Some Characterizations And Judgements Of Quantum Steering In Bipartite Systems

Quantum steering,as a very important quantum property,was firstly found by Schroodinger in the context of famous Einstein-Podolsky-Rosen(EPR)paradox.It is then called the EPR-steering.This important property exhibits correlations and nonlocality of a composite quantum system and so becomes a valuable resource of quantum information processing.In this dissertation,we introduce some concepts on quantum steering based on positive operator-valued measurements and obtain their characterizations and sufficient conditions.Secondly,we introduce and discuss the steered states induced by a measurement and prove some conditions for a steered state to be a conditional pure state.Lastly,we derive an EPR-steering inequality,with which the EPR steerability of the maximally entangled states are checked.This dissertation is divided into the following four chapters.In Chapter 1,we introduce some research backgrounds and status related to our main contents,and review some basic definitions in quantum information which will be used in this paper.In Chapter 2,we give the definitions and characterizations of quantum steering and prove some properties on it and give some examples.In Chapter 3,we introduce the definition of a steered state and prove some conditions for a steered state to a conditional pure sate with some propositions and corollaries.In Chapter 4,we study the steering conditions for a bipartite quantum state and obtain a steering inequality,which can be used to determine whether a quantum state is steerable.Furthermore,we give some examples and prove that a maximally entangled state is steerable by using the derived steering inequality.