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arXiv:2507.10282 · Physical Review Research

Thermal rectification in a qubit-resonator system

Luca Magazzù, Elisabetta Paladino, Jukka P Pekola, Milena Grifoni

Published Sep 22, 2025• 1 citation
arXivHTMLPDF

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 subsystems, in the ultrastrong coupling regime the junction is a unique, highly hybridized system and 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 superlinearly 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.

DOI
10.1103/qx79-py6k

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We theoretically investigate a quantum heat diode based on two interacting flux qubits coupled to two heat baths. Rectification of heat currents is achieved by asymmetrically coupling the qubits to the reservoirs, which are modeled as dissipative RLCRLCRLC resonators. We find that the coherent interaction between the qubits can be exploited to enhance the rectification factor, which otherwise would be constrained by the temperatures and couplings of the baths. Remarkably high values of the rectification ratio, up to $\mathcal{R}\ensuremath{\sim}3.5$, can be obtained for realistic system parameters, with an enhancement up to approximately $230\mathrm{%}$ compared to the noninteracting case. The system features the possibility of manipulating both the rectification amplitude and direction, allowing for an enhancement or suppression of the heat flow to a chosen bath. For the parameter regime in which rectification is maximized, we find a significant increase of the rectification above a critical interaction value, which corresponds to the onset of a nonvanishing entanglement in the system. Finally, we discuss the dependence of the rectification factor on the bath temperatures and couplings.
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Nonequilibrium thermal transport in circuit quantum electrodynamics emerges as one interdisciplinary field, due to the tremendous advance of quantum technology. Here, we study steady-state heat flow in a two-mode qubit-resonator model under the influence of both the qubit-resonator and resonator-resonator interactions. The heat current is suppressed and enhanced by tuning up resonator-resonator interaction strength with given weak and strong qubit-resonator couplings respectively, which is cooperative contributed by the eigen-mode of coupled resonators and qubit-photon scattering. Negative differential thermal conductance and significant thermal rectification are exhibited at weak qubit-resonator coupling, which are dominated by cycle transition processes. Moreover, the heat flow through the resonator decoupled from the qubit can be dramatically enhanced via the resonator-resonator interaction, which is attributed by the generation of eigen-mode channels of resonators.
We put forward a quantum-optical model for a thermal diode based on heat transfer between two thermal baths through a pair of interacting qubits. We find that if the qubits are coupled by a Raman field that induces an anisotropic interaction, heat flow can become nonreciprocal and undergoes rectification even if the baths produce equal dissipation rates of the qubits, and these qubits can be identical, i.e., mutually resonant. The heat flow rectification is explained by four-wave mixing and Raman transitions between dressed states of the interacting qubits and is governed by a global master equation. The anisotropic two-qubit interaction is the key to the operation of this simple quantum thermal diode, whose resonant operation allows for high-efficiency rectification of large heat currents. Effects of spatial overlap of the baths are addressed. We discuss the possible realizations of the model in various platforms, including optomechanical setups, systems of trapped ions, and circuit QED.
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Recent experiments in hybrid-quantum systems facilitate the potential realization of one of the most fundamental interacting Hamiltonian-reservoir systems, namely the single-site Bose-Hubbard model coupled to two reservoirs at different temperatures. Using Redfield equations in a Born-Markov approximation, we compute nonequilibrium average particle number, energy, and currents beyond linear response regime, both time dynamics and steady state, and investigate its dependence on various tunable parameters analytically. We find interesting scaling laws in high-temperature regimes that are independent of choice of bath spectral functions. We also demonstrate that the system shows very interesting particle and energy current rectification properties which can be controlled via the relative strength of interaction and temperatures, as well as via the degree of asymmetry in system-bath coupling. Specifically, we find inversion of direction of energy rectification as a function of the relative strength of the interaction strength and the temperatures. We also show that, in the limit of low-temperature and high interaction strength, our results are consistent with the nonequilibrium spin-Boson model. Our results are experimentally relevant not only to hybrid quantum systems but also in other areas such as molecular junctions.