Research On Superconducting Qubit And Quantum Correlation Of Squeezed Thermal State

The main research results point to the following three aspects:1.We investigate the impact of the coupling model between the qubits and theenvironment on the entanglement dynamics in non-Markov process. We find that theentanglement degree is strongly depends on the initial quantum state and the couplingways between the qubits and the environment. The sudden death of entanglement(ESD) can be prevented by choosing the adymmetric coupling between the qubits andthe environment. We also find the dissipation phenomenon always exists when thequantum qubits system is initially in the maximally entangled mixed states.2.We study the dynamic evolution of quantum correlation of two interactingcoupled qubits system in non-Markov environment, and quantify the quantumcorrelation using concurrence and quantum discord. We find that the quantum discordis more robust than concurrence, since it can keep a positive value even when theESD happens. And we also find that by keeping the coupling between qubits andenvironment in completely symmetric, we can completely avoid the effect thedecoherence influenced on the quantum correlation and effectively prolong thesurvival time of quantum discord and concurrence. We also find that the stronger theinteraction between qubits is, the more conducive the death of the quantumcorrelation is resisted.3.We study the dynamical evolution of the concurrence and quatum discord ofinitial entangled two qubits system and squezed thermal reservoir. We find when thesystem initially at the pure decoherence-free space, the evolution of concurrence andquantum discord will never change over time and will be maintain on the initial value.What we studied before is the case of ignore the influence of temperature, but this isan ideal situation, and in the real situation the influence of temperature is inevitable.So we consider the effect of thermal disturbance of environment. We find the higherthe temperature is, the faster the concurrence decay is and the sooner the concurrencesudden death occurs. The concurrence sudden death happens at larger temperature,and the phenomenon of concurrence surrvive will never occur. In this case although the quantum discord will not be zero, but it will tend to a small constant which meansin the case of considering the exist of temperature, no matter whether concurrencesudden death occurs or not, the quantum discord will continuously reflect thequantum correlation between qubits.