Thermal rectification in a qubit-resonator system

TL;DR

This paper investigates heat rectification and diode effects in a qubit-resonator system, revealing how coupling strength and system parameters influence heat current direction, magnitude, and the role of coherence.

Contribution

It provides a systematic analysis of heat rectification in a circuit QED model, highlighting the impact of coupling regimes and coherence on heat transport and rectification sign.

Findings

Rectification sign can invert depending on coupling and bias.

Steady-state coherence suppresses current and enhances rectification.

Transport mechanisms shift from resonant to hybridized regimes with coupling strength.

Abstract

A qubit-oscillator junction connecting as a series two bosonic heat baths at different temperatures can display heat valve and diode effects. In particular, the rectification can change in magnitude and even in sign, implying an inversion of the preferential direction for the heat current with respect to the temperature bias. We perform a systematic study of these effects in a circuit QED model of qubit-oscillator system and find that the features of current and rectification crucially depend on the qubit-oscillator coupling. While at small coupling, transport occurs via a resonant mechanism between the sub-systems, in the ultrastrong coupling regime the junction is a unique, highly hybridized system and the current becomes largely insensitive to the detuning. Correspondingly, the rectification undergoes a change of sign. In the nonlinear transport regime, the coupling strength determines whether the current scales sub- or super-linearly with the temperature bias and whether the rectification, which increases in magnitude with the bias, is positive or negative. We also find that steady-state coherence largely suppresses the current and enhances rectification. An insight on these behaviors with respect to changes in the system parameters is provided by analytical approximate formulas.