arXiv subjects

Yasuyuki Matsuo

Publications and source records attributed to Yasuyuki Matsuo.

3 recordsLinked to original sources

arXiv2015

Completely-positive quantum operations generating thermostatistical states: A comparative study

Nonunitary quantum operations generating thermostatistical states and forming positive operator-valued measures (POVMs) are of current interest as a useful tool for operational approach to quantum thermodynamics. Here, two different operations generating the same thermostatistical state are studied: one is related to thermofield dynamics and the other is the one proposed in a recent work [S. Abe, A. R. Usha Devi, A. K. Rajagopal, J. Phys. A: Math. Theor. 43 (2010) 045303]. A comparable study on them shows different behaviors of the von Neumann entropy under repeated applications of these two operations. It is shown that the entropy does not behave monotonically, in general, and can even decrease under the thermofield-dynamical one, in contrast to monotonic increase under the other.

cond-mat.stat-mech↗

arXiv2015

Phase-space representation of completely positive quantum operation: Two-mode squeezed vacuum and thermal states

Completely positive quantum operations are frequently discussed in the contexts of statistical mechanics and quantum information. They are customarily given by maps forming positive operator-values measures. To intuitively understand physical meanings of such abstract operations, the method of phase-space representations is examined. This method enables one to grasp the operations in terms of the classical statistical notions. As an example of physical importance, here, the phase-space representation of the completely positive quantum operation arising from the single-mode subdynamics of the two-mode squeezed vacuum state, which maps from the vacuum state at vanishing temperature to mixed states with perfect decoherence including the thermal state, is studied. It is found in the $P$ representation that remarkably this operation is invertible, implying that coherence lost by the quantum operation can be recovered.

cond-mat.stat-mech↗

arXiv2014

Role of parity transformation for the fluctuation theorem: Limit cycle and symmetry breaking

The fluctuation theorem of the Crooks type is studied for thermodynamic nonlinear- multivariate systems. In particular, a bivariate system having a limit cycle is discussed in detail. It is explicitly shown how the time reversal operation has to be combined with the parity transformation in order to derive the fluctuation theorem for the change of the renormalized entropy. Furthermore, breakdown of the symmetry in a limit-cycle model due to the effect of fluctuations is also discussed.

cond-mat.stat-mech↗