# Theoretical Physics

**7 December 2016**

**Time:**n/a

**Location:**

Theoretical Physics & Chemistry Seminar: Yoshitaka Tanimura (Kyoto)

**Quantum heat current under nonperturbative and non-Markovian conditions: Application to heat machines**

Quantum heat transport problems involving quantum heat machines have been studied with approaches developed through application of open quantum dynamics theory. Moreover, the advent of micro-technology allows us to investigate quantum heat current experimentally. In quantum case, system-bath entanglement as well as bath-bath entanglements play essential role to characterize the thermodynamic behavior of a system that interacts with thermal environments. In this talk, we first derive reduced hierarchy equations of motion (HEOM) [1,2] from correlated thermal equilibrium state,[3,4] which can deal with non-Markovian and non-perturbative system-bath interactions at finite temperature without approximation. Building on these results, we show that the violation of the positivity condition encountered in many other reduced equation of motion approaches results from the Markovian assumption.[2, 3] We then numerically demonstrate roles of system-bath entanglement as well as bath-bath entanglements for a spins-Bosons system [5] and three-level heat engine model [6] under non-equilibrium condition using HEOM approach. We observe cyclic behavior of the heat currents and the work performed by the heat engine, and we find that their phases depend on the system-bath coupling strength. Through consideration of the bath heat current, we show that the efficiency of the heat engine decreases as the strength of the system-bath coupling increases, due to the contribution of correlations among system-bath interactions (CASBI).

[1] Y. Tanimura and R. Kubo, J. Phys. Soc. Jpn. 58, 101 (1988).

[2] Y. Tanimura, J. Phys. Soc. Jpn. 75, 082001 (2006)

[3] Y. Tanimura, J. Chem. Phys. 141, 044114 (2014).

[4] Y. Tanimura, J. Chem. Phys. 142, 144110 (2015).

[5] A. Kato and Y. Tanimura, J. Chem. Phys. 143, 064107 (2015).

[6] A. Kato and Y. Tanimura, arXiv:1609.08783

© Copyright Leeds 2011