| Relativistic quantum information is a frontier research field of quantum information theory,quantum field theory,the theory of relativity,quantum optics and many other disciplines.It greatly enriches and improves the quantum information theory,and can also help us deeply understand and research the theory of relativity and other gravity theories.On the one hand,we can discuss quantum information processing tasks in the framework of relativity theory,such as the information encoding,transmission and processing of quantum resources.On the other hand,we can also with the help of quantum information measurement to conduct high-precious measurement,so as to detect the properties of spacetime,relativistic effects and related physical quantities.Therefore,It provides us with a new way for experimental verification.Without doubt,the study of quantum information in the framework of relativity theory will not only help us carry out and implement the quantum information processing tasks in reality,but also promote and guide the effective conduct of quantum information experiments in noninertial systems and curved spacetime.In this dissertation,we try to investigate the quantum coherence of multipartite systems and the effect of atomic radiation properties on entanglement in noninertial systems and curved spacetime,as well as the quantum estimation in the theory of quantum gravity.The main studies come as follows:Firstly,we discuss,in the framework of open quantum system,how the electromagnetic field of quantum fluctuation affects the quantum coherence of multi-partite systems without and with the presence of a reflecting boundary,and find the conditions under which the quantum coherence can be protected from the environment.We find:(i)in the case that a atom coupled in the multipolar scheme to a bath of fluctuating vacuum electromagnetic field,for both a single-qubit and two-qubit systems,the quantum coherence will always be damaged due to the influence of the vacuum fluctuation without a boundary.However,with the presence of a reflecting boundary,the quantum coherence can be effectively protected only when the atom is very close to the boundary and is transversely polarizable.The quantum coherence can also be protected in some degree under other conditions;(ii)in the case that a atom coupled in the multipolar scheme to a thermal bath of fluctuating vacuum electromagnetic field,without a boundary,the quantum coherence of a two-level atom will inevitably decrease due to the effect of thermal fluctuation.With the presence of a reflecting boundary,the quantum decoherence is effectively inhibited when the atom is very close to the boundary and is transversely polarizable.In particular,with the presence of two parallel reflecting boundaries,if we take some special distances for the boundaries and the atom with a parallel polarization,thus no matter where the atoms are placed between these two boundaries,the quantum decoherence is completely inhibited.Then,we study,using the formalism proposed by Dalibard,Dupont-Roc and Cohen-Tannoudji,the radiation process of two entangled atoms coupled with a massless scalar field prepared in the de Sitter-invariant vacuum.The effects of vacuum fluctuation and radiation reaction on the generation of quantum entanglement and the degradation of entangled states are identified in a quantitative way.We find that when the distance between two atoms is far less than the characteristic length scale which is a function of the radius of curvature,the cross correlation in de Sitter-invariant vacuum recovers to that in the thermal Minkowsiki spacetimeas expected.However,when the distance between atoms larger than the characteristic length scale,the cross correlation in de Sitter-invariant vacuum behaves differently compared with that in the thermal Minkowsiki space-time.In particular,the generation and degration of quantum entanglement can be enhanced or inhibited,depending not only on the specific entangled state,but also on the distance between the atoms.Finally,We analyze the quantum estimation in the theory of quantum gravity.(i)We treat the relativistic motion of a two-level atom interacting with ?-deformed massless scalar field as a detector,constructing ?-Minkowsiki spacetime in commutative spacetime,and study the ultimate precision in the estimation of the deformation parameter ?.We find that the population measurement on the detector is the optimal measurement in the estimation of the deformation parameter?.And more importantly,the relativistic motion of the detector can effectively improve this precision comparing to that of the static detector case by many orders of magnitude;(ii)We discuss,using the quantum estimation theory,the optimal estimation of parameters for scalar fields in expanding universe exhibiting Lorentz invariance violation(LIV).In the case of the LIV parameter estiation,the ultimate precision allowed by quantum mechanics can be obtained under the conditions of proper particle momentum,the maximum allowable expansion parameter of the universe and performing projective measurements onto the eigenvectors of specific probe states.In the other case of expansion parameters estimation,the ultimate precision is dependent not only on choosing the particles with some appropriate momentum mode and LIV parameter,but also on performing projective measurements onto the eigenvectors of specific probe states,which can be achieved within the current technologies. |
PDF Full Text Request