Quantum thermodynamics in strong coupling: heat transport and refrigeration

TL;DR

This paper investigates quantum heat transport and refrigeration in a non-Markovian system with asymmetric double-well molecules, revealing rectification, heat flow control, and refrigeration effects influenced by system-bath coupling and external driving.

Contribution

It introduces a non-Markovian quantum model for heat rectification and refrigeration using a stochastic surrogate Hamiltonian approach with asymmetric double wells.

Findings

Heat always flows from hot to cold, respecting the second law.

Asymmetry causes heat rectification, reversing heat flow when baths are exchanged.

External periodic driving can induce refrigeration by reversing heat flow.

Abstract

The performance characteristics of a heat rectifier and a heat pump are studied in a non Markovian framework. The device is constructed from a molecule connected to a hot and cold reservoir. The heat baths are modelled using the stochastic surrogate Hamiltonian method. The molecule is modelled by an asymmetric double-well potential. Each well is semi-locally connected to a heat bath composed of spins. The dynamics is driven by a combined system-bath Hamiltonian. The temperature of the baths is regulated by a secondary spin bath composed of identical spins in thermal equilibrium. A random swap operation exchange spins between the primary and secondary baths. The combined system is studied in various system-bath coupling strengths. In all cases the average heat current always flows from the hot towards the cold bath in accordance to the second law of thermodynamics. The asymmetry of the double well generates a rectifying effect meaning that when the left and right baths are exchanged the heat current follows the hot to cold direction. The heat current is larger when the high frequency is coupled to the hot bath. Adding an external driving field can reverse the transport direction. Such a refrigeration effect is modelled by a periodic driving field in resonance with the frequency difference of the two potential wells. A minimal driving amplitude is required to overcome the heat leak effect. In the strong driving regime the cooling power is non-monotonic with the system-bath coupling.