Nonequilibrium thermal entanglement in three-qubit $XX$ model

摘要

Making use of the master equation and effective Hamiltonian approach, weinvestigate the steady state entanglement in a three-qubit $XX$ model. Bothsymmetric and nonsymmetric qubit-qubit couplings are considered. The system(the three qubits) is coupled to two bosonic baths at different temperatures.We calculate the steady state by the effective Hamiltonian approach and discussthe dependence of the steady state entanglement on the temperatures andcouplings. The results show that for symmetric qubit-qubit couplings, theentanglements between the nearest neighbor are equal, independent of thetemperatures of the two baths. The maximum of the entanglement arrives at$T_L=T_R$. For nonsymmetric qubit-qubit couplings, however, the situation istotally different. The baths at different temperatures would benefit theentanglement and the entanglements between the nearest neighbors are no longerequal. By examining the probability distribution of each eigenstate in thesteady state, we present an explanation for these observations. These resultssuggest that the steady entanglement can be controlled by the temperature ofthe two baths.