Quantum Coherence And Quantum Correlations In Relativistic Framework

Relativistic quantum information is an emerging cross-cutting field and consists of quantum information,quantum mechanics,quantum field theory and relativi-ty.It mainly studies the influence of gravity on quantum correlations,quantum coherence and quantum key distribution.It also probes the property of spacetime through quantum information.In addition,Schwinger predicted that the vacuum is unstable and decays into particle-antiparticle pairs under strong electromanetic field.This is the Schwinger effect.In this article,we will study the influence of gravity on multipartite coherence,Gaussian coherence and Gaussian steering,and study the redistributions of entanglement,discord and mutual information under the Schwinger effect.The article mainly includes the following works:Firstly,we study quantum coherence in curved spacetime.?1?We study the quantum coherence of Greenberger-Horne-Zeilinger-like states for multimode Dirac fields in the background of a Schwarzschild black hole.We find that the evolu-tions of l₁-norm of coherence and relative entropy of coherence are similar,though the two measures are not completely compatible.The accessible coherence always degrades monotonically by the Hawking effect,and the inaccessible coherence in-creases from zero monotonically or non-monotonically,depending on the ratio of mode number between the inaccessible modes and the accessible modes.Both the accessible and inaccessible coherences have the phenomenon of freezing.The monogamies for the l₁-norm of coherence between the accessible and inaccessible modes are established.?2?We study the quantum coherence and monogamy rela-tionship of a tripartite W-State entangled system for Dirac fields in the background of a Schwarzschild black hole.We find that quantum coherence first decreases and then shows the phenomenon of freezing with the growth of the Hawking tem-perature.We also find that the l₁norm of coherence of a tripartite W-State is always equal to the sum of coherence of all bipartite systems for any Hawking temperature,while the monogamy relationship between the REC of tripartite W-State and the sum of REC of all bipartite systems changes with the increase of the Hawking temperature.Moreover,we extend related investigations to the N-partite W-State.The monogamy relationship for l₁norm of coherence is still satisfied.In the infinite Hawking temperature limit,quantum coherence for the case of one accelerated observer asymptotically approaches initial quantum coherence when N??,and quantum coherence for the case of N-1 accelerated observers also maintains half of initial coherence when N??.These results show that the N-partite W-State is a good quantum resource for the task of processing relativis-tic quantum information.?3?We study quantum coherence of two-mode Gaussian states in the background of an asymptotically flat black hole.An inertial observer Alice observes mode A;an accelerated Bob who hovers near the event horizon of the black holes observes mode B;an imaginary observer Anti-Bob inside the event horizon of the black holes observes mode?B.We find that quantum coherence between mode A and mode B is reduced by the Hawking thermal bath.However,it does not vanish in the limit of infinite Hawking temperature but is frozen to a certain value that is an increasing function of the squeezing parameter.We also find that the quantum coherence between mode A and mode?B,mode B and mod-e?B,increases with the Hawking temperature,which implies the transfer and/or generation of the quantum coherence assisted by the Hawking effect.Finally the monogamy relationship of quantum coherence is discovered.Secondly,we study quantum steering in curved spacetime.?1?We study the Gaussian steering in the two-mode squeezed states shared by two accelerated ob-servers.We find that the steerability degrades with the increasing of the accel-erations of the two observers.An interesting discovery is that the observer who has larger acceleration has stronger steerability than the other one.We find the condition for the occurrence of maximal steering asymmetry.We also find the parameter regions for two-way,one-way and no-way steering.?2?We study the effects of Hawking radiation and bath temperature on quantum steering and en-tanglement for a two-mode Gaussian state exposed in the background of a black hole and immersed in the two independent thermal baths.We find that both the two effects can destroy the quantum steering and entanglement.Quantum steering always exists sudden death for finite Hawking temperature and bath temperature,but entanglement does not in zero temperature thermal bath.Both the Hawking radiation and the asymmetry of thermal baths can induce the asymmetry of quan-tum steering,but the latter effect is much weaker than the former.An unintuitive result is that the observer who stays in the Hawking radiation or in the thermal bath with higher temperature has more stronger steerability than the other one.We also find that Hawking radiation and thermal noise can change the asymptotic behavior of steering and entanglement versus the squeezing parameter.Finally,we study the Schwinger effect of Gaussian correlations?quantum en-tanglement,discord and mutual information?of a two-mode Gaussian state shared by Alice and Bob,paying special attention to the comparison between our result and that of fermion-fermion and qubit-bosonic systems studied previously.We also study the redistribution and conservativeness of the correlations under the Schwinger effect.