi Nishikawa*Dr. Michal Kubovic
Low-Dimensional Nanomaterials Research Group:
Dr. Yoshihiro Kobayashi (Group Leader)
Dr. Fumihiko Maeda
Dr. Hiroki Hibino
Dr. Satoru Suzuki*
Akio Tokura
Dr. Daisuke Takagi
Molecular and Bio Science Research Group:
Dr. Keiichi Torimitsu (Group Leader)
Dr. Keisuke Ebata
Dr. Kazuaki Furukawa*Dr. Nahoko Kasai
Dr. Akiyoshi Shimada
Dr. Yoshiaki Kashimura
Toichiro Goto

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Dr. Hisashi Sato
Dr. Yoshitaka Taniyasu
Dr. Chiun-Lung TsaiDr. Hiroo Omi
Dr. Ilya Sychukov

Dr. Koji Sumitomo
Dr. Hiroshi Nakashima
Dr. Youichi ShinozakiPhysical Science Laboratory

Executive Manager,

Dr. Hiroshi Yamaguchi

Assistant Manager,

Dr. Kenji Yamazaki
Dr. Yukinori Ono*
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
Dr. Kenji Yamazaki*
Dr. Hajime Okamoto
Dr. Koji Onomitsu
Dr. Vijay Singh

Toru Yamaguchi
Dr. Imran Mahboob

Quantum Solid State Physics Research Group:
Dr. Koji Muraki (Group Leader)
Dr. Toshimasa Fujisawa*
Dr. Kiyoshi Kanisawa
Dr. Satoshi Sasaki*
Dr. Kyoichi Suzuki
Dr. Toshiaki Hayashi
Dr. Takeshi Ota
Dr. Norio Kumada
Dr. Kei Takashina
Dr. Kasper Grove-Rasmussen
Dr. Gerardo Gamez
Superconducting Quantum Physics Research Group:
Dr. Kouichi Semba (Group Leader)Dr. Hayato Nakano
Dr. Tetsuya Mukai
Dr. Shin-ichi Karimoto
Hirotaka Tanaka
Dr. Ying-Dan Wang*
Dr. Yoshiharu Yamada
Dr. Alexandre Kemp
Dr. Xiaobo Zhu
Spintronics Research Group:
Dr. Tatsushi Akazaki (Group Leader)
Dr. Yuichi Harada
Dr. Hiroyuki Tamura
Dr. Yoshiaki Sekine

Dr. Shiro Saito
Dr. Kousuke Kakuyanagi
Dr. Hideyuki Sawamura

Dr. Masumi Yamaguchi

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Optical Science Laboratory

Executive Manager,

Dr. Yasuhiro Tokura

Assistant Manager,

Dr. Satoshi Sasaki
Dr. Atsushi Yokoo*

Quantum Optical State Control Research Group:
Dr. Yasuhiro Tokura (Group Leader)
Dr. Kaoru Shimizu
Kazuhiro Igeta
Dr. Makoto Yamashita
Dr. Hiroyuki Shibata
Dr. Fumiaki Morikoshi
Dr. Toshimori Honjo
Daisuke Hashimoto
Dr. Ken-ichi Harada
Quantum Optical Physics Research Group:
Dr. Hidetoshi Nakano (Group Leader)
Dr. Tadashi Nishikawa
Dr. Hideki Gotoh
Dr. Kouta Tateno
Dr. Takehiko Tawara
Dr. Atsushi Ishizawa
Dr. Haruki Sanada
Dr. Keiko Kato
Photonic Nano-Structure Research Group:
Dr. Masaya Notomi (Group Leader)
Dr. Satoki Kawanishi
Dr. Atsushi Yokoo
Dr. Akihiko Shinya
Dr. Hideaki Taniyama
Dr. Hisashi Sumikura
Dr. Kengo NozakiResearch Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Masami Kumagai
Dr. Hiroki Takesue
Dr. Kiyoshi Tamaki

Hidehiko Kamada
Dr. Katsuya Oguri
Dr. Guoquiang Zhang

Dr. Eiichi Kuramochi
Dr. Takasumi Tanabe
Dr. Young-Geun Roh

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, hejoined 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 Research Laboratories
since 1999, and is currently working on light-propagation control by use ofvarious 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 (2003- ). 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 a member of
the Japan Society of Applied Physics, APS, IEEE/LEOS, 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 NTT Basic Research Laboratories in 1996. Since 1994, he has
been engaged in research on silicon nanostructures and their application to
single-electron devices. He was a guest researcher at the National Institute ofStandards and Technology (NIST), Gaithersburg, MD, USA during 2003-2004.
He received the SSDM Young Researcher Award in 1998, SSDM Paper Award in
1999, and Japanese Journal of Applied Physics (JJAP) Paper Awards in 2003 and2006. He was awarded the Young Scientist Award from the Minister of MEXT
(Ministry of Education, Culture, Sports, Science, and Technology) in 2006. He isa member of the Japan Society of Applied Physics and IEEE.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Advisory Board (2008 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,
École 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 Quantenoptik, Germany

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Invited / Guest Scientists (2008 Fiscal Year)
Name

Affiliation

PeriodDr. Go Yusa

Japan Science and Technology
Agency (JST), Japan

Apr. 2008 – Mar. 2009

Assoc. Prof. Takaaki Koga

Hokkaido University, Japan

Apr. 2008 – Mar. 2009

Dr. Keiko Kato

National Institute for Materials
Science (NIMS), Japan

Apr. 2008 – Jun. 2008

Dr. Hideomi Hashiba

Institute of Quantum Science,
Nihon University, Japan

Apr. 2008 – Mar. 2009

Dr. Shoko Utsunomiya

National Institute of Informatics, Japan

Apr. 2008 – Mar. 2009

Dr. Takashi UchidaToyo University(School of Engineering), JapanMay 2008 – Mar. 2009

Dr. Chandra Ramanujan

University of Oxford, U.K.

Nov. 2008 – Dec. 2008

Dr. Nicolas Clement

Institut of Electronics, Microelectronics and April 2008
Nanotechnology (IEMN), France

Prof. Stephen Hughes

Department of Physics,
Queen’s University, Canada

Sep. 2008 – Oct. 2008

Prof. Amnon Aharony

Ben-Gurion University of the Negev, Israel

October 2008

Prof. Ora Entin-Wohlman

Ben-Gurion University of the Negev, Israel

October 2008

Prof. Christos Flytzanis

École Normale Supérieure (ENS), France

Nov. 2008 – Dec. 2008

Prof. Jocelyn Achard

University of Paris XIII, France

Dec. 2008 – Jan. 2009

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Overseas Trainees (2008 Fiscal Year)
Name

Affiliation

PeriodChristoph Hufnagel

University of Heidelberg, Germany

Jun. 2006 –Yosia

Nanyang Technological University, Singapore

Apr. 2007 – Apr. 2008

Edita Kirpsaite

Kaunas University of Technology, Lithuania

Jan. 2008 – Aug. 2008

John McGurk

Imperial College London, U.K.

Jan. 2008 – Aug. 2008

Miron Sadziak

Warsaw University, Poland

Jan. 2008 – Aug. 2008

Zhenzhong Wang

Chinese Academy of Sciences, China.

Jan. 2008 – Dec. 2008

Thibaut Balois

École Normale Supérieure, France

Feb. 2008 – Jul. 2008

Thomas Panier

École Normale Supérieure, France

Feb. 2008 – Jul. 2008

Benjamin Miquel

École Normale Supérieure, France

Feb. 2008 – Jul. 2008

Samir Etaki

Delft University of Technology, the Netherlands

May 2008 – Dec. 2008

Taige Hou

MIT (Massachusetts Institute of Technology), U.S.A. May 2008 – Aug. 2008

Jaap Kautz

University of Twente, the Netherlands

May 2008 – Aug. 2008

Christopher Jackson

University of Nottingham, U.K .

Jun. 2008 – Aug. 2008

Aurelien Peilloux

ESPCI (École Superieure de Physiqueet de Chimie Industrielle), France

Jul. 2008 – Dec. 2008

Charline Froitier

ESPCI (École Superieure de Physiqueet de Chimie Industrielle), France

Jul. 2008 – Dec. 2008

Paul Boniface

ESPCI (École Superieure de Physique etde Chimie Industrielle), France

Jul. 2008 – Dec. 2008

Thomas Keen

University of Oxford, U.K .

Aug. 2008 – Aug. 2008

Ferry Prins

Delft University of Technology, the Netherlands

Sep. 2008 – Oct. 2008

Jelena Baranovic

University of Oxford, U.K.

Sep. 2008 – Oct. 2008

Maarten Nijland

University of Twente, the Netherlands

Jan. 2009 – Apr. 2009

Stefano Salvatore

Technical University, Milan, Italy

Sep. 2008 – Oct. 2008

Corentin Durand

University of Lille/ ISEN-Lille, France

Feb. 2009 – Jul. 2009

Pauline Renoux

INSA (Institut National des Sciences
Appliquées de Toulouse), France

Feb. 2009 –Laurent-Daniel Haret Institut d’ Optique Graduate School, France

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Feb. 2009 –Domestic Trainees (2008 Fiscal Year)
Name

Affiliation

PeriodMizuki Miyamoto

Shonan Institute of Technology, Japan

Apr.2008 – Mar.2009

Hiroshi Sakai

Tokyo University of Science, Japan

Apr.2008 – Mar.2009

Kenji Yamaya

Tokyo University of Science, Japan

Apr.2008 – Mar.2009

Norihito Hibino

Keio University, Japan

Apr.2008 – Mar.2009

Hiroyuki Wakahara

Keio University, Japan

Apr.2008 – Mar.2009

Akira Wada

Tohoku University, Japan

Apr.2008 – Mar.2009

Satoru Miyamoto

Keio University, Japan

Apr.2008 – Mar.2009

Yasuaki Miyazaki

Keio University, Japan

Apr.2008 – Mar.2009

Kuniaki Yamada

Keio University, Japan

Apr.2008 – Mar.2009

Keiichiro Nonaka

The University of Tokyo, Japan

Apr.2008 – Mar.2009

Kojiro Tamaru

The University of Tokyo, Japan

Apr.2008 – Mar.2009

Takehito Kamata

Tohoku University, Japan

Apr.2008 – Mar.2009

Kenichi Hitachi

The University of Tokyo, Japan

Apr.2008 – Mar.2009

Gou ShinkaiTokyo Institute of Technology, Japan

Apr.2008 – Mar.2009

Takashi Kobayashi

Tohoku University, Japan

Apr.2008 – Mar.2009

Kenichiro Kusudo

The University of Tokyo, Japan

Apr.2008 – Mar.2009

Hiroshi Kamata

Tokyo Institute of Technology, Japan

Apr.2008 – Mar.2009

Keita Kimura

The University of Tokyo, Japan

Apr.2008 – Mar.2009

Shun Takahashi

The University of Tokyo, Japan

Apr.2008 – Mar.2009

Lee Sang-Yoon

The University of Tokyo, Japan

Apr.2008 – Mar.2009

Yuma Okazaki

Tohoku University, Japan

Apr.2008 – Mar.2009

Naoyuki Masumoto

The University of Tokyo, Japan

Apr.2008 – Mar2009

Yoshitaka Niida

Tohoku University, Japan

Apr.2008 – Mar.2009

Haruki Kiyama

The University of Tokyo, Japan

Apr.2008 – Mar.2009

Atsufumi Inoue

The University of Tokyo, Japan

Apr.2008 – Mar.2009

Yasushi Kanai

The University of Tokyo, Japan

Apr.2008 – Mar.2009

Tatsuki Takakura

The University of Tokyo, Japan

Apr.2008 – Mar.2009

Tomohiro Nagase

Tokyo Institute of Technology, Japan

Apr.2008 – Mar.2009

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)



10

Name

Affiliation

PeriodSeiichiro Kagei

Tokyo University of Science, Japan

Apr.2008 – Mar.2009

Ryota Koibuchi

Tokyo University of Science, Japan

Apr.2008 – Mar.2009

Hiroki Morishita

Keio University, Japan

Apr.2008 – Mar.2009

Sanae Iida

Keio University, Japan

Apr.2008 – Mar.2009

Hirotaka Masuyama

Tokyo University of Science, Japan

Apr.2008 – Mar.2009

Hiroaki Koguchi

Tokyo University of Science, Japan

Apr.2008 – Mar.2009

Yuuki Ichigo

Tokyo University of Science, Japan

Apr.2008 – Mar.2009

Hiroshi Takahashi

Tokyo Institute of Technology, Japan

Apr.2008 – Mar.2009

Hiroyuki Suzuki

Tokyo Institute of Technology, Japan

Apr.2008 – Mar.2009

Takayuki Yamamoto

The University of Tokyo, Japan

Apr.2008 – Mar.2009

Hiroyuki Fukasaka

Nara Institute of Science and Technology

May2008 – Feb.2009

Norihito Kitajima

The University of Tokyo, Japan

May2008 – Mar.2009

Yasuhiko Oda

The University of Tokyo, Japan

May2008 – Mar.2009

Tadakiyo Seki

Osaka University, Japan

Jul.2008 – Sep.2008

Tatsuya Kukita

Osaka University, Japan

Aug.2008 – Aug.2008

Yuuto Ueno

Hokkaido University, Japan

Aug.2008 – Aug.2008

Takayuki Watanabe

Tohoku University, Japan

Aug.2008 – Mar.2009

Makoto Igarashi

Tohoku University, Japan

Sep.2008 – Sep.2008

Tsubasa Takanami

Nagaoka University of Technology, Japan

Oct.2008 – Feb.2009

Takashi Otani

Nagaoka University of Technology, Japan

Oct.2008 – Feb.2009

Hironori Endo

Nagaoka University of Technology, Japan

Oct.2008 – Feb.2009

Kohei Morita

Kyushu University, Japan

Oct.2008 – Mar.2009

Tetsuya Miyawaki

Tohoku University, Japan

Nov.2008 – Mar.2009

Kikombo Andrew Kilinga

Hokkaido University, Japan

Dec.2008 – Mar.2009

Kohei Kawasaki

Toyohashi University of Technology, Japan

Jan.2009 – Feb.2009

Masayuki Sugawara

The University of Tokyo, Japan

Jan.2009 – Mar.2009

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Ⅰ．Research Topics

Overview of Research in Laboratories
Materials Science Laboratory
Keiichi Torimitsu
The aims of the Materials Science Laboratory (MSL) are to discover novel functions ofmaterials, produce new functions and design advanced devices based on these novel functions
and materials, including biological functions and materials. Our approach to accomplishingthese goals involves controlling the configuration and coupling of atoms and molecules. Bionano research and diamond-device research constitute our principal fields of study.
We have three research groups whose work ranges from semiconductor devices, such as
GaN devices, to organic materials, such as receptor proteins. The characteristic feature of
the MSL is the effective sharing of unique materials and measurement techniques among thegroups. This allows the fusion of research fields and techniques, which leads to innovative
material research for the IT society.
We established a European laboratory in the U.K. for bio-nano research in October 2004
and thus strengthened our research activities. We promote collaboration with internationalorganizations to develop a firm foundation 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 improvements of quality of entangled photon pairs from silicon wire
waveguide, magneto-optical spectroscopy of charged excitons and trions in quantum dots, andshort pulse generation by adiabatic wavelength tuning in a photonic crystal high-Q cavity.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)11

Boron-Implanted Diamond FETs Formed by Ion-Implantation andHigh-Pressure and High-Temperature Annealing
Kenji Ueda and Makoto Kasu
Materials Science Laboratory
Ion implantation is a widely used doping technique for Si and GaAs. However, in the caseof diamond, implantation-induced damage cannot be recovered by conventional thermal
annealing because its annealing condition is not located in diamond stable phase but ingraphite stable phase. Previously, we reported that high pressure and high-temperature (HPHT)
annealing in diamond stable phase is highly effective to recover damages induced during ionimplantation [1]. In this study, we achieved higher hole concentration and mobility using thistechnique and successfully fabricated diamond FETs [2].
CVD homoepitaxial diamond films were grown on Ib (100) substrates by microwave plasma
CVD. Then, boron (B) ions were implanted in the films at an acceleration energy of 60 keV–2with a dose of 1015~1016 cm . HPHT annealing of the B-implanted films was performed
at ~7 GPa and 1350oC for activation of dopants. Using these diamond films, FETs were
fabricated (Fig. 1). The source and drain contacts were formed by Ti/Au with annealing at
600oC. The Schottky-gate contact was formed by the evaporation of Al.
–2
We obtained a higher hole concentration for a dose of 1~5×1015 cm while keeping high–2
mobility. For a dose of 3×1015 cm , we obtained sheet concentration and mobility at 300 K–2
13
2
of 1.6×10 cm and 41 cm /Vs, respectively. These values are comparable to those of–2
H-terminated diamond (~1013 cm and ~100 cm2/Vs) widely used so far. Using this film with–2
15
a dose of 3×10 cm , we fabricated FETs. The gate length and the width were 2 μm and100 μm, respectively. Current saturation and pinch-off characteristics were clearly observed.
The maximum I DS of 0.15 mA/mm was obtained at V GS of – 2 V (Fig. 2). The forward
breakdown voltage (VBR) of the FET was 530 V. Breakdown of the point was destructive andpart of Al Schottky and Au/Ti ohmic electrodes melted. The breakdown electric field wasestimated to be ~1.1 MV/cm. The Ec is comparable to those of Al-Schottky diodes using
B-doped CVD homoepitaxial diamond films [1, 2]. The result also indicates the high qualityof our B-implanted layers.
This work was partly supported by the SCOPE project of the Ministry of Internal Affairs andCommunications, Japan.
[1] K. Ueda, M. Kasu, and T. Makimoto, Appl. Phys. Lett. 90 (2007) 122102.
[2] K. Ueda and M. Kasu, Physica Status Solidi (c) 5 (2008) 3175.

Fig. 1. Schematic cross-section of B-implanted
diamond FET.

12

Fig. 2. DC drain current voltage characteristics for
the B-implanted diamond FETs.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

High Performance Nitride-Based Heterojunction Bipolar Transistors on
GaN Substrates
Kazuhide Kumakura and Toshiki Makimoto
Materials Science Laboratory
There are large mismatches between III-nitride semiconductors and conventionally usedsapphire substrates in terms of the lattice constant or thermal expansion coefficient. Therefore,
the most suitable substrate for GaN growth is no doubt the GaN substrate. From the viewpointsof device applications, the merits of using GaN substrates are as follows: a low dislocation of
the substrate itself, resulting in improving the device performance, or a relatively large thermal
conductivity, making it possible to spread heat generated under a high-power operation. In
principle, heterojunction bipolar transistors (HBTs) have the ability to operate with uniform
threshold voltages and high current densities. A normally off characteristic is advantageous
for a fail-safe system. Therefore, nitride-based HBTs are one of the attractive devices for highpower electronics. In this work, we fabricated the pnp AlGaN/GaN HBTs on GaN substrates
and showed their high performance at room temperature (RT).
Figure 1 shows current gains as a function of the collector current (Ic) of pnp AlGaN/
GaN HBTs on sapphire and GaN substrates measured at RT. The HBTs on GaN substrates
exhibited a high performance: a maximum current gain of 85 at a collector current of 30 mA
and a maximum collector current density of 7.3 kA/cm2 at a collector-emitter voltage of 30 V,
which corresponds to the maximum power dissipation density of 219 kW/cm2. The current
gain and the collector current density increased compared to those on sapphire substrates. The
calculated minority carrier diffusion length agreed well with that determined from electron
beam induced current measurements [1]. Therefore, these results indicate that the current gain
was dominated by the minority hole diffusion in the neutral base at high Ic for the HBTs on
the GaN substrates, and that the increase in the current gain is ascribed to the low dislocation
density in the HBTs. For the HBT with the large emitter area, the current gain was still as highas 47 and the maximum collector current reached as high as 1 A, and this single HBT showeda high-power dissipation of 30 W as shown in Fig. 2. This high performance of the HBTs is
ascribed to the low dislocation density and relatively high thermal conductivity of the GaN
substrate.
[1] K. Kumakura et al., Appl. Phys. Lett. 86 (2005) 052105

Fig. 1. Current gain as a function of collector currentof the HBTs measured at RT. The solid andbroken lines correspond to the data for HBTs
on GaN and sapphire substrates, respectively.

Fig. 2. Maximum collector current and the
maximum power dissipation as a functionof the emitter perimeter of the HBTs on
GaN substrates.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

13

―

Anisotropic In-Plane Strains in Non-Polar Al1-xGaxN (1120) Films (x<0.2)
Tetsuya Akasaka, Yasuyuki Kobayashi, and Makoto Kasu
Materials Science Laboratory――

Nitride semiconductor films with non-polar faces, such as (1100) and (1120) faces, areattracting much attention, because emission efficiency of quantum wells using the nonpolar faces is higher than those using polar faces, such as (0001) face, by the eliminationof piezoelectric polarization fields [1]. On the other hand, SiC has been widely used as thesubstrate for heteroepitaxy of nitride semiconductors, because of its high electrical and thermal
conductivities and the smaller lattice mismatches (~1% for AlN). However, there is anisotropy
in the lattice mismatches between nonpolar nitride semiconductors and SiC substrates and thelattice matching of the heteroepitaxy is complicated. For example, the a- and c-axes of AlN
are 1.05% longer and1.13% shorter than those of SiC,
respectively. In this study, we have――grown Al1-xGaxN (1120) thin films (x<0.2) on SiC (1120) substrates and evaluated the lattice
constants, in-plane strains and crystallinity of the films.
The pseudomorphic growth (lattice-matched with substrate) is essential for heteroepitaxy
for reducing the densities of dislocations
and stacking faults. Figure 1 shows dependence of―in-plane strains
in
Al
Ga
N
(11
20)
thin
films on the Ga composition. The in-plane strains
1-x
x―along the [1100] and [0001] directions, εxx and εzz, are on the pseudomorphic lines at the Ga
compositions lower than 0.06, which means that the in-plane lattice constants of the films
are almost the same as those of SiC. This pseudomorphic
growth is successfully achieved―
by balance between compressive stress along [1 100] andtensile one along [0001] [2].
―Dependence of full width at half maximum (FWHM) of (1120) X-ray rocking curves (XRC)
is plotted as a function of the Ga composition in Fig. 2. The tilt angle toward [0001], tilt [0001],
which is related to the density of stacking faults parallel to the (0001) plane, decreases by
increasing the Ga composition. This is because the in-plane strain along the [0001] direction,
εzz, decreases by increasing the Ga composition (see Fig. 1).
―
The pseudomorphic growth of Al1-xGaxN (1120) thin films (x<0.06) are achieved in thisstudy. In addition, our findings can provide a basic guideline for the design of nonpolar lightemitting devices, because both the band structures and the polarization of the emitted lights
can be modified by anisotropic strains.
[1] P. Waltereit et al., Nature 406 (2000) 865.
[2] T. Akasaka, Y. Kobayashi, and M. Kasu, Appl. Phys. Lett. 93 (2008) 161908.

―

Fig. 1. In-plane strains along the [1100] direction,
εxx (●) and along the [0001] direction, εzz (▲)
plotted as a function of the Ga composition.

14

Fig. 2. Tilt angle along the [0001] direction plotted asa function of the Ga composition.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Molecular Beam Epitaxial Growth of Hexagonal Boron Nitride on Ni(111)
Substrate
Chiun-Lung Tsai, Yasuyuki Kobayashi, and Tetsuya Akasaka
Materials Science Laboratory
Hexagonal boron nitride (h-BN), with its wide bandgap in the deep ultraviolet region,
has been gaining interest since it was proposed as a promising material for optoelectronic
applications. The h-BN epitaxial growth has been achieved using the metalorganic vapor
phase epitaxy (MOVPE) [1]. Parasitic reactions between sources in BN epitaxy by MOVPE
can be avoided in molecular beam epitaxy (MBE) growth of h-BN. However, a polycrystalline
BN structure was obtained by MBE and no successful MBE-grown h-BN epitaxy has beenreported yet.
Here, we report the epitaxial h-BN growth on Ni(111) substrate by MBE [2]. Elemental
boron evaporated by an electron-beam gun and active nitrogen generated by a radio-frequency(RF) plasma source were used as the group-III and -V sources, respectively. Figure 1 shows―
in-situ reflection high energy electron diffraction (RHEED) pattern taken along the [110]azimuth of Ni(111) surface at the end of 1000 Å BN growth. The unreconstructed intense
streaky (1×1) patterns were seen immediately upon initiation of the MBE growth of BN, andthe consistent streaky (1×1) pattern was recorded during the entire process till the end of1000 Å BN growth. The streaky patterns observed throughout the entire growth carried out at
a relatively low temperature of 890oC not only indicate the formation of single-crystalline BN,
but also mean the growth proceeded with a smooth growth front.
A representative XRD for the 1000 Å h-BN epitaxial film is shown in Fig. 2. Diffraction
peaks from both the h-BN(0002) and h-BN(0004) planes along with the underlying Ni(111)substrate prove the formation h -BN with the orientation of h -BN[0001] parallel to theNi[111] direction. The inset of Fig. 2 shows the x-ray rocking curve of the h-BN epitaxial
film characterized by the full width at half maximum (FWHM) of 0.61o. This FWHM from a1000 Å film is narrower than the best value ever reported [1], and can possibly be further
decreased by optimizing the growth conditions and/or increasing the epitaxial film thickness.
From the RHEED observation and XRD, ―the alignments
between― the h-BN film
and the―――Ni substrate are [0001]h-BN || [111]Ni, [1120]h-BN || [110]Ni and [1100]h-BN || [112] Ni . The
achievement of h-BN epitaxial growth by MBE allows us to clarify fundamental properties,
such as near-band-gap luminescence.
[1] Y. Kobayashi et al., J. Crystal Growth 298 (2007) 325.
[2] C.L. Tsai et al., J. Crystal Growth (in press).

Fig. 1. The RHEED pattern at the end of 1000 Å BN
growth.

Fig. 2. The 2θ/ω XRD of the h-BN epitaxial filmwith an inset displaying the XRC.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)15

Simultaneous Optical and Electrical Characterization at Nanoscale with
Scanning Probe Microscope
Hiroo Omi, Ilya Sychugov, and Yoshihiro Kobayashi
Materials Science Laboratory
Optical and electrical properties of nanostructures can be addressed using electromagnetic
radiation or electrical current as a probe. In general, a near-field type of electromagnetic
interaction is necessary for an optical probe to enter nanoscale regime in spatial resolution
by overcoming the optical diffraction limit (~1 μm). A typical aperture scanning near-field
optical microscope (aperture-SNOM) provides such an opportunity both for the excitationand collection of light. However, this instrument employs a dielectric fiber tip as an aperture,
which makes it unsuitable for electrical measurements. An apertureless SNOM, on thecontrary, has a metallic, needle-like opaque tip. The local field enhancement at the tip apex
due to the plasmon effect enhances signal in the light scattering experiments. But, unlike thecase of aperture-SNOM, the far-field optics alignment is necessary and the scattered light fromthe tip shaft can distort the measurements. In addition, the aperture-SNOM can operate in the
combination with a scanning tunnelling microscope (STM) and it was demonstrated that sucha combination can yield superior resolution for SNOM imaging compared to the conventional
shear-force approaching method. On the other hand, the STM, which is capable of atomicresolution measurements using electrical current, can also cause an optical response inmaterials. The collection of light in ordinary STM machines with opaque metal tips is realizedby far-field optics. When the carriers are tunnelled to the sample it is the excitation (tunnelling)area that limits the spatial resolution; the achieved resolution of such an instrument wasreported to be as small as ~10 nm. The collection efficiency of the emitted light can be
improved by employing a transparent STM tip, where the light is coupled directly to the tip
rather than to a far-field detector. However, only the electrical probing of nanostructures wasproven feasible in such a scanning tunnelling microscope luminescence (STML) experiment.
We expand the STML approach to show an ultimate STM-based configuration with theaperture metal tip (Fig. 1), where both optical and electrical excitations are available (Fig. 2).
This method enabled us to characterize the same area in near-field of the sample through theaperture of transparent tip covered with metals [1].
[1] I. Sychugov, H. Omi, T. Murashita, and Y. Kobayashi, Nanotechnology 20 (2009) 145706.

Fig. 1. Aperture metal tip.

16

Fig. 2. Electro- and photoluminescence from the
GaAs wafer on a nanoscale.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Diameter Dependence of Hydrogen Adsorption
on Single-Walled Carbon Nanotubes
Akio Tokura1, Fumihiko Maeda1, Yuden Teraoka2, Akitaka Yoshigoe2, Daisuke Takagi3,
Yoshikazu Homma3, Yoshio Watanabe4, and Yoshihiro Kobayashi11Materials Science Laboratory
2
Synchrotron Radiation Research Center, Japan Atomic Energy Agency
3
Department of Physics, Tokyo University of Science and CREST-JST
4
Japan Synchrotron Radiation Research InstituteSingle-walled carbon nanotubes (SWNTs) are of great interest as a promising material for a
new generation of electronics. Controlling their properties is an impotant challenge. Bacause
the properties deeply depend on the SWNT structure, surface modification is suitable for suchcontrol. Additionally, selecting reactions in SWNTs is attractive as a way to extract nanotubes
having desirable properties. It has been predicted theoretically that C-H bonds are stable forsmall-diameter SWNTs [1], and that the band-gap modulation depends on the coverage ofhydrogen [2]. In this work, we investigated the adsorption of atomic hydrogen on SWNTs
with the aim of controlling SWNT properties through surface modification.
In situ core level photoelectron spectroscopy (PES) was used for the chemical analysis,
and ex situ Raman spectroscopy was used for the structural deformation analysis. By fitting
the C1s core level spectrum captured after atomic hydrogen irradiation, we found the C-Hbonds in the nanotubes as shown in Fig. 1. Before and after PES measurement, Raman spectra
were captured as shown in Fig. 2. The spectra demonstrate that, by the irradiation, the radialbreathing-mode (RBM) intensity of small-diameter SWNTs (less than about 1.2 nm in thiswork) is severely decreased compared to that of large-diameter SWNTs. Raman spectroscopy
results indicate adsorption-induced bonding-structure deformation is generated more easily
on small-diameter SWNTs. Taken together, these results indicate that hydrogen atoms adsorb
more preferentially on SWNTs with small diameters [3]. Our results suggest that SWNT
properties can be modified selectively by controlling hydrogen adsorption.
[1] T. Yildirim et al., Phys. Rev. B 64 (2001) 075404.
[2] K. A. Park et al., J. Phys. Chem. B 109 (2005) 8967.
[3] A. Tokura et al., Carbon 46 (2008) 1903.

Fig. 1. Peak fitting result of C1s spectrum of
SWNT sample captured after hydrogen
irradiation.

Fig. 2. Raman spectra in the RBM region of SWNT
sample captured before and after hydrogen
irradiation.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)17

Number-of-Layers Dependence of Electronic Properties of Epitaxial
Few-Layer Graphene
Hiroki Hibino, Hiroyuki Kageshima*, and Fumihiko Maeda
Materials Science Laboratory, *Physical Science Laboratory
Graphene is attracting intense attention as a future electronic material due to its superior
electronic transport properties. Epitaxial few-layer graphene (FLG) grown on SiC by thermal
decomposition can be easily scaled-up and is promising for device integration. However, it isstill difficult to grow epitaxial FLG to an intended thickness. To overcome this problem, we
have developed a method for evaluating the number of graphene layers NG in epitaxial FLG
microscopically using low-energy electron microscopy (LEEM) and have used it to control thegrowth [1]. For device applications of epitaxial FLG, it is also important is to clarify how the
SiC substrate influences the electronic properties of FLG. The influence of the substrate resultsin the NG dependence of the electronic properties, which was investigated using spectroscopic
photoemission and LEEM (SPELEEM) at SPring-8 [2].
Figure 1 shows photoemission electron microscopy (PEEM) images of epitaxial FLG
grown on 6H-SiC(0001). The PEEM images were made by secondary electrons (SEs) emitted
under irradiation of photons of 400 eV. Numbers indicated in (b) are NG values determinedby LEEM. Areas with different NG can be discriminated in the SE PEEM images, but theirrelative intensities depend on the SE energy. Figure 2 shows the SE emission spectra obtained
from the sequential SE PEEM images at different energies. The SE emission spectra dependon NG in two aspects; the threshold start voltage of the SE emission and the spectrum shape.
The threshold voltage corresponds to the vacuum level. Monolayer graphene has a work
function about 0.3 eV smaller than bulk graphite, and the work function of epitaxial FLG
increases with NG. The NG dependence of the spectrum shape is explained by unoccupied
electronic states in epitaxial FLG discretized due to its finite thickness. Similar experiments
for C1s core level photoelectrons indicated that the C1s binding energy also depends on NG.
The NG dependences of the work function and C1s binding energy are consistent with theshift of the electronic structure of epitaxial FLG caused by the electron doping from the SiC
substrate [3].
[1] H. Hibino et al., Phys. Rev. B 77 (2008) 075413; H. Hibino et al., e-J. Surf. Sci. Nanotechnol.
6 (2008) 107.
[2] H. Hibino et al., Phys. Rev. B 79 (2009) 125437.
[3] T. Ohta, A. Bostwick, T. Seyller, K. Horn, and E. Rotenberg, Science 313 (2006) 951.

Fig. 1. SE PEEM images of epitaxial FLG grownon 6H-SiC(0001).

18

Fig. 2. SE emission spectra of epitaxial FLG obtained
from the sequential SE PEEM images.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Precise Control of Gold Nanorod Arrays
Hiroshi Nakashima
Materials Science Laboratory
Gold nanorods have a fascinating optical property, whose origin is localized surface
plasmon resonance, and this property is dependent on their structural aspect ratio [1]. Goldnanorods assembled on a solid surface exhibit unique optoelectronic properties arising fromcollective interactions in an ordered state, and these properties make it possible to incorporate
nanomaterials into nanophotonic, electronic devices, and biosensors. Here we synthesize novel
gold nanorods coupled with thiol-terminated lipids (Fig. 1). We use a controlled self-assembly
process to achieve precise control of the structures of the gold nanorod arrays including theirstructural dimensions, orientation and particle gap distance [2].
The lipid modified gold nanorods form 1D ordered structures with side-to-side configurations
on a Si substrate, that are induced by the self-assembly of lipids during the drying process[Fig. 2(a)]. The distance between neighboring nanorods is uniform at 5.0 nm, which is tothe same as the thickness of the lipid bilayer. Interestingly, high-density nanorod composites
exhibit an extensive 2D self-assembly. Furthermore, we observe anisotropically oriented
nanorods in a 2D assembly that are dependent on the nature of the Si surface. On a hydrophilic
Si surface, the nanorods are organized laterally in relation to the substrate [Fig. 2(b)].
In contrast, on a hydrophobic Si surface, the nanorods are perpendicular to the substrate[Fig. 2(c)]. As regards the 2D self-assembly of the nanorods, our results constitute the firstexample of the precise control of the interparticle spacing and of anisotropic orientation in alateral or perpendicular fashion dependent on the interfacial hydrophilicity or hydrophobicity.
The lipid modified gold nanorod is a biocompatible nanomaterial. Therefore, various
biomolecules such as membrane proteins, enzymes and antibodies can be attached to thenanorod surface and function while retaining their physiological properties. The gold nanorod
array on a solid surface will be utilized for surface enhanced Raman scattering or fluorescence
substrates. Our future goal is to use the gold nanorod array to develop highly sensitive
biochips that can detect intermolecular interactions on a single (bio)molecular scale.
[1] D. P. Sprünken et al., J. Phys. Chem. C 111 (2007) 14299.
[2] H. Nakashima et al., Langmuir 24 (2008) 5654.

Fig. 1. Lipid modified gold nanorods and theirself-assembled structures.

Fig. 2. Gold nanorod arrays with (a) 1D, (b) 2D lateral, and(c) 2D perpendicular configurations.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

19

Observation of Ligand-Induced Conformational Changes in Single ATP
Receptors with Fast-Scanning Atomic Force Microscopy
Youichi Shinozaki1, Koji Sumitomo1, Makoto Tsuda2, Schuichi Koizumi3,
Kazuhide Inoue2, and Keiichi Torimitsu1
1Materials Science Laboratory, 2Kyushu University, 3Yamanashi University
Proteins, known as "receptors" that exist in cells, exhibit their functions via binding withsmall compounds such as hormones. When the receptor is a type of ion channel, it opens its
pore after binding with compounds thereby flowing ions through it and resulting in exhibiting
its function. We observed the topology and stimulation-induced conformational changes
in adenosine triphosphate (ATP) receptor [1], an important receptor in pain sensation, withatomic force microscopy (AFM).
ATP receptor gene was over-expressed in immortalized cells. ATP receptor proteins were
purified from their cell membranes and receptors for AFM observation were adsorbed on
fleshly cleaved mica. Non-stimulated ATP receptor exhibited circular feature and that afterATP stimulation was in tripartite morphology (Fig. 1). To study whether structural difference
between these two state is derived from the stimulation-induced conformational change in
ATP receptor, we performed time-lapse imaging of conformational changes in ATP receptor
with fast-scanning AFM. Before stimulus, ATP receptor exhibited circular feature (Fig. 2,–2.5~0.0 s). After stimulus, ATP receptor immediately changed its structure into trimeric
topology (Fig. 2, 0.5 s). Detailed analysis of trimeric ATP receptor revealed that it exhibitedthe further disengagement of three subunits and large pore-like structure in its center (Fig. 2,
2.0~5.0 s). To confirm whether these structural changes are related to the physiological
functions, we measured permeability of ATP receptor channel using fluorescent molecules.
ATP receptor exhibited permeability to calcium ions and appeared to be functional. Whenimaging buffer contains no calcium, ATP receptor exhibited permeability to larger molecules(ethidium bromide) but not when imaging buffer contains calcium. These results indicate thatstructural changes in ATP receptor appeared to correspond to the physiological function via
flowing ions through its pore. Thus, we succeeded in observation of topology and structuralchanges related to physiological functions of ATP receptor. We will reconstitute receptors
into artificial lipid bilayer on a flat substrate [2] and analyze the relationship of receptor-lipid
interaction and receptor topology/function.
[1] Y. Shinozaki et al., PLoS Biol. (accepted).
[2] Y. Shinozaki et al., Jpn. J. Appl. Phys. 47 (2008) 6164.

Fig. 1. Schematics of ATP receptors before(left) and after (right) stimulation.

20

Fig. 2. Time-lapse imaging of stimulation-induced
conformational changes in ATP receptor.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

The Preferential Reconstitution of Receptor Proteins into Model Lipid
Domains Studied by Atomic Force Microscopy
Nahoko Kasai, Chandra S. Ramanujan*, Kamal Marwaha*,John F. Ryan*, and Keiichi Torimitsu
Materials Science Laboratory, *University of Oxford
Receptor proteins play a fundamental role in biological membranes. They bind to ligand
molecules and transfer signals into the cells by means of electricity and by chemical
modification of proteins. Biological membranes are principally made of lipid molecules.
Recent studies have revealed that lipid membrane in the synaptic junctions of central nervous
system (CNS) is heterogeneous in composition and consists of small regions known as rafts [1].
These raft-like domains are loci for insertion of receptor proteins and are believed to act as
signalling platforms that organize and compartmentalize receptor proteins to modify thesynaptic signalling.
We report atomic force microscopy (AFM) measurements of the glutamate receptors (GluRs),
the most common membrane receptor proteins found in the CNS. GluRs are implicatedin learning and memory, and up-regulation of its numbers in the post-synaptic membrane
possibly being a key component of this process. In this work we have investigated thedependence of protein reconstitution in model membranes on lipid composition.
We reconstituted purified GluRs into a lipid mixture system consisting of a mixture thatmakes up approximately 60% of the synaptic membrane. As shown in Fig. 1, the mixture
formed two distinct domains when immobilized on mica: a high domain (HD) at 7 nm height
and a low domain (LD) at 5 nm. The lateral extent of HD is typically ~100 nm, which has
structural similarities with the raft-like domains in synaptic membranes, albeit with much
simpler composition. Then we reconstituted GluRs and found that the receptors preferentiallyinsert into the HD comparing to the LD as shown in Fig. 2 [2]. This result demonstrates thatbilayer thickness is a significant factor in the membrane self-assembly process. This can be
expected to reveal signalling mechanism in synapses.
This research was supported in part by Bio-nanotechnology IRC in UK and by the Strategic
International Cooperative Program, Japan Science and Technology Agency (JST).
[1] J. A. Allen et al., Nat. Rev. Neurosci. 8 (2007) 128.
[2] C. S. Ramanujan et al., 52nd Biophys. Soc. Meeting Abst. (2008) B363.
(A)

(B)

Fig. 1. (A) AFM image of raft-like domains in lipid membraneon mica (2.5 μm square）and (B) height profile.

Fig. 2. AFM image of lipid domain withreconstituted membrane proteins(1 μm square).

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)21

Effect of Nanogap on Dynamics of Lipid Bilayer
Yoshiaki Kashimura and Kazuaki Furukawa
Materials Science Laboratory
Cell membranes play an important role in the activity of bio-molecules, for example,
membrane proteins. A lipid bilayer, which is a basic component of a cell membrane, can be
fabricated artificially on a hydrophilic surface by spontaneous growing characteristic (selfspreading). Such membranes remain the fluidity based on lateral diffusion. Using thesecharacteristics, in this study, we investigated the dynamics of a lipid bilayer on a nanopatterned surface and the molecular transport using the lipid bilayer as a molecule carrier [1].
L-α-Phosphatidylcholine (extracted from egg yolk) containing 5 mol% of dye-conjugatedlipid was prepared. Dyes used were Texas Red, fluorescein and NBD with different molecularsize. Nanogap (10~200 nm) using Au was fabricated on an SiO2 surface. Microchannel that
had wells at both ends was fabricated on this nanogap structure using a photoresist [Fig. 1(a)].
A small amount of a lipid source was adhered inside the well. The self-spreading of a single
lipid bilayer was initiated by immersing the device in a buffer solution. Fluorescence from thelipid bilayer was observed by a confocal laser scanning microscope.
Figure 1(b) shows a time evolution of a self-spreading lipid bilayer before and after passage
through a nanogap. The single lipid bilayer developed along a microchannel and successfully
passed through the nanogap without development on photoresist and gold pattern. Figure 2
shows a fluorescence image and corresponding fluorescence intensity profile obtained after
a sufficient time interval. This result clearly shows that the fluorescence intensity decreases
discontinuously in the vicinity of the nanogap. This behavior strongly depends on the sizeof the nanogap and dye moiety. The dye molecules experience interference when they passthrough the nanogap although the nanogap size is much larger than that of the dye moiety (atmost 3 nm).
[1] Y. Kashimura et al., Jpn. J. Appl. Phys. 47 (2008) 3248.
Fig. 1. (left) (a) Device structure used in this study.
(b) Time evolution of the self-spreading lipid
bilayer. The time at which an advancing lipid
bilayer reaches a nanogap is set at t=t0 s.

Fig. 2. Fluorescence image and fluorescence intensity
profile after a sufficient time interval.

22

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Stochastic Data Processing Based on Single Electrons
Using Nano Field-Effect Transistors
Katsuhiko Nishiguchi, Yukinori Ono, and Akira Fujiwara
Physical Science Laboratory
Although the miniaturization of Si metal-oxide-semiconductor field-effect transistors(MOSFETs) continues to improve the performance of various consumer electronics, theneed to guarantee error-free operation of MOSFETs makes it difficult to reduce supply
voltage, which leads to ever increasing current density and power consumption. In this work,
conversely, we reduce the current density of nanoscale FETs ultimately and then utilize its
shot noise to realize a stochastic data processing for pattern recognition with high flexibility [1].
The device is composed of two transistors fabricated on a silicon-on-insulator wafer (Fig. 1).
The first transistor (T-FET) has a two-layer gate: an upper gate (UG) is used to induce aninversion layer and a lower gate (LG) forms an energy barrier in the undoped channel of
T-FET. As a result, an electron-storage node (MN) electrically isolated from an electron source(ES) is formed. The two layer gate can eliminate undesired leakage current originating fromp-n junctions, which is a well-known issue in conventional FETs [1, 2]. Therefore, highly
controllable single-electron transfer from the ES to the MN can be achieved using the LG. The
single electrons transferred to the MN are detected by the other transistor (D-FET) as shownin Fig. 2. The optimization of the device structure and operation conditions allows singleelectron detection even at room temperature [3]. As analysis of the time interval δ t of eachelectron transfer to the MN revealed that the single-electron transfer is based on a Poissonian
process (inset of Fig. 2), which corresponds to the real-time monitoring of shot noise in FETs
with single-electron resolution.
The Poissonian stochastic behavior of such single-electron transfer can be applied to astochastic data-processing circuit for image-pattern recognition. The circuit recognizes the
input pattern as one of the reference patterns with probability correlating to the similarity
between the reference and input patterns as shown in Fig. 3. Such probability can beelectrically controlled by the LG. These features allow flexible pattern recognition especiallyfor corrupted input patterns, which promises to apply high time and power efficiency to thecircuit like in the human brain.
[1] K. Nishiguchi et al., Appl. Phys. Lett. 92 (2008) 062105.
[2] K. Nishiguchi et al., IEEE Electron Device Lett. 28 (2007) 48.
[3] K. Nishiguchi et al., Jpn. J. Appl. Phys. 47 (2008) 8305.

Fig. 1. Device structure based on Si transistors.
(a) Schematic view. (b) Scanning electron
microscope.

Fig. 2. Real-time monitoring of
single-electron transfer.
Inset: Histogram of thetime interval between
each single-electrontransfer to the MN.

Fig. 3. Stochastic patternrecognition. The
reference pattern mostsimilar to the input
pattern is selected.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)23

Identification of Single Dopant Position in Silicon Nanotransistor
Yukinori Ono, Mohammed A. H. Khalafalla, Katsuhiko Nishiguchi, and Akira Fujiwara
Physical Science Laboratory
Future nanoscale field-effect transistors are expected to be fatally sensitive to electronic
charges of a small number of dopants in the channel. On the other hand, there are reportsof emerging devices using dopant atoms as functional part, such as quantum dots, for the
manipulation of electronic charges. It is therefore important to establish a technology for
detecting and controlling the dopant charges. We have so far reported the detection of single
boron atoms in nanoscale silicon transistors [1]. Here, we report the measurements andanalysis for identifying the depth position of observed single boron atoms [2].
Nano transistors whose gate length is 40 nm were fabricated on a silicon-on-insulator
substrate [3]. The transistors comprise the channel lightly doped with boron, p-type source/
drain, and electrically formed leads inserted between the channel and the source/drain.
The insertion of the leads prevents dopant diffusion from the source/drain and enables us
to investigate the conductance of the channel containing only a few dopant atoms. The
conductance G was measured at 6 K. Figure 1 shows the contour plot of dLogG/dVF asa function of the front-gate voltage (VF) and of the substrate back-gate voltage (VB). The
conductance modulation, indicated by the arrows, was observed in transistors containing
a single boron atom [Figs. 1(b) and (c)] but not in an undoped one [Fig. 1(a)]. These
modulations are due to the trapping of a single hole by the boron atom. From the capacitanceanalysis of the data, we have identified the depth position of the single boron atom as near thefront interface (b) and around the middle of the silicon layer (c).
By doing similar analysis using drain bias as a parameter, we will also be able to obtain
information about the dopant’s lateral position, i.e., the position along the transport channel,
which will lead us to a complete identification of dopant locations in a nanotransistor.
[1] Y. Ono et al., Appl. Phys. Lett. 90 (2007) 102106.
[2] M. A. H. Khalafalla et al., Appl. Phys. Lett. 91 (2007) 263513.
[3] Y. Ono et al., Appl. Surf. Sci. 254 (2008) 6252.

Fig. 1. Measurement results for an undoped transistor (a), and for transistors containing a single boron atom near
the front-gate interface (b) and around the mid of the silicon layer (c). OX and BOX are the gate oxides ofthe front and back gates, respectively.

24

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Bit Operation in a Parametrically Pumped Electromechanical Resonator
Imran Mahboob and Hiroshi Yamaguchi
Physical Science Laboratory
More than 150 years ago Charles Babbage originated the idea of a programmable computer.
Babbage conceived his analytical engine in a mechanical architecture where logic was
performed by moving parts. In the microelectronics age these ground breaking ideas were
forgotten as silicon transistor technology was the system of choice for implementing logic. We
demonstrate that in the era of nanotechnology the mechanical computer can be revived andlogic can be implemented by electromechanical systems.
The Parametron is a logic processing system first developed 50 years ago [1]. It utilizes
the parametrically excited resonance of a harmonic oscillator, where this oscillation has two
stable phases separated by π radians, as the basis for logic operations. The computationalarchitecture based on this principle was well developed using LC oscillators but was renderedobsolete by the transistor due to its high power consumption and integration difficulties indense system architectures. To remedy these drawbacks, we propose to implement mechanicallogic in the mould of the Parametron with electromechanical systems.
In the first steps to this goal, we demonstrate both bit storage and bit flip operations in
an electromechanical oscillator [2]. We do this by integrating a two dimensional electron
system into the mechanical oscillator which enables electromechanical transduction via
the piezoelectric effect [3]. This enables on-chip all electrical actuation of the parametricresonance and detection of the fundamental mode as well as switching between the twophases of oscillation i.e. all the necessary prerequisites for the electromechanical Parametroncomputer. The electromechanical bit operation demonstrated here paves the way for realizing
a nanomechanical computer.
[1] E. Goto, Proc. IRE 47 (1959) 1304.
[2] I. Mahboob and H. Yamaguchi, Nature Nanotechnol. 3 (2008) 275.
[3] I. Mahboob and H. Yamaguchi, Appl. Phys. Lett. 92 (2008) 173109.

Fig.1. A microscope image of the electromechanicalresonator integrating a two dimensional electron
system, multiple Schotkky contacted gold
electrodes and a simplified circuit diagram whichenabled the bit-flip operation to be implemented.

Fig.2. (a): a schematic of the pulse sequence at
frequency fs which enables bit storage andbit flip operations. (b) and (c): Experimental
realization of the protocol described in (a)with fs=0.01 and 0.03 Hz.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)25

In-plane Conductance Measurements of Few-Layer Graphene on SiC
Substrate
Masao Nagase, Hiroki Hibino*, Hiroyuki Kageshima, and Hiroshi Yamaguchi
Physical Science Laboratory, *Materials Science Laboratory
Graphene has recently attracted much attention due to its superior electric properties.
Epitaxial graphene grown on SiC substrate is a promising material for beyond CMOS era
because of its compatibility with existing wafer-scale manufacturing. Recently, a thickness
determination method using low-energy electron microscopy (LEEM) with nanometer
resolution has been established [1]. This technique enables us to control the layer number
and morphology of few-layer graphene. The next challenge toward carbon based single-layerelectronics using few-layer graphene is the characterization of local electric properties in orderto evaluate the quality of grown graphene layers. We have developed several types of nanotools
integrated on the Si cantilever of a scanning probe microscope (SPM) for measuring of theelectrical properties of nanomaterials [2]. Here, we discuss local conductance images of fewlayer graphene measured using our integrated nanogap probe with nanometer resolution [3].
Figure 1 show an in-plane conductance image of graphene nano-islands. The coverage ofgraphene is carefully controlled by LEEM observation to make the graphene nano-islands.
The conductance measurement reveals the islands consist of single- and double-layer
graphene. The measurement with this nanotool enables us to measure electrical properties ofnanostructures on insulative substrate without the need for fabrication processes including
lithography. Figure 2 is an in-plane conductance image of double-layer graphene grown on
SiC substrate. It was confirmed by LEEM that the domain size of the single-crystal doublelayer graphene is larger than terrace width of SiC substrate and up to few micrometers.
As shown in Fig. 2, the local conductance of graphene is strongly affected by the surface
morphology of the SiC substrate. Notably, an atomic layer step buried under the graphene
layer remarkably reduces the conductance of graphene. The conductance mapping withnanometer resolution will be helpful in developing carbon-based single-layer electronics.
This work was partly supported by KAKENHI (19310085, 20246064).
[1] H. Hibino et al., Phys. Rev. B 77 (2008) 075413.
[2] M. Nagase et al., Jpn. J. Appl. Phys. 46 (2007) 5639.
[3] M. Nagase et al., Nanotechnol. 19 (2008) 495701.

Fig. 1. In-plane conductance image of graphene nanoislands on SiC substrate. Inset is a conductanceprofile of an individual nanoisland.

26

Fig. 2. In-plane conductance image of double-layer
graphene measured using integrated nanogap
probe. Inset is a conductance profile at an
atomic layer step.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Fabrication of Three-Dimensional Nanostructures
by Electron Beam Lithography
Kenji Yamazaki and Hiroshi Yamaguchi
Physical Science Laboratory
Three-dimensional (3D) nanostructures are now attracting great interest because of their
possible applications, such as to nanomechanical devices and nanorobotics. To build various
3D nanostructures, we have devised and are developing 3D electron beam (EB) lithography(3D-EBL). Although our technique has some advantages, such as high resolution and fast
fabrication, it has so far shown drawbacks related to the electron scattering/proximity effectand to the poor precision of structure/3D alignment, compared with some other 3D fabrication
techniques. We have newly devised two methods in 3D-EBL to significantly improve the 3Dalignment and reduce the proximity effect.
When we make complicated 3D structures with this technique, the EB writes from largely
different directions and therefore should be well positioned three-dimensionally; highaccuracy of 3D alignment is necessary. The high accuracy is achieved by using a transmission
electron image to accurately control sample rotation (< 1 mrad) and obtain sufficient accuracyof 2D positioning of EB writing on a rotated sample [1]. In a 3D nanostructure we created innegative resist (hydrogen silsesquioxane, HSQ), the 3D alignment accuracy is on the orderof 10 nm (Fig. 1). When we use positive resist, the proximity effect is very serious. However,
we have succeeded in suppressing the proximity effect by leaving buffer areas (not exposed
to EB) that surround the target structure and have sizes similar to the range of fast secondary
electrons. As a result, we have reduced undesirable dissipated energy, which changes
vertically in the resist [2]. Figure 2 shows SEM images of a 3D nanostructure in positive resist[poly(methyl methacrylate), PMMA], which demonstrates a high aspect ratio and the great
flexibility of structures that can be created by the technique.
These methods will accelerate the development of 3D-EBL, making it promising for various
nanotechnology applications.
This work was supported in part by KAKENHI (20246064).
[1] K. Yamazaki and H. Yamaguchi, J. Vac. Sci. Technol. B 26 (2008) 2529.
[2] K. Yamazaki and H. Yamaguchi, Appl. Phys. Exp. 1 (2008) 098001.

Fig. 1. 3D nanostructure in HSQ, made by writing
arrays of dots from +/–X, +/–Y, and Z directions.

Fig. 2. 3D nanostructure in PMMA, made by leaving
buffer areas to suppress the proximity effect.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)27

Direct Measurement of the Binding Energy and Bohr Radiusof a Single Hydrogenic Defect in a Semiconductor Quantum Well
Simon Perraud, Kiyoshi Kanisawa, Zhao-Zhong Wang, and Toshimasa Fujisawa
Physical Science Laboratory
Impurities are fundamentally important for semiconductor device fabrication. In thesimplest approximation, an impurity, or a point defect, inside a semiconductor is described asa hydrogen atom. The two essential properties of such impurity are the binding energy and the
Bohr radius (αB1). Impurities in quantum wells (QWs) are affected by the confining potential
if αB1 ≥ l, where l is the QW thickness. (111)A-oriented, nominally undoped In0.53Ga0.47As
surface QWs were grown by molecular beam epitaxy (MBE) [1]. We used the scanningtunneling microscope (STM) and the spectroscopy (STS) at the low-temperature (5 K) tostudy point defects behaving like donor impurities, which are natively located at the epitaxial
surface of a QW. The electronic local density of states (LDOS) was measured with nanoscale
resolution in the vicinity of single point defects. By measuring the LDOS in the QW, we areable to determine both the binding energy and the Bohr radius of single defects. Four different
QW thicknesses were investigated in this work (l=2, 6, 10, and 14 nm). The obtained spatial
dependence as the function of the distance r is well fitted by an exponential decay proportional
to exp(–2r/aB1), representing the 1s hydrogenic wave function. Figure 1 summarizes the STS
data obtained in this work. The smaller l, the larger binding energy E1 －ε1, and the smaller
aB1, i.e. the tighter the electron is bound to the point defect. Here, E1 is the bottom of the twodimensional subband of the QW, and ε1 is the ground level of the impurity bound states. We
clearly observe the influence of quantum confinement on the bound states, as expected in thecase aB1 ≥ l. If STS data are compared with a calculation of hydrogenic impurity states, thebinding energy and the Bohr radius were found to be functions of the quantum well thickness,in quantitative agreement with variational calculations of hydrogenic impurity states [2]. It
is remarkable that this calculation requires no adjustable parameter. The increase of E1 －ε1(or, equivalently, the decrease of aB1) with decreasing l is enhanced by the conduction band
nonparabolicity.
[1] S. Perraud, K. Kanisawa, Z.-Z. Wang, and T. Fujisawa, Phys. Rev. B 76 (2007) 195333.
[2] G. Bastard, Phys. Rev. B 24 (1981) 4714.

Fig. 1. Binding energy E1 － ε1 and Bohr radius aB1 as a function of QW thickness l : STS data (each circle
corresponds to a single point defect at the In0.53Ga0.47As QW surface), and hydrogenic model (solid curves).

28

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Electrons and Holes in a Single Silicon SlabKei Takashina and Koji Muraki
Physical Science Laboratory
Electron-hole bilayers in which a two-dimensional electron gas (2DEG) and a twodimensional hole gas (2DHG) coexist in close proximity have received considerable interest
owing to the possibility of their hosting a condensation of indirect dipolar excitons [1]. Here,
we examine the low temperature transport properties of a device in which electrons and holes
are simultaneously generated but separately contacted [2] in a 40 nm thick layer of silicon.
The device consists of a Silicon-On-Insulator transistor [Fig. 1(a)] in which the front- andback-gates allow sufficient electric field in the silicon quantum well to overcome the band-gap
so that a 2DEG and 2DHG can be generated simultaneously at opposite sides of the well. The
device is cut into a Hall-bar where each of the arms is terminated by p- and n-type contacts[Fig. 1(b)] made by ion implantation of B and P respectively [3]. The n-contacts (p-contacts)
connect to the 2DEG (2DHG) but the p-contacts (n-contacts) do not due to the depletion
regions formed at each junction between the 2DEG (2DHG) and the p-contacts (n-contacts)
leading to independent contacts.
Low temperature measurements of Shubnikov de Haas oscillations [Fig. 1(d) and Fig. 1(e)]show that the charge carriers are generated at the expected positions in the structure [Fig. 1(c)]and that their densities can be controlled by an interlayer bias applied between the 2DEG and
2DHG in addition to the gate voltages. This allows the electric field (confinement potential)
to be tuned in the quantum well, and in turn allows the physical properties of the carriers suchas the strength of disorder and electronic valley splitting to be controlled [4]. We confirm thatdrag measurements are possible with the structure [5]. We expect that the structure will allow
many new measurements to probe the physics of electron-hole systems.
[1] Y. E. Lozovik and V. I. Yudson, JETP Lett. 22 (1975) 556.
[2] U. Sivan, P. M. Solomon, and H. Shtrikman, Phys. Rev. Lett. 68 (1992) 1196.
[3] K. Takashina et al., Extended Abstracts of the 2006 International Conference on Solid State
Devices and Materials, Yokohama 2006, pp.830-831; K. Takashina et al., Jpn. J. Appl. Phys.
46 (2007) 2596; M. Prunnila et al., Appl. Phys. Lett. 93 (2008) 112113.
[4] K. Takashina et al., Phys. Rev. Lett. 96 (2006) 236801.
[5] K. Takashina et al., Appl. Phys. Lett. 94 (2009) 142104.

Fig. 1. (a) A schematic diagram of the device. (b) An optical micrograph of a Hall bar. The voltage probes are
terminated by n- and p-type contacts. (c) Schematics of the confinement potential in different regions of(VFG, VBG) for data shown in (d) and (e). (d) and (e) show conductivity at B=15 T, T~250 mK taken using nand p-type contacts respectively with an interlayer bias voltage of 0.6 V.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)29

New Readout Method for Josephson Persistent-Current Qubits Using a
Josephson Bifurcation Amplifier
Kosuke Kakuyanagi, Seiichiro Kagei*, Ryota Koibuchi*, and Kouichi Semba
Physical Science Laboratory, *Tokyo University of Science
A superconducting flux qubit has potential for use as a device in quantum computing. To
read the qubit state, we usually use a SQUID to detect the small magnetic field generated by
the supercurrent of a superconducting flux qubit [1]. However, this readout method changes
the SQUID state to the voltage state, so the backaction of the measurement is large and highspeed measurement is also difficult. This makes it hard to execute the quantum algorithm,
which reads the qubit state several times during the coherence time. Therefore, we attempt
to read flux qubits using a Josephson bifurcation amplifier (JBA) [2], which employs thebistability of a non-linear resonance circuit. With this readout method, the Josephson junction
superconducting state is maintained during the measurement thus making it possible to achievea fast and ultimately small backaction readout as with a quantum non-demolition measurement.
We design the flux qubit and SQUID structure at the center of a coplanar waveguide, bothsides of which are connected to a capacitor. We then measure the transmission characteristicsof this sample. Because of the non-linearity of the Josephson junction, the resonancefrequency shifts to the lower frequency side with increases in applied microwave power, andthe resonance spectrum shows a jump above the critical microwave power. This is a transition
from one stable state to another and means that the bistable state of the non-linear resonatorhas appeared. The stable resonance state that appears depends on the resonator state. So, by
realizing magnetic coupling between a nonlinear resonator and a qubit, we can reflect theflux qubit state to the resonator and read the qubit state. We can measure the qubit state by
the homodyne detection of a transmission microwave because the amplitude and phase of thetransmission microwaves of each stable resonance state are different. Then we attempt to readthe qubit state by employing pulsed microwaves. Figure 1 shows a block diagram of a pulse
measurement system and an example readout. A pulse-modulated microwave passes throughthe JBA circuit and is amplified. The signal interferes with the reference microwave, and thenwe can obtain 0-degree and 90-degree phase components. From this amplitude and phase
information, we can clearly separate two states and successfully read the flux qubit state [3].
This work was supported by KAKENHI(18201018,18001002).
[1] Caspar H. van der Wal et al., Science 290 (2000) 773.
[2] I. Siddiqi et al., Phys. Rev. Lett. 93 (2004) 207002.
[3] K. Semba, K. Kakuyanagi et al., Quantum Information Processing 8 (2009) 199.

Fig.1. Block diagram of JBA pulse readout (left) and result of qubit state readout (right).

30

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Evidence of Noise-Suppression with Superconductive Atom Chip
Tetsuya Mukai, Christoph Hufnagel, and Fujio Shimizu*
Physical Science Laboratory*The University of Electro-Communications / NTT Research Professor
Strong confinement in trapping neutral atoms is necessary to realize full quantum control
over atomic system. Although micro-magnetic trap on chip is a promising candidate torealize a strong trapping confinement, the electro-magnetic noise and thermal noise reduce
the trapping lifetime seriously in the vicinity of a chip surface. To overcome this problem wedeveloped a persistent supercurrent atom chip [1], and in 2008 we have shown an evidenceof noise-suppression of superconductive atom chip even in the vicinity of a strip with largetransporting current.
The experiment was done by measuring the number of atoms leftover after keeping atoms
in a chip potential with specific atom-surface distance. An absorption measurement withreflected image was employed for precise trap height identification (Fig. 1). The chip patternthat we used for this experiment has an MgB2 superconductive loop circuit as shown in Fig. 2.
Figure 3 represents the measured trapping lifetime over the atom-surface distance, which was
deduced from the decay late of trapped atoms. The lifetime of our persistent supercurrent atom
chip was reaching more than an order longer than that of normal conductive counterparts. With
miniaturized wire strip, we will realize a strong trapping confinement in quantum regime, andin future we will pursue the realization of full quantum control over atomic system.
This research was partially supported by Japan Science and Technology Agency CREST.
[1] T. Mukai, C. Hufnagel et al., Phys. Rev. Lett. 98 (2007) 260407.

Fig. 1. Sample absorption image of trapped atomic cloud with reflection in the vicinity of a chip surface.

Fig. 2. (a) Chip pattern of persistent supercurrent
atom chip. (b) Cross section of the chip wire
and the trap geometry.

Fig. 3. Trapping lifetime over the atom-surface distance.
(Ref: Eur. Phys. J. D 51 (2009) 173 and Phys. Rev.
A 66 (2002) 041604.)

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)31

Single-Shot Readout of a Josephson Persistent Current Quantum Bit
Kouichi Semba, Hirotaka Tanaka, Shiro Saito, and Hayato Nakano
Physical Science Laboratory
In order to measure the quantum state of a persistent current quantum bit (a flux qubit), we
use a dc-SQUID as a detector [1]. By carefully designing the junction parameters, the inner
loop of Fig. 1(a) can be made to behave as an effective quantum two-state system, qubit. The
qubit is described by the Hamiltonian Hq=(εf σz+Δσx)/2, where σx,z are the Pauli matrices.
Due to the fluxoid quantization, the two eigenstates of σz are almost localized states with thesupercurrent circulating in opposite directions, i.e., the clockwise state |R> and the counterclockwise state |L>. The dc-SQUID picks up a signal that is proportional to σz . Figure 2(a)shows the modulation of the measured dc-SQUID switching current against the external
magnetic flux as a function of f =Φext/Φ0, where Φ0 is a flux quantum h/2e. Each dot in thegraph corresponds to every single readout without averaging. The classically stable current
eigenstates |L> and |R> are no longer stable in the presence of quantum tunneling Δ. As
shown in Fig. 2(b), qubit energy eigenstates |0> and |1> are superpositions of macroscopicallydistinct states |L> and |R>. In Fig. 2(e) near f =1.5, where Δ >> εf ~0 and the switching current
distribution is sharp enough to observe the χ -shaped qubit step clearly. The thicker stripe
corresponds to the ground state |0> and the other stripe corresponds to the excited state |1>.
These facts clearly show that we can carry out a single-shot σz projection measurement to |L>
or |R> with the aid of a Φext shift pulse, in the same way as the Stern-Gerlach apparatus formeasuring a superposed spin-state. The merit of our dc-SQUID readout is that we can control
interaction strength between the qubit and the detector dc-SQUID, at will. In the SternGerlach case, it was always fixed and was definitely larger than energy difference of the spin
eigenstates. This gives us a possibility of realtime control of the quantum readout itself.
[1] K. Semba et al., Quantum Information Processing 8 (2009) 199.

Fig. 1. (a) Scanning electron micrograph of asuperconducting qubit (inside loop) and a dcSQUID (outside loop) as a detector. A pair ofarrows indicate distinct supercurrent states |L>and |R> of the qubit. (b) The potential energyof the qubit in phase space. (c) Schematic
diagram of the measurement setup. Qubit wasmeasured at dilution temperature of 25 mK.

32

Fig. 2. (a) Switching current of the dc-SQUID detector.
f=Φext/Φ0, where Φext is the external magnetic
flux penetrating the qubit loop. (b) Schematics ofthe qubit energy eigenstates{ |0>, |1>} and current
eigenstates { |L>, |R>}. (c) Expected readout forstates{ |0>, |1>}. (d) Zoom in near f=0.5. (e) Zoom
in near f=1.5. Qubit states |0> and |1> can bereadout distinctly.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Photoluminescence Spectroscopy of Nonlinear- and Linear-Screening
Regimes in a Low-Density Two-Dimensional Electron System
Masumi Yamaguchi1, Shintaro Nomura2, Yoshiro Hirayama3,
Hiroyuki Tamura1, and Tatsushi Akazaki1
1
Physical Science Laboratory,
2
University of Tsukuba/NTT Research Professor, 3Tohoku University
A high-quality low-density two-dimensional electron system (2DES) in semiconductors canbe formed on gated undoped GaAs quantum wells (QWs) grown by molecular beam epitaxy.
Some interesting phenomena, such as Wigner crystallization, are predicted to appear in lowdensity 2DES theoretically because the large Coulomb interaction between electrons plays
a role. However, the unavoidable potential randomness in real samples disturbs the ideal 2D
condition. Investigating the screening of the potential randomness by the induced electrons
would therefore help us to better understand the low-density 2DES properties.
In this study, we performed photoluminescence (PL) measurements on an undoped GaAs
QW for different electron densities with a gate bias. We found a two-stage transition reflecting
the change of the potential-screening properties when the electrons were induced [1]. By
PL measurement, we can seamlessly follow the transition from the insulating to the metallic–
regimes through the PL spectrum change from the exciton (X0) and charged excion (X ) to
the 2DES-hole recombination. The typical PL spectra are shown in Fig. 1 from the bottom
to top with increasing gate bias voltage. The two-stage change of PL intensity and linewidth
against the gate bias voltage, shown in Fig. 2, corresponds to the transition from the electron
localization in the insulating regime to the linear screening in the metallic regime through a
non-linear screening regime. In the linear screening regime, the induced electrons effectively
screen the random potential, whereas the electrons partially screen the random potential
valley in the non-linear screening regime. The randomness of our sample may originate fromelectrons trapped in the surface state. A sample with a larger distance from the surface to the
QW may reduce the random potential at low electron density.
This work was partly supported by CREST program of Japan Science Technology Agency.
[1] M. Yamaguchi et al., Phys. Rev. Lett. 100 (2008) 207401.

Fig. 1. Photoluminescence spectra fordifferent gate bias voltages.

Fig. 2. Photoluminescence intensity and linewidth against
the bias voltage.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

33

Negative Photoconductivity in In0.52Al0.48As/In0.7Ga0.3As Heterostructures
Tatsushi Akazaki1, Masumi Yamaguchi1, Kohei Tsumura2,
Shintaro Nomura3, and Hideaki Takayanagi4
1
Physical Science Laboratory, 2University of Tsukuba,
3
University of Tsukuba/NTT Research Professor, 4Tokyo University of Science
InGaAs-based heterostructures with a large Rashba spin-orbit interaction are very attractive
for applications in semiconductor spintronics [1]. In terms of spin manipulation, it is very
important to investigate the optical effect on the transport properties in these InGaAs-based
heterostructures. This is because spin-aligned carriers are generated when electrons are excitedby circularly polarized light. In this study, we investigated the transport of a two-dimensional
electron gas (2DEG) in an In0.52Al0.48As/In0.7Ga0.3As heterostructure when exposed to lightfrom infrared laser diodes (λ=0.78, 1.3 μm) [2].
In the dark, the sheet carrier density nHall and mobility μ of the 2DEG at 1.8 K obtained with
–2
Hall-effect measurements were found to be ~2.3×1012 cm and ~161,000 cm2/Vs, respectively.
To investigate the optical effect, the laser light was guided through an optical fiber close to thesurface of a Hall-bar sample placed in a magnetic field of 0.5 T at 1.8 K. The Hall voltage wasmeasured before, during and after illumination. The nHall was estimated using the measured
Hall voltage. Figure 1 shows the time dependence of nHall before, during and after illumination
with (a) 1.3 μm and (b) 0.78 μm light. When the sample was illuminated with 1.3 μm light,
nHall immediately decreased and became constant, although photo-induced carriers weregenerated in the In0.7Ga0.3As channel layer. After the illumination was switched off, nHall slowly
increased and regained its initial value after about one hour. In contrast, when the sample
was illuminated with 0.78 μm light, nHall increased slightly only during illumination. We
concluded that negative photoconductivity occurs in In0.52Al0.48As/In0.7Ga0.3As heterostructures
when they are illuminated by photons with λ=1.3 μm, namely at the longer wavelength (lower
energy), in contrast to several previous reports stating that negative photoconductivity in InAs/
AlSb heterostructures occurs only when they are illuminated by photons with a relatively
high energy [3]. We would speculate that the negative photoconductivity in In0.52Al0.48As/
In0.7Ga0.3As heterostructures is attributed to the presence of the deep impurity levels in the
In0.52Al0.48As layer.
This work was partly supported by CREST program of Japan Science Technology Agency.
[1] J. Nitta et al., Phys. Rev. Lett. 78 (1997) 1335.
[2] T. Akazaki et al., Physica E 40 (2008) 1341.
[3] Yu. G. Sadofyev et al., Appl. Phys. Lett. 86 (2005) 192109.

Fig. 1. Time dependence of sheet carrier density nHall at 1.8 K before, during and after illumination with(a) 1.3 μm and (b) 0.78 μm light.

34

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Numerical Simulation of Ultracold Atoms Trapped in Optical Lattices
Makoto Yamashita
Optical Science Laboratory
Ultracold atoms have been stimulating many researchers＇ interest after a successful
realization of Bose-Einstein condensation in 1995. Recent noteworthy progress on atom
manipulation techniques has led to unprecedented experiments demonstrating an extremely
high controllability. An optical lattice, formed by a standing wave of counter-propagating
laser lights as shown in Fig. 1, is a typical example that allows us to investigate fundamental
quantum many-body problems found in condensed matter physics via atomic gases.
We have developed a highly efficient numerical method based on the Gutzwiller
approximation and analyzed the ground state properties of ultracold atoms trapped in opticallattices [1]. To examine the quantitative ability of our method, we numerically simulated
the recent experiment performed by MIT group [2] which precisely observed the quantum
phase transition of bosonic atoms in a three-dimensional optical lattice. Figure 2(a) shows theaverage number distribution of atoms over the lattice sites in the y=0 plane for the superfluid
phase where the depth of optical lattice is relatively shallow. Note that 560,000 lattice sites
and 300,000 atoms are assumed in our calculations. The smooth and convex atom distribution
is obtained reflecting a weak magnetic confining potential in the experiment. Figure 2(b),on the other hand, shows the number distribution for the Mott-insulator phase where thelattice depth is deep enough. Due to the strong repulsive interactions between the atoms, theaverage number takes the discrete values ranging from n=1 to n=5, which leads to a stepwise
distribution. From this result, we understand that ultracold atoms in the Mott-insulator phaseform an intriguing shell structure in their spatial distribution. The calculated results in Fig. 2
agree well with the experimental observations of MIT group and we have confirmed an
excellent quantitative performance of our numerical simulations.
This work was supported in part by Japan Science and Technology Agency, CREST.
[1] M. Yamashita and M. W. Jack, Phys. Rev. A 79 (2009) 023609.
[2] G. K. Campbell et al., Science 313 (2006) 649.

Fig. 1. Schematic diagram of ultracold atomic gas
trapped in an optical lattice.

Fig. 2. Number distributions in the y=0 plane:(a) superfluid state and (b) Mott-insulator state.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)35

Single Photon Detection Using MgB2 Superconductor
Hiroyuki Shibata
Optical Science Laboratory
Quantum cryptography is the ideal way to achieve secure communications, since thesecurity is guaranteed by the physical principle of quantum mechanics. To realize a quantum
cryptography network, it is necessary to strongly increase the communications distanceand speed, which are limited by the performance of conventional single photon detectors.
Recently, a new type of single photon detector that uses NbN superconducting nanowire(SSPD) has been developed. In quantum key distribution (QKD) experiments, NbN-SSPD has
substantially outperformed conventional semiconducting single photon detectors [1]. Here, we
are investigating single photon detection using MgB2 superconductor. Since Tc of MgB2 is 40
K, which is much higher than the 16 K of NbN, a MgB2-SSPD would have a higher operating
temperature. Moreover, the short electron-phonon relaxation time of MgB2 means that the
MgB2-SSPD would operate faster than a NbN-SSPD.
To fabricate the MgB2-SSPD, it is necessary to develop a technique for MgB2 utlta-thin film
growth and to develop a MgB2 nano-fabrication process. We use the molecular-beam epitaxy(MBE) for the ultra-thin film growth, and have obtained the 10-nm-thick MgB2 film with Tcof 20 K. For nano-fabrication of NbN, reactive ion etching (RIE) with fluorine-based gas has
been established, but no etching gas has been reported for MgB2. We have developed a new
lift-off process using a Si/C bilayer mask, which can withstand the high temperatures neededfor MgB2 deposition. Using the method, we have fabricated a MgB2 nanowire with a widthof 200 nm. Figure 1 shows the MgB2 nanowire, which is illuminated by a laser pulse froman optical fiber. When the nanowire is biased by a dc current source, electrical signals witha repetition frequency of 100 MHz appear, corresponding to the laser pulse [Fig. 2(a)]. The
signals become intermittent as the intensity of the laser pulse strongly decreases [Fig. 2(b), (c)],indicating that the MgB2 nanowire works in the photon detection regime [2].
[1] H. Takesue et al., Nature Photon. 1 (2007) 343.
[2] H. Shibata et al., IEEE Trans. Appl. Supercond. 19 (in press).

Fig. 1. Photograph of the MgB2 nanowire photon
detector illuminated by laser light from an
optical fiber.

36

Fig. 2. Optical power dependence of output
signals.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Generation of High-Purity Entangled Photon Pairs
Using Silicon Wire WaveguideKen-ichi Harada, Hiroki Takesue, Hiroshi Fukuda*, Tai Tsuchizawa*,
Toshifumi Watanabe*, Koji Yamada*, Yasuhiro Tokura, and Sei-ichi Itabashi*
Optical Science Laboratory, *Microsystem Integration Laboratories
Recently, 1.5-μm band entangled photon pair generation using spontaneous four-wave
mixing (SFWM) in a silicon wire waveguide (SWW) has been drawing attention [1]. An
SWW is expected to function as a high-purity entangled photon pair generation device. By
using an SWW, we obtained two-photon interference fringes of time-bin entangled photons
with > 95% visibilities [2].
An SWW is a nano-scale silicon waveguide fabricated on silicon-on-insulator wafer [3]. An
SWW exhibits very large third order nonlinearity because of its extremely small effective area,
and thus we can obtain efficient SFWM in a waveguide whose length is ~1 cm.
Figure 1 shows experimental setup. The laser light is modulated into double pulses with arepetition frequency of 100 MHz by using an intensity modulator (IM). The pulse width andinterval are 90 ps and 1 ns, respectively. The double pulses are input into an SWW. The SWW
used in the experiment is 460 nm wide, 200 nm thick, and 1.15 cm long. The excess loss of
the SWW is 1.0 dB. Consequently, time-bin entangled photon pairs are generated through the
SFWM in the SWW. The photons from the SWW are launched into a fiber Bragg grating (FBG)
to suppress the pump photons, and input into an arrayed waveguide grating (AWG) to separate
the signal and idler photons. The signal and idler wavelengths are ± 3.2 nm from the pumpwavelength. Each photon is then launched into a 1-bit delayed interferometer fabricated using
planar lightwave circuits (PLC) based on silica waveguide technology. The phase difference
between two paths of the interferometer is precisely controlled by adjusting the temperatureof the substrate. The photons from the PLC interferometers are received by single photon
detectors (SPD) operated in a gate mode whose gate frequency is 100 MHz.
We fixed the signal interferometer temperature and counted the coincidences whilechanging the idler interferometer temperature (fig. 2). The solid and dashed lines represent themeasurement results obtained with nonorthogonal measurement bases for the signal photons.
The visibilities of fitted curves are 96.3% (solid) and 95.2% (dashed). Thus, we successfully
confirmed the generation of a high-purity entangled state in the 1.5-μm band.
[1] H. Takesue et al., Appl. Phys. Lett. 91 (2007) 201108.
[2] K. Harada et al., Opt. Express 16 (2008) 20368.
[3] T. Tsuchizawa et al., IEEE J. Sel. Top. Quantum Electron. 11 (2005) 232.

Fig. 1. Experimental setup. PC: polarization controller,
FM: focusing module, BPF: band pass filter, TIA:
time interval analyzer.

Fig. 2. Two-photon interference fringes.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)37

Efficient Carrier Envelope Offset Locking for a Frequency Combby Modifying a Collinear f -to-2f Interferometer
Atsushi Ishizawa, Tadashi Nishikawa, and Hidetoshi Nakano
Optical Science Laboratory
The development of the mode-locked laser has contributed to our ability to control of thecarrier envelope offset (CEO), which is the absolute phase slip between laser pulses. The
mode-locked laser also contains various frequency components in the hundred of terahertz
region. These regularly spaced components are called a "frequency comb". By controlling thephase and amplitude of individual comb lines, it would be possible to synthesize an opticalfield waveform directly like an electric pulse waveform can, which would contribute to thecontrol of laser-matter interactions.
We need a CEO-locked frequency comb with more than a 10-GHz repetition rate in order toresolve each mode of the frequency comb with an arrayed-waveguide grating. The problem isthat the pulse energy decreases as the repetition rate increases. We therefore need to achieve
CEO locking with a small and high-repetition-rate device with low pulse energy. Recently, wedemonstrated a CEO-locked frequency comb with 230-pJ fiber coupling pulse energy [1]. To
generate an octave-bandwidth spectrum in a nonlinear fiber and of the second harmonic in an
f -to-2 f interferometer with low pulse energy, we used a tellurite photonic crystal fiber (PCF)
and a periodically poled LiNbO3 ridge waveguide, respectively. However, we had to use a pulse
energy of about 1 nJ because the coupling efficiency of the output of the laser to the PCF. To
solve this problem, we propose a method for modifying the optical components in a collinear
f -to-2 f interferometer. We use angled V-groove splicing between the tellurite PCF and a high-NA
fiber to increase coupling efficiency into the tellurite PCF. In addition, we set up the collinear
f -to-2 f interferometer with the minimum number of optics without an additional dispersion
compensation fiber in order to reduce connection and propagation losses. Using our method,
we have demonstrated a CEO-locked frequency comb at telecommunications wavelengths with
500-pJ pulse energy, which breaks the previous record of 600 pJ [2] and is, to the best of ourknowledge, the lowest pulse energy ever achieved for CEO locking [3]. We believe that our
method is useful for lower pulse energy and for long-term stability due to the simple setup.
[1] A. Ishizawa et al., Opt. Express 16 (2008) 4706.
[2] I. Hartl et al., Opt. Express 13 (2005) 6490.
[3] A. Ishizawa et al., CLEO/IQEC 2009, Baltimore, U.S.A. (May 2009).

Fig. 1. Experimental setup for the CEO locking with low pulse energy. SMF: single-mode fiber.
TEC: thermally expanded core.

Fig. 2. (a) Self-referencing beat signal of the 250-MHz laser. f0: CEO frequency. fr: repetition rate of the laser.
(b) The phase difference between the beat signal and local oscillator.

38

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Cavity Emission and Photon Statistics in Exciton-Cavity Coupled
Systems
Takehiko Tawara, Hidehiko Kamada, and Stephen Hughes*
Optical Science Research Laboratory, *Queen＇s University
Interaction between single exciton and single cavity mode are fundamentally interesting anduseful in the context of single-photon source for quantum information processing. A curious
feature in recent studies using semiconductor photonic-crystal (PhC) is much brighter cavity
emission under large detuning than theoretically expected from standard emission formulas [1].
Here, we undertake an experimental study to identify the cavity mode emission at non-zerodetuning and its influence on single photon statistics [2].
We use PhC cavities which consist of a GaAs membrane containing a single InAs dot layer.
The left panel of Fig. 1 is image of PL intensity mapping with cavity mode detuning at 4 K.
The GaAs barrier was excited by Ar-ion laser (2.54 eV) in this measurement. We found that
this system show the bright cavity emission even under fairly-large detunings. The integrated
PL intensity when the cavity mode and the exciton are resonant (zero detuning), increases by
a factor of about 9 compared with the off resonant case.
To explore the influence of the cavity emission on the photon statistics, we measured thesecond-order autocorrelation function of the photon intensity. When off-resonant cavity mode,(2)
anti-bunching was not observed where gC (0) ~1. This absence of the non-classical correlationon the cavity mode is attributed to independently emitted photons from the background suchas deep defect level in the GaAs layer. The off-resonant exciton exhibited partial anti-bunching(2)
with gX (0)=0.57, indicating that quantum mechanical coupling prevails. Interestingly, at zerodetuning the autocorrelation of the overlapping exciton and cavity modes shows a better anti(2)bunching with gC+X (0)=0.35. As the exciton-cavity coupling is stronger, the relative weightof the deep states recombination contribution decrease, thereby the anti-bunching behavior is(2)
recovered to a better g (0), indicating that the photon statistics becomes more non-classical.
These measurements are well explained using a medium-dependent master equation model.
This work was partially supported by Strategic Information and Communications R&D
Promotion Programme (SCOPE) of Japan.
[1] For example, K. Hennessy et al., Nature 445 (2007) 896.
[2] T. Tawara et al., Opt. Express 17 (2009) 6643.

Fig. 1. PL intensity mapping with cavity mode detuning and 2nd order autocorrelation functions.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)39

Magneto-Optical Spectroscopy of Charge-Tunable Quantum DotsHaruki Sanada, Tetsuomi Sogawa, Hideki Gotoh,
Yasuhiro Tokura, and Hidehiko Kamada
Optical Science Laboratory
Spin states in semiconductor nanostructures are expected to act as quantum information
carriers in solid-state systems. One approach that allows us to access single electron spin insemiconductor quantum dots (QDs) is to use negative trions, which serve as an intermediaryfor the initialization [1] and readout [2] of single electron spins. Most experimental studies
have focused on their lowest radiative states, however, their excited states have a rich varietyof configurations because Coulomb and/or exchange interactions between different shells
are quite different from those in the lowest shells. In this study, we investigated the magnetophotoluminescence (PL) properties of excited trions in a charge-tunable QD [3].
Our sample consists of monolayer-fluctuation GaAs QDs embedded in an n-i-Schottky diodegrown by molecular beam epitaxy. For micro-PL measurements, the sample was cooled to 6
K in a cryostat placed in a magnetic field B, which was applied to the sample in the Faraday
geometry. A Ti:sapphire laser excited QDs within an aperture in the metal mask/electrode, and
the PL spectra were measured with a monochromator and CCD detector.
–
Figure 1 shows typical PL spectra obtained at B=0. Two lines labeled X0 and X are assigned
to the lowest-lying neutral exciton and negative trion, respectively. Figure 2 shows a magnetic–
field dependence of polarization-resolved PL spectra. In addition to X0 and X emissions, wefound several PL lines (labeled A~E), most of which exhibit much complex B dependencies.
To understand the origin of these PL lines, we consider shell and spin configuration of excitedtrions. From a configuration-interaction calculation using an elliptic Fock-Darwin model, we
obtained the B dependence of trion and electron energies, and found possible assignmentsof shell and spin configurations for the origin of lines A-E. We believe that the present work
opens the possibility of developing a novel scheme for the optical control of single electron
spins using the excited states of trions in QDs.
This work was partly supported by KAKENHI (19310067).
[1] M. Atatüre et al., Science 312 (2006) 551.
[2] D. Press et al., Nature 456 (2008) 218.
[3] H. Sanada et al., Phys. Rev. B 79 (2009) 121303.

Fig. 1. PL spectra at zero magnetic field.

40

Fig. 2. Magnetic field evolution of the polarization resolved PL
spectra at (a) 0, (b) 0.25 (c) 0.3 V.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Short Pulse Generation by Adiabatic Wavelength Shifting
Takasumi Tanabe, Masaya Notomi, Hideaki Taniyama, and Eiichi Kuramochi
Optical Science Laboratory
Photonic crystal (PhC) nanocavities can trap light for longer than a ns in a volume of lessthan a μm3 [1]. We propose a new concept for controlling light that involves manipulating theproperties of photons while holding them. This approach has not been previously considered
because of the high speed of light. For example, we can change the wavelength of light in thesame way as the tone of a vibrating string. The tone of a string can be changed by modulating
its tension even after it has been plucked. When the photon lifetime of a cavity is sufficiently
long we can change the wavelength of the trapped light by changing the resonance of thecavity [2]. We call this phenomenon adiabatic wavelength shifting. Here we describe an
adiabatic wavelength shifting experiment and a demonstration of a short pulse released froma high-Q cavity by applying this phenomenon [3]. The demonstration of photon release with
arbitrary timing from a high-Q cavity on a chip is the first step toward the development of atrue optical memory.
Figure 1 is a scanning electron microscope image of a width-modulated line defect PhC
nanocavity [1, 4]. Because the cut-off wavelength of a line defect depends on its width, acavity is created by shifting the air holes slightly towards the outside of a narrow line defect.
Wider line defects are used as i/o waveguides. The cavity is charged with input laser light, andthen the input is suddenly turned off to record the behavior of the trapped photons (Fig. 2).
We resolved the output wavelengths, and then recorded their waveforms and confirmed thatthe output decays exponentially without any change in its wavelength when no modulation
is applied to the cavity. However, when we apply a pump pulse at a timing of 0 ps from the
top of the slab, a short wavelength component appears, which is due to adiabatic wavelength
shifting. As a result of the carrier-plasma dispersion effect, both the cavity resonance and thetrapped photons shift toward a shorter wavelength.
When the trapped photons shift towards a shorter wavelength, they become closer to the
cut-off wavelength of the narrow line defects. As a result, the confinement barriers become
shallower and the light in the cavity can couple more strongly with the i/o waveguides. This
enables the immediate extraction of the captured light into the waveguides (Fig. 3). We showedthat a pulse with a very small width can be obtained by dynamically changing the couplingstrength of the trapped light with the i/o waveguides via adiabatic wavelength shifting.
[1] T. Tanabe et al., Nature Photon. 1 (2007) 49.
[2] M. Notomi et al., Phys. Rev. A 73 (2006) 051803.
[3] T. Tanabe et al., Phys. Rev Lett. 102 (2009) 043907.
[4] E. Kuramochi et al., Appl. Phys. Lett. 93 (2008) 111112.

Fig. 1. Width-modulated line
defect PhC nanocavity.

Fig. 2. Spectrogram of the output light.
(up) w/o modulation (down) w/
modulation.

Fig. 3. Output waveform w/
and w/o modulation.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)41

Ultrahigh-Q Photonic Crystal Slab Nanocavities in Very Thin Barriers
Eiichi Kuramochi, Hideaki Taniyama, Takasumi Tanabe,
Akihiko Shinya, and Masaya Notomi
Optical Science Laboratory
We have developed width-modulated photonic crystal (PhC) slab line-defect nanocavities
with an ultrahigh Q (calculation: ~108, experiment: ~106) [1]. The main advantage of a PhC
nanocavity over other micro-cavities is its ultrasmall mode volume, which is usually about
0.1 μm3 or less. However, conventional PhC nanocavity designs require a thick PhC barrier,which considerably increases the net cavity size. It was believed that a thick photonic bandgap
barrier was needed to prevent light leaking from the nanocavity. In this study, we propose a
new design scheme that uses a pair of long air slots, which act as low refractive index barriersin the side directions, instead of thick PhC barriers. Here the main role of the thin side PhC is
to create a mode-gap barrier in the line defect direction. We demonstrate that the new design
scheme preserves most of the performance characteristics of ultrahigh-Q nanocavities [1] evenwhen the PhC slab barriers are very thin [2].
Figure 1 shows suitably designed nanocavities with air slots fabricated in a Si membrane. A
width modulated nanocavity is placed exactly at the center of the narrow part. In spite of thevery thin side PhC barrier (rows of holes in side PhC: q was 3 and 4), the samples show very
high Q values of 5.2×105 and 1.3×106, respectively. Figure 2 compares nanocavities with andwithout air slots as a function of PhC barrier thickness. The highest Q obtained for the thickbarrier sample was 1.8×106. Figure 2 clearly demonstrates that the air slots greatly improve
the Q value when the side PhC barrier is very thin. Very recently, an advanced design realized
an experimental Q of 106 at q=3 and 3.2×105 at q=2 [3]. The new cavity design greatly reduces
the net size of an ultrahigh-Q PhC nanocavity. Moreover, the new cavity design is very
suitable for the study of opto-mechanics because it easily realizes a compact narrow beamwith very light weight. A possible application is a mechanical oscillator with built-in high-Q
optical nanocavity.
[1] Kuramochi et al., Appl. Phys. Lett. 88 (2006) 041112.
[2] Kuramochi et al., Appl. Phys. Lett. 93 (2008) 111112.
[3] Kuramochi et al., The 8th International Photonic & Electromagnetic Crystal Structures
Meeting (PECS-VIII), Sydney, Australia (April 2009).

Fig. 1. Electron microscope images and resonant
spectra for q=4 and q=3, respectively.

42

Fig. 2. Experimental Q value of nanocavities inthin PhC barriers (thickness: q rows).

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Dynamic High-Q Cavity Formation and Photon Pinning by Index
Modulation
Masaya Notomi and Hideaki Taniyama
Optical Science Laboratory
Recently, ultrahigh-Q nanocavities have been realized by small local structural modulationof (typically, several nm shift of the air hole position) line-defect waveguides in twodimensional photonic crystals [1] [Fig. 1(a)]. This confinement mechanism has been applied tovarious systems. Periodic structural modulation has realized large-scale ultrahigh-Q couplednanocavities [2], and ultrahigh-Q nanocavity modes have been also found in one-dimensional
systems for the first time by the structural modulation scheme [3].
Here we report that we have found similar ultrahigh-Q cavity modes can be formed only byrefractive-index modulation of line-defect waveguides without any structure modulation [4].
The most amazing feature of this finding is that extremely small index modulation can realize
ultra-strong light confinement. For example, a Q value higher than 107 is possible with index–4–3modulation as small as Δn/n=4×10 . In the case of Δn/n=3×10 , the calculated Q reaches asurprisingly high value of 5 billions.
Such small index modulation can be achieved by various ultrafast optical nonlinearity. Thus,
it may become possible to dynamically form an ultrahigh-Q cavity by local optical pumping.
If so, we can pin (in other words, freeze) a part of an optical pulse traveling in a line-defectwaveguide by shining a focused light pulse from the top surface. Figure 2 shows a numericalsimulation of this process, which indeed shows that the light intensity inside the tuned area
marked by a circle is pinned in a dynamically-formed cavity mode [4]. Detailed analysis has
showed that this process is driven by adiabatic wavelength conversion recently experimentallyobserved in our group [5].
These results indicate that we can freely control ultrastrong light confinement by very small
modulation, which may open up novel functionalities in future optical devices.
[1] T. Tanabe et al., Nature Photon. 1 (2007) 49.
[2] M. Notomi, E. Kuramochi et al., Nature Photon. 2 (2008) 741.
[3] M. Notomi et al., Opt. Express 16 (2008) 11095.
[4] M. Notomi and H. Taniyama, Opt. Express 16 (2008) 18657.
[5] T. Tanabe et al., Phys. Rev Lett. 102 (2009) 043907.

Fig. 1. Ultrahigh-Q cavities formed by local
modulation of line-defect waveguide.

Fig. 2. Numerical simulation of photon pinning induced bydynamic index modulation of a line-defect waveguide.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)43

Ⅱ．DataScience Plaza 2008
"Science Plaza 2008", an open-house event at NTT Basic Research Laboratories (BRL),
was held at NTT Atsugi R&D Center on Thursday, November 21st, 2008. Under the banner"Nanoscience Opens Up the Quantum World", Science Plaza aimed to present our latest
research accomplishments to a wide variety of people both inside and outside NTT and togather a wide range of opinions.
Following an opening address by Dr. Junji Yumoto, the director of BRL, one of distinguishedtechnical members of NTT BRL, Dr. Masaya Notomi, gave a lecture entitled "Stopping,
Caging Light - Manipulation of light by photonic crystals -". In the afternoon session, Prof.
Hiroyuki Sakaki, the vice-president of Toyota Technological Institute, gave a special lecture
entitled "Quantum Physics of Nano Space and the World of the 21st Century - Think about
the ideal way of science and technology in the future -". Each lecture was well attended andfollowed by stimulating question-and-answer sessions.
Forty-eight poster exhibits, including 16 from Photonics Laboratories and Microsystem
Integration Laboratories, presented our latest research accomplishments. These poster exhibits
revealed the originality and impact of our research achievements, as well as their future
prospects. The posters were intensively discussed, and many thought-provoking opinions were
heard. Each year we offer a "Lab Tour", which is a guided tour of the research facilities at
NTT BRL that has received high praise from visitors over the years. This year＇s tour included
four different labs, so that as many people as possible could participate. This time we also
opened a booth explaining the NTT R&D recruitment system for job-seeking researchers andstudents. After all the lectures, presentations, and exhibitions had finished, we held a banquet
in the center＇s dining room, where lively conversation among the participants helped to forge
personal bonds.
More than 180 people from research institutes, universities, and industry, as well as fromNTT Group, attended Science Plaza 2008. Thanks to the efforts of all the participants, theconference ended on a high note. We would like to take this opportunity to express our sincere
gratitude to everyone who took part.

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)45

International Symposium on
Nanoscale Transport and Technology (ISNTT2009)
The International Symposium on Nanoscale Transport and Technology (ISNTT2009) was
held from January 20 to 23, 2009, at the NTT Atsugi R&D Center. Since 2000, we haveorganized two series of international symposia at NTT. One was the International Symposium
on Nanoelectronics, Nanostructures, and Carrier Interactions (NNCI) and the other was the
Mesoscopic Superconductivity and Spintronics (MS+S). We found that the two symposia had
a large overlap in scope in areas such as quantum computation, spintronics, nanoelectronics,
or mesoscopic transport. With the aim of further advancing studies in these areas, the idea of
jointly organizing these two symposia was then discussed and we finally decided to merge
them as a new series, ISNTT, in order to stimulate discussions among researchers in theseclosely related fields. The symposium was chaired by Dr. Hiroshi Yamaguchi and Dr. Koichi
Semba of NTT Basic Research Laboratories, together with Prof. Toshimasa Fujisawa of theTokyo Institute of Technology. It aspired to gather leading scientists and provide a forum fordiscussing the most recent topics in the research fields.
In this symposium, we had an excellent opportunity to hear many extremely interestingand very high-quality scientific talks that highlight new aspects and future directions in
the research fields of nanoscale transport and technology. There were totally 25 excellent
invited talks, including the plenary talk by Prof. Heiblum from Weizmann Institute in Israel,
and the special talk by Prof. Leggett from the University of Illinois in the US. Totally 104
contributed oral and poster presentations were given in 17 sessions. The major topics were
semiconductor nanodevices, semiconductor micro/nanomechanics, quantum solid statephysics, superconducting quantum physics, and semiconductor spintronics. The total numberof attendees was 202. We believe that we provided a very nice opportunity for mutualcommunication within and among the related research fields.

46

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

The 5th Advisory Board
The Advisory Board, an external committee whose role is to evaluate the work of NTT Basic
Research Laboratories (BRL), met from February 16~18, 2009. This was the fifth meetingof the Advisory Board, which was first convened in 2001 to provide an objective evaluationof our research plans and activities to enable us to employ strategic management in a timely
manner. On this occasion, we were happy to welcome a new member.
Over the course of the three days the board made valuable suggestions and comments
related to our research and management activities. They agreed that the research level isgenerally high on an international scale, and that it is important for us to maintain this toplevel research and transmit information about our research achievements to the world. They
also raised several issues related to human resources, the research budget and internal andexternal collaboration. We plan to make improvements based on these valuable suggestions.
At this meeting we held a poster session for the first time, and offered researchers an
opportunity to communicate with the board members. This included a dinner party for the
researchers at which they met and talked with the board members. For the BRL and NTT
executives, we organized a Japanese style dinner, which provided a good chance to discuss the
future management strategy of NTT BRL from an international perspective. The next board
meeting will held in two years.

Board Members
Prof. G. Abstreiter
Prof. B. Altshuler
Prof. T. Hänsch
Prof. S. Haroche
Prof. M. Jonson
Prof. T. Leggett
Prof. H. Mooij
Prof. J. Ryan
Prof. K. von Klitzing

Affiliation
Walter Schottky
Columbia Univ.
Max-Planck-Inst.
École Normale
Chalmers Univ. of Tech.
Univ. of Illinois
Delft Univ. of Tech.
Univ. of Oxford
Max-Planck-Inst.

Research Field
Low-dim. Semiconductor Physics
Condensed Matter Physics
Quantum Optics
Quantum Optics
Condensed Matter Physics
Quantum Physics
Quantum Physics
Nano-bio Technology
Semiconductor Physics

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

47

Award Winners’ List (Fiscal 2008)
ITU-T Kaleidoscope
Academic Conference:
Innovations in NGN Future Network andServices
Best Paper Award, Second
Place

H. Takesue
T. Honjo
K. Tamaki
Y. Tokura

Differential Phase Shift Quantum Key
Distribution

May 13,2008

The 52nd International
Conference on Electron,
Ion, and Photon
Beam Technology
and Nanofabrication(EIPBN-2008) MicrographContest Best Video AwardK. Yamazaki
H. Yamaguchi

The Mini-faces of Egypt

May 28,
2008

The Laser Society of JapanThe 32st Original Paper
Award

K. Oguri
Y. Okano
T. Nishikawa
H. NakanoSpatiotemporally Dynamics Studyof a Femtosecond Laser Ablation
Plume Based on Ultrafast XAFS
Spectroscopy

May 30,2008

JJAP Award for the Best
Original Paper

K. Suzuki
K. Kanisawa
S. Perraud
M. UekiK. Takashina
Y. Hirayama

Imaging of Interference Between
Incident and Reflected Electron
Waves at an InAs/GaSb
Heterointerface by Low-temperature
Scanning Tunneling Spectroscopy

Sep. 2,
2008

H. Okamoto

Q-control and Self-oscillation of
GaAs Cantilevers by Carrier
Excitation

Sep. 2,
2008

The 141st Committee
on Microbeam Analysis
of Japan Society for the
Promotion of Science(JSPS)
Sakaki Encouragement
Award

H. Hibino

Dynamical Observations of Crystal
Growth and Phase Transition by
Surface Electron Microscopy

Sep. 16,
2008

JSPS Prize

M. Notomi

Discovery and Applications of Novel
Functions of Photonic Crystals

Mar. 9,2009

Japan Academy Medal

M. Notomi

Discovery and Applications of Novel
Functions of Photonic Crystals

Mar. 9,2009

The Japan Society ofApplied Physics Young
Scientist Award for the
Presentation of Excellent
Paper

48

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

In-house Award Winners’ List (Fiscal 2008)
Idea Contest 2008
Highest Award for Service
Idea
Bronze Award for NGN
Application

M. Yamaguchi
K. Uchiyama
T. Hashimoto
N. Taniguchi
K. Shimizu

Time-capsule Service on
Denwa-channel

Nov. 11,2008

NTT R&D Award

T. Honjo
H. Takesui
K. Inoue

Differential Phase Shift Quantum
Cryptography

Dec. 18,
2008

NTT R&D Award

I. Mahboob

Development of ElectromechanicalDevices for Logic Processing
Utilizing Tiny Mechanical Vibration

Dec. 18,
2008

Award for Achievements
by Director of Basic
Research Laboratories

A. Shinya
T. Tanabe
E. Kuramochi
H. Taniyama
M. Notomi
S. Matsuo
T. Kakitsuka
T. SatoDevelopment of All-optical Bit
Memory by Photonic Crystals

Mar. 19,2009

Award for Achievements by
Director of Basic ResearchLaboratories

Y. OnoM. Khalafalla

Development of Single-dopant
Technology

Mar. 19,2009

Award for Excellent Papers
by Director of Basic
Research Laboratories

I. Mahboob"Bit Storage and Bit Flip Operationsin an Electromechanical Oscillator",
Nature Nanotechnol. 3 (2008) 275.

Mar. 19,
2009

K. Nishiguchi"Stochastic Data Processing Circuit
Based on Single Electrons Using
Nanoscale Field-effect Transistors",
Appl. Phys. Lett. 92 (2008) 062105.

Mar. 19,2009

Award for Excellent Papers
by Director of Basic
Research Laboratories

H. Nakashima"Self-Assembly of Gold Nanorods
Induced by IntermolecularInteractions of Surface-Anchored
Lipids", Langmuir 24 (2008) 5654.

Mar. 19,2009

Special Award by Directorof Basic ResearchLaboratories

K .Oguri
T. Tawara
H. Sumikura
H. Okamoto
H. Shibata

Contribution to the Rearrangement of
the Laboratory Equipments

Mar. 19,2009

Special Award by Directorof Basic ResearchLaboratories

A. Tokura
Y. Kobayashi

Health Risk Management of Carbon
Nanotubes

Mar. 19,2009

Award for Excellent Papers
by Director of Basic
Research Laboratories

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)49

List of Visitors’ Talks (Fiscal 2008)l. Materials Science
Date

50

Speaker

Affiliation"Title"May. 23

Prof. Erhard Kohn

University of Ulm, Germany"Recent Progress in Diamond Related Device Work at
Ulm"

Sep. 29

Prof. Satoru Tanaka

Kyushu University"Formation of Heterostructures by SiC Surface NanoFacets and Surface Self-Reformation"

Sep. 29

Mr. Kenjiro Hayashi

Kyushu University"Analysis of Stacking Sequence of Graphene Layers
Formed on SiC Surface"Oct. 7

Prof. Jonathan Heddle

Tokyo Institute of Technology"Bionanoengineering with Protein Rings"

Oct. 14

Prof. Seigi Mizuno

Kyushu University"Analysis of Surface Structure by Low-Energy Electron
Diffraction and Development of Nano Area Probes"

Dec. 12
Dec. 19
Dec. 26

Prof. Jocelyn Achard

Université Paris 13, France"Fundamentals of Diamond CVD Growth Process"Mar. 24

Mr. Yoshihiko Kuroki

Sony Coporation"Improvements in Motion Image Quality by High Frame
Rate"

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

II. Physical Science
Date

Speaker

Affiliation"Title"Dr. Nicolas Clément

University of Sciences and Technologies of Lille,
France"Toward Electrical Detection of Single Molecules:
Description of the Project and Presentationof Dynamic Electrical Transport and Noise in
Molecular Junctions"Jun. 9Dr. Norikazu Mizuochi

University of Tsukuba"Generation and Retrieval of Entangled States fromSingle Spins in Diamond at Room Temperature"Jun. 23

Dr. Simon J. Devitt

University of Cambridge, U.K.
University of Melbourne, Australia"Subspace Confinement: How Good Is Your Qubit?"Jul. 2

Dr. Ryosuke Ishiguro

Tokyo University of Science"Supersolid vs. Superfluid at Grain Boundaries"

Prof. Seth Lloyd

Massachusetts Institute of Technology, U.S.A.
"Quantizing the Global Positioning System""Quantum Computation and Photosynthesis"

Prof. Cun-Zheng Ning

Arizona State University, U.S.A.
"Semiconductor Nanolasers: Is There an End to
Miniaturization?"

Nov. 25

Prof. Yasuhiro Hatsugai

University of Tsukuba"Universality of the Zero Gap Semiconductors:
From Graphene and d-wave Superconductors toTopological Insulators"

Dec. 4

Dr. Samuel Deléglise

École Normale Supérieure, France"Generation and Time-resolved Reconstruction of
Cavity Field Quantum States"

Apr. 15

Jul. 3

Jul. 29

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)51

Dec. 17

Prof. Saverio Pascazio

University of Bari, Italy"Antibunching and Correlations of Field-Emitted
Electrons from a Superconductor"

Jan. 19

Prof. Jörg Schmiedmayer

Technische Universität Wien, Austria"Atom Chips"

Feb. 23

Prof. Wilfred G. vander Wiel

University of Twente, the Netherlands"Hybrid Organic-inorganic Systems for (Spin)
Electronics"

Feb. 26

Prof. Klaus H. Ploog

Paul-Drude-Institut, Germany"Challenges in Materials Science for Sustainable
Energy"Mar. 2

Mr. Nobuyuki Kambe,
CTO

NanoGram Corporation, U.S.A.
"Global Nanotech Venture: Publick Contribution
through Innovative Technologies"

III. Optical Science
Date

Affiliation"Title"Prof. Tsuneyuki Ozaki

University of Quebec, Canada"Unique High-order Harmonic Generation from
Plasma at the Advanced Laser Light Source"

Oct. 9Prof. Stephen Hughes

Queen＇s University, Canada"Unraveling the Light-matter Interactions of"Disorder-induced Scattering" and the "Strongcoupling Regime" in Semiconductor Nanostructures"

Oct. 10

Prof. Amnon Aharony

Ben-Gurion University of the Negev, Israel"Spin Filtering by a Periodic Spintronic Device"

Aug. 1152

Speaker

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

Prof. Ora Entin-Wohlman

Ben-Gurion University of the Negev, Israel"The Conductance of Superconducting-normal
Hybrid Structures"Prof. Yong-Hee Lee

Korea Advanced Institute of Science andTechnology, Korea"Spatial and Spectral Nano-control of Microresonators"

Prof. Christos Flytzanis

Ecole Normale Supérieure, France"Coherent Optically Driven Electron Charge/Spin
Transport and Magnetic Ordering in Polar Photonic
and Magnetophotonic Structures"

Dr. Yasumitsu Miyata

National Institute of Advanced Industrial Scienceand Technology"Optical properties of metallic and semiconducting
single-wall carbon nanotubes"

Dec. 22

Dr. Tetsuya Ido

National Institute of Information andCommunications Technology"Pulse Amplification of Optical Frequency Combs
by Using a Passive Optical Cavity and 1S0-3P1
Transition of Sr in Optical Lattice Clock"Jan. 7

Mr. Akira Ozawa

Max-Planck-Institut, Germany"Towards Precision Spectroscopy with XUVFrequency Comb"

Oct. 15

Oct. 23

Nov. 18

Dec. 2

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)53

Research Activities in Basic Research Laboratories in 2008
The numbers of papers published in international journals, presentations at international
conferences and applied patents in year 2008 amounted to 180, 257, and 48, respectively. The
numbers for each research area are as follows;
Papers Published in International Journals(Jan. - Dec. 2008)
Materials Science

49

Physical Science

75

Optical Science

56

0

20

40

60

80

100

Number of Papers

Presentations at International Conferences(Jan. - Dec. 2008)
Materials Science62

Physical Science

113

Optical Science

82

0

20

40

60

80

100

120

140

Number of Presentations

Applied Patents (Jan. - Dec. 2008)
Materials Science22

Physical Science

17

Optical Science

0

54

9

5

10

15

20

Number of Applied Patents

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

25

The numbers of research papers published in the major journals are shown below.
Journals
Advanced Materials
Applied Physics Express
Applied Physics Lettters
Applied Surface Science
Diamond and Related Materials
Japanese Journal of Applied Physics
Journal of Applied Physics
Langmuir
Nano Letters
Nanotechnology
Nature Nanotechnology
Nature Photonics
Nature Physics
Optics Express
Physica E-Low-Dimensional Systems & Nanostructures
Physical Review A
Physical Review B
Physical Review Letters*IF2007: Impact Factor 2007 (Journal Citation Reports,2007)(IF2007*)
8.191
3.596
1.406
1.788
1.247
2.171
4.009
9.627
3.31
14.91714.677
3.709
0.834
2.893
3.172
6.944

Numbers
1
3
16
6
7
19
4
2
3
3
1
1
5
12
19
3
16
10

The average IF2007 for all research papers from NTT Basic Research laboratories is 3.07.

The numbers of presentations in the major conferences are shown below.
Conferences
Numbers
The Conference on Lasers and Electro-Optics and the Quantum Electronics and Laser
13
Science Conference
The IEEE Nanotechnology Materials and Device Conference 2008
10
International Symposium on Physics of Quantum Technology
10International Symposium on Surface Science and Nanotechnology
10
The International Conference on the Physics of Semiconductors
925th International Conference on Low Temperature Physics
82008 International Conference on Solid State Devices and Materials
7
21st International Microprocesses and Nanotechnology Conference6
The 9th International Symposium on Foundations of Quantum Mechanics
6in the Light of New Technology
13th Advanced Heterostructures and Nanostructures Workshop
4
The American Physical Society
4
18th International Conference on High Magnetic Fields
4in Semiconductor Physics and Nanotechnology
Mechanical Systems in the Quantum Regime, the Gordon Research Conferences
4
The 5th International Conference on Physics and4
Applications of Spin-related Phenomena in Semiconductors
The International Symposium on Graphene Devices: Technology, Physics, and Modeling4
The 23rd Nishinomiya-Yukawa Memorial International Workshop
4
The 21st Annual Meeting of The IEEE Lasers & Electro-Optics Society
4
The 9th International Conference on Quantum Communication, Measurement and Computing
4
International Symposium on Growth of III-Nitrides
4

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

55

List of Invited Talks at International Conferences (2008)
I. Materials Science Laboratory

56

(1)

H. Hibino, "Microscopic determination of number of graphene layers on SiC", Symposium on Surface
and Nano Science 2008, Appi, Japan (Jan. 2008).

(2)

S. Suzuki and Y. Kobayashi, "Low-energy irradiation damage in single-walled carbon nanotubes:
defect characteristics and electric property control", International Carbon Nanotube Conference in Nagoya
University, Nagoya, Japan (Feb. 2008).

(3)

K. Torimitsu, Y. Shinozaki, and Y. Furukawa, "Magnesium effect on brain neural development", Gordon
Research Conferences, Magnesium in biochemical processes and medicine, Ventura, USA, (Mar. 2008).

(4)

K. Torimitsu, Y. Shinozaki, and Y. Furukawa, "Magnesium effect on rat brain neural development invitro", European Magnesium Meeting 2008, Paris, France, (May 2008).

(5)

Y. Taniyasu and M. Kasu, "Influence of dislocation on AlN deep-UV light-emitting diodes", 4th Asian
Conference on Crystal Growth and Technology, Sendai, Japan (May 2008).

(6)

Y. Kobayashi, T. Akasaka, and T. Makimoto, "Boron Nitride Grown by MOVPE", 14th International
Conference of Metalorganic Vapor Phase Epitaxy, Metz, France (June 2008).

(7)

K. Torimitsu, "Development of Nanobio Interface using Neurons and Receptor Proteins", Asia-PacificSymposium on Nanobionics, Wollongong, Australia (June 2008).

(8)

A. Shimada, N. Kasai, and K. Torimitsu, "Conductive-Polymer Microelectrode Array for Neural Signal
Measurements", 16th Anuual International Conference on Composites/Nano Engineering, Kuming, China(July 2008).

(9)

H. Hibino, "Number-of-layers dependence of electronic properties of epitaxial graphene investigated by
SPELEEM", 5th International Workshop on Nanoscale Spectroscopy and Nanotechnology, Athens, U.S.A.
(July 2008).

(10)

H. Omi, D. P. Sprunken, K. Furukawa, H. Nakashima, I. Sychugov, Y. Kobayashi, and K. Torimitsu,"Determination of Aspect Ratio Distribution of Gold Nanorods from Absorption Spectra using Gans
Theory", 16th Anuual International Conference on Composites/Nano Engineering, Kuming, China (July
2008).

(11)

Y. Taniyasu and M. Kasu, "MOVPE Growth of Single-crystal Hexagonal AlN on Cubic Diamond", 2ndInternational Symposium on Growth of III-Nitride, Izu, Japan (July 2008).

(12)

M. Kasu, K. Ueda, H. Kageshima, and Y. Taniyasu "Challenges of Diamond-based Electronic Devices",
International Conference on Electronic Materials 2008, Sydney, Australia (July 2008).

(13)

K. Torimitsu, Y. Shinozaki, A. Shimada, and Y. Furukawa, "Receptor based nano-bio research:
application to medical bionics", Sir Mark Oliphant International Frontiers of Science and Technology
Conference Series, Inaugural Conference on Medical Bionics, Lorne, Australia (Nov. 2008).

(14)

K. Torimitsu, "Receptor protein functions and its application for biomimetic device", The 5th SwedenJapan Workshop on Bio-Nanotechnology, Stockholm, Sweden (Nov. 2008).

(15)

H. Hibino, H. Kageshima, M. Kotsugi, and Y. Watanabe, "Local work function measurements ofepitaxial few-layer grapheme", 5th International Symposium on Surface Science and Nanotechnology,
Tokyo, Japan (Nov. 2008).

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

(16)K. Torimtisu, "Protein-based nanobio research for medical bionics", 8th International Symposium on
Advanced Fluid Information and Transdisciplinary Fluid Integration, Sendai, Japan (Dec. 2008).

II. Physical Science Laboratory(1)

Y. Ono, "Single boron detection in nano-scale SOI MOSFETs", The 2009 International Meeting for
Future of Electron Devices, Kansai, Osaka, Japan (May 2008).

(2)

K. Kanisawa, "Imaging surface states bound to native donors at the epitaxial InAs surface", Nanoscale
Spectroscopy & Nanotechnology 5 - Spin-Polarized Scanning Tunneling Microscopy 2, Athens, U.S.A. (July
2008).

(3)

A. Fujiwara and Y. Ono, "Single-Electron Device", ITRS (International Technology Roadmap for
Semiconductors) - ERD (Emerging Research Devices) Workshop on Maturity Evaluation for SelectedBeyond CMOS Emerging Technologies, San Francisco, U.S.A. (July 2008).

(4)

I. Mahboob and H. Yamaguchi, "The quantum Hall effect probed via a parametrically pumped
electromechanical resonator", Frontiers of Low Temperatrue Physics, London, U.K. (Aug. 2008).

(5)

H. Yamaguchi and I. Mahboob, "Micro/Nanomechanical Systems for Information Processing", The 9thInternational Symposium on Foundations of Quantum Mechanics in the Light of New Technology, Saitama,
Japan (Aug. 2008).

(6)

H. Yamaguchi, I. Mahboob, H. Okamoto, and K. Onomitsu, "Micro/Nanomechanical Systems Basedon Semiconductor Heterostructures", The International Symposium on Compound Semiconductors, Rust,
Germany (Sep. 2008).

(7)

Y. Ono, M. A. H. Khalafalla, A. Fujiwara, K. Nishiguchi, K. Takashina, S. Horiguchi, Y. Takahashi, and H.
Inokawa, "Single-dopant effect in Si MOSFETs", IEEE Nanotechnology Materials and Device Conference,
Kyoto, Japan (Oct. 2008).

(8)

K. Semba, "Cavity-QED with Quantum Superconducting Circuits", Quantum information, quantum
coherence and related topics, Tokyo, Japan (Sep. 2008).

(9)

H. Nakano, S. Saito, K. Semba, and H. Takayanagi, "Quantum Analysis on Superconducting Qubit
Readout with a Josephson Bifurcation Amplifier", Quantum Dynamics in Dots and Junctions: Coherent
Solid State Systems, Riva del Garda, Italy (Oct. 2008).

(10)

K. Grove-Rasmussen, H. I. Jorgensen, T. Hayashi, P. E. Lindelof, and T. Fujisawa, "Electronic transport
in carbon nanotube quantum dots", Korea Conference on Innovative Science and Technology, Phoenix
Park, Korea (Oct. 2008).

(11)

H. Yamaguchi, "Novel Functionalilties in Semiconductor-based Micro/Nanomechanical Systems", 21stInternational Microprocesses and Nanotechnology Conference, Fukuoka, Japan (Oct. 2008).

(12)

I. Mahboob and H. Yamaguchi, " Bit operation in a parametrically pumped electromechanical resonator",
Nano Technology 2008, Ishikawa, Japan (Oct. 2008).

(13)

A. Fujiwara, K. Nishiguchi, Y. Ono, H. Inokawa, and Y. Takahashi "Silicon Single-Electron Devices andTheir Applications", TND 2008 Technical Forum, Seoul, Korea (Oct. 2008).

(14)

T. Ota, T. Hayashi, and T. Fujisawa, "Quantum information processing devices with nano-scale
semiconductor quantum dots", 1st Russian-Japanese Young Scientists Conference on Nanomaterials andNanotechnology, Moscow, Russia (Oct. 2008).

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

57

(15)

K. Semba, "Quantum control of the f lux qubit coupled to microwave photon system", Solid State
Quantum Information, Pisa, Italy (Dec. 2008).

(16)

K. Grove-Rasmussen, "Quantum Transport in Carbon Nanotubes", Workshop on novel phenomena at
nanoscale interface, Hsinchu, Taiwan (Dec. 2008).

III. Optical Science Laboratory

58

(1)

H. Takesue, "Quantum communication experiments using entangled photons generated in dispersion
shifted fiber", LEOS Winter Topical Meeting of Nonlinear Photonics, Sorrento, Italy (Jan. 2008).

(2)

M. Notomi, T. Tanabe, E. Kuramochi, A. Shinya, and H. Taniyama, "Nonlinear and adiabatic control oflight in a photonic crystal chip", LEOS Winter Topical Meeting of Nonlinear Photonics, Sorrento, Italy (Jan.
2008).

(3)

T. Tanabe, E. Kuramochi, A. Shinya, H. Taniyama, and M. Notomi, "Photonic crystal nanocavities withextremely long photon lifetime and their applications", The 6th Asia Pacific Laser Symposium, Nagoya,Japan (Jan. 2008).

(4)

S. Kawanishi, M. Tanaka, M. Ohmori, and H. Sakaki, "Photonic bandgap fiber for new wavelength
range", Optical Fiber Communication Conference and Exposition/National Fiber Optics Engineers
Conference, San Diego, U.S.A. (Feb. 2008).

(5)

M. Notomi, "Cont rol of Light by Photonic Cr ystal Nanocavities", JST-DFG Workshop on
Nanoelectronics, Aachen, Germany (March 2008).

(6)

M. Yamashita and M.W. Jack, "Number squeezing of an array of Bose-Einstein condensates trapped in a
1D optical lattice", 17th International Laser Physics Workshop, Trondheim, Norway (June 2008).

(7)

T. Honjo, S. W. Nam, H. Takesue, Q. Zhang, H. Kamada, Y. Nishida,O. Tadanaga, M. Asobe, B. Baek,
R. Hadfield, S. Miki, M. Fujiwara, M. Sasaki, Z. Wang, K. Inoue, and Y. Yamamoto, "Entanglement-based
BBM92 QKD experiment using superconducting single photon detectors", 17th International Laser Physics
Workshop, Trondheim, Norway (June 2008).

(8)

T. Tanabe, A. Shinya, E. Kuramochi, and M. Notomi, "Nonlinear Switching in High-Q Photonic Crystal
Nanocavities", Integrated Photonics and Nanophotonics Research and Applications, Boston, U.S.A. (July
2008).

(9)

S. Kawanishi, "Recent Progress in Photonic Crystal Fiber Technologies", Opto-Electronics andCommunications Conference, Sydney, Australia (July 2008).

(10)

M. Notomi, T. Tanabe, E. Kuramochi, and H. Taniyama, "Slow Light Media Based on Ultrahigh-Q
Nanocavities", OSA Topical Meeting on Slow and Fast Light, Boston, U.S.A. (July 2008).

(11)

H. Takesue, H. Fukuda, T. Tsuchizawa, T. Watanabe, K. Yamada, Y. Tokura, and S. I. Itabashi,"Entanglement generation using silicon wire waveguide", 5th International Conference on Group IV
Photonics, Sorrento, Italy (Sep. 2008).

(12)

H. Takesue, K. Harada, H. Fukuda, T. Tsuchizawa, T. Watanabe, K. Yamada, Y. Tokura, and S. I.
Itabashi, "Entanglement generation using silicon wire waveguide", International Conference on Quantum
Optics and Quantum Information, Vilnius, Lithuania (Sep. 2008).

(13)

H. Nakano, A. Ishizawa, and K. Oguri, "Dependence of surface harmonics generation properties oncarrier-envelope phase of few-cycle laser field", Advanced coherent light sources, Hilo, U.S.A. (Sep. 2008).

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)

(14)H. Takesue, H. Fukuda, T. Tsuchizawa, T. Watanabe, K. Yamada, Y. Tokura, and S. I. Itabashi,"Entangled photon-pair generation using silicon photonic wire waveguide", The IEEE Nanotechnology
Materials and Device Conference, Kyoto, Japan (Oct. 2008).

(15)

M. Notomi, A. Shinya, T. Tanabe, E. Kuramochi, H. Taniyama, S. Matsuo, T. Kakitsuka, and T.
Sato, "On-chip All-optical Processing Based on Photonic Crystal Nanocavities", Asia Optical Fiber
Communication & Optoelectronic Exposition and Conference, Shanghai, China (Oct. 2008).

(16)

S. Kawanishi, "Recent Progress in Photonic Bandgap Fiber Technology", Asia Pacific OpticalCommunications, Hangzhou, China (Oct. 2008).

(17)

Y. Tokura, "Quantum spin transport in magnetic-field-engineered nano-structures", Spin Transport in
Condensed Matter, The 23rd Nishinomiya-Yukawa Memorial International Workshop, Kyoto, Japan (Oct.
2008).

(18)

H. Takesue and T. Honjo, "Quantum communication experiments using telecom-band entangled
photons", The 21st Annual Meeting of The IEEE Lasers & Electro-Optics Society, Newport Beach, U.S.A.
(Nov. 20008).

(19)

K. Oguri, Y. Okano, T. Nishikawa, and H. Nakano, "Dynamic imaging of femtosecond laser ablation
plume by using laser-generated soft x-ray", The 21st Annual Meeting of The IEEE Lasers & Electro-Optics
Society, Newport Beach, U.S.A. (Nov. 20008).

(20)

H. Nakano, A. Ishizawa, and K. Oguri, "Interference between surface harmonics of carrier-envelope
phase controlled few-cycle laser field", International Society for Photo-optical Instrumentation Engineers,
Wuahn, China (Nov. 2008).

(21)

K. Tamaki, "Unconditional security proof of QKD and imperfections of devises", Updating Quantum
Cryptography 2008, Tokyo, Japan (Dec. 2008).

(22)

Y. Tokura, "Latest progress in QKD experiments at NTT", Updating Quantum Cryptography, Tokyo,
Japan (Dec. 2008).

Research Activities in NTT Basic Research Laboratories Vol. 19 (2008)59

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/