Dynamics Of Quantum Correlations For Two Qubits In Environments

Quantum entanglement,quantum discord,and quantum deficit are vital physical quantities in the study of non-classical correlations,all of them taking a crucial role in completing quantum information tasks.So far,the studying of quantum discord has mostly focused on two-qubit X-type states because of the complicated calculation.The analytical expressions of quantum discord are available only for Gaussian states,specific two-qubit states,and some symmetric states.In this work,we investigate quantum entanglement,quantum discord,quantum deficit for non X-type states in two qubits in environment,where the entanglement is measured via the generalized negativity and concurrence.In addition,some comparisons between them are made.Firstly,we introduce the theory of quantum information.We give the definitions of entanglement measures,the generalized negati-vity and concurrence,which are used extensively.Also,the measurement induced correlations,quantum discord and quantum deficit,are presented.Additionally,two.important-numerical methods,Monte Carlo simulation and Downhill simplex method,are introducedSecondly,using those two methods,we numerically simulate quantum discord and quantum deficit for non X-type states in two qubits in environment,where entanglement negativity and concurrence are calculated.It shows that negativity and concurrence exhibit similar decay in the dynamical evolution.For a given initial state,they are sudden death at the same time when thermal photon number and spontaneous emission rate are properly chosen.Moreover,quantum discord and quantum deficit behave similarly.For example,both of them have their maximal and minimal values.However,quantum discord increases while quantum deficit decreases in the middle time of evolution.Remarkably,quantum deficit exhibit a sudden change,and it exists an unchanged segment for proper parameters of thermal reservoir.In addition,the decay of entanglement is more quickly than discord and deficit.These non-classical correlations for various model parameters are useful in the understanding of the dynamical characters of quantum correlations for two qubits in environment.In summary,we have characterized the quantum correlations for non X-type states in two-qubit systems.We hope those could motive one to explore the influence of environment on quantum correlations,and characterize quantium discord and entanglement in multipartite systems.