Strong coupling effects in quantum thermal transport with the reaction coordinate method

TL;DR

This paper introduces a semi-analytical method based on the reaction coordinate approach to study quantum thermal transport beyond weak coupling, capturing strong coupling effects and thermal diode behavior efficiently.

Contribution

The paper develops an effective Hamiltonian method that accurately models strong system-bath interactions in quantum thermal transport, extending beyond traditional weak coupling approximations.

Findings

Properly captures heat current turnover behavior at strong coupling

Moderately improves thermal diode rectification ratio with strong coupling

Provides a computationally efficient approach for quantum thermal machine analysis

Abstract

We present a semi-analytical approach for studying quantum thermal energy transport beyond the weak system-bath coupling regime. Our treatment, which results in a renormalized, effective Hamiltonian model is based on the reaction coordinate method. In our technique, applied to the nonequilibrium spin-boson model, a collective coordinate is extracted from each environment and added into the system to construct an enlarged system. After performing additional Hamiltonian's truncation and transformation, we attain an effective two-level system with renormalized parameters, which is weakly coupled to its environments, thus can be simulated using a perturbative Markovian quantum master equation approach. We compare the heat current characteristics in our method to other techniques, and demonstrate that we properly capture strong system-bath signatures such as the turnover behavior of the heat current as a function of system-bath coupling strength. We further investigate the thermal diode effect and demonstrate that strong couplings moderately improve the rectification ratio relative to the weak coupling limit. The effective Hamiltonian method that we developed here offers fundamental insight into the strong coupling behavior, and is computationally economic. Applications of the method towards studying quantum thermal machines are anticipated.