Recent progress in nanotechnology enables us to directly address quantum transport of electrons in nano-devices made of metal or semiconductor. For example, the wave nature of electrons can be controlled in electronic interferometers ("Aharonov-Bohm rings"), while their particle nature is accessible in quantum dots ("artificial atoms"). We can even combine these two kinds of devices into one, where the wave-particle duality in quantum mechanics manifests itself. The advantage of such research field, which is called "mesoscopic physics" or "nanophysics", lies in the controllability and the versatile degrees of freedom in the device design. We try to understand and control various novel quantum, many-body, and nonequilibrium effects in nano-devices in terms of the dynamical aspects of electron transport.

Scanning electron microscope image of the artificial atom (yellow). The single spin inside the atom (indicated by the arrow) causes the Kondo effect, one of the most representative quantum many-body effects. We measure how electrons are scattered by the Kondo state. Such an experiment can be viewed as "collision experiments" on a chip and will shed new light on Kondo physics.

1.

S. Nakamura, Y. Yamauchi, M. Hashisaka, K. Chida, __K. Kobayashi__, T. Ono, R. Leturcq, K. Ensslin, K. Saito, Y. Utsumi, and A. C. Gossard, "Fluctuation Theorem and Microreversibility in a Quantum Coherent Conductor", *Phys. Rev.* B **83,** 155431 (2011) [Editors' Suggestion].

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3.

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4.

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5.

M. Sato, H. Aikawa, K. Kobayashi, S. Katsumoto, and Y. Iye, "Observation of the Fano-Kondo Anti-Resonance in a Quantum Wire with a Side-Coupled Quantum Dot", *Phys. Rev. Lett.* **95,** 066801 (2005).

6.

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