Managing Quantum Heat Transfer in a Nonequilibrium Qubit-Phonon Hybrid System with Coherent Phonon States

We investigate quantum heat transfer in a nonequilibrium qubit-phonon hybrid open system, dissipated by external bosonic thermal reservoirs. By applying coherent phonon states embedded in the dressed quantum master equation, we are capable of dealing with arbitrary qubit-phonon coupling strength. It is counterintuitively found that the effect of negative differential thermal conductance is absent at strong qubit-phonon hybridization, but becomes profound at weak qubit-phonon coupling regime. The underlying mechanism of decreasing heat flux by increasing the temperature bias relies on the unidirectional transitions from the up-spin displaced coherent phonon states to the down-spin counterparts, which seriously freezes the qubit and prevents the system from completing a thermodynamic cycle. Finally, the effects of perfect thermal rectification and giant heat amplification are unraveled, thanks to the effect of negative differential thermal conductance. These results of the nonequilibrium qubit-phonon open system would have potential implications in smart energy control and functional design of phononic hybrid quantum devices.