| Quantum weak measurement, which is a generalization of Von Neumann measurements and associated with a positive-operator valued measure (POVM), has drawn much attention, recently. Based on the quantum weak measurement, schemes for protecting quantum entanglement from depolarizing noise environment and improving parameter estimation precision have been proposed, respectively. Investigating black hole information from the view of quantum information not only promises a deeper comprehension about relativity theory, quantum mechanics and quantum field theory, but also offers a new method of understanding the information paradox existing in black hole. This paper also explored the property of various correlation measures for open Dirac system with Hawking effect in Schwarzschild space-time. The major results have been listed as the following:(1) Weak measurements can effectively suppress amplitude-damping decoherence. In the paper, we have studied the effect of this method in protecting the entanglement of two qubits from independent depolarizing noisy channels. The scheme consists of prior weak measurement on each qubit before the interaction with the noisy channel followed by a post recovering measurement. It has shown that the two-qubit entanglement can be enhanced to an optimal value by performing weak measurement and adjusting measurement parameter on one qubit. The effectiveness of our scheme is more pronounced in improving the two-qubit system with less initial entanglement. In addition, the maximal value of entanglement does not depend on the initial-state parameters.(2) As an indicator of estimation precision, quantum Fisher information (QFI) lies at the heart of quantum metrology theory. In this work, an effective scheme for enhancing QFI has been proposed by utilizing quantum weak measurements. Two kinds of strategies for the arbitrary two-qubit pure state with weight parameter α and phase parameter β are implemented under different situations, respectively. We have derived the explicit conditions for the optimal measurement strengths, and verified that the QFI can be enhanced quite well. Meanwhile, due to the relation of quantum correlation and QFI, the maximal value of QFI associated with phase parameter is always equal to 1. It is worth noting that since weak measurement operation does not induce any disturbance on the value of phase parameter, the optimal measurement strength is only related to the weight parameter. Additionally, the scheme also can be extended to improve the parameter estimation precision for an N-qubit pure state.(3) The performance of various correlation measures for open Dirac system with Hawking effect in Schwarzschild space-time has been explored. The results have indicated that the impact of Hawking effect on physical accessible entanglement is weaker than that of decoherence. For generalized amplitude damping (GAD) channel, the entanglement sudden death (ESD) has been analyzed in detail, and the inequivalence of quantization for Dirac particles in the black hole and Kruskal space-time has been verified via quantum discord measure. In addition, as an example for interpreting Bell non-locality, we also have investigated the GAD channel with Hawking effect. It can be noticed that there is a boundary line of Bell violation for physically accessible states. That is, quantum non-locality would disappear when Hawking temperature exceeds a certain value. This critical temperature increases as decoherence parameter decreases. In the case of phase damping (PD) channel, the interaction between the particle and noise environment does not produce bipartite system-environment entanglement. Then we have discussed entanglement distributions, and found that the reduced physically accessible entanglement can be redistributed to physical inaccessible region. At last, we have extended our investigation to an N-qubit system, and obtain a universal expression of the physical accessible entanglement. |
PDF Full Text Request