Impact of counter-rotating-wave term on quantum heat transfer and phonon statistics in nonequilibrium qubit-phonon hybrid system

TL;DR

This paper demonstrates that counter-rotating-wave terms significantly influence quantum heat transfer and phonon statistics in a nonequilibrium qubit-phonon hybrid system, even with weak dissipation, challenging traditional assumptions.

Contribution

It reveals the crucial role of CRWTs in quantum heat transfer and phonon behavior, providing a detailed analysis using coherent phonon states and quantum master equations.

Findings

CRWTs enhance heat current and fluctuations at large temperature bias.

Including only RWTs suppresses heat transfer and phonon correlations.

CRWTs can dramatically cool phonons via cooperative transitions.

Abstract

Counter-rotating-wave terms (CRWTs) are traditionally viewed to be crucial in open small quantum systems with strong system-bath dissipation. Here by exemplifying in a nonequilibrium qubit-phonon hybrid model, we show that CRWTs can play the significant role in quantum heat transfer even with weak system-bath dissipation. By using coherent phonon states, we obtain the quantum master equation with heat exchange rates contributed by rotating-wave-terms (RWTs) and CRWTs, respectively. We find that including only RWTs, steady state heat current and current fluctuations will be significantly suppressed at large temperature bias, whereas they are strongly enhanced by considering CRWTs in addition. Furthermore, for the phonon statistics, the average phonon number and two-phonon correlation are nearly insensitive to strong qubit-phonon hybridization with only RWTs, whereas they will be dramatically cooled down via the cooperative transitions based on CRWTs in addition. Therefore, CRWTs in quantum heat transfer system should be treated carefully.