Information
Solid State Quantum Bits are in Action—
Conference Report on “Mesoscopic
Superconductivity and Spintronics 2006”

From February 27 to March 2, NTT Basic ResearchLaboratories (NTT BRL) and CREST-JST (CoreResearch for Evolutional Science and Technology,
Japan Science and Technology Agency) held aninternational symposium on physics entitled “Mesoscopic Superconductivity and Spintronics”(MS+S2006) at NTT Atsugi R&D Center. These
fields have recently been attracting considerable
attention from scientific researchers and engineers
because they are fundamental areas that may lead tothe physical realization of quantum information processing and computation. MS+S is a series of biennial symposia that started in 2000.
Many distinguished researchers in these fields fromall over the world have joined every event and given
important presentations. It is now recognized as animportant international symposium on mesoscopic
physics although, strangely, it is better known among
European and American researchers than Japanese
ones. MS+S2006 included 46 oral presentations andapproximately 80 poster presentations.
At the symposium this year, we were impressed by
the fact that mesoscopic superconductivity is attracting attention in terms of applications in addition to
the academic interest that dominated MS2000. This
has accompanied the development of research onsuperconducting quantum bits (SCQ), which arebasic elements of quantum computers.
Professor J. Martinis of UC Santa Barbara, Professor F. W. J. Hekking of Centre National de laRecherche Scientifique and Université Joseph Fourier, Professor D. Esteve of CEA-Saclay, Professor J.
Clark of UC Berkeley, Professor C. J. P. M. Harmansof Delft University of Technology, Dr. K. Semba ofNTT BRL, Dr. Y. Nakamura of NEC, Dr. Wallraff ofSwiss Federal Institute of Technology Zurich andYale University, and Professor A. Ustinov of University of Erlangen-Nuremberg gave talks on new resultsin their SCQ experiments. These people represent
almost all the research groups throughout the worldthat actually have SCQs in operation.
Vol. 4 No. 7 July 2006

Single quantum bits can now be controlled almost
perfectly. Next, we have to move on to experimentswith two or more bits, including an investigation ofquantum entanglement between quantum bits. In thisrespect, Professor J. Martinis’s group has had thegreatest success. They observed two-quantum-bit
entanglement and provided the quantum tomography
charts of their system. On the other hand, the Yale
University group showed the entanglement between
their SCQ and a transmission line resonator, and theNTT BRL group demonstrated entanglement manipulation of their SCQ and a sub-millimeter LC resonance circuit coupled system, which is known as“vacuum Rabi oscillation” in the field of quantum
electrodynamics. These two studies are the first clear
demonstrations of entanglement in macroscopic
quantum objects. The NEC group analyzed their SCQ
and found some important properties of noise thatcaused decoherence in it.
We also found that rapid progress is being made inspintronics. In particular, electrical ways of manipulating spins in semiconductor systems generated
great interest in this symposium. A talk on the generation and detection of spin entanglement in double
quantum dots was presented by Professor C. Marcus
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Informationof Harvard University. Dr. S. Sasaki of NTT BRL
described a gate-controlled RKKY interaction in a
double quantum dot-quantum wire coupled system.
Much attention has focused on the spin-orbit interaction in semiconductors because it can produce aneffective magnetic field without a real magnetic field.
Professor D. Awschalom of UC Santa Barbara
demonstrated optical detection of the spin Hall effectin GaAs and InGaAs, where spin up and down electrons were accumulated at opposite edges without
any external magnetic fields.
Gate control of spin precession in InGaAs 2DEGs(two-dimensional electron gases) was reported byProfessor J. Nitta of the CREST project and Tohoku
University. Professor H. Ohno of Tohoku University
observed current-induced domain wall motion in

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GaMnAs. This was due to the interaction between
spin-polarized current and localized spins inside amagnetic domain.
Midway through the symposium, a special lecture
on entanglement manipulations with trapped ions
was given by Dr. H. Häffner of Innsbruck. Most participants were surprised by the admirable skill shownin manipulating ions although they were not very
familiar with the system.
The symposium welcomed approximately 200 participants, of whom a quarter were from overseas.
They have now returned home with the dream offruitful interaction between fundamental physics andinformation sciences, which will become common in
the near future.

NTT Technical Review