A polaron theory of quantum thermal transistor in nonequilibrium three-level systems

TL;DR

This paper develops a polaron-based theoretical framework to analyze quantum thermal transistors in nonequilibrium three-level systems, revealing heat amplification effects across various coupling regimes.

Contribution

It introduces a unified approach combining polaron transformation with Redfield equations to study heat currents in different coupling limits, highlighting the role of middle bath transitions.

Findings

Giant heat amplification in strong coupling regime

Heat amplification occurs at moderate coupling strengths

Transitions mediated by the middle bath are crucial

Abstract

We investigate the quantum thermal transistor effect in nonequilibrium three-level systems by applying the polaron transformed Redfield equation combined with full counting statistics. The steady state heat currents are obtained via this unified approach over a wide region of system-bath coupling, and can be analytically reduced to the Redfield and nonequilibrium noninteracting blip approximation results in the weak and strong coupling limits, respectively. A giant heat amplification phenomenon emerges in the strong system-bath coupling limit, where transitions mediated by the middle thermal bath is found to be crucial to unravel the underlying mechanism. Moreover, the heat amplification is also exhibited with moderate coupling strength, which can be properly explained within the polaron framework.