The Influence Of The Common Non-equilibrium Environment On The Quantum Correlation Of The Two-level Composite System

Quantum entanglement is the rare resource to realize quantum information,but the actual quantum system is always inevitably contact with the external environment and cause dissipation,resulting in the attenuation of quantum entanglement.Therefore,it is of great significance to study the dynamic properties of quantum entanglement in various environments.In this article,the effects of various parameters on the entanglement and the thermodynamic properties are studied,including the following aspects.1.We study the steady-state entanglement and thermalization of two coupled qubits embedded in two common baths with different temperatures.With the quantum master equation constructed and resolved in the eigenstate representation of the coupled qubits,we demonstrate the variations of steady-state entanglement with respect to various parameters of the qubits' system in both thermal equilibrium and nonequilibrium cases.The coupling strength and energy detuning of the qubits as well as the temperature difference of the lower temperature baths are found to be beneficial to the enhancement of the entanglement.We note a dark state of the qubits that is free from time-evolution and its initial population can greatly influence the steady-state entanglement.By defining the effective temperature,we also study the thermalization of the coupled qubits and their variations with energy detuning.It is found that two qubits can be thermalized to the same temperature as the heat baths in the thermal equilibrium case,but it can not be realized in the nonequilibrium environment.2.We investigate the thermalization and steady-state entanglement of three qubits XX model.Consider the system formed by three qubits,which are coupled to two bosonic thermal reservoirs,where the two adjacent quantum qubits contact with the same thermal reservoirs.Both symmetric and nonsymmetric couplings including qubit-qubit and qubit-thermal reservoir are considered.By establishing and solving the master equation,we discuss the dependence of thermalization of system on the couplings and thermal reservoirs' temperature.The results show that for symmetric case,the effective temperature of mediate qubit is always higher than mean temperature of two thermal reservoirs except the coupling strength between intermediate qubit and two reservoirs is low.For nonsymmetric systems,when the coupling strength between the intermediate qubit and one of the thermal reservoirs is large,the heat currents between the another qubit which connected to the same thermal reservoir and the intermediate qubit is unidirectional.We also investigate the thermal entanglement of three qubits chain model.We discuss the dependence of entanglement of subsystem on the couplings and thermal reservoirs' temperature.The results show that,when the symmetric system is in the thermal equilibrium,thesteady-state entanglement between two qubits is at different extremes based on the mean temperature of the two thermal reservoirs.If the temperature of two thermal reservoirs are equal,the steady-state entanglement is not affected by the intensity of the coupling strength between the intermediate qubit and the two thermal reservoirs(for simplicity,we assumed that the intermediate qubit has the same coupling strength with two thermal reservoirs).But in a nonsymmetric case,the coupling strength plays a key role for steady-state entanglement.Finally,the summary and prospect of this article are given.