05 (2012 Selected)：

Quantum non-equilibrium statistical physics and thermodynamics in the control and detection of quantum coherent processes

Control and detection of quantum coherent systems such as charge, flux and spin qubits, have attracted a lot of attention. Recently, it has become possible to generate a coherent state consisting of a few photons using a superconducting qubit coupled to a transmission line oscillator. It has also been demonstrated that a coherent ensemble of nuclear spins in a GaAs semiconductor quantum dot can be controlled. These recent developments have been achieved by applying ideas based on quantum optics.

Independently, considerable progress has been made with regard to the statistical physics and thermodynamics of mesoscopic systems, based on concepts such as the fluctuation theorem. In mesoscopic systems, statistical physics and thermodynamics are formulated based on the distribution function of non-equilibrium fluctuations under the influence of a time-dependent driving force. For a quantum system, this distribution function can be obtained by adopting techniques developed in the context of the control and detection of quantum coherent systems. Measurement of the probability distribution in a single-electron tunneling current has already been achieved using a quantum point contact electrometer. Precise measurement of the distribution of work done in a superconducting single-electron transistor has also been carried out. These experiments have verified the fluctuation theorem at a single-electron level. As a next step, it would be of interest to study non-equilibrium quantu  m statistical physics and thermodynamics using nanoscopic solid state devices.

For this purpose, several questions need first be answered. How should the experimental setup be designed? How can the probability distribution in a quantum system be experimentally measured? What protocol can be used to control and detect the quantum coherent state? Finally, what role is played by the electromagnetic environment, 1/f noise, and the back-action of the measurements in mesoscopic statistical physics and thermodynamics? In the present project, these problems will be theoretically investigated using full counting statistics, which is a convenient framework for studying the probability distribution of non-equilibrium fluctuations. Using this approach, it is hoped that methods of minimizing the heat generated during the control and detection processes can be elucidated, paving the way for the development of future quantum information devices.

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