Quantum Correlation And Multipartite Entanglement In The Background Of Schwarzschild Black Hole

In this paper, we investigate the effect of Hawking radiation on the quantum correlation and multipartite entanglement of Dirac particles in the background of a Schwarzschild black hole. In addition, an optimal scheme is proposed to suppress decoherence in independent non-Markovian environments by performing prior weak measurement and post measurement reversal. Firstly, we summarize the measurement methods of quantum entanglement and quantum correlation, including Concurrence, Entanglement of formation,π-tangle, Quantum discord, and so on. Then, we obtain some research results, which are listed as follows:(1) We analytically explore the effect of the Hawking radiation on the quantum correlation and Bell non-locality for Dirac particles in the background of Schwarzschild black hole. It is shown that when the Hawking effect is almost nonexistent, corresponding to the case of an almost extreme black hole, the quantum properties of physically accessible state are same for the initial situation. For finite Hawking temperature T, the accessible quantum correlation monotonously decreases along with increasing T owing to the thermal fields generated by the Hawking effect, and the accessible quantum non-locality will be disappeared when the Hawking temperature more than a fixed value which increases with the parameter r of Werner state growing. Then we analyze the redistribution of quantum correlation, and find that for the case of the Hawking temperature is infinite, corresponding to the case of the black hole evaporating completely, the quantum correlation of physically accessible state equals to one of the inaccessible states. For Bell non-locality, we also find that the quantum non-locality is always extinct for the physically inaccessible states, and the strength of non-locality decreases with enlarging the intensity of Hawking effect when the non-locality is existent in physically accessible state.(2) The effect of Hawking radiation on the multipartite entanglement of Dirac particles in the background of a Schwarzschild black hole is investigated. It is shown that all the one-tangles decrease as the Hawking temperature growing and the Coffman-Kundu-Wootters (CKW) monogamy inequality is always saturated in this system. It is also shown that the entanglement’s status of subsystems, which have the same quantum state, depend on its detector’s position, and this proposition can be generalized to multipartite system. Then we find that the Hawking effect does not change the entanglement structure of the quantum state in Schwarzschild space-time. In addition, we discuss the distributions of quantum information, and find that not only the entanglement is redistributed but also the mutual information is distributed to physical unaccessible region. At last, we calculate the mutual information of a N-qubit multipartite system: and draw a conclusion that when the black hole approximates evaporating completely, the mutual information of this system will close to (N-1)/N of original if a particle freely falls in toward a Schwarzschild black hole and locates near the event horizon, and the other particles remain at the asymptotically flat region.(3) We investigate the dynamics of concurrence and quantum discord (QD) for the Werner state in independent non-Markovian environment. Our result manifests QD reveal more properties about quantum correlations than concurrence for the given system. Additionally, an optimal scheme is proposed to suppress decoherence by performing prior weak measurement and post measurement reversal. It is worth noticing that the effect of our scheme is better for the larger measurement strengths, and the stronger decoherence suppression induces smaller selection probability.