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JAPAN NANONET BULLETIN
-- 88th Issue -- January 25, 2007
Nanotechnology Researchers Network Center of Japan
Ministry of Education, Culture, Sports, Science and Technology (MEXT)
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JAPAN NANO 2007: Call for Registration
-Nanotechnology, Progress for Five Years and Expectation to The Future-
The Nanotechnology Researchers Network Center of Japan (nanonet), MEXT
organizes the 5th International Symposium on Nanotechnology (JAPAN
NANO 2007) on February 20 - 21, 2007, at Tokyo Big Sight (Ariake,
Tokyo).
The constitution of JAPAN NANO 2007 is : Plenary lectures, symposia on
nano-IT devices, nano-physics, nano-materials, nano-biology, nano-
process, metrology and nano-implications and the oral presentation &
poster session.
Lectures will be given by the world-leading researchers on the state-
of-the-art nano science and technology. Posters will be introduced by
the best young researchers who will lead the next generation of this
area. JAPAN NANO 2007 provides you the current topics and future
perspective of nano science and nanotechnology.
For more information,
http://www.nanonet.go.jp/english/event/japannano2007/index.html
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IN THIS ISSUE
Nanonet Interview:
"The century of quantum engineering
--Aiming for a superconducting quantum computer --"
Hideaki TAKAYANAGI, Professor, Department of Applied Physics, Tokyo
University of Science, Former Fellow/Executive Director, NTT R&D and
Former Director, NTT Basic Research Laboratories
Young Researchers' Introduction:
"Carbon nano-peapod electronics"
Yutaka OHNO, Assistant Professor, Department of Quantum Engineering,
Nagoya University and Researcher, Precursory Research for Embryonic
Science and Technology (PRESTO), Japan Science and Technology Agency
(JST)
-- NANO CALENDAR --
For information on nanotechnology related symposiums and conferences
held in the world,
http://www.nanonet.go.jp/english/calendar/
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NANONET INTERVIEW
The century of quantum engineering
--Aiming for a superconducting quantum computer --
(Issued in Japanese: February 9, 2005)
Hideaki TAKAYANAGI, Professor, Department of Applied Physics, Tokyo
University of Science, Former Fellow/Executive Director, NTT R&D and
Former Director, NTT Basic Research Laboratories
Since becoming an executive director at NTT R&D in July 2003, Dr.
Takayanagi has been trying to establish the research organization to
enhance quantum information processing and nanobiotechnology. In quantum
information processing, four types of quantum bits or qubits are studied
to develop a quantum computer. He says, "I personally think
superconductors are most appropriate for developing a quantum computer
because I have a background in superconductivity."
A qubit, which is the basic unit of information, has to be able to take
a quantum superposition of the "0" and "1" states. A superconducting
flux qubit is comprised of an aluminum loop with three Josephson
junctions embedded in it and is about five micrometers in size. Dr.
Takayanagi says, "The flux that penetrates the loop in a superconductive
state is quantized. When a magnetic field which adjusts the number of
flux quanta to 0.5 is applied, the number of flux quanta may be one due
to a larger current flow in the loop or may be zero due to the current
flow in the opposite direction in the loop, and the probability to be
either one or zero is the same. Thus, the state at half a flux quantum
is a superposition of clockwise and counter-clockwise circulating
supercurrent states." The state of a qubit can be read using a
superconducting quantum interference device (SQUID) that surrounds the
qubit and is about seven micrometers in size. "When the current
direction in the qubit changes, the flux that penetrates the SQUID loop
changes. Since a SQUID is extremely sensitive to magnetism, the maximum
superconducting current of the SQUID changes depending on the changes in
the flux, and therefore, changes in the state of a qubit can be observed,"
says Dr. Takayanagi.
Normally, determining a qubit state through one measurement was
difficult, and several measurements were carried out and averaged for
the determination. However, Dr. Takayanagi and his team were able to
distinguish between the ground state and the first excited state, i.e.,
the "0" and "1" states, respectively, with one measurement by improving
the sensitivity of the SQUID, when the number of the flux quanta that
penetrate a qubit was 1.5.
One of the advantages of the superconducting flux qubit that Dr.
Takayanagi points out is that the decoherence time, within which the
coherent superposition of quantum states is destroyed, is longer than
that of other solid state qubits. Currently, the longest decoherence
time in solid state qubits is 3 microseconds in the superconducting flux
qubits prepared at Delft University of Technology. While trying to
extend the decoherence time, which is "the key to developing qubits," Dr.
Takayanagi observed multiphoton absorption in the superconducting flux
qubits. He says, "This phenomenon in atoms/molecules has been widely
observed, but it was the first observation in giant artificial atoms.
This observation provided clues to understand how the qubits are bound
to the surrounding and how the bonds are weakened to extend the
decoherence time."
There is, as well, decoherence that is induced by Josephson junctions
which are the basic building blocks of superconducting flux qubits. So,
research on materials in order to prevent decoherence has started. Dr.
Takayanagi expects researchers in materials science to launch research
on quantum information processing. However, in order to develop a
quantum computer, not only researchers in materials science but also
researchers involved in information science, mathematics, electrical
engineering, electronic engineering and other various fields must work
together. "It is contradictory that we want to observe qubit states, but
we cannot observe them because the quantum superposition states are
destroyed by observation. Therefore, we have to know how much of the
noise must be reduced and how high-speed measurements may be conducted.
For that, new technology will be required. This won't be possible only
with researchers in physics."
Dr. Takayanagi was involved in developing a SQUID, when he was in school,
and was attracted by Josephson junctions. After he joined NTT, he was
committed to doing what he liked. From his experience, he strongly
advises young researchers to let themselves do whatever they like and to
strive for it. He says, "Although the 20th century was said to be the
century of quantum mechanics, quantum mechanics is being truly utilized
in the 21st century. The essentials of quantum mechanics are quantum
superposition and quantum entanglement. From that viewpoint, we have
just started to establish engineering that uses quantum mechanics." Even
if a quantum computer is not developed, the spin-off effects, such as
the development of novel materials, metrological engineering and
algorithm, are enormous. Now, there is technology with potential for
commercialization such as quantum cryptography. "Developing a quantum
computer means that quantum mechanics can be experimentally confirmed.
So, I want young researchers to be fascinated with developing a quantum
computer," says Dr. Takayanagi.
(Interviewer: Kuniko Ishiguro, Cosmopia Inc.)
For more information including figures,
http://www.nanonet.go.jp/english/mailmag/2007/088a.html
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YOUNG RESEARCHERS' INTRODUCTION
Carbon nano-peapod electronics
(Issued in Japanese: April 5, 2006)
Yutaka OHNO, Assistant Professor, Department of Quantum Engineering,
Nagoya University and Researcher, Precursory Research for Embryonic
Science and Technology (PRESTO), Japan Science and Technology Agency
(JST)
The electronic structures of carbon nanotubes can be modulated by
inserting various molecules inside the nanotubes. Carbon nanotubes that
have encapsulated fullerenes "peapods" are interesting materials due to
not only their structure but also their possible applications in
electronics. This is because the peapod is an excellent conductor
originating from the carbon nanotube, and because quantum phenomena
occur due to energy band modulation by the fullerene encapsulation.
Recently, we have fabricated peapod field-effect transistors and
characterized their transport properties. As a result, the bandgap of
the peapods varied depending on the type of encapsulated fullerenes.
This suggests that band engineering may be possible in carbon nanotubes.
By exploiting this feature of the peapods, we are aiming to produce
quantum-effect devices. Specific types of fullerenes, which are used as
the building blocks, are regularly inserted in a carbon nanotube to form
heterojunctions in the peapod. The heterojunctions form tunneling
barriers and quantum well structures. This bottom-up method will make it
possible to develop functional quantum devices in a carbon nanotube.
For more information including figures,
http://www.nanonet.go.jp/english/mailmag/2007/088b.html
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