Steady-state entanglement of two coupled qubits in two independent squeezed thermal reservoirs

Abstract

The steady-state entanglement of two mutually coupled qubits (each qubit interacts with its own local squeezed thermal reservoir) is investigated based on the Bloch–Redfield master equation beyond the secular approximation. In equilibrium settings (the temperatures of the two local thermal reservoirs are the same), the squeezing on both sides of the reservoir suppresses the steady-state entanglement. The steady-state entanglement is a nonmonotonic function with respect to the reservoir temperature in the equilibrium setting. Moreover, entanglement is suppressed under both squeezed vacuum reservoir and high-temperature thermal reservoir conditions irrespective of the value of the squeeze parameter. On the other hand, in non-equilibrium settings (the temperatures of the two local thermal reservoirs differ), asymmetrical squeezing significantly enhances the steady-state entanglement, which leads to higher maxima compared to the equilibrium scenarios. The temperature difference of the two reservoirs is found to be beneficial to the enhancement of the entanglement when the temperature of the high-temperature reservoir is fixed. The variations in effective temperature and eigenstate populations of the two-qubit system with respect to the squeeze parameter are also studied.