Research Activities
in
NTT Basic Research Laboratories
Volume 18
Fiscal 2007

July 2008
NTT Basic Research Laboratories,
Nippon Telegraph and Telephone Corporation (NTT)http://www.brl.ntt.co.jp/

Epitaxial graphenegrown on SiC

Low-energy electron microscopy
images of epitaxial graphene

Electron reflectivity map

Evaluation of Number of Graphene Layers Grown on SiC
Recently, graphene has attracted much attention as a material for future electronics. Epitaxial graphenegrown on SiC substrates by annealing can be easily scaled up and is promising for device integration.
Aiming at establishing a reproducible way of growing large and uniform epitaxial graphene, we demonstrated that the number of graphene layers grown on SiC can be determined by low-energy electron
microscopy (LEEM) using quantized oscillations of electron reflectivity. In-situ microscopic determination of the number of graphene layers using LEEM would greatly contribute to the growth control of
epitaxial graphene. (Page 19)

Scanning electron microscopic imageof an arched InAs/AlGaSb beam

Beam shape measured with an
atomic force microscope andcalculation results

Measurement results: relationship between resistance andbeam deflection

Piezoelectric Effect on Piezoresistance of
InAs/AlGaSb Heterostructure Nanobeam
Nanoelectromechanical systems comprising compound semiconductors are promising for ultrahighsensitivity sensors and other applications. In these systems, piezoresistance (i.e., resistance change
due to mechanical strain) is an important parameter. We measured the piezoresistance of InAs/AlGaSb
heterostructure nanobeams and found that it strongly depends on whether the beams are arched or
straight. This can be explained in calculations of piezoresistance by considering the piezoelectriceffect. Our results reveal the importance of the piezoelectric effect in mechanical systems using verythin heterostructures. (Page 26)

Scanning electron micrograph of device andmeasurement setup(a,b) Electron accumulation and (c,d) holeaccumulation near quantum dot

Energy Distribution Measurement of Nonequilibrium Carriers
Using a Quantum Dot
The quantized energy levels of electrons in a semiconductor quantum dot (QD) can be easily tuned
by controlling the gate voltage, thus enabling us to use a QD as a high-resolution energy analyzer (orspectrometer) for the electrons near the QD. We used this feature of QDs to measure the energy distribution of ballistic nonequilibrium electrons and holes emitted from a quantum wire. Nonequilibrium
carriers were emitted by applying a bias voltage (Vpc) to a quantum point contact. The emitted current
was again focused by applying a perpendicular magnetic field (B⊥) and analyzed with a QD. When theenergy of the nonequilibrium carriers coincides with the quantized energy levels, those carriers canresonantly tunnel through the QD and can be detected as an electric current. (Page 31)

Excitonic wavefunction on four different sized nanotube structures

Topology of Exciton in Artificial Structure
We have theoretically demonstrated that the excitons in nanotube structures show the variety of topological states depending on the size of the nanotube. This is due to the fact that an exciton has its own
characteristic size and it determines the confinement feature of the exciton in the structure. It is also
shown that the topology of the exciton wavefunction can be controlled through the dielectric constantof the barrier material surrounding the nanotubes. (Page 35)

Message from the Director
We are deeply grateful for your interest andsupport with respect to our research activities.
The three research areas at NTT-BRL, namely
Materials Science, Physical Science, and Optical
Science, are undertaking work designed tocontribute to the success of NTT’s business andpromote advances in science that will ultimately
benefit all mankind.
A fundamental goal of these research activities
is to improve global competitiveness. Therefore,
BRL is collaborating with many universities andresearch institutes throughout the world as wellas with other NTT laboratories. BRL organizes
international conferences related to quantum
physics and also holds a "Science Plaza" to enhance
public understanding of our activities and ensurea frank exchange of opinions. Moreover, one ofour missions is the education of young researchers and we sponsor the biennial "BRL School",which boasts distinguished researchers as lecturers. In November 2007, thirty-five Ph.D.
students and young researchers from universities and institutes in 12 countries participated in
the BRL School. We hope that this endeavor will encourage research and contribute to its future
growth.
It gives us immense pleasure to fulfill our mission of being an open laboratory in this way, andto disseminate our research output worldwide. Your continued support is greatly appreciated.

Junji Yumoto
Director
NTT Basic Research Laboratories

Contents
page

Member List ............................................................................................................................. 1
I. Research Topics◆ Overview of Research in Laboratories ................................................................................................... 11◆ Materials Science Laboratory ................................................................................................................. 12♦ Polarized Emission of AlN Deep-UV LED by a Negative Crystal-field Splitting Energy♦ Doping of Diamond by Combining Ion-implantation and High-pressure andHigh-temperature Annealing♦ Quasi Two-dimensional Hole Channel in Diamond FETs
♦ High-temperature Characteristics of npn-type GaN/InGaN Double Heterojunction

Bipolar Transistors♦ Raman Spectroscopy of Carbon Nanotubes at CVD Growth Temperature and the Assignmentsof their Chiral Indices♦ Low-Energy Irradiation Damage in Carbon Nanotubes♦ Combined Scanning Tunneling and Aperture Near-field Microscopy: Tip Modeling♦ Evaluation of Number of Graphene Layers Grown on SiC♦ Elastic Modulus of Suspended Membrane Protein Measured by Atomic Force Microscopy♦ Quantitative Analyses of FRET Efficiency of Dye Molecules Confinedwithin 2-Dimensional Space♦ AFM Observation of a Single Receptor Reconstituted into Lipid Bilayer◆ Physical Science Laboratory .................................................................................................................. 23♦ Nanoampere Charge Pump by Single-electron Ratchet Using Silicon Nanowire MOSFET♦ Infrared Detection with Silicon Nano-transistors♦ Detection of the Mechanical Friction Caused by Electron Systems♦ Piezoelectric Effect on Piezoresistance of InAs/AlGaSb Heterostructure Nanobeam♦ Electron Spins in Bilayer Quantum Hall Systems Investigated by Nuclear Spin Measurements♦ Imaging Percolation of Localized States in a Semiconductor Quantum Well
♦ Persistent Supercurrent Atom Chip
♦ A Selective and Long-distance Coupling Scheme for Plural Flux Quantum Bits
♦ Energy Distribution Measurement of Nonequilibrium Carriers Using a Quantum Dot♦ Density Dependence of Electron and Hole Effective Masses in GaAs Gated Quantum Well
◆ Optical Science Laboratory .................................................................................................................... 33♦ Quantum Key Distribution over 200 km of Fiber♦ Field Trial of Differential-phase-shift Quantum Key Distribution Using Polarization

Independent Frequency Up-conversion Detectors♦ Topology of Exciton in Artificial Structure♦ Efficient and Low Noise Single-photon Detection in 1550-nm Communication Bandby Frequency Upconversion in Periodically Poled LiNbO3 Waveguides♦ InAs Nanowire-channel Field Effect Transistors♦ Demonstration of a CEO-locked Frequency Comb at Telecommunications Wavelengths

with Low Pulse Energy♦ Ultra High-Q Photonic Crystal Nanocavities Based on Compound Semiconductors♦ All-optical Bit Memory Based on Photonic Crystal Nanocavity♦ Slow Light Propagation in Large-scale Photonic Crystal Coupled Resonator Waveguides

II. Data◆ 4th NTT-BRL School ............................................................................................................................. 43◆ Science Plaza 2007 ................................................................................................................................. 44◆ Award Winners＇ List................................................................................................................................ 45◆ In-house Award Winners＇ List................................................................................................................. 46◆ List of Visitors＇ Talks .............................................................................................................................. 47◆ Research Activities in Basic Research Laboratories in 2007 ................................................................. 51◆ List of Invited Talks at International Conferences.................................................................................. 53

Cover photograph:
Persistent Supercurrent Atom Chip
Atoms in room temperature are moving like a bullet of a handgun, but with a laser cooling technique we cancool them down to one millionth, then the ultra cold atoms start falling down according to gravity. We havesucceeded in trapping cold atoms with a practically noise free magnetic potential generated by a persistentcurrent running through a superconducting loop circuit. A silhouette of atoms revealed the fact. A part ofthis research is supported by the Japan Science and Technology Agency CREST.

Member List
As of March 31, 2008(* moved to another position within a year)

NTT Basic Research Laboratories

Director,Dr. Junji YumotoResearch Planning Section

Executive Research Scientist,

Dr. Toshiki Makimoto
Dr. Itaru Yokohama*Senior Research Scientist,

Dr. Hideki Gotoh

Senior Research Scientist, Supervisor,

Dr. Koji Muraki

Senior Research Scientist, Supervisor,

Dr. Yuichi Harada*

NTT R&D Fellow
Prof. Yoshihisa Yamamoto(Stanford University, U.S.A)
Prof. Hideaki Takayanagi(Tokyo University of Science)

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

Executive Manager,

Dr. Keiichi Torimitsu

Assistant Manager,

Dr. Hiroo Omi
Dr. Katsuhiro Ajito*
Dr. Isao Tomita*

Dr. Yuko Ueno*

Thin-Film Materials Research Group:
Dr. Makoto Kasu (Group Leader)
Dr. Toshiki Makimoto*Dr. Yasuyuki Kobayashi
Dr. Hideki Yamamoto
Dr. Tetsuya Akasaka
Dr. Kazuhide Kumakura
Dr. Yoshitaka Taniyasu
Dr. Kenji Ueda
Dr. Chiun-Lung TsaiDr. Michal Kubovic
Low-Dimensional Nanomaterials Research Group:
Dr. Yoshihiro Kobayashi (Group Leader)
Dr. Fumihiko Maeda
Dr. Hiroki Hibino
Akio Tokura
Dr. Ilya Sychugov
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
Touichiro Goto
Dr. Jonas Rundqvist*－－Dr. Hisashi Sato
Dr. Shin-ichi Karimoto*
Dr. Atsushi Nishikawa

Dr. Satoru Suzuki

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

Executive Manager,

Dr. Hiroshi Yamaguchi

Assistant Manager,

Dr. Yukinori Ono
Takeshi Karasawa

Nanodevices Research Group:
Dr. Akira Fujiwara (Group Leader)Dr. Hiroyuki Kageshima
Dr. Katsuhiko Nishiguchi
Nanostructure Technology Research Group:
Dr. Hiroshi Yamaguchi (Group Leader)
Dr. Masao Nagase
Dr. Kenji Yamazaki
Junzo Hayashi
Dr. Hajime Okamoto
Dr. Imran Mahboob
Dr. Vijay Singh
Quantum Solid State Physics Research Group:
Dr. Toshimasa Fujisawa (Group Leader)
Dr. Kiyoshi Kanisawa
Dr. Satoshi Sasaki
Dr. Toshiaki Hayashi
Dr. Takeshi Ohta
Dr. Kei Takashina
Dr. Paula Giudici*
Dr. Kasper Grove-Rasmussen
Superconducting Quantum Physics Research Group:
Dr. Kouichi Semba (Group Leader)Dr. Hayato Nakano
Dr. Tetsuya Mukai
Hirotaka Tanaka
Dr. Shiro Saito
Dr. Ying-Dan Wang
Dr. Yoshiharu Yamada
Spintronics Research Group:
Dr. Tatsushi Akazaki (Group Leader)
Dr. Yuichi Harada
Dr. Hiroyuki Tamura
Dr. Masumi Yamaguchi
Toshiyuki Kobayashi*－－Dr.Mohammed Khalafalla

Toru Yamaguchi
Dr. Koji Onomitsu

Dr. Kyoichi Suzuki
Dr. Norio Kumada
Dr. Gerardo Gamez

Dr. Shin-ichi Karimoto
Dr. Kousuke Kakuyanagi

Dr. Yoshiaki Sekine
Dr. Hideomi HashibaOptical Science Laboratory

Executive Manager,

Dr. Yasuhiro Tokura

Assistant Manager,

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. Jens Tobiska*
Quantum Optical Physics Research Group:
Dr. Hidetoshi Nakano (Group Leader)
Dr. Tetsuomi Sogawa*Dr. Tadashi Nishikawa
Dr. Kouta Tateno
Dr. Takehiko Tawara
Dr. Atsushi Ishizawa
Dr. Haruki Sanada
Photonic Nano-Structure Research Group:
Dr. Masaya Notomi (Group Leader)
Dr. Satoki Kawanishi
Dr. Eiichi Kuramochi
Dr. Akihiko Shinya
Dr. Takasumi Tanabe
Dr. Young-Geun Roh*－－

Masami Kumagai
Dr. Hiroki Takesue
Dr. Kiyoshi Tamaki

Hidehiko Kamada
Dr. Katsuya Oguri
Dr. Guoquiang Zhang

Dr. Hideaki Taniyama
Dr. Hisashi Sumikura

Distinguished Technical Members
Toshimasa Fujisawa was born in Tokyo on May 23, 1963. He received the
B.E., M.S. and Ph.D. degrees in electrical engineering from Tokyo Instituteof Technology in 1986, 1988 and 1991, respectively. He joined NTT Basic
Research Laboratories in 1991. He was a guest scientist in Delft University ofTechnology, Delft, the Netherlands during 1997-1998. Since 2003, he is also aguest associate professor in Tokyo Institute of Technology. Since 1991 he has
engaged in the study of semiconductor fine structures fabricated by focusedion-beam technique and electron-beam lithography technique, transportcharacteristics of semiconductor quantum dot. His current interests are singleelectron dynamics in quantum dots and their application to quantum information
technologies. He received Sir Martin Wood Prize in 2003 and JSPS (Japan
Society for the Promotion of Science) Award in 2005. He is a member of theJapan Society of Applied Physics, and the Physical Society of Japan.
Masaya Notomi was born in Kumamoto, Japan, on 16 February 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 using
various types of photonic crystals. During 1996-1997, he worked for Linköping
University in Sweden as a visiting researcher. He is also a guest associate
professor in Tokyo Institute of Technology (2003- ). He received 2006/2007
IEEE/LEOS Distinguished Lecturer Award. He is a member of the Japan Societyof Applied Physics, the American Physical Society, and IEEE/LEOS.
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 the LSI Laboratories,
Nippon Telegraph and Telephone (NTT) Corporation, Kanagawa, Japan. He
moved to the Basic Research Laboratories (BRL) 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 Awardin 1999, and Japanese Journal of Applied Physics (JJAP) Paper Awards in 2003
and 2006. He was also awarded the Young Scientist Award from the Ministerof MEXT (Ministry of Education, Culture, Sports, Science, and Technology) in2006. He is a member of the Japan Society of Applied Physics and the IEEE.

－－Advisory Board (2007 Fiscal Year)
Name

Title
Affiliation

Gerhard Abstreiter

Professor
Walter Schottky InstituteGermany

Boris L. Altshuler

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

Serge Haroche

Professor
Département de Physique
De l＇ Ecole Normale Supérieure, FranceMats Jonson

Professor
Department of Physics,
Göteborg University, Sweden

Anthony J. Leggett

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

Johan E. Mooij

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

John F. Ryan

Professor
Clarendon Laboratory
University of Oxford, U.K.

Klaus von Klitzing

Professor
Max-Planck-Institut für Festkörperforschung
Germany－－Invited / Guest Scientists (2007 Fiscal Year)
Name

Title
Affiliation

Dr. Go Yusa

Japan Science and Technology Agency (JST), Japan
October 05 ~Assoc. Prof. Shin-ichi Warisawa The University of Tokyo, JapanMay 07 – March 08
Dr. Kasper Grove-Rasmussen

University of Copenhagen, Denmark
July 07

Assoc. Prof. Taka-aki Koga

Hokkaido University, Japan
November 06 ~Dr. Akira Yamazaki

Meiji University, Japan
November 06 – March 08

Dr. Alexandre Kemp

Japan Science and Technology Agency (JST), Japan
December 06 – March 08

Dr. Hongwu LiuJapan Science and Technology Agency (JST), Japan
February 07 – March 08

Dr. Chandra Ramanujan

University of Oxford, U.K.
April 07

Dr. Takashi Uchida

Japan Science and Technology Agency (JST), Japan
April 07 – March 08

Dr. Qiang Zhang

Stanford University, U.S.A.
June 07 – July 07

Prof. Shmuel Gurvitz

Weizmann Institute, Israel
July 07 – September 07

Assoc. Prof. Hongxiang Li

Chinese Academy of Sciences, China
August 07 – October 07

Dr. Na Young Kim

Stanford University, U.S.A.
November 07 – December 07

Dr. Keiko Kato

National Institute for Materials Science (NIMS), Japan
December 07 – June 08－－Overseas Trainees (2007 Fiscal Year)
Name

Affiliation

PeriodSimon Perraud

University of Paris 6 / CNRS, France

Oct. 04 – Sep. 07

Christoph Hufnagel

University of Heidelberg, Germany

June 06 – June 07

Michailas Romanovas

Vilnius Gediminas Technical University, Lithuania

Jan. 07 – Aug. 07

Joana Durao

University of Porto, Portugal

Jan. 07 – Aug. 07

Ari Siitonen

University of Kuopio, FinlandJan. 07 – Aug. 07

Daan Sprunken

University of Twente, The Netherlands

Jan. 07 – Aug. 07

Sylvain Sergent

INSA (Institut National des Sciences Appliquéesde Rennes), France

Jan. 07 – Aug. 07

Florian Domengie

INSA (Institut National des Sciences Appliquéesde Toulouse), France

Feb. 07 – Sep. 07

Guillaume Vincent

INSA (Institut National des Sciences Appliquéesde Toulouse), France

Feb. 07 – Sep. 07

Yosia

Nanyang Technological University, Singapore

Apr. 07 – Apr. 08

Marcus Eichfelder

Institut für Halbleiteroptik und Funktionelle
Grenzflächen, Germany

June 07 – Oct. 07

Stephane SalibESPCI (Ecole Superieure de Physiqueet de Chimie Industrielle), France

July 07 － Aug. 07

Akira Matsudaira

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

May 07 － July 07

Matthieu Delbecq

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

July 07 － Dec. 07

Charlie Koechlin

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

July 07 － Dec. 07

Edita Kirpsaite

Kaunas University of Technology, Lithuania

Jan. 08 － Aug. 08

Miron Sadziak

Warsaw University, Poland

Jan. 08 － Aug. 08

John McGurk

Imperial College London, U.K.

Jan. 08 － Aug. 08

Zhenzhong Wang

Chinese Academy of Sciences, R.O.C.

Jan. 08 － Dec. 08

Thibaut Balois

Ecole Normale Supérieure, France

Feb. 08 － July 08

Thomas Panier

Ecole Normale Supérieure, France

Feb. 08 － July 08

Benjamin Miquel

Ecole Normale Supérieure, France

Feb. 08 － July 08

Justin Pinkney

University of Oxford, U.K.

Feb. 08 － Mar. 08

Paul Köcher

University of Oxford, U.K.

Feb. 08 － Mar. 08－－Domestic Trainees (2007 Fiscal Year)
Name

Affiliation

periodYuichi Igarashi

The University of Tokyo

Apr. 07 – Mar. 08

Daisuke Itoh

Tohoku University

Apr. 07 – Mar. 08

Shoko Utsunomiya

The University of Tokyo

Apr. 07 – Mar. 08

Taichi Urayama

Keio University

Apr. 07 – Mar. 08

Akira Oiwa

The University of Tokyo, Lecturer

Apr. 07 – Mar. 08

Minoru Oda

The University of Tokyo

Apr. 07 – Mar. 08

Seiichiro Kagei

Tokyo University of Science

Apr. 07 – Mar. 08

Ryo Kajiura

Tokyo Institute of Technology

Apr. 07 – Mar. 08

Keiichi Katoh

The University of Tokyo

Apr. 07 – Mar. 08

Takayuki Kaneko

Meiji University

Apr. 07 – Mar. 08

Takehito Kamada

Tohoku University

Apr. 07 – Mar. 08

Ken-ichiro Kusudo

The University of Tokyo

Apr. 07 – Mar. 08

Takashi Kobayashi

Tohoku University

Apr. 07 – Mar. 08

Jonathan BaughThe University of Tokyo, Visiting researcher

Apr. 07 – Aug. 07

Go ShinkaiTokyo Institute of Technology

Apr. 07 – Mar. 08

Masaya Tazawa

Tokyo University of Science

Apr. 07 – Mar. 08

Koujiro Tamaru

The University of Tokyo

Apr. 07 – Mar. 08

Shun Chikamori

Tokyo Institute of Technology

Apr. 07 – Mar. 08

Shouei Tsuruta

Tokyo University of Science

Apr. 07 – Mar. 08

Eigo Totoki

The University of Tokyo

Apr. 07 – Mar. 08

Keiichiro Nonaka

The University of Tokyo

Apr. 07 – Mar. 08

Takuro Hashimoto

Shibaura Institute of Technology

Apr. 07 – Mar. 08

Ken-ichi Hidachi

The University of Tokyo

Apr. 07 – Mar. 08

Hirotaka Masuyama

Tokyo University of Science

Apr. 07 – Mar. 08

Takao Yamaguchi

Tokai University

Apr. 07 – Mar. 08

Mizuki Miyamoto

Shonan Institute of Technology

Apr. 07 – Mar. 08

Shin Yabuuchi

Keio University

Apr. 07 – Mar. 08

Michihisa Yamamoto

The University of Tokyo, AssistantApr. 07 – Mar. 08

Hiroshi Kamata

Tokyo Institute of Technology

Apr. 07 – Mar. 08

Hiroki Nose

Tokyo Institute of Technology

Apr. 07 – Mar. 08

Yuki Ichigo

Tokyo University of Science

Apr. 07 – Mar. 08

Hiroyuki Suzuki

Tokyo Institute of Technology

Apr. 07 – Mar. 08

－－

Name

Affiliation

PeriodRyota Koibuchi

Tokyo University of Science

May 07 – Mar. 08

Satoru Miyamoto

Keio University

May 07 – Mar. 08

Keita Kimura

The University of Tokyo

May 07 – Mar. 08

Shun Takahashi

The University of Tokyo

May 07 – Mar. 08

Sangyoon Lee

The University of Tokyo

May 07 – Mar. 08

Hiroki Morishita

Keio University

May 07 – Mar. 08

Takayuki Yamamoto

The University of Tokyo

June 07 – Mar. 08

Tomoyuki Mizuno

Keio University

June 07 – Mar. 08

Yasuno Ozaki

The University of Tokyo

June 07 – Jan. 08

Yasutaka Nakai

The University of Tokyo

June 07 – Mar. 08

Yuji Sakai

Tokyo University of Science

June 07 – Mar. 08

Kenji Yamaya

Tokyo University of Science

June 07 – Mar. 08

Yasuaki Miyazaki

Keio University

June 07 – Mar. 08

Naoyuki Masumoto

The University of Tokyo

July 07 – Mar. 08

Yuma Okazaki

Tohoku University

Aug. 07 – Mar. 08

Lei Zhu

The University of Tokyo

Aug. 07 – Aug. 07

Ichiro Yamato

The University of Tokyo

Aug. 07 – Aug. 07

Yoshitaka Niida

Tohoku University

Aug. 07 – Mar. 08

Yuki Iwai

Osaka University

Sep. 07 – Mar. 08

Norihito Hibino

Keio University

Oct. 07 – Mar. 08

Kazuya Saginawa

Nagaoka University of Technology

Oct. 07 – Feb. 08

Kuniaki Yamada

Keio University

Nov. 07 – Mar. 08

Yoshiaki Ogasawara

Kyoto University

Nov. 07 – Dec. 07

Takenori Matsumoto

Tokai University

Dec. 07 – Feb. 08

Eiji Ueno

Tokai University

Dec. 07 – Feb. 08

Junichi Sato

Tokai University

Dec. 07 – Feb. 08

Monica Craciun

The University of Tokyo, Postdoc

Dec. 07 – Mar. 08

Saverio Russo

The University of Tokyo, Postdoc

Dec. 07 – Mar. 08

Hiroshi Takahashi

Tokyo Institute of Technology

Dec. 07 – Mar. 08

Kouhei Hatafuku

Toyohashi University of Technology

Jan. 07 – Feb. 08

Atsushi Yamamoto

Osaka University

Feb. 08 – Mar. 08

Akira Wada

Tohoku University

Feb. 08 – Mar. 08－ 10 －

Ⅰ．Research Topics

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Overview of Research in Laboratories
Material Science Laboratory
Keiichi Torimitsu
The Materials Science Laboratory aims at producing new functional materials anddesigning of advanced device based on novel materials and biological function. Controllingthe configuration and coupling of atoms and molecules is our approach to accomplish thesegoals. Bio-nano research and diamond-device research are set as the principle research in ourlaboratory.
We have three research groups covering from semiconductor devices, such as GaN, toorganic materials, such as receptor proteins. The characteristic feature of our laboratory is
the effective sharing of the unique materials and measurement techniques of each group. This
enables fusion of research fields and techniques, which leads to innovative material research
for the IT society.
We set up European laboratory in U.K. for bio-nano research, our principal research,in October 2004 and strengthen our research activities. We promote collaborations withinternational organizations to develop a firm basis of basic science.
Physical Science Laboratory
Hiroshi Yamaguchi
We are studying semiconductor and superconductor-based solid-state devices, which will
have a revolutionary impact on communication and information technologies in the 21st
century. In particular, we promote research of nanoscale devices fabricated using high-quality
crystal growth and fine lithographic techniques.
The five groups in our laboratory are working in the following areas: precise and dynamical
control of single electrons, nanodevices operating with ultra low power consumption, novel
nanomechanical systems utilizing mechanical degrees of freedom in solid-state architechtures,
coherent quantum control of semiconductor and superconductor systems, carrier interactions
in semiconductor hetero- and nanostructures, atom chips, spintronics manipulating bothelectron and nuclear spins. We also promote the studies of cutting-edge nanolithography
techniques, high-quality crystal growth, and theoretical studies including first-principle
calculations.
Optical Science Laboratory
Yasuhiro Tokura
This laboratory aims for the development of core-technologies that will innovate on opticalcommunications and optical signal processing, and seeks fundamental scientific progresses.
The groups in our laboratory are working for the quantum state control by very weak light,
the search for intriguing phenomena using very intensive and short pulse light, and verysmall optical integrated circuits using two-dimensional photonic crystals, based on the opticalproperties of semiconductor nanostructures like a quantum dot.
In this year, we realized improvements of quantum cryptography using entangled photon
pairs, optical properties of high quality semiconductor nanowires, and a coupled resonatorwaveguide formed by ultrahigh-Q photonic crystal nano-resonators.

－ 11 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Polarized Emission of AlN Deep-UV LED
by a Negative Crystal-field Splitting Energy
Yoshitaka Taniyasu and Makoto Kasu
Materials Science Laboratory
Aluminum nitride (AlN) is a direct-bandgap semiconductor with a bandgap energy of 6eV, the largest among semiconductors, and is therefore promising for light-emitting devices
with the shortest wavelength. We have succeeded in p-type and n-type doping of AlN andhave fabricated an AlN light-emitting diode (LED). In this study, to gain insight into the lightemission mechanism, we characterized the radiation properties.
An AlN LED was grown on SiC (0001) substrate by metalorganic vapor phase epitaxy.
Figure 1 shows the radiation properties of the AlN LED. The radiation angle θ is definedas the angle from the surface normal (c-axis direction) to the detection direction. As theradiation angle increases, the intensity of the near-band-edge emission at 210 nm increases.
To clarify the reason, we analyzed the relationship between the emission intensity and theradiation angle as shown in Fig. 2. Solid lines are calculated results for different polarization
ratios P. P = 1 corresponds to polarized light parallel to the c-axis (E||c), P = －1 corresponds
to polarized light perpendicular to the c-axis (E⊥c), and P = 0 corresponds to unpolarized
light. The experimental values follow the calculated one for P = 0.995. This indicates thatthe emission strongly polarizes for E||c. As a result, the emission intensity has the maximum
perpendicular to the c-axis and the minimum parallel to it. Therefore, as the radiation angle
increases from the c-axis, the emission intensity increases as shown in Fig. 1 [1].
The origin of the strong polarization can be explained by the band structure. Because AlN
has strong ionicity, the lattice is strongly distorted. As a result, the crystal-field splittingenergy has a negative value and the top valence band therefore becomes the Г7V band. A
transition between the top valence band Г7V and conduction band Г7C is allowed for E||c but
is almost completely prohibited for E⊥c. Therefore, the near-band-edge emission strongly
polarizes for E||c. Using a crystal-field splitting energy ∆CRY = –230 meV and a spin orbital
splitting energy ∆SO = 20 meV, P was calculated to be 0.997, which is in good agreement withthe experimentally obtained value. Thus, we found that the strong polarization results from thenegative crystal-field splitting energy.
This work was partly supported by Grant-in-Aid for Young Scientists (A), 19686003, from
the Ministry of Education, Culture, Sports, Science and Technology, Japan.
[1] Y. Taniyasu, M. Kasu, and T. Makimoto, Appl. Phys. Lett. 90 (2007) 261911.

Fig. 1. Radiation properties of AlN LED.

Fig. 2. Light emission intensity as a function ofradiation angle.
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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Doping of Diamond by Combining Ion-implantation and High-pressureand High-temperature Annealing
Kenji Ueda and Makoto Kasu
Materials Science Laboratory
Ion implantation is a widely used doping technique for semiconductors such as Si and
GaAs. However, ion implantation severely damages the crystal. In Si and GaAs, the damage
can be easily recovered by thermal annealing in a vacuum or in an inert gas. However, it isextremely difficult to recover the damage in diamond by thermal annealing. One possible
reason is that the annealing condition is not located in diamond’s stable region but rather ingraphite’s stable region. Therefore, we propose high-pressure and high-temperature (HPHT)
annealing as a new activation method for ion-implanted dopants in diamond. The concept
is to recover from implantation-induced damage by annealing under high pressure, that is,under diamond’s stable condition (Fig. 1) [1, 2]. Here, we show that HPHT annealing ishighly effective for damage recovery in ion-implanted diamond.
Homoepitaxial diamond films were grown on Ib-type diamond (100) single crystals by
microwave plasma CVD. Boron (B) ions were implanted at an acceleration voltage of 60 keVwith a dose of 1×1015 cm-2. The HPHT annealing of the B-implanted films was performed
using a cubic-anvil-type high-pressure apparatus. The pressure was fixed at ~7 GPa andthe annealing temperature was changed from 1200 to 1400 oC. Thermal annealing of theB-implanted films was also performed in a vacuum for comparison.
Figure 2 compares the annealing temperature (Ta) dependence of doping efficiency of theB-implanted films after HPHT annealing and conventional thermal annealing evaluatedfrom Hall measurements. The doping efficiency of HPHT-annealed films increased
exponentially as Ta increased and reached 7.1 % at 1400 oC. In contrast, the doping efficiency
for conventional thermal annealing increased linearly and reached 0.73 % at 1400 oC. At thesame Ta of 1400 oC, the doping efficiency for HPHT-annealed films is 10 times higher thanthat for conventional thermal annealing. These results indicate HPHT annealing is much more
effective for activation of ion-implanted dopants than conventional thermal annealing.
This work was partly supported by the SCOPE project of the Ministry of Internal Affairs
and Communications, Japan.
[1] K. Ueda, M. Kasu, A. Tallaire, and T. Makimoto, Diamond Relat. Mater. 15 (2006) 1789.
[2] K. Ueda, M. Kasu, and T. Makimoto, Appl. Phys. Lett. 90 (2007) 122102.

Fig. 1. Phase diagram of carbon, which shows
conditions for HPHT annealing andconventional thermal annealing.

Fig. 2. Doping efficiency of the B-implanted films
after HPHT annealing and conventional
thermal annealing.
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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Quasi Two-dimensional Hole Channel in Diamond FETs
Makoto Kasu and Kenji Ueda
Materials Science Laboratory
Diamond is expected to exhibit the best performance as an RF power transistor because
it has the highest breakdown field strength and thermal conductivity and relatively highmobility and saturation velocity. Recently, we have reported high RF performance in diamond
FETs using H surface-termination as p-type doping: cut-off frequencies of the current gain,fT (transition frequency), of 45 GHz and of the power gain, fMAX (maximum frequency ofoscillation), of 120 GHz, and RF output power density of 2.1 W/mm at 1 GHz in class-A
operation. These values are the highest among diamond at present and high enough for power
amplifiers in wireless base stations. However, the mechanism of H surface-termination indiamond FETs is still controversial, and the band diagram of a diamond FET has not beenclarified yet.
We have extracted the gate voltage dependence VGS of RF transconductance gm and gatesource capacitance CGS from S-parameter measurements of an FET with gate length (LG) of
0.1 µm and gate width (WG) of 50 µm, as shown in Fig. 1 [1]. The most significant findingis that CGS shows a plateau for -0.5 V < VGS < -2.0 V. In the FET fabrication process, Al gate
metal was deposited directly on H-terminated diamond surface. However, this characteristic
unambiguously indicates that an energy barrier forms between the gate metal and twodimensional hole channel and that the diamond FET functions as a MISFET. We haveproposed the energy band diagram of the diamond FET, as shown in Fig. 2.
As shown in Fig. 1, for VGS > -0.5 V, as positive VGS increases, gm decreases and CGS
decreases. This means that as positive VGS increases, the depletion layer below the energy
barrier extends to the substrate side (Fig. 2). For VGS < -2.0 V, as negative VGS increases, gm
decreases and at the same time CGS increases steeply. This characteristic indicates that theenergy barrier becomes a triangular potential barrier and then holes penetrate the energy
barrier, and consequently CGS increases. In Fig. 1, the CGS value at the plateau is 0.037 pF
and its capacitance normalized by the gate area is estimated to be 0.74 µF/cm2. Assuming thedielectric constant of diamond and Al2O3, the interfacial-layer thickness is estimated to be
7~10 nm. By cross-sectional TEM observation, we have confirmed a 7~10 nm-thick interfacial
layer between Al gate metal and H-terminated diamond [2].
This work was partly supported by the SCOPE project, "Diamond RF Power Amplifiers",
from the Ministry of Internal Affairs and Communications, Japan.
[1] M. Kasu, et al., Appl. Phys. Lett. 90 (2007) 043509.
[2] M. Kasu, et al., Diamond and Relat. Mater. 17 (2008) in press.

Fig. 1. Gate voltage dependence of gate
capacitance and transconductance.

Fig. 2. Proposed band diagram of the diamond FET.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

High-temperature Characteristics of npn-type GaN/InGaN
Double Heterojunction Bipolar Transistors
Atsushi Nishikawa, Kazuhide Kumakura, and Toshiki Makimoto
Materials Science Laboratory
GaN-based electronic devices are expected to be advantageous for high-power and hightemperature operation compared with conventional GaAs- or Si-based devices because of
the wide band gap of GaN. In the previous studies, we have succeeded in obtaining the highcurrent gain of over 2000 [1] and high-power characteristics of 270 kW/cm2 [2] for the npntype GaN/InGaN double heterojunction bipolar transistors (DHBTs). Our next target is todemonstrate the high-temperature operation of these DHBTs. In this study, we investigated thetemperature dependence of the common-emitter current-voltage (I-V) characteristics of npntype GaN/InGaN DHBTs [3].
GaN/InGaN DHBT structures were grown on SiC substrates using low-pressure metalorganic vapor phase epitaxy. The sample structure consisted of a 40-nm-thick n-GaN emitter,a 100-nm-thick p-InGaN base, a 30-nm-thick graded InGaN layer, a 500-nm-thick n-GaN
collector, a 1-µm-thick n-GaN sub-collector, and an AlN buffer layer. The In composition of
p-InGaN base was 7%. The emitter size was 50×30 µm2.
Figure 1 shows the common-emitter I-V characteristics of the GaN/InGaN DHBT measured
at 300 oC. The base current is 50 µA/step. Even though the current gain (β =∆IC/∆IB) decreases
with increasing temperature, the maximum current gain at 300 oC is still as high as 308. The
maximum current density at 300 oC is calculated to be as high as 5.5 kA/cm2. As shown in
Fig. 2, the temperature dependence of the maximum current gain of the GaN/InGaN DHBT
follows an exponential dependence with activation energy of 0.13 eV. Since the activationenergy of the reduction of the current gain is larger than the expected value assuming theincrease in the hole back-injection current from the base into the emitter (0.06 eV), an increasein the carrier concentration of the p-In0.07Ga0.93N base, which activation energy is 0.12 eV, isconsidered to be attributed to the reduction of the current gain.
[1] T. Makimoto, K. Kumakura, and N. Kobayashi, Appl. Phys. Lett. 83 (2003) 1035.
[2] T. Makimoto, Y. Yamauchi, and K. Kumakura, Appl. Phys. Lett. 83 (2004) 1964.
[3] A. Nishikawa, K. Kumakura, and T. Makimoto, Appl. Phys. Lett. 91 (2007) 133514.

Fig. 1. Common-emitter I-V characteristics measured at
300 oC.

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Fig. 2. Temperature dependence of the maximum
current gain of GaN/InGaN DHBT.

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Raman Spectroscopy of Carbon Nanotubes at CVD Growth Temperatureand the Assignments of their Chiral Indices
Takashi Uchida and Yoshihiro Kobayashi
Materials Science Laboratory
Whether we will be successful in applying carbon nanotubes (CNTs) to electronic devices
highly depends on our ability to synthesize CNTs with a desired chirality, because theelectronic structures of CNTs strongly depends on their chirality. To control the growth of
CNTs, it is important to clarify their growth mechanism. We have investigated CVD growth
processes of CNTs by in-situ Raman observation. Raman spectra are strongly temperaturedependent because they reflect the vibrational properties of observed materials. In order todiscuss the details of the growth process observed by in-situ Raman spectroscopy, temperatureeffects in the Raman spectra of CNTs should be elucidated.
Figure 1 shows an atomic force microscope (AFM) image of a CNT-grown sample.
Individual CNTs lie on the substrate. Figure 2 shows (a) the experimental Kataura plot and(b) RBM signals observed at 720 oC (during CVD) and at room temperature (after CVD). The
chiral indices of the RBM signals observed at room temperature can be assigned as shownin Fig. 2(b) on the basis of the experimental Kataura plot. The RBM peak frequencies tend
to simply decrease with increasing temperature. This is a commonly observed phenomenon
originating from the softening of the force constant with increasing temperature. In addition,
the relative intensities of each RBM peak change with temperature. This temperaturedependence is explained by the change in the resonance condition of each RBM peak. The
optical transition energy of nanotubes decreases with increasing temperature, resulting ina shift of each point in the Kataura plot to the lower left as shown in Fig. 2(a). From thisanalysis, the chiral indices of the RBM peaks observed at CVD growth temperature of 720 oC
are successfully assigned as shown in Fig. 2(b) [1]. These results encourage us to further
investigation of the chirality-dependent growth behavior of CNTs observed with in-situ
Raman spectroscopy and, in future, will lead us to clarifying growth mechanism and thereby
achieve the chirality-controlled growth of CNTs.
[1] T. Uchida, et al., Appl. Surf. Sci., in press.

Fig. 1. AFM image of the CNT sample.

Fig. 2. (a) Experimental Kataura plot: RBM frequencies ωRBM
vs the optical transition energies Eii. (b) RBM signals
observed during CVD at 720 oC and after CVD at 25 oC.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Low-Energy Irradiation Damage in Carbon Nanotubes
Satoru Suzuki and Yoshihiro Kobayashi
Materials Science Laboratory
Single-walled carbon nanotubes (SWNTs) are promising material as a constituent of futurenano-electronics because of their nanometer-scale diameter and excellent electric, chemical,
and mechanical properties. We have reported that SWNTs are damaged by low-energy
electron and photon irradiation and that their electric properties are largely altered frommetallic to semiconducting, or even to insulating, by moderate damage [1]. Recently, we havefound that defects induced by low-energy irradiation have some unique characteristics.
In the case of knock-on damage caused by high-energy particle irradiation, the SWNTs can
not be fully recovered by annealing because ejected atoms are lost. On the other hand, oneof important properties of low-energy irradiation damage is that the SWNTs can recover [2].
Raman spectra (radial breathing mode [RBM] region) of pristine, irradiated, and annealed
SWNTs are shown in Fig. 1. The RBM frequency depends on the diameter, and thinnernanotubes have larger frequencies. All of the RBM peaks disappeared except for that of the
thickest SWNTs, but they reappeared after annealing. This indicates that the number of carbon
atoms remains constant with defect formation. Our results also reveal that the damage andrecovery strongly depends on the diameter: that is, thinner SWNTs are more easily damaged
and hardly recover (see Fig. 1). Moreover, the damaged SWNTs were found to recover evenat room temperature or below. The activation energy of the defect healing was estimatedto be about 1 eV (depending on the diameter) by observing recovery process by means ofelectric conductivity [3]. Whereas, the threshold energy of defect formation was determined
to be about 6 eV from the results of monochromated vacuum ultra-violet light irradiation
experiments. The energetics of the defect formation and healing is summarized in Fig. 2. We
will try to determine the detailed atomic structure of the defects and to control the device
performance by defect engineering.
[1] A. Vijayaraghavan, et al., Nano Lett. 5 (2005) 1575.
[2] S. Suzuki and Y. Kobayashi, Chem. Phys. Lett. 430 (2006) 370.
[3] S. Suzuki and Y. Kobayashi, J. Phys. Chem. C 111 (2007) 4524.

Fig. 1. Raman spectra of pristine, irradiated, andFig. 2. Schematic energy diagram of the defectannealed SWNTs.

formation and healing.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Combined Scanning Tunneling and Aperture Near-field Microscopy:
Tip Modeling
Ilya Sychugov and Hiroo Omi
Materials Science Laboratory
Optical and electrical properties of nanostructures can be addressed using radiation orelectrical current as a probe. In general, a near-field type of electromagnetic interaction isnecessary for an optical probe to enter nanoscale regime in the spatial resolution domain
by overcoming the optical diffraction limit (~ 1 µm). A typical scanning near-field optical
microscope (aperture-SNOM) provides such an opportunity both for the excitation andcollection of light for spectroscopy applications. However, this instrument utilizes a dielectric
fiber tip as an aperture, which makes it unsuitable for electrical measurements. On the other
hand, a scanning tunneling microscope (STM), capable of atomic-resolution measurements
by electrical current, can also cause luminescence of materials. Here, in order to realize bothelectrical and optical probing at nanoscale, we combine these two kinds of instruments into asingle unit (Fig. 1).
In order to evaluate tip geometry influence on its performance for various operation regimes
finite element method (FEM) simulations were carried out. It was found that tip transmittancefor SNOM excitation mode depends strongly on tip geometry away from the edge. A variationof nearly two orders of magnitude is a result of constructive/destructive interference of theexcitation light (Fig. 2). Furthermore, the role of the opening in protective metal film in lightcollection efficiency was simulated for the STM-luminescence mode. Based on the present
simulations one can choose a suitable tip configuration from the interplay between the
instrument collection efficiency and its spatial resolution [1].
We aim at concurrent optical and electrical characterization of nanostructures (e.g. quantum
wells, dots, etc.) with high spatial resolution. In addition, this approach may find its niche
where electrical modification with subsequent in situ optical probing is desirable.
[1] I. Sychugov, H. Omi, T. Murashita, and Y. Kobayashi, Appl. Surf. Sci., in press.

Fig. 1. Schematic representation of the setup.

Fig. 2. Calculated tip transmittance.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Evaluation of Number of Graphene Layers Grown on SiC
Hiroki Hibino1 and Hiroyuki Kageshima2
1
Materials Science Laboratory, 2Physical Science Laboratory
Recently, graphene has attracted much attention as a material for future electronics [1]. So
far, electronic device properties have been investigated for graphene layers produced in two
ways: graphene flakes exfoliated from bulk graphite [1] and epitaxial graphene grown on SiC
substrates by annealing [2]. Epitaxial graphene grows on a wafer scale and is promising for
device integration. To make epitaxial graphene applicable, however, we need to grow wide
epitaxial graphene with the intended number of layers. As a base of this growth control, we
have established a way of determining the number of graphene layers microscopically [3].
We evaluated the number-of-layers distribution in epitaxial graphene grown on SiC by lowenergy electron microscopy (LEEM) using quantized oscillations of electron reflectivity.
Figure 1 shows LEEM images of epitaxial graphene on 4H-SiC(0001) at various electron
beam energies, which corresponds to the mappings of the secular electron reflectivity inthe normal incidence. These images show that the electron reflectivities in different regions
change with the energy in different manners. Figure 2 shows the energy dependence of theelectron reflectivities in areas A-H. The reflectivity oscillates with the electron beam energy.
Bulk graphite has continuous electronic bands normal to the graphene sheet, but thesebands split into discrete energy levels in graphene layers due to their finite thickness. Whenthe energy of incident electrons coincides with one of the discrete energy levels, the electrons
resonantly transmit through the layers, resulting in dips in the reflectivity. Therefore, thenumber of graphene layers can be counted directly as the number of dips in the reflectivity.
The validity of this scenario was confirmed by the result that the quantized conduction bandstates calculated using tight-binding and first-principles methods well reproduce the dip
positions in the reflectivity. In-situ microscopic determination of the number of graphene
layers using LEEM would greatly contribute to the growth control of epitaxial graphene.
This work was partly supported by KAKENHI (19310085) from the Ministry of Education,
Culture, Sports, Science and Technology of Japan.
[1] K. S. Novoselov and A. K. Geim, Nature Materials 6 (2007) 184.
[2] C. Berger, et al., Science 312 (2006) 1191.
[3] H. Hibino, et al., Phys. Rev. B 77 (2008) 075413; H. Hibino, et al., e-J Surf. Sci. Nanotechnol.
6 (2008) 107.

Fig. 1. LEEM images of graphene layers grown on
4H-SiC(0001) at the electron beam energiesof (a) 3.0 and (b) 4.5 eV.
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Fig. 2. Electron reflectivities in areas A-H
in Fig. 1 versus the electron beamenergy.

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Elastic Modulus of Suspended Membrane Protein
Measured by Atomic Force Microscopy
Koji Sumitomo1, Ari M. Siitonen1, Chandra S. Ramanujan2, and Youichi Shinozaki1
1
Materials Science Laboratory, 2University of Oxford
Using the atomic force microscopy (AFM), we have studied the mechanics of purple
membrane (PM) suspended over nanostructures. By doing this we could evaluate theproperties of the biological membrane free from interaction with the substrate. Biologicalmembranes containing lipids and proteins are important components of bio-nanostructureswith many potential applications, e.g. single-molecule biosensors, and reliable measurementsof their mechanical properties are essential.
PMs of Halobacterium salinarium strain S9 were adsorbed on a Si substrate with nanotrenches fabricated using a photolithographic technique. After locating the suspended PM
using the AFM in imaging mode, force-displacement measurements were performed. Figure
shows AFM images of PM suspended over nano-trenches (a) before and (b) after indentationand (c) the force-displacement curve measured during indentation. The indentation mark leftby the AFM tip can be clearly seen in (b) as indicated by the arrow. As the force is increased
the suspended membrane was stretched and finally punctured. The force-displacement curve
during membrane stretching reflects its mechanical property directly. To evaluate the surface
tension, a simple theoretical model was made, and theoretical force curves were obtained tosimulate the experimental force curves. From the best-fit curve, the elastic modulus of PM
was estimated to be 8±1 MPa [1].
We have demonstrated that AFM measurements provide a very good approach to evaluate
the mechanics of biological membranes in their native conditions. Proteins in the suspended
potion of the membrane are not affected by the substrate and are more likely to function
as they would in vivo. The next stage of this project is to measure changes in properties in
response to an external stimulus such as mechanical stimulus, light irradiation, and chemicalbinding.
This research was supported in part by the Strategic International Cooperative Program,
Japan Science and Technology Agency (JST).
[1] Ari M. Siitonen, et al., Appl. Surf. Sci., in press.

Fig. AFM images of the PM suspended over nano-trenches: (a) before and (b) after indentation;(c) the force-displacement curve measured for suspended PM.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Quantitative Analyses of FRET Efficiency of Dye Molecules Confinedwithin 2-Dimensional Space
Kazuaki Furukawa
Materials Science Laboratory
Lipid bilayer, the fundamental component of cell membranes, can form at the solid-liquidinterface by self-organization. We have developed a new type of microchannel device using
this self-spreading characteristic of the lipid bilayer [1]. The validity of the device has been
confirmed by observing fluorescence resonance energy transfer (FRET). This report is of thesuccessful application of the device to the quantitative determination of FRET efficiency [2].
L-α-PC (extracted from egg yolk) containing 1 mol % of NBD- (a dye for donor) or Texas
Red (TR, a dye for acceptor)-conjugated lipid is prepared. They are self-spread from theeach side of the straight line pattern with a 10 µm width. Figure 1A shows the confocal laser
scanning microscope images from the moment the lipid bilayers collide (set as t = 0) to 600 s.
The observation conditions are NBD: 488 nm excitation and 505-525 nm emission, TR: 543
nm excitation and > 610 nm emission. Figure 1B plots the fluorescence intensities averaged
over the widths against the position x at each time. The collision position is set as x = 0.
After the collision, two self-spreading bilayers are unified and form a single bilayer thatprovides the 2-dimensional field for the NBD- and TR-conjugated lipids to diffuse. The
average fluorescence intensities can be expressed by the solution of 1-dimensional diffusion
equation [2]. As the initial concentration of dye-conjugated lipids are both 1 mol % and theirdiffusion constants should be almost equal, the sum of the concentrations of two dye lipids
are constant, 1 mol %, at any x. By analyzing the data in Fig. 1B using these reasonableassumptions, the quantitative determination of FRET efficiency depending on the donor-toacceptor ratio becomes possible as shown in Fig. 2. A large number of data follow a uniquecurve, which supports the reliability of our experiments.
[1] K. Furukawa, et al., Lab Chip 6 (2006) 1001.
[2] K. Furukawa, et al., Langmuir 24 (2008) 921.

Fig. 2. (top) Donor-to-acceptor ratio dependent FRET
efficiency.
Fig. 1. (left)
A. Confocal laser scanning microscope images of theself-spreading L-α-PC containing 1 mol % NBD
and Texas Red before and after the collision.
B. Fluorescence intensities averaged over the 10 µm
width.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

AFM Observation of a Single Receptor Reconstituted into Lipid Bilayer
Nahoko Kasai1 and Chandra S. Ramanujan2
1
Materials Science Laboratory, 2University of Oxford
Ionotropic receptors (ligand-gated ion channel receptors) are important membrane proteinsfor signaling in the neuronal networks of the central nervous system. They are regulated by aligand which binds to the extracellular ligand binding domains. This binding gives an allostericchange in the structure and opens the ion channel incorporated in the transmembrane domain
to allow cations flow into the cell (Fig. 1). Atomic force microscopy (AFM) enables the nanoscale observation of proteins in a liquid environment, offering a unique opportunity to observefunctional biological molecule such as single proteins under physiological conditions.
In this study, we have succeeded in observing the structure of single purified and ionotropic
receptor proteins in the solution using the AFM. Receptor proteins were purified from overexpressed insect cells, and then reconstituted into an artificial lipid bilayer by dialysis because
the receptors would function as in vivo when reconstituted into the lipid bilayer. We thenimaged the reconstituted receptor proteins on a substrate in a buffer solution using AFM.
Before reconstitution, receptors were observed at the edge of small lipid patch on mica (Fig.2(A)), while after the reconstitution, receptor proteins settled in the large lipid domain on
mica (Fig. 2(B)) which provides for the structural observation of the single receptor. Thenby zooming in on the single receptor protein, we could observe that it consisted of four
protrusions suggesting the four subunits of the receptor protein.
This study demonstrates that AFM can observe functioning single ionotropic receptors,
which suggests the possibility of determining a real-time conformational change of afunctioning membrane protein using AFM [1].
This research was supported in part by Bio-nanotechnology IRC in U.K. and by the Strategic
International Cooperative Program, Japan Science and Technology Agency (JST).
[1] N. Kasai, et al., Neurosci. Res. 58 (2007) S193.

Fig. 1. Illustration of a receptor.

Fig. 2. AFM images of receptors before (A) and after (B)reconstituted into artificial lipid bilayer (2×2 µm).
Black area: mica substrate, gray: lipid bilayer, white
dots: receptor proteins.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Nanoampere Charge Pump by Single-electron Ratchet
Using Silicon Nanowire MOSFET
Akira Fujiwara, Katsuhiko Nishiguchi, and Yukinori Ono
Physical Science Laboratory
Clocked transfer of single electrons is attracting a great deal of interest in its application
to current standards in metrology and integrated single-electron (SE) circuits. While theconventional metal-based SE pumps and turnstiles employ fixed tunnel junctions of metaloxide, the use of gate-induced electrostatic tunable barriers in semiconductors has a clear
advantage for higher-frequency operation because the tunnel resistance can be tuned to reduce
the RC time. Although we showed 100-MHz operation of an SE turnstile using Si nanowire
MOSFETs with two barriers modulated by two phase-shifted AC signals [1], higher-frequency
operation is desired because nanoampere current is necessary for the so called metrologicaltriangle experiment.
We recently developed a nanoampere SE pump operated based on a simple scheme using
only one AC signal applied to one gate [2]. We named the proposed device an SE ratchet
since it utilizes the asymmetry potential to capture electrons from the source and eject themto the drain, thereby causing directional SE transport without any source-drain bias. Figures
1(a) and 1(b) show a top-view scanning-electron-microscope (SEM) image of the device anda schematic diagram of the ratchet potential, respectively. We apply AC pulse voltage VG1
at frequency f to the center gate and constant lower voltage VG2 to the drain-side gate. SEs
are captured from the source into the island, and then ejected to the drain. The number oftransferred electrons per cycle is controlled by the upper gate voltage, VUG. As shown in Fig.
1 (c), current plateaus (I = mef, m: integer) are clearly observed at 20 K in a wide range ofthe drain bias (VD), which indicates that the SE transfer is directional regardless of the bias
polarity. The VD range can be much larger than the charging energy of the island (~10 meV)
thanks to the potential control of the island as well as the barrier. Nanoampere charge pumping
is obtained at f =2.3 GHz as shown in Fig. 2. The transfer accuracy is roughly estimated to bein the order of 10-2. It is found that the nonadiabacity of the electron capture affects the shapeof the current steps. This is an important finding for further study towards higher accuracy.
The SE ratchet is a promising device in the application to large-current source for metrologicalstandards. This work was partially supported by KAKENHI (16206038, 19310093).
[1] A. Fujiwara, et al., Appl. Phys. Lett. 84 (2004) 1323.
[2] A. Fujiwara, et al., Appl. Phys. Lett. 92 (2008) 042102.

Fig. 1. (a) SEM image before upper gate formation.
(b) Schematic diagram of SE ratchet.
(c) Contour plots of current for VD and VUG.
－ 23 －

Fig. 2. Pump current at f = 2.3 GHz.

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Infrared Detection with Silicon Nano-transistors
Katsuhiko Nishiguchi, Akira Fujiwara, Yukinori Ono, and Hiroshi Yamaguchi
Physical Science Laboratory
Continuously growing information technology markets have been expanding the application
fields of sensor devices. Among the various kinds of sensors, Si-based image sensors using
charge-coupled devices, photo diodes, and so on, have been used extensively because of
their highly useful features, such as high miniaturization and integration, compared to thosemade of other materials. A basic mechanism of these sensors is that photons with visible
wavelengths, whose energy is larger than the band gap of Si, generate electron-hole pairs.
Whereas an infrared (IR) signal with wavelength longer than the visible one is useful fornumerous applications, such as remote sensing, thermal sensing, and material analysis, a Sibased IR sensor is not good at detecting IR signal, compared to other sensors, because it does
not have enough energy for electron-hole pairs to be generated.
We thus developed a new method of detecting an IR signal using a Si-based device [1]. The
device is composed of two transistors fabricated on a silicon-on-insulator wafer (Fig. 1). The
first transistor (FET1) has a two-layer gate: an upper gate (UG) is used to induce an inversion
layer and a lower gate (LG) forms an energy barrier in the undoped channel of FET1. As aresult, an electron-storage node (MN) electrically isolated from an electron source (ES) is
formed. IR irradiation to FET1 excites electrons in the ES and some of the excited electrons
diffuse into the MN over the energy barrier formed by the LG. The tiny charge originatingfrom electrons in the MN are detected with high charge sensitivity by the other transistor(FET2), whose channel is capacitively coupled to the MN.
Figure 2 shows the change in FET2 current with and without IR radiation. The FET2 current
decreased stepwise with the same height, which means that one electron, which entered the
MN from the ES, was detected as one step of the FET2 current owing to the high charge
sensitivity of FET2. The increase in electron injection into the MN by IR radiation means thatelectrons in the ES were excited and then injected into the MN over the energy barrier under
the LG, which enables a function of IR-signal detection. An IR signal with shorter wavelength
caused more frequent electron injection into the MN. This enables the device to function asa short-wave length pass filter by controlling the energy barrier using the LG. Additionally,
since the number of electrons excited by an IR signal is proportional to electron density in theES, which is controlled by the UG, IR signal sensitivity can be controlled by the UG. Since
the demonstrated Si-based device can detect an IR signal with new functions electricallycontrolled by gates, its applications could be expanded to various fields.
[1] K. Nishiguchi, et al., Appl. Phys. Lett. 90 (2007) 223108.

Fig. 1. IR detector device structure.

Fig. 2. IR-detection characteristics.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Detection of the Mechanical Friction Caused by Electron Systems
Hiroshi Yamaguchi1, Hajime Okamoto1, Sunao Ishihara2, and Yoshiro Hirayama1,31
Physical Science Laboratory, 2University of Tokyo, 3Tohoku University
Novel methods for investigating the electron behavior in low-dimensional semiconductor
structures have been recently developed by integrating these structures into micro/
nanomechanical systems. Using the methods, remarkable strain effects on transport properties[1] and the electron magnetization have been studied. We integrated a high mobility twodimensional electron system (2DES) in micromechanical cantilevers to study the strain effecton magnetotransport properties in the quantum Hall regime. In addition to the remarkablestrain effect at the localized-delocalized electronic state transition, we detected electroninduced internal friction against the cantilever motion with the help of the high mechanicalperformance of the single crystalline cantilever [2].
A 2DES Hall bar with low-temperature mobility of 2.4 ⊗ 106 cm2/Vs was integrated near
the clamping point of a 200-µm long and 60-µm wide cantilever with the thickness of 1.3µm (Fig.1). Using a piezoelectric ceramic to drive the cantilever mechanical motion, theinduced resistance change was measured as a function of magnetic field. The obtained‘magnetopiezoresistance’curve showed a strongly enhanced piezoresistance at the transition
between the localized and delocalized electronic states. We obtained a maximum piezoresistive
gauge factor of as much as 25,000 near the ν=4 transition.
We found that the cantilever mechanical motion is affected by friction exerted by theelectron system, demonstrating its availability for studying the electron energy dissipation.
The quality factor of mechanical resonance strongly depended on the applied magnetic field;
the value was about 106 near the localized states but only 3⊗105 for fully delocalized states,
indicating the suppression of electron energy dissipation by electron localization (Fig. 2).
The strong coupling of the mechanical and electronic degrees of freedom in such integrated
structures provides us with a novel method with which to undertake a detailed study ofelectron behavior in low-dimensional semiconductor structures.
This work was partly supported by Japan Society for the Promotion of Science (JSPS)
KAKENHI (16206003).
[1] H. Yamaguchi, et al., Appl. Phys. Lett. 86 (2005) 052106.
[2] H. Yamaguchi, et al., Jpn. J. Appl. Phys. 46 (2007) L658.

Fig. 1. Fabricated cantilever structure.

Fig. 2. Mechanical resonance.
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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Piezoelectric Effect on Piezoresistance of
InAs/AlGaSb Heterostructure Nanobeam
Kenji Yamazaki1, Samir Etaki2, Herre S. J. van der Zant2, and Hiroshi Yamaguchi1
1
Physical Science Laboratory, 2Delft University of Technology
Nanoelectromechanical systems (NEMS) are attracting much interest as sensors with very
high sensitivities and as new-principle devices. Our group has reported mechanical systems
using InAs/AlGaSb heterostructures and sensitivity enhancement using quantum effects onelectrons in the structures. However, the basic mechanism of piezoresistance (i.e., resistancechange due to mechanical strain) in such systems has not been understood well. In thisstudy, we fabricated InAs/AlGaSb NEMS and measured/analyzed its piezoresistance. The
results strongly imply that the piezoresistance in such systems is significantly affected by thepiezoelectric effect and thus reveale, for the first time, the importance of the piezoelectriceffect in mechanical systems using very thin heterostructures.
Figure 1 shows an atomic force microscopy (AFM) image of a fabricated double-clamped
nanobeam made of an InAs/AlGaSb heterostructure. The thicknesses of InAs and AlGaSb
layers are 15 and 35 nm, respectively. Depending on the depth of wet etching, which makes
the nanobeam suspended, the shape of the beam becomes straight or arched. This is because
the shear stress due to the lattice mismatch curls the wide suspended supports upward, andthe beam linking the two supports thus becomes arched. The piezoresistance measured
using an AFM tip for deflecting the beam had large dependence on the beam shape. That is,
the gauge factor (GF) derived from the resistance change and strain, which usually reflects
material properties, was positive or negative depending on whether the beam was straight orarched, and the magnitude was much larger than for bulk (See Table) [1]. To try to understandthese surprising phenomena, we calculated the piezoresistance, including the piezoelectriceffect (Fig. 2). The results suggest that the piezoresistance is significantly affected by thepiezoelectric effect for heterostructure thin film. That is, additional charges on the beam
surface, which are induced by the piezoelectric effect when the structure is strained, change
the resistance, and this effect is larger when the conductive layer is thinner and thus the carrier
density is lower. Moreover, the opposite signs were also obtained for the arched and straightbeams by calculation, which means that our understanding roughly explains the experimental
results.
These results enhance our understanding of piezoresistance in NEMS, which could lead tomore effective designs for them.
This work was supported in part by Japan Society for the Promotion of Science (JSPS)
KAKENHI(16206003) and the Dutch NWO VICI-grant.
[1] K. Yamazaki, S. Etaki, H. S. J. van der Zant, and H. Yamaguchi, J. Cryst. Growth 301-302(2007) 897.

Fig. 1. AFM image of fabricated50-nm-thick arched beam.

Fig. 2. Calculated resistance withand without the piezoelectriceffect (PE).
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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Electron Spins in Bilayer Quantum Hall Systems Investigated by
Nuclear Spin Measurements
Norio Kumada1, Koji Muraki1, and Yoshiro Hirayama2
1
Physical Science Laboratory, 2Tohoku University
Two-dimensional electron system (2DES) formed in a high-mobility semiconductor
heterostructures can be an ideal laboratory to study many-body phenomena in low dimensions.
In a quantum Hall (QH) system, which appears by applying magnetic field perpendicular toa 2DES, the kinetic energy of electrons is quantized into Landau levels and electron-electroninteractions completely dominate physics. In particular, in a bilayer system consisting of closely
separated 2DESs, interplay between the spin and layer degrees of freedom leads to various
broken symmetry states called QH magnets. We developed nuclear magnetic resonance (NMR)
techniques for QH systems and studied static and dynamic properties of electron spin in QH
magnets [1-3].
NMR is commonly used as a powerful probeof spin states in various electronic systems.
For QH systems, however, a small number ofnuclei in contact with the 2DES have restricted
NMR measurements to multiple-layer samples.
To perform NMR in a bilayer QH system, we
exploit current-induced nuclear spin polarizationand its resistive detection. The Knight shift of
the NMR spectrum, which is proportional to theelectron spin polarization, shows the existenceof the canted antiferromagnetic state between
the ferromagnetic and spin-singlet states withfull and null spin polarizations, respectively (Fig.
(a)). Furthermore, the nuclear spin relaxation
rate reveals that, in the canted antiferromagnetic
state, low-frequency electron spin fluctuations
do not freeze out even in the low-temperature
limit (Fig. (b)). The collective fluctuation at low
temperature is characteristic behavior of broken
symmetry states in two dimensions.
[1] N. Kumada, et al., Phys. Rev. Lett. 94(2005) 096802.
[2] N. Kumada, K. Muraki, and Y. Hirayama,
Science 313 (2006) 329.
[3] N. Kumada, K. Muraki, and Y. Hirayama,
Phys. Rev. Lett. 99 (2007) 076805.
Fig. (a) Electron spin polarization and(b) nuclear spin relaxation rate measured
by NMR. The nuclear spin relaxation
rate reflects electron spin fluctuations.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Imaging Percolation of Localized Statesin a Semiconductor Quantum Well
Simon Perraud1,2, Kiyoshi Kanisawa1, Zhao-Zhong Wang2, and Toshimasa Fujisawa1
1
Physical Science Laboratory, 2LPN-CNRS
One of the advantages of two-dimensional electron system (2DES) formed in semiconductor
heterostructures is the possibility to control the main system parameters, including electron
confinement tuned by varying the thickness of the grown layers and electron density tuned
by applying an external electric field. Recently, we found that the Fermi level was mostly
unpinned at the (111)A clean surface of n-type In0.53Ga0.47As [1]. Therefore, it could bepossible to vary the electron density in the (111)A-oriented In0.53Ga0.47As surface quantum
well (QW) to access 2DES by using scanning tunneling spectroscopy (STS) measurementsin the ultra-high vacuum (UHV). This allows us to perform studies of electron phenomena
in disordered 2DES at the nanometer-scale spatial resolution. The effect of disorder is very
important to understand various electron behaviors, especially the many-body phenomena inthe semiconductor structures.
An In0.53Ga0.47As/In0.52Al0.48As multi-subband surface QW was grown by molecular beam
epitaxy on lattice-matched InP(111)A substrate, and the electronic local density of states(LDOS) in this QW was measured at 5 K by low-temperature STS in UHV. The LDOS inthe conduction band has a clear step-like energy dependence, revealing that 2DES subbands
are formed in the QW (Fig. 1). At a given energy, the LDOS shows strong spatial fluctuationsin the QW plane due to the presence of a disorder potential. The formation of the localizedstates is due to quantum-mechanical interference between electron waves that have undergone
multiple scatterings by the disorder potential. Percolation of localized states with increasingenergy is observed in each subband tail. This percolation is explained by using a semiclassicalmodel. The origin of the disorder potential is ascribed to a random distribution of native point
defects located at the QW surface [2].
This work was partly supported by a Grant-in-Aid for Scientific Research from the Japan
Society for the Promotion of Science, JSPS KAKENHI (16206003).
[1] S. Perraud, et al., Appl. Phys. Lett. 89 (2006) 192110.
[2] S. Perraud, et al., Phys. Rev. B 76 (2007) 195333.

Fig. 1. Measured dI/dU spectrum averaged over the whole area (214 nm ⊗ 214 nm) of the InGaAs surface QW at 5
K in UHV. Each arrow indicates the percolation threshold of each subband calculated by the semiclassicalmodel. Observed dI/dU spatial maps at several values of U covering the transition (a) from the band gap to
the first subband, (b) from the first to the second subband, and (c) from the second to the third subband.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Persistent Supercurrent Atom Chip
Tetsuya Mukai1, Christoph Hufnagel1, and Fujio Shimizu2
1
Physical Science Laboratory,
2
The University of Electro-Communications/NTT Research Professor
Neutral single atoms are promising candidate for producing quantum devices. An important
technology for developing these quantum devices is a precise control of the external motionof each single atom. In general, room temperature (300 K) atoms are moving with relatively
high speed at around 1,000 km/h, but with laser cooling techniques, atoms can be quickly
decelerated to velocities slower than the walking speed of a human being, i.e., lower than 100µK in temperature. At such a low temperature gravitational acceleration is significant andatoms start falling down just like a macroscopic object.
Atoms with non-zero magnetic moment have weak field-seeking states. They can be trappedwith a magnetic potential which competes against the gravity. The magnetic potential can beeasily generated by a current. It is widely used for trapping large number of atoms. However,trapping single atoms with a magnetic field generated by a current has never been successful
because of the short lifetime caused by the current noise. This is significant in a short atomsurface distance which is suitable for making strong confining single atom traps.
Recently, we have succeeded in developing a persistent supercurrent atom chip and trappingof atoms in the vicinity of a solid surface with a practically noise free magnetic field which
is highly expected to trap single atoms. As plotted in Fig. 1, 0.5 million rubidium atoms aretrapped about 300 µm away from the atom chip surface, on which a trap is generated bydriving a persistent current of 2.5 Ampere through a MgB2 superconducting loop circuit ona sapphire substrate. Apart from trapping atoms with a persistent supercurrent, we have also
succeeded in controlling the persistent current with an on-chip thermal switch driven by alaser (Fig. 2) [1].
In future we will miniaturize the atom chip pattern and try to make single atom traps with apersistent supercurrent on a solid surface as a resource for quantum devices.
This research is partially supported by the Japan Science and Technology Agency CREST"Creation of new technology aiming for the realization of quantum information processing
systems".
[1] T. Mukai, C. Hufnagel, et al., Phys. Rev. Lett. 98 (2007) 260407.

Fig. 1. Trapped atoms: (a) experiment and (b) calculation.

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Fig. 2. Persistent current control.

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

A Selective and Long-distance Coupling Scheme
for Plural Flux Quantum Bits
Hayato Nakano1, Kosuke Kakuyanagi1, Kouichi Semba1, and Masahito Ueda2
1
Physical Science Laboratory, 2Tokyo Inst. Tech./NTT Research Professor
A quantum computer is composed of many two-state elements called quantum bits (qubits).
A quantum calculation should be completed within the coherence time (during which, thequantum superposition is maintained). To achieve this, two-qubit operations where we canchoose two arbitrary qubits from a large number are advantageous. Moreover, there is a strong
need for an operation that can be performed even if the two qubits are not next to each other.
However, to achieve two-qubit operation, we employ the physical interaction between thetwo qubits, therefore performing a qubit operation on a spatially remote pair is usually very
difficult.
We developed a structure and an operating principle to enable such two-bit operation
for superconducting qubit systems, and clarified the physical characteristics by theoreticalanalysis (Fig. 1) [1].
Every qubit interacts with the same superconducting resonance circuit (e.g. an LC circuit
or a transmission line), but the resonance frequencies of individual qubits are sufficiently
different to ignore direct interactions between qubits. We use indirect interaction through thisresonance circuit and realize the function described above.
Assume that a two-bit operation is performed only between a specific qubit pair (withfrequencies of ω1, and ω2). It is important that the resonance frequency ωr can be varied
by changing the dc bias-current (Ib) supplied to the Josephson junction in the resonancecircuit. When the resonator frequency is tuned to ωr ～ (ω1 + ω2)/2 and a microwave with thefrequency ωex ～ (ω2 – ω1)/2 is applied from the outside, the two qubits are operated without
affecting a state of a resonance circuit via a two-photon Rabi process. This means that it ispossible to operate two qubits that do not interact directly.
Because only a qubit pair that simultaneously satisfies the two above ωr and ωex conditions
can react, we can choose two of specified qubits by tuning the resonator and the microwave(Fig. 2). In addition, this enables the two-bit operation of spatially longer-distance remote
qubits because the resonance circuit can be 1 mm for an LC circuit [2], or more for atransmission line. This work was partially supported by CREST-JST, JSPS-KAKENHI(18201018, 18001002).
[1] H. Nakano, K. Kakuyanagi, M. Ueda, and K. Semba, Appl. Phys. Lett. 91 (2007) 032501.
[2] J. Johansson, S. Saito, T. Meno, H. Nakano, M. Ueda, K. Semba, and H. Takayanagi, Phys.
Rev. Lett. 96 (2006) 127006.

Fig. 1. Schematic structure of our coupler.

Fig. 2. Example of a two- operation(entanglement formation).
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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Energy Distribution Measurement of Nonequilibrium Carriers
Using a Quantum Dot
Toshiyuki Kobayashi1,4, Shoei Tsuruta1,3,4, Satoshi Sasaki1, Toshimasa Fujisawa1,
Yasuhiro Tokura2, and Tatsushi Akazaki1,4
1
Physical Science Laboratory, 2Optical Science Laboratory, 3Tokyo University of Science,
4
JST-CREST
A semiconductor quantum dot (QD) confines electrons in a nanometer-scale region. This
results in discrete quantized energy levels of electrons in a QD. These quantized energy levels
can be easily tuned by controlling the gate voltage, thus enabling us to use a QD as a highresolution energy analyzer (or spectrometer) for the electrons near the QD.
We used this feature of QDs to measure the energy distribution of ballistic nonequilibrium
electrons and holes emitted from a quantum wire (Fig. 1). Nonequilibrium carriers were
emitted by applying a bias voltage (Vpc) to a quantum point contact. The emitted current wasagain focused by applying a perpendicular magnetic field (B⊥) and analyzed with a QD (Fig.
2). When the energy of the nonequilibrium carriers coincides with the quantized energy levels,
those carriers can resonantly tunnel through the QD and can be detected as an electric current.
Therefore, when the quasi-chemical potential of the carriers is aligned at the energy levelsof the QD, the differential conductance of the QD exhibits a peak and appears as a Coulomb
diamonds (Fig. 3).
We found that when the bias energy is small, the energy distribution does not broaden.
However, at a high bias (~1 meV), the distribution broadened owing to enhanced electronelectron scattering, which causes carrier energy relaxation [1]. This result is important for
future experiments related to quantum information transfer between quantum bits.
[1] T. Kobayashi, et al., Phys. Stat. Sol. (c) 5 (2008) 162.

Fig. 1. Scanning electron micrograph ofdevice and measurement setup.

Fig. 2. (a,b) Electron accumulation and(c,d) hole accumulation near quantum dot.

Fig. 3. (a) Coulomb diamond realized by ballistic hot carrier injection. Arrows indicate peaks
caused by hot carriers tunneling through QD levels. (b) Normal Coulomb diamond by Vsd.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Density Dependence of Electron and Hole Effective Masses in GaAs
Gated Quantum Well
Masumi Yamaguchi1,2 and Shintaro Nomura2,3
Physical Science Laboratory, 2CREST-JST, 3University of Tsukuba/NTT Research Professor

1

Several scattering mechanisms, such as scattering by surface charge and by donor
ions, interfacial scattering, and the impurity scattering, limit the electron mobility ofsemiconductors. In the case of the conventional semiconductor hetero-junction, the scatteringby donor ions at the doped layer causes an unavoidable reduction of the electron mobility at
low electron density. The enhancement of the electron effective mass or the increase in the spin
susceptibility, which has been observed by the Subnikov-de Hass oscillation measurements at
low electron density, is attracting much attention in the semiconductor physicists. However,
it is hard to observe them with low-mobility samples since these phenomena are induced
by electron–electron interaction. Because our gated undoped quantum well has no donor
layer, a high mobility is maintained even at low electron density and the electron density canbe controlled continuously by the gate bias. In addition to conventional electric transportmeasurements, we performed photoluminescence measurements over the insulator to metallic
regime by changing the electron density (ns). We determined the electron and hole effective
masses within a wide range of the electron density [1].
The electron and hole effective masses in the low magnetic field regime were obtained
from the Landau level splitting of the photoluminescence peaks (Fig. 1). An increase of theelectron effective mass with decreasing electron density was obtained at ns< 1⊗1011 cm-2 (Fig.
2). Moreover, we found that the hole effective mass also increases with decreasing electronic
density and that the hole is localized at ns< 3⊗1010 cm-2.
Using this gated quantum well, we are exploring the spin polarized state predicted to appear
due to the electron-electron interaction in ultralow electron density.
[1] S. Nomura, et al., Phys. Rev. B 76 (2007) 201306R .

Fig. 1. Landau level fan obtained fromthe photoluminescence peaks.

Fig. 2. Electron and hole effective masses－ 32 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Quantum Key Distribution over 200 km of Fiber
Hiroki Takesue1, Sae Woo Nam2, Qiang Zhang3, Robert H. Hadfield2,
Toshimori Honjo1, Kiyoshi Tamaki1, and Yoshihisa Yamamoto3
1
Optical Science Laboratory, 2NIST, 3Stanford University
It is important to establish the technologies to increase key distribution distance and key
rate for realizing practical quantum key distribution (QKD) systems. We have recently
demonstrated a 200-km QKD, which set the world record of key distribution distance, using a
10-GHz clock system and superconducting single photon detectors (SSPD) [1].
Figure 1 shows the system configuration, in which the differential phase shift (DPS)
protocol is implemented [2]. At Alice＇ s site, a continuous light is modulated into 10-GHz
clock pulses using a high-speed intensity modulator, and the phase of each pulse is randomly
modulated by {0, π}. Then, the pulses are attenuated so that the average photon number per
pulse becomes 0.2, and sent to Bob through an optical fiber. Bob inputs the pulse train intoa 1-bit delayed interferometer with which he can measure the phase differences of adjacentpulses: if the phase difference is 0 (π), the photon output from port 1 (2) and is detectedby SSPD1 (2). Then, Bob informs Alice the time instances in which he observed photons
through a conventional communication line. As a result, Alice and Bob share the phasedifference information at those time slots, which can be converted to "keys" for one-time pad
cryptography.
The working principle of the SSPD is explained as follows. When a photon hits a currentbiased superconducting NbN nanowire, it "breaks" the superconductivity, and a macroscopic
voltage pulse is generated. By discriminating the voltage pulse, we can detect the arrival of thephoton. Although the current quantum efficiency is relatively small (about 1 %), the SSPD hasvery low dark count rate (about 10 Hz), and so is suitable for long-distance QKD. In addition,
the SSPD can detect the 10-GHz clock signal without suffering from errors due to inter-bit
interference, thanks to its good timing resolution (60 ps).
Figure 2 shows the obtained secure key rate as a function of the fiber length. Here, the secure
key rate was calculated based on a security model considering general individual attacks[3]. We successfully distributed secure keys over 200 km of fiber. In addition, we obtained
17-kbit/s secure key rate at 105 km of fiber, which is two orders of magnitude larger than theprevious bit-rate record at 100 km of fiber.
This research was supported in part by CREST program of Japan Science and Technology
Agency and National Institute of Information and Communications Technology of Japan.
[1] H. Takesue, et al., Nature Photonics 1 (2007) 343.
[2] K. Inoue, E. Waks, and Y. Yamamoto, Phys. Rev. Lett. 89 (2002) 037902.
[3] E. Waks, H. Takesue, and Y. Yamamoto, Phys. Rev. A. 73 (2006) 012344.

Fig. 1. System configuration.

Fig. 2. Experimental result.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Field Trial of Differential-phase-shift Quantum Key Distribution
Using Polarization Independent Frequency Up-conversion Detectors
Toshimori Honjo1, Shuto Yamamoto2, Takashi Yamamoto2,
Hidehiko Kamada1, Yoshiki Nishida3, Osamu Tadanaga3, Masaki Asobe3, and Kyo Inoue4
1
Optical Science Laboratory, 2NTT Network Innovation Laboratories,
3
NTT Photonics Laboratories, 4Osaka University/NTT Research Professor
Quantum key distribution (QKD) has been studied as a way to realize unconditionally securecommunications. We had been intensively working on differential-phase-shift QKD (DPSQKD) experiment where randomly phase-modulated coherent pulse stream was used [1, 2].
Recently, we performed a field trial of DPS-QKD using polarization independent frequency
up-conversion detectors to show the feasibility of our QKD scheme [3].
In this experiment, a sender generated a 1-GHz coherent pulse stream, and each pulse was
randomly phase-modulated by 0, π . The pulse was attenuated to 0.2 photons per pulse andthen transmitted to a receiver’s site over the 17.6-km installed fiber. At the receiver’s site,
the pulse stream was input into a planar lightwave circuit Mach-Zehnder interferometer.
The output ports of the interferometer were connected to the polarization independent upconversion detectors. Figure 1 shows the setup of our detector. A signal pulse (photon) was
input into a polarization beam splitter (PBS), which split the polarization of the incoming
photon into horizontally and vertically polarized pulses. The horizontally polarized pulse
was directly input into a 50:50 coupler. The vertically polarized pulse was input into a fiber
delay line as a horizontally polarized pulse. After 50:50 coupler, horizontally polarized pulses
were combined with a strong pump light, and injected into a periodically poled lithium
niobate (PPLN) waveguide. In the PPLN waveguide, a 600 nm photon was generated via thesum frequency generation (SFG) process. After suppressing the pump, the SFG photon was
detected with a single photon counting module (SPCM) based on a Si-APD. The detectedsignals were input into a time interval analyzer to record the photon detection events.
With this setup, we performed a long-term stability test. We successfully demonstrated
stable operation for 6 hours and achieved a sifted key generation rate of 120 kbps and an
average quantum bit error rate of 3.14 %, which revealed the feasibility of our QKD scheme.
This research was supported in part by National Institute of Information and Communications
Technology of Japan.
[1] K. Inoue, et al., Phys. Rev. A 68 (2003) 022317.
[2] H. Takesue, et al., New J. Phys. 7 (2005) 232.
[3] T. Honjo, et al., Opt. Express 15 (2007) 15920.

Fig. 1. Polarization independent frequency up-conversion detector.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Topology of Exciton in Artificial Structure
Masami Kumagai
Optical Science Laboratory
Topology of an electron wavefunction in artificial structures is determined by the structuralparameters if the disturbance of the electron can be neglected [1]. The topology of an exciton
wavefunction, however, heavily depends on the delocalized feature of the relative motion of anelectron-hole pair making an exciton as well as the structural parameters. We focused our eyesto this situation and investigate the topological aspects of the exciton in nanotube structures [2].
It has been demonstrated that the exciton wavefunction shows variety of spatial distribution
patterns depending on the structural parameters of the nanotube structure. We found that theorigin of the change of the exciton wavefunction by controlling the tube circumference length
comes from the topological transition. As shown in Fig. 1, the kinetic energy of the groundstate exciton in nanotubes decreases monotonically when the circumference length decreased.
This is somewhat curious because smaller confinement region yields larger confinement
kinetic energy in conventional artificial structures. The exciton wavefunction is delocalized
and it is connected in small circumference nanotubes, while the exciton wavefunction is
localized in large circumference ones. The connected wavefunction has ring-like topology andit yields the flat wavefunction for a ground state electron and exciton reducing the confinement
energy.
We have also found that the topological transition can be controlled even by changing
the barrier dielectric constant of the nanotubes. Figure 2 plots the ground state exciton
wavefunctions on developments of two nanotubes with different barrier dielectric constants,
12 and 3. It can be clearly seen that the wavefunction of ε =12 case is delocalized in the
direction of circumference (horizontal in the figure) and connected, while the wavefunctionof ε =3 case is localized in a small area and disconnected. This implies that we can control
the topology of the exciton wavefunction simply by changing the dielectric constant or othermaterial parameters. We expect the control of the artificial structure to provide a novel guiding
principle for creating functional devices through the topological control of excitons.
[1] M. Kumagai and T. Ohno, Solid State Commun. 83 (1992) 837.
[2] M. Kumagai, et al., Solid State Commun. 145 (2008) 154.

Fig. 1. Tube circumference dependence of theconfinement energy.

Fig. 2. Topological control of exciton bychanging dielectric constant.

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Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Efficient and Low Noise Single-photon Detection in 1550-nm
Communication Band by Frequency Upconversion in Periodically Poled
LiNbO3 Waveguides
Hidehiko Kamada
Optical Science Laboratory
In recent years, the increasing demand for secure communication has accelerated thedevelopment of a new generation of telecommunication techniques based on quantum
mechanics. Specifically, quantum key distribution (QKD) is expected to be a key
technology; practical fiber-based QKD systems have been intensively studied in the
1500-nm wavelength band. For distributing keys over a long distance at a high rate,
efficient and low noise single-photon detection is important. We demonstrate 1500-nmband single photon detection with low dark count noise and a potentially high efficiency. Bydeveloping frequency up-conversion devices based on sum-frequency generation (SFG) in
periodically poled LiNbO3 (PPLN) waveguide, which are specifically designed to use a pumpwavelength longer than that of communication-band photons, we eliminate the dark countnoise caused by parasitic nonlinear processes in the waveguide [1].
Periodic poling relaxes the wavenumber mismatch among three waves, thus realizing
quasi-phase matching (QPM), and tight mode confinement in a LN waveguide enhances
the SFG. Our devices are specifically designed to use a pump wavelength at 1810 nm. The
PPLN wafers were fabricated by directly bonding a thin periodically poled wafer to a
LiTaO3 cladding wafer. Subsequently, the bonded wafer was cut into pieces, then a seriesof 7- μ m thick, 6~8- μ m wide and 35 or 50-mm long ridge stripes were defined with adicing saw.
We observed internal conversion efficiency as high as 40 % (Fig. 1, 2), and demonstrated
scaling down to the single photon level. Favored by long wavelength pump, which neverinduces parasitic χ2 process thus eliminates the noise photons in 1500-nm band. By carefully
eliminate noise photons from the pump laser, a background dark count rate less than 102 sec-1
was achieved (Fig. 2). Using the as-measured coupling of 65~70 % of a 1500-nm wave
into the waveguide, and a Si-APD efficiency of ~57 %, we predict an overall photon
detection efficiency of about 34~40 %.
This work was partly supported by NICT.
[1] H. Kamada, M. Asobe, T. Honjo, H. Takesue, Y. Tokura, Y. Nishida, O. Tadanaga, and H.
Miyazawa, Opt. Lett. 33 (2008) 639.

Fig.1. SFG output power (left), transmitted signal (middle)
and pump (right). The temperature was set at 24 ˚C.

－ 36 －

Fig.2. Efficiency and dark count rate as afunction of coupled 1810-nm pump
power: throughput was ~20 %. The
DC rate is reduced to below 100 cps.

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

InAs Nanowire-channel Field Effect Transistors
Guoqiang Zhang, Kouta Tateno, and Hidetoshi Nakano
Optical Science Laboratory
Recently, nanowires (NWs) have become the center of attention due to the exceptionalversatility and promise a wide range of potential applications, from electronics and photonics
to biochemistry and medicine [1]. Semiconductor NWs are expected to play an importantrole as functional device elements in nanoscale electronic devices. InAs NWs are very
promising for high-speed device applications due to their high mobility. We have established a
reproducible fabrication process for NW field effect transistors (FETs) and the performance of
the InAs NW-channel FETs were evaluated [2].
Au colloidal particles were used as the catalyst for the growth of InAs NWs by vaporliquid-solid mode in a low-pressure (76 Torr) metalorganic vapor phase epitaxy system[3]. The precursors were trimethyl-indium and AsH3. Transmission electron microscopy
measurement indicates that the NWs are wurtzite-structure without stacking faults. The NWs
were dispersed on a SiO2/Si (SiO2 thickness: 500 nm) substrate and then Ni/Au metals wereselectively deposited on the NWs to form electrical contacts after patterning by electron beamlithography. The contacts were annealed at 300 ºC for 30 s by rapid thermal processing. Figure
1 shows a NW-channel FET with a number of electrodes.
Using the underlying heavily doped Si substrate as the gate electrode, we measured the DC
characteristics of InAs NW-channel FETs with a semiconductor parameter analyzer at room
temperature. Figure 2 shows typical characteristics of Id-Vd of 2 and 4-terminal measurements.
Compared with NW resistance, the contact resistance is very small and the specific contact
resistivity is estimated to be 2.0 × 10-7 Ωcm2. Figure 3 shows typical Id-Vg characteristics at
different drain voltages. The feature that the current increases with the gate voltage indicatesthat the NW is n-type. The NW-channel FETs show a maximum transconductance (gm) in
the range of 0.24-0.36 μS at Vd of 0.1 V. For FET devices, the normalized transconductanceg*m = gm/wg is an important figure of merit, where wg is the channel width (in the case of NW
channel, the width is the NW diameter). The g*m varies in the range of 2.5-3.7 mS/mm at Vd of
0.1 V. Based on the FET properties, the electron concentration (N) and mobility (μ) of the NW
segment could be estimated. N and μ are in the range of 2.3-5.8×1017 cm-3 and 1.29-1.53×103
cm2 V -1 s-1, respectively. We are investigating how to further improve the FET properties andfabricate functional quantum devices.
This work was partly supported by JSPS-KAKENHI (16206003, 18310074).
[1] Y. Li, et al., Mater. Today 9(10) (2006) 18; C. Thelander, et al., ibid. 9(10) (2006) 28; P. J.
Pauzauskie and P. Yang, ibid. 9(10) (2006) 36.
[2] G. Zhang, et al., ISCS2007, Kyoto, Japan, Oct. 2007, p. 142.
[3] G. Zhang, et al., J. Appl. Phys. 103 (2008) 014301.

Fig. 1. SEM image of a
InAs NWFET.

Fig. 2. Vd-Id characteristics of 2 and4-terminal measurements.
－ 37 －

Fig. 3. Id-Vg characteristics atvarious drain voltages.

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Demonstration of a CEO-locked Frequency Comb at Telecommunications
Wavelengths with Low Pulse Energy
Atsushi Ishizawa, Tadashi Nishikawa, and Hidetoshi Nakano
Optical Science Laboratory
The carrier-envelope offset (CEO) is an absolute phase slip between pulses of a modelocked laser. Recently, progress in the mode-locked laser techniques has made it possible togenerate a CEO-locked frequency comb from a mode-locked laser pulse and contains various
frequency components in the hundreds of terahertz region which are regularly spaced. The
CEO-locked frequency comb can be used as an "optical frequency ruler" with a cesium atomic
clock for controlling the spacing. Optical frequency measurement is one of applications ofthe "ruler". Lasers for applications, such as precision spectroscopy and telecommunications,should be small and have a high repetition rate.
However, CEO frequency detection needs an octave bandwidth spectrum because selfreferencing is employed. As a result, a fiber laser needs amplification, which makes it difficult
to reduce the size of the laser system. Furthermore, telecommunications and precision
spectroscopy applications require a CEO-locked frequency comb with a high repetition
rate. The problem in this case is that the pulse energy becomes smaller as the repetition rateincreases. We therefore need to achieve CEO locking with a small and high-repetition rate
device with low pulse energy.
Our new method employs a tellurite photonic crystal fiber (PCF) for supercontinuum(SC) generation with low pulse energy, and a periodically poled lithium niobate (PPLN)
ridge waveguide for efficient second harmonic generation. We found the optimum condition
for generating the SC spectrum by changing the polarization of the laser, the PCF length,
and the core size. We found that a SC spanning more than an octave can be generated with
80 pJ fiber-coupling pulse energy (Fig. 1). The CEO frequency is measured with an MachZehnder interferometer by combing the second harmonic into a PPLN ridge waveguide withthe short wavelength components of the SC light. From the SC shape, we found the optimum
wavelength in the 965 nm region in order to observe the CEO frequency. Hartl et al. succeeded
in locking the CEO with a 600 pJ fiber coupling pulse energy [1]. We have demonstrated
a CEO-locked frequency comb at the telecommunications wavelengths with a 230 pJ fiber
coupling pulse energy, which, to the best of our knowledge, is the lowest fiber coupling pulse
energy ever achieved (Fig. 2) [2]. Due to the improvement of the coupling efficiency to the
PCF, it would be possible to lock the CEO by using a fiber laser oscillator with a low pulse
energy.
[1] I. Hartl, et al., Opt. Express 13 (2005) 6490.
[2] A. Ishizawa, et al., Opt. Express 16 (2008) 4706.

Fig. 1. Spectrum spanning more than an octave (black)and the spectrum of fiber laser (gray).
－ 38 －

Fig. 2. CEO frequency signal (black) and the phasedifference between the CEO signal and alocal oscillator (gray).

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Ultra High-Q Photonic Crystal Nanocavities Based on Compound
Semiconductors
Akihiko Shinya1, Shinji Matsuo2, Yosia1, Takasumi Tanabe1, Eiichi Kuramochi1,
Takehiko Tawara1, Kouta Tateno1, Tomonari Sato2, Takaaki Kakitsuka2,and Masaya Notomi1
1
Optical Science Laboratory, 2NTT Photonics Laboratories
Photonic crystal (PhC) is a promising candidate as a platform to construct devices withdimensions of several wavelengths. A PhC is an artificial structure with light wavelength
periodicity that can confine light in an ultra small area of about 0.1 µm3 with an ultra high Q
factor. We have been studying ways of strongly confining light in ultra small areas with theaim of minimizing the light propagation speed and enhancing the light-material interaction byusing Si based PhCs. In this report, we adopt new materials, namely InGaAsP and AlGaAsP,
to develop a new photonic technology. These materials have certain features that Si does nothave, e.g. they exhibit large refractive index modulation owing to optical nonlinearity, andthey are expected to be used for PhC based active devices.
Figure 1 shows a scanning electron micrograph of an InGaAsP PhC and transmission spectraof InGaAsP and AlGaAs PhC nanocavities. The PhCs are composed of air holes arranged 420
nm apart in a triangular pattern and they function as a light insulator at a wavelength of around1.55 µm. The area with no linearly arranged holes is the light waveguide and the area wheresome holes are shifted few nanometers away from the center of the waveguide functions asa cavity that can confine light [1]. InGaAsP and AlGaAs PhC nanocavities have estimated Q
factors of 130,000 and 690,000, respectively. These values are around ten times larger thanthose previously reported for PhC nanocavities with these materials. They are expected toprovide all-optical memories with very low operating power [2] and highly efficient opticalmechanical power converters [3].
This work was supported by the National Institute of Information and Communications
Technology (NICT).
[1] E. Kuramochi, et al., Appl. Phys. Lett. 89 (2006) 241124.
[2] T. Tanabe, et al., Opt. Lett. 30 (2005) 2575.
[3] M. Notomi, et al., Phys. Rev. Lett. 97 (2006) 023903.

Fig. 1. PhC cavity structure and transmission spectra of InGaAsP and AlGaAs PhCs.
－ 39 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

All-optical Bit Memory Based on Photonic Crystal Nanocavity
Akihiko Shinya1, Shinji Matsuo2, Yosia1, Takasumi Tanabe1, Eiichi Kuramochi1,
Tomonari Sato2, Takaaki Kakitsuka2, and Masaya Notomi1
1
Optical Science Laboratory, 2NTT Photonics Laboratories
We have focused on a resonant tunneling filter on a Si based photonic crystal (PhC) platform
where single-mode waveguides (WGs) are effectively coupled with an ultrasmall cavity witha high Q factor. The photon density in the cavity is extremely high owing to its small sizeand effective coupling with PhC-WGs, and this results in a large optical nonlinearity thatenables us to realize all-optical memories with very low operating power [1]. However, it isvery difficult to achieve a long memory time for a Si based PhC because of its small opticalnonlinearity. In this work, we developed an InGaAsP based PhC nanocavity and realized an
all-optical bit memory that can operate at very low power and achieve a long memory time.
Figure 1 shows the bit memory operation of the InGaAsP based PhC nanocavity [2]. The
initial state of the memory is OFF and it outputs a low level signal (gray line). When a set
pulse with a width of 100 ps is input from the waveguide to write one bit of information, thememory turns ON and outputs a high level signal (black line). The memory remains in the ON
state after the set pulse has been applied, which means that the bit information is stored. The
longest memory time is 150 ns, which is much longer than that of a Si-PhC memory (2.5 ns).
The minimum bias power for the memory operation is 40 µW, which is ten times lower thanfor a Si-PhC and around 100 times lower than that of a conventional optical memory based onbistable lasers. This technology is expected to eliminate certain photonic device bottlenecks
such as the difficulty of dense integration on a chip and the difficulty of achieving low power
consumption in all-optical memories.
This work was supported by the National Institute of Information and Communications
Technology (NICT).
[1] T. Tanabe, et al., Opt. Lett., 30 (2005) 2575.
[2] A. Shinya, et al., CLEO/QELS2008, San Jose, U.S.A., May 2007.

Fig. 1. Bit memory operation of InGaAsP based PhC.

－ 40 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Slow Light Propagation in Large-scale Photonic Crystal Coupled
Resonator Waveguides
Eiichi Kuramochi, Takasumi Tanabe, Hideaki Taniyama, and Masaya Notomi
Optical Science Laboratory
A periodic chain of optical resonators (coupled resonator optical waveguide: CROW) is
expected to be a promising candidate as a slow light medium [1]. In the last annual report, we
mentioned that CROWs composed of ultrahigh quality factor (Q, ~106) Si photonic crystal(PhC) resonators [2] could couple more than 60 resonators with a very low propagation
loss, which is a unique advantage of the PC-CROW [3]. We also reported the dispersion of
the PC-CROWs, which corresponded to a very low group velocity (vg) [3]. In this work, wegreatly improved the passband spectrum of PC-CROW to realize distortion-free short pulse
propagation because a short pulse occupies a wide frequency range.
Figure 1 is a schematic of the improved PC-CROW structure. We employed an inline
coupling structure to maximize the coupling between the CROW and external waveguides. In
addition, the resonator interval was apodized for the same purpose. The passband exhibitedclose to the ideal low loss, and was wide and flat as shown in Fig. 2. We performed a time
domain pulse propagation experiment using a short pulse (FWHM: 16 ps, wavelength: ~1563
nm). The pulse was transmitted through the CROW and was delayed by 35 ps (N=30) and 75
ps (N=60), respectively (N: resonators in CROW), which agreed well with the vg of 0.0085c(c: light speed in a vacuum) evaluated by dispersion measurement (Fig. 3). The delay was
several times larger than the original pulse width, which is unachievable with existing slow
light media. Moreover, the pulse distortion and the ringing after-pulse were well suppressed.
The results [4] clearly demonstrated the feasibility of a PC-CROW as a slow light medium forhigh-speed optical communication.
This work was partly supported by CREST of the Japan Science and Technology Agency.
[1] A. Yariv, et al., Opt. Lett. 24 (1999) 711.
[2] E. Kuramochi, et al., Appl. Phys. Lett. 88 (2006) 041112.
[3] E. Kuramochi, et al., CLEO/QELS2007, Baltimore, U.S.A., May 2007, 2.
[4] E. Kuramochi, et al., CLEO/QELS2008, San Jose, U.S.A., May 2008, 3.

Fig. 1. (a) In-line coupling structure. (Lcc: resonator interval; Lcw: the distance between the external
waveguide and the center of the outermost resonator.) (b) PC-CROW structure studied here.
The lattice constant, hole radius, and slab thickness were 420, 110, and 205 nm, respectively.
Holes (A/B) were shifted (8/4 nm) away from the line defect.

Fig. 2. Transmission spectra of long PC-CROWs(N: number of resonators).
－ 41 －

Fig. 3. Time-resolved data of optical pulses
after passing through sample recordedwith oscilloscope.

Ⅱ．DataResearch Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

4th NTT-BRL School
The fourth NTT Basic Research Laboratories (BRL) school was held in November 19-22,
2007 at the NTT Atsugi R&D Center. The aim of the NTT BRL school is to foster young
researchers in the physics field, as well as to promote the international visibility of NTT BRL.
This year the theme was "Recent Status in Quantum Information Technology".
The theam is closely related to the research on quantum information processing that NTT
BRL is conducting intensively. Prestigious professors and researchers were invited to theschool as lecturers. There were thirty-five participants, mainly Ph. D students, from twelve
countries.
On the first day, after the director of NTT BRL had provided an overview of NTT BRL,
Prof. Yoshihisa Yamamoto (Stanford University, U.S.A.) presented lectures entitled "Recent
Progress in Quantum Information Technology". He also gave lectures on the second andthird day that covered related fundamental theories, reviews of experiments and somerecent results. Dr. Jaw-Shen Tsai (NEC Nano-electronics Laboratories, Japan) gave a talkon "Superconducting Qubits" on the afternoon of the second day. In this BRL school, there
were several lectures by researchers working at NTT BRL. Dr. Toshimasa Fujisawa gave alecture on "Single-electron Charge and Spin Dynamics in Quantum Dots". Dr. Koichi Semba
talked about the "Josephson Circuit QED". Dr. Tetsuya Mukai gave a talk entitled "PersistentSupercurrent Atom Chip". A poster session was held in the evening of the second day, where
each student gave a presentation about his/her research at the university. All the students,
lecturers, and NTT BRL researchers had a good time exchanging information on current
research topics in various fields. On the third and fourth day we provided an overview of NTT
BRL. A laboratory tour was conducted so that the students could see the research facilities.
Managers of NTT BRL gave talks on recent activities at each laboratory. After that, all theparticipants attended in NTT BRL Science Plaza 2007, which is an exhibition of recent
research achievements and activities. They
enjoyed discussions with researchers about ongoing research topics indetail.
At the farewell party, best poster prizes wereawarded to the students who gave noteworthy
presentations. The students were able to build
friendships and exchange contact addresses.
NTT BRL will continue to provide these kindsof occasions to support young researchers andhelp establish human networks in the fields ofphysics and applied physics.

－ 43 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Science Plaza 2007
"Science Plaza 2007", an open-house event of NTT Basic Research Laboratories (BRL),
was held at NTT Atsugi R&D Center on Thursday, November 22nd, 2007. Under the banner"Nanoscience Opens Up the Quantum World", Science Plaza aimed to disseminate our latest
research accomplishments through various sections of people inside and outside of NTT andto gather diverse opinions.
Following an opening address from the director, Dr. Yumoto, Exective Managers
briefly summarized research strategy and exhibited posters. In the afternoon session, twodistinguished technical members of NTT BRL, Toshimasa Fujisawa and Akira Fujiwara, gave
lectures on "Controlling and detecting single-electron states" and "Control of Single Electronsin Silicon Nanodevices", respectively. Each lecture was well-attended and followed by heatedquestion-and-answer sessions.
As regards the poster exhibits, 34 posters, including four from Photonics Laboratories
and Microsystem Integration Laboratories, presented our latest research accomplishments.
While explaining the originality and impact—as well as the future prospects—of our researchaccomplishments, these posters were intensively discussed, and many meaningful opinions
were heard. This year’s "Lab Tour"—a guided tour of research facilities at NTT BRL that has
been receiving high reputation from visitors over the years—took place at four different labs,
each presented five times in total, so that as many people as possible could join the tour. This
time we also opened a booth to introduce the NTT R&D recruitment system for job-seeking
researchers and students. After all lectures, presentations, and exhibitions, a banquet was heldin Center’s dining room, where lively conversation among participants deepened their amity.
More than 200 people from research institutes, universities, and general industries, as well
as from NTT Group, attended Science Plaza 2007. Thanks to the efforts of all participants, theconference ended on a high note. We would thus like sincerely to express our gratitude to allof the participants.

－ 44 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Award Winners’ List (Fiscal 2007)
Photonic &Electromagnetic Crystal
Structures (PECS) VII First
Place Poster Award

E. Kuramochi

Low Loss Long Coupled Resonator
Optical Waveguides Realized Using
Ultrahigh-Q Photonic Crystal
Resonators

Apr. 10,2007

14th Semiconducting andInsulating Materials
Conferences (SIMC XIV)
Young Scientist Award

Y. Taniyasu

For Outstanding Contributions in
Developing and Implementing
Aluminum Nitride Deep-ultraviolet
Light-emitting Diodes

May 17,
2007

The Laser Society of JapanThe 31st Original Paper
Award

T. Tanabe
A. Shinya
S. Kawanishi
M. Notomi

All-optical Switching and 5-GHz RZ(Return to Zero) Optical Pulse Train
Modulation Using Silicon Photonic
Crystal Cavities

May 31,2007

12th Optoelectronics andCommunication Conference
IEEE/LEOS Japan Chapter
Student AwardT. Yamaguchi

Fabrication and Optical Properties ofHybrid-type Pillar Microcavity

July 11,
2007

SSDM Young Researcher
Award

A. Nishikawa

High Critical Electric Field Exceeding
8 MV/cm Measured Using AlGaN
p-i-n Vertical Conducting Diode on
n-SiC Substrate

Sep. 19,
2007

SSDM Paper Award

T. Sogawa
H. Gotoh
Y. Hirayama
T. Saku
P. V. Santos
K. H. Ploog

Optical Properties ofDynamically-modulated Dots andWires Formed by Surface Acoustic
Waves

Sep. 19,2007

The 6th Annual Scientific
American 50

T. Tanabe

Storing Photons in a Photonic Crystal

Nov. 30,
2007

Gordon Research
Conferences: Magnesium in
Biochemical Processes& Medicine
Best Poster Presentation
Award

K. Torimitsu
Y. Shinozaki
Y. Furukawa

Magnesium Effect on Brain NeuralDevelopment

Mar. 13,2008

The Japan Society for the
Advancement of Invention
Special Award

A. Shimada（TESTRONICS
CO., LTD）

Extensometers for Fine Wires

Mar. 18,
2008

Young Scientist Award of
the Physical Society ofJapan

N. KumadaElectron Spins in Bilayer Quantum
Hall Systems Investigated by Nuclear
Spin Measurement

Mar. 23,2008－ 45 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

In-house Award Winners’ List (Fiscal 2007)
NTT R&D Award

A. Fujiwara
K. Nishiguchi
Y. OnoK. Yamazaki

Manipulation and Detection of aSingle Electron Using Silicon Nano
MOSFET

Dec. 13,2007

NTT R&D Award

T. Tanabe
M. Notomi
E. Kuramochi
A. Shinya
H. Taniyama

Slowing Down Light to One 50
Thousandth of Its Speed

Dec. 13,
2007

Award for Achievements
by Director of Basic
Research Laboratories

S. Saito
J. Johansson
K. Kakuyanagi
T. MenoH. Nakano
K. Semba

Quantum Electrodynamics Using
Superconducting Quantum Circuits

Mar. 17,
2008

Award for Achievements
by Director of Basic
Research Laboratories

K. Suzuki
K. Kanisawa

Imaging of Electron Wave Interference
by Scanning Tunneling Spectroscopy
on Cleaved Semiconductor
Heterostructure Surfaces

Mar. 17,
2008

Award for Achievements
by Director of Basic
Research Laboratories

A. YokooH. Namatsu

Nanoelectrode Lithography

Mar. 17,
2008

Award for Excellent
Papers by Director of
Basic ResearchLaboratories

T. Mukai"Persistent Supercurrent Atom Chip",Phys. Rev. Lett. 98 (2007) 260407.

Mar. 17,2008

Special Award by Directorof Basic ResearchLaboratories

M. Yamaguchi
K. Suzuki
H. ItoH. Ueshima
Y. OnoSubstantial Improvement in the
Recycling Rate of Liquid Helium by
the Web-Based System

Mar. 17,2008

Special Award by Directorof Basic ResearchLaboratories

S. Sasaki

Electron Beam Exposure System at
NTT Basic Research Laboratories

Mar. 17,2008－ 46 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

List of Visitors’ Talks (Fiscal 2007)
I. Materials Science
Date

Speaker

Affiliation
Title

Apr. 24

Dr. Chandra S. Ramanujan

University of Oxford, U.K.
"The NTT Oxford Collaboration: Studying Biological
Systems Using Atomic Force Microscopy"

May 8

Dr. Simon Koblar

University of Adelaide, Australia"Stem Cell Therapy for Improvement in Stroke
Outcome"May 18

Prof. Robert Vink

University of Adelaide, Australia"Role of Magnesium in Brain Damage and the Receptor
Relation"

May 29Dr. Hideyuki Maki

Keio University"Carrier Injection Control and Bandgap Control of
Carbon Nanotubes"

June 1

Prof. Erhard Kohn

University of Ulm, Germany"Electronic Diamond Surface Characteristics"

June 14

Prof. Shingo Tsukada

The Graduate University of Japan Traditional Medicine
and Science"Monitoring of Biological Information Using Meridian
Related Impedance Measurement"

Sep. 18

Dr. Achillefs Kapanidis

University of Oxford, U.K.
"Studying Biomachines and Biosensors Using Singlemolecule Fluorescence"

Oct. 24

Prof. David J. Rogers

University of Technology of Troyes, France"Use of ZnO Thin Films as Sacrificial Templates for
MOVPE and Chemical Lift-off of GaN"

Oct. 25

Dr. Kimiko Yamamoto

The University of Tokyo"Regulation of Circulatory Function by VascularEndothelial P2X4 Receptor"

Nov. 16

Prof. Jun Suda

Kyoto University"Growth of High-quality AlN on SiC (0001) by Stepheight Control and Growth of Novel-polytype AlN on
SiC with Non-polar Crystal Faces"

Dec. 18

Prof. Seiji Samukawa

Tohoku University"Damage-free Neutral Particle Beams for Nano-device
Fabrication"－ 47 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

II. Physical Science
Date

Speaker

Affiliation
Title

Apr. 9

Mr. Takahiro Morimoto

Chiba University"Non-local Transport Measurement Approach to 0.7
Structure in Quantized Conductance"

July 25

Prof. Gerald Bastard

National Center for Scientific Research, France"Quantum Cascade Lasers in a Magnetic Field"

July 26

Dr. Kris Helmerson

National Institute of Standards and Technology, U.S.A.
"Vortices and Persistent Currents in Bose-Einstein
Condensates"

Aug. 21

Prof. Robert H. Blick

University of Wisconsin-Madison, U.S.A.
"Nano-electromechanical Systems"

Aug. 22

Prof. Hongqi Xu

Lund University, Sweden"Symmetry, Spin Hall Effect and Zitterbewegung inElectron Waveguides with Spin-orbit Interaction"

Oct. 9Prof. Tetsuo Ogawa

Osaka University"Mechanism of Optical Gain Production in the Presenceof Carrier-carrier Interaction in Quantum Wires:
Screened Hartree-Fock Approximation and Dynamical
Mean-field Approximation"

Oct. 22

Dr. Henning Riechert

Qimonda AG, Germany"GaN and Si Nanowires: Growth Studies and Transistor
Results"

Oct. 29

Prof. Alexey Ustinov

University of Erlangen-Nuremberg, Germany"Temperature-induced Decoherence in Josephson Phase
Qubits"Nov. 5

Prof. Klaus H. Ploog

Paul Drude Institute, Germany"III-Nitrides Seem to be Good for Everything"Nov. 2

Prof. Hong Zhang

Sichuan University, China"Oxygen Adsorption on the Ir(111): A First Principle
Study"

Nov. 8

Dr. William D. Oliver

Massachusetts Institute of Technology, U.S.A.
"Mach-Zehnder Interferometry and Microwave-induced
Cooling in Persistent-current Qubits"

Nov. 8

Dr. Tristan Meunier

Delft University of Technology, the Netherland"Relaxation and Coherent Manipulation in Spin Qubits"

Nov. 22

Mr. Erik Lucero

University of California, Santa Barbara, U.S.A.
"Recent Advances in Josephson Phase Qubits: High
Fidelity Gates, Quantum Memory, and Bell Violation"－ 48 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Dec. 5

Dr. Hiroaki Koga

National Institute for Materials Science, Japan Society
for the Promotion of Science"First-principles Study on Elementary Processes in the
Growth of Thin Films and Nano-structures"Dec. 13

Dr. Tiefu Li

NEC-RIKEN, Tsinghua University, China"Making Use of Suspended Metal Nanostructures"Dec. 18

Prof. Vladimir Antonov

Royal Holloway, University of London, U.K.
"Toward Passive Terahertz Imaging"

Dec. 25

Mr. Zhongchang Wang

The University of Tokyo"First-principles Study toward the Understanding of
Ag2S Atomic Switch"

Jan. 30

Dr. Masafumi Jo

Hokkaido University"Towards the Realization of Superconductor-based Light
Emitting Diodes"

Feb. 25

Dr. Alberto Morpurgo

Delft University of Technology, the Netherland"Quantum Transport through Graphene Single- andDouble-layers"

March 17

Mr. Hiroki Morishita

Keio University"Electrically Detected Electron and Nuclear Spin
Resonance of Phosphorus in Silicon"

III. Optical Science
Date

Speaker

Affiliation
Title

Apr. 6

Prof. Robert M. Westervelt

Harvard University, U.S.A.
"Integrated Circuit / Microfluidic Chips for the
Manipulation of Biological Cells"

May 15

Mr. Hong C. Nguyen

University of Sydney, Australia"Enhanced Kerr Nonlinearity in As2Se3 Chalcogenide
Fibre Tapers with Sub-wavelength Diameter"

May 31

Prof. Kazuki Koshino

Tokyo Medical and Dental University, JST PRESTO"Use of the Classical Input for Solving the Two-photon
Nonlinear Dynamics"

June 22

Dr. Qiang Zhang

Stanford University, U.S.A.
"Experimental Quantum Teleportation of a Two-qubit
Composite System"

June 27

Prof. Norio Kawakami

Kyoto University"Orbital Kondo Effect in Quantum Dot Systems Application of the Exact Solution -"－ 49 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Aug. 3

Prof. Shmuel Gurvitz

Weizman Institute, Israel"Lapse of Transmission Phase and Electron Moleculesin Quantum Dots"

Aug. 8

Dr. Tatsuya Fujii

The University of Tokyo"Formula of Shot Noise in a Mesoscopic Conductor
Based on Keldysh Formalism"

Aug. 22

Prof. Shmuel Gurvitz

Weizman Institute, Israel"Quantum Mechanical Approach to Decoherence andRelaxation Generated by Fluctuating Environment"

Sep. 10

Prof. Xin-Qi Li

Chinese Academy of Science, China"Particle-number-resolved Master Equation to Quantum
Transport, Quantum Measurement, and QuantumControl"

Oct. 22

Dr. Paulo V. Santos

Paul Drude Institute, Germany"Control of Photons and Excitons Using Surface
Acoustic Waves"Nov. 9

Mr. Tomohiro Amemiya

The University of Tokyo"Ferromagnet-semiconductor Composite Devices for
Waveguide Isolators"

Nov. 26

Mr. Odilon D. D. Couto Jr.

Paul Drude Institute, Germany"Spin Transport and Relaxation in (110) GaAs Quantum
Wells Using Surface Acoustic Waves"Nov. 30

Dr. Andrew Shields

Toshiba Research Europe Ltd., Cambridge ResearchLaboratory, U.K.
"Single Photon Technology for Quantum Information
Applications"Jan. 9Dr. Jean Benoit Heroux

The University of Tokyo"Characterization of GaMnAs by Time-resolved Midinfrared Transmittance and THz Emission"

Jan. 29

Dr. Renato Renner

Swiss Federal Institute of Technology, Switzerland"Symmetries and Cryptography"

Feb. 27

Mr. Tony Pisano

NP Photonics, U.S.A.
"Recent Status in Optical Fiber Lasers in Telecom-band"

March 17

Prof. Takaaki Mukai

Osaka City University"Modulation Characteristics in Semiconductor Lasers
with Fiber Bragg Gratings"－ 50 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

Research Activities in Basic Research Laboratories in 2007
The numbers of papers published in international journals, presentations at international
conferences and applied patents in year 2007 amounted to 140, 269, and 48, respectively. The
numbers for each research area are as follows;
Papers Published in International Journals(Jan. - Dec. 2007)50

Materials Science

55

Physical Science

Optical Science

35
0

10

20

30

40

50

60

Number of Papers

Presentations at International Conferences(Jan. - Dec. 2007)
Materials Science

65

119

Physical Science

85

Optical Science
0

20

40

60

80

100

120

140

Number of Presentations

Applied Patents (Jan. - Dec. 2007)
12

Materials Science

10

Physical Science

Optical Science

26
0

5

10

15

Domestic－ 51 －

20

25

30

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

The numbers of research papers published in the major journals are shown below.
Journals(IF2006*)
Applied Physics Letters
3.977
Chemical Communications
4.521
IEEE Electron Device Letters
2.716
IEEE Transactions on Electron Devices
2.052
Japanese Journal of Applied Physics
1.222
Journal of Applied Physics
2.316
Journal of Crystal Growth
1.809
Journal of the American Chemical Society
7.696
Nano Letters
9.960
Nature26.681Nature Photonics
Nature Physics
12.040
Neuroscience Research
1.953
New Journal of Physics
3.754
Optics Express
4.009
Physica E-Low-Dimensional Systems & Nanostructures
1.084
Physical Review B
3.107
Physical Review Letters
7.072*IF2006 : Impact Factor 2006 (Journal Citation Reports,2006)

Numbers
26
1
2
2
19
3
12
1
2
1
2
1
2
3
7
4
9
9

The average IF2006 for all research papers from NTT Basic Research Laboratories is 3.23.

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

Numbers

International Conference on Nanoelectronics, Nanostructures and Carrier Interactions
International Conference on Electronic Properties of Two-dimensional Systems andModulated Semiconductor Structures
The 34th International Symposium on Compound Semiconductors
2007 International Conference on Solid State Devices and Materials
9th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures
Frontiers in Nanoscale Science and Technology Workshop
2nd International Symposium on Nanometer-Scale Quantum Physics
The American Physical Society
The Conference on Lasers and Electro-Optics and the Quantum Electronics and Laser Science
Conference
17th International Vacuum Congress, 13th International Conference on Surface Science andInternational Conference on Nano Science and Technology
International Symposium on Advanced Nanodevices and Nanotechnology
Fourth International Conference on Molecular Electronics and Bioelectronics
The 1st Conference of New Diamond and Nano Carbons
Silicon Nanoelectronics Workshop
The 3rd Workshop of the UK-Japan Bionanotechnology Collaboration
15th International Conference on Nonequilibrium Carrier Dynamics in Semiconductors
Asian Conference on Quantum Information Science
20th International Symposium on Superconductivity－ 52 －

27
24
17
13
10
9
7
7
7
7
7
4
4
4
4
4
4
4

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

List of Invited Talks at International Conferences (2007)
I. Materials Science Laboratory(1)

H. Omi, T. Kawamura, Y. Kobayashi, S. Fujikawa, Y. Tsusaka, K. Kagoshima, and J. Matsui, "Strain
Analysis of Semiconductor Nanoscale Thin Films by Grazing Incidence X-ray Diffraction", Symposium on
Surface and Nano Science 2007, Appi, Japan (Jan. 2007).

(2)

K. Furukawa, "FRET Observation Using Lipid-flow Chip", International Mini-symposium of Surface
Forces, Matsushima, Japan (Mar. 2007).

(3)

K. Kumakura, A. Nisikawa, and T. Makimoto, "Nitride-based Heterojunction Bipolar Transistors
for High-power and High-temperature Electronics", The 4th International Symposium on Ubiquitous
Knowledge Network Environment, Sapporo, Japan (Mar. 2007).

(4)

Y. Taniyasu, M. Kasu, and T. Makimoto, "AlN p-n Junction UV-LEDs", The 3rd Asia-Pacific Workshop
on Widegap Semiconductors, Jeonju, Korea (Mar. 2007).

(5)

M. Kasu, K. Ueda, A. Tellaire, and T. Makimoto, "Diamond RF Power Transistors", 2nd International
Industrial Diamond Conference, Rome, Italy (Apr. 2007).

(6)

K. Torimitsu, "Functional Analysis of Neurons and Receptor Proteins for Device Application", 1stInternational Symposium on Nanomedicine from Basic to Applications, Okazaki, Japan (Apr. 2007).

(7)

Y. Taniyasu, M. Kasu, and T. Makimoto, "AlN Deep-ultraviolet Light-emitting Diodes", 14th
Semiconducting and Insulating Materials Conference, Arkansas, U.S.A. (May 2007).

(8)

Y. Taniyasu, M. Kasu, and T. Makimoto, "AlN Deep-UV Light-emitting Diodes by MOVPE", 12th
Euroepan Workshop on Metalorganic Vapour Phase Epitaxy, Slovakia, Bratislava (Jun. 2007).

(9)

K. Ueda and M. Kasu, "Diamond Transistors for RF Power Amplifiers", IEEE MTT-S International
Microwave Symposium, Hawaii, U.S.A. (Jun. 2007).

(10)

K. Ajito, "Teahertz and Raman Spectoroscopy for Biological Applications", 2007 SURA Terahertz
Applications Symposium, Washington, DC, U.S.A. (Jun. 2007).

(11)

H. Omi, "Scaling and Universality of Morphological Transition at the SiO2/Si(001) Interface", Gordon
Research Conference on Thin Film and Crystal Growth Mechanisms, South Hadley, U.S.A. (Jun. 2007).

(12)

K. Ajito, "Terahetz and Raman Biospectroscopy", 3rd Asian and Pacific Rim Symposium on
Biophotonics, Cairns, Australia (Jul. 2007).

(13)

Y. Taniyasu, M. Kasu, and T. Makimoto, "AlN Deep-UV Light-emitting Diodes", 18th European
Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, and Nitrides, Berlin, Germany (Sep.
2007).

(14)

K. Torimitsu, "Protein Nanobio Device and its Configuration", 33rd International Conference on Microand Nano- Engineering, Copenhagen, Denmark (Sep. 2007).

(15)

M. Kasu, K. Ueda, H. Kageshima, and Y. Taniyasu, "Diamond RF FETs and Other Applications inElectronics", The 34th International Symposium on Compound Semiconductors, Kyoto, Japan (Oct. 2007).

(16)

K. Torimitsu, "Receptor Protein Analysis and Neurological Functions for Nanobio Interface", The 2nd
Neural Stem Cells & Frontier Technologies for Brain Repair Workshop combined with The 2nd AustralianWorkshop on Computational Neuroscience, Adelaide, Australia (Dec. 2007).

－ 53 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

II. Physical Science Laboratory(1)

K. Semba, "Vacuum Rabi Oscillations Observed in a Flux Qubit LC-oscillator System", American
Physical Society March Meeting, Denver, U.S.A. (Mar. 2007).

(2)

K. Muraki, N. Kumada, and Y. Hirayama, "Low Frequency Spin Dynamics in a Quantum Hall Canted
Antiferromagnet", American Physical Society March Meeting, Denver, U.S.A. (Mar. 2007).

(3)

K. Kanisawa, "Imaging Donor States in Semiconductor Structures", Frontiers in Nanoscale Science andTechnology Workshop (FNST2007), Tokyo, Japan (Mar. 2007).

(4)

G. Shinkai, T. Hayashi, Y. Hirayama, and T. Fujisawa, "Electrostatic Coupling Between Two Doublequantum Dots: Toward Two-qubit Manipulation", Quantum Information Processing on Quantum Dots,Windermere, U.K. (Apr. 2007).

(5)

H. Kageshima, M. Uematsu, T. Akiyama, and T. Ito, "Microscopic Mechanism of Silicon Thermal
Oxidation Process", ECS Meeting, 2007 Spring, Chicago, U.S.A. (May 2007).

(6)

H. Tamura, M. Yamaguchi, S. Nomura, T. Akazaki, T. Maruyama, S. Miyashita, and Y. Hirayama,"Simultaneous Measurement of Photoluminescence and Capacitance Spectra in a GaAs Quantum Well",Optical Properties of Low-Dimensional Systems, Ottawa, Canada (May 2007).

(7)

K. Nishiguchi, Y. Ono, A. Fujiwara, H. Inokawa, and Y. Takahashi, "Room-temperature-operating
Single-electron Devices Using Silicon Nanowire MOSFET", 2007 Asia-Pacific Workshop on Fundamentals
and Applications of Advanced Semiconductor Devices, Jeonju, Korea (Jun. 2007).

(8)

N. Kumada, K. Muraki, and Y. Hirayama, "NMR Study of a Canted Antiferromagnet in a Bilayer
Quantum Hall System", International Conference on Electronic Properties of Two-dimensional Systems,
Geneva, Italy (Jul. 2007).

(9)

I. Suemune, H. Kumano, Y. Hayashi, K. Tanaka, T. Akazaki, M. Jo, and Y. Idutsu, "Controlled Photon
Generation Processes from Semiconductor Quantum Dots and their Applications", The 34th International
Symposium on Compound Semiconductors, Gwangju, Korea (Sep. 2007).

(10)

C. Hufnagel, T. Mukai, and F. Shimizu, "Manipulation of Cold Atoms on a Superconductive Atom Chip",
BOSE-EINSTEIN CONDENSATION 2007- Frontiers in Quantum Gases -, Sant Feliu de Guixols (Costa
Brava), Spain (Sep. 2007).

(11)

Y. Ono, M. Khalafalla, K. Nishiguchi, K. Takashina, A. Fujiwara, S. Horiguchi, H. Inokawa, and Y.
Takahashi, "Charge Transport in Boron-doped Nano MOSFETs: Towards Single-dopant Electronics", Fifth
International Symposium on Control of Semiconductor Interfaces, Tokyo, Japan (Nov. 2007).

(12)

I. Suemune, H. Kumano, Y. Hayashi, K. Tanaka, T. Akazaki, M. Jo, and Y. Idutsu, "Photon Generation
Processes from Semiconductor Quantum Dots: Their Control and Applications", 8th Chitose International
Forum, Chitose, Japan (Nov. 2007).

(13)

H. Yamaguchi, I. Mahboob, H. Okamoto, and K. Onomitsu, "Micromechanical Devices for
Characterizing Electron Behavior in Quantum Systems", International Symposium on Advanced
Nanodevices and Nanotechnology, Hawaii, U.S.A. (Dec. 2007).

(14)

K. Muraki, "Nuclear Spin Manipulation in Semiconductor Nanostructures", Microelectronics, MEMS,
and Nanotechnology 2007, Canberra, Australia (Dec. 2007).

(15)

I. Suemune, H. Kumano, Y. Hayashi, K. Tanaka, T. Akazaki, M. Jo, and Y. Idutsu, "Possibility of
Semiconductor-based Single Photon Sources for Quantum Information Networks", International Conferenceon Microwaves and Optoelectronics, Aurangabad, India (Dec. 2007).

－ 54 －

Research Activities in NTT Basic Research Laboratories Vol. 18 (July 2008)

III. Optical Science Laboratory(1)

M. Notomi, "Adiabatic Wavelenth Conversion and Optomechanical Energy Conversion in Photonic
Crystal Cavities", Photonics West, San Jose, U.S.A. (Jan. 2007).

(2)

H. Nakano, K. Oguri, Y. Okano, and T. Nishikawa, "Femtosecond Laser-induced Ablation Processes
Observed by Picosecond-time-resolved XAFS Using Femtosecond Laser-produced Plasma Soft X-ray
Pulses", The 2nd Canada-Japan SRO-COAST Symposium on Ultrafast Intense Laser Science, Quebec,
Canada (Mar. 2007).

(3)

M. Notomi, A. Shinya, T. Tanabe, E. Kuramochi, and H. Taniyama, "Photonic-Crystal-Based Chip-Scale
Optical Integration", Optical Fiber Communication Conference/National Fiber Optic Engineers Conference,
Anaheim, U.S.A. (Mar. 2007).

(4)

M. Notomi, T. Tanabe, E. Kuramochi, H. Taniyama, and A. Shinya, "All-Optical Control of Light in
Ulrahigh-Q Photonic Crystal Cavities", International Symposium on Photonic and Electrmagnetic Crystal
Structures VII, Montrey, U.S.A. (Apr. 2007).

(5)

M. Notomi, T. Tanabe, E. Kuramochi, A. Shinya, and H. Taniyama, "All-Optical Control of Light in
Ulrahigh-Q Photonic Crystal Cavities", The European Conference on Lasers and Electro-Optics and theInternational Quantum Electronics Conference, Munich, Germany (Jun. 2007).

(6)

H. Nakano, "Spatiotemporally Resolved XAFS Measurement using Femtosecond Laser Plasma Soft
X-ray", 3rd Asian Symposium of Intense Laser Science, Cameron Highlands, Malaysia (Jul. 2007).

(7)

M. Notomi, T. Tanabe, E. Kuramochi, H. Taniyama, and A. Shinya, "Dynamic Control of Light in
High-Q Photonic Crystal Nanoavities", OSA Topical Meeting of Nonlinear Optics, Cona, U.S.A. (Jul. 2007).

(8)

M. Yamashita, "Metal-insulator Transition in the Three-dimensional Hubbard Model with Harmonic
Confinement", 16th International Laser Physics Workshop, Leon, Mexico (Aug. 2007).

(9)

T. Honjo, H. Takesue, H. Kamada, K. Nishida, O. Tadanaga, M. Asobe, and K. Inoue, "Long-distanceDistribution of Time-bin Entangled Photon Pairs over 100 km Using Frequency Up-conversion Detectors",
16th International Laser Physics Workshop, Leon, Mexico (Aug. 2007).

(10)

M. Notomi, T. Tanabe, E. Kuramochi, A. Shinya, and H. Taniyama, "Photonic Crystal Nanocavities:
Slow Light, All-optical Processing, Wavelength Conversion, Optical MEMS", Group IV Photonics 2007,
Tokyo, Japan (Sep. 2007).

(11)

Y. Tokura, "Latest Achievement in QKD Experiments at NTT", Updating Quantum Cryptography 2007,
Tokyo, Japan (Oct. 2007).

(12)

H. Takesue, "R&D of Quantum Relay Technology at NTT", Updating Quantum Cryptography 2007,
Tokyo, Japan (Oct. 2007).

(13)

M. Notomi, "Photonic Quasicrystal Distributed Feedback Lasers", The First International Congress on
Advanced Electromagnetic Materials for Microwaves and Optics, Rome, Italy (Oct. 2007).

(14)

M. Notomi, "Control of Light in Photonic Crystals", Korea Photonics Conference, Jeju, Korea (Nov. 2007).

(15)

Y. Tokura, "Single Spin Manipulation by Electric Field in a Quantum Dot", 2nd International Workshop
on Materials Science and Nano-Engineering, Awaji, Japan (Dec. 2007).

(16)

M. Notomi, T. Tanabe, E. Kuramochi, H. Taniyama, and A. Shinya, "Dynamic Control of Light by
Photonic-Crystal Nanocavities", International Symposium on Advanced Nanodevices and Nanotechnology
Waikoloa, Hawaii, U.S.A. (Dec. 2007).

(17)

M. Notomi, T. Tanabe, E. Kuramochi, H. Taniyama, and A. Shinya, "Dynamic Control of Light by
Photonic-Crystal Nanocavities", The 5th International Conference on Advanced Materials and Devices,Jeju, Korea (Dec. 2007).
－ 55 －

Editorial Committee
Hiroo Omi
Nahoko Kasai
Kyoichi Suzuki
Fumiaki Morikoshi
Mizuki Otani
NTT Basic Research Laboratories
3-1 Morinosato Wakamiya, Atsugi
Kanagawa, 243-0198 Japan
URL: http://www.brl.ntt.co.jp/