Theoretical And Experimental Research On Quantum Coherence And Related Problems

At present,quantum information science has become a research hotspot of cutting-edge science.It has attracted much attention because of its quantum superiority beyond classical systems.In 2021,it was listed as a new undergraduate major by the Ministry of Education.In-depth research has significant and far-reaching strategic implications.In this paper,quantum coherence and quantum guidance are the main research contents,In theoretical research,the coherence migration in high-dimensional bipartite systems is studied,and in experimental research,the coherent complementary relationship is verified by using linear optical systems,and both aspects have achieved innovative results of certain significance,mainly including the following aspects:1.Coherence migration in high-dimensional bipartite systemsThe conservation law for first-order coherence and mutual correlation of a bipartite qubit state is firstly proposed by Svozilík et al.,and their theories laid the foundation for the study of coherence migration under unitary transformations.In this paper,we generalize the framework of first-order coherence and mutual correlation to an arbitrary(m(?)n)-dimensional bipartite composite state by introducing an extended Bloch decomposition form of the state.We also generalize two kinds of unitary operators in high-dimensional systems,which can bring about coherence migration and help to obtain the maximum or minimum first-order coherence.Meanwhile,the coherence migration in open quantum systems is investigated.We take depolarizing channels as examples and establish that the reduced first-order coherence of the principal system over time is completely transformed into mutual correlation of the(2(?)4)-dimensional system-environment bipartite composite state.It is expected that our results may provide a valuable idea or methods for controlling the quantum resource such as coherence and quantum correlations.2.Experimental verification of the relationship about coherence and steerabilityCoherence and steerability are two essential characteristics of quantum systems.For a two-qubit state,the first-order coherence and the maximal violation of linear steering inequality are used to operationally measure the degree of coherence and steerability,respectively.Recently,a complementary relation between first-order coherence and linear steerability has been proposed.In this paper,we report an experimental verification of the complementary relation by preparing biphoton polarization entangled states in an all-optical setup.We propose an operable method for experimental measurement of the first-order coherence and linear steerability and calculate the purity of the initial states by reconstructing the density matrices of them.The experimental results coincidence with the theoretical predictions very well,which provides a valuable reference for the application of optical quantum technology.