Abstract
Quantum thermal transport and two-photon statistics serve as two representative nonequilibrium features in circuit quantum electrodynamics (cQED) systems. Here we investigate quantum heat flow and two-photon correlation function at steady state in a composite qubit-resonator model, where one qubit shows both transverse and longitudinal couplings to a single-mode optical resonator. With weak qubit-resonator interaction, we unravel two microscopic transport pictures, i.e., cotunneling and cyclic heat exchange processes corresponding to transverse and longitudinal couplings, respectively. The nonmonotonic behavior of the heat current is exhibited by tuning the temperature bias with the weak longitudinal coupling. At strong qubit-resonator coupling, the heat current also exhibits a nonmonotonic feature by increasing qubit-resonator coupling strength, which tightly relies on the scattering processes between the qubit and the corresponding thermal bath. Furthermore, the longitudinal coupling is preferred to enhance heat current in the strong qubit-resonator coupling regime. For two-photon correlation function, it exhibits an antibunching-to-bunching transition by tuning the composite angle, which is mainly dominated by the modulation of the energy gap between the first and the second excited eigenstates. Our results are expected to deepen the understanding of nonequilibrium thermal transport and nonclassical photon radiation based on the cQED platform.
Highlights
Deep understanding and efficient characterization of nonequilibrium excitation processes via quantum light-matter interactions constitute an active frontier for quantum optics and quantum transport [1–5]
It is found that for small θ, the heat current exhibits a monotonic increase by increasing the temperature bias T, in the limit of θ = 0, i.e., the dissipative quantum Rabi model (QRM)
In the large θ regime, the heat current is changed to shown nonmonotonic behavior, i.e., the current is first enhanced and later suppressed with the increase of T, which identifies the signature of the negative differential thermal conductance (NDTC) [84–88]
Summary
Deep understanding and efficient characterization of nonequilibrium excitation processes via quantum light-matter interactions constitute an active frontier for quantum optics and quantum transport [1–5]. For the influence of the composite qubit-photon interaction on nonequilibrium heat flow and the microscopic picture in dissipative qubit-resonator hybrid systems, e.g., QRM, there currently is a lack of exploration, which is crucial to deepen the understanding of nonequilibrium heat transport based on the cQED platform. For the cQED systems, an alternative scheme, i.e., longitudinal coupling between the qubit and the resonator, can be realized based on the superconducting circuit engineering [64,65], which has pronounced consequences for nonclassical-photon-state generation [66–68], scalable circuit design [69,70], and fast nondemolition qubit readout [71,72]. The current is changed to show a nonmonotonic feature with longitudinal qubit-resonator coupling, which is dominated by cyclic heat exchange transitions These two distinct microscopic processes are crucial to unraveling the physics pictures of quantum thermal transport in dissipative cQED systems.
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