Studies On Quantumness And Classicality Of Quantum States

Many quantum technologies,such as quantum teleportation,quantum dense coding,are based on quantum coherence and quantum entanglement of quantum states.These quantities are closely related to the quantumness of quantum states.Quantumness and classicality of quantum states have important theoretical significance and application value for the development of quantum technologies.Firstly,the influence of intermediate many measurements on the quantumness of a damped and driven qubit system is studied.Uniform and random time-interval sequences(TISs)are respectively considered.The quantumness is identified by the quantum witness(wq).Numerical results show that when intermediate measurement time N is tens,the value of wq at given evolution time ? and dephasing intensity y depends on the kind of TIS,while when N is larger,it is almost independent of the kind of TIS.Further,Wq ?Wqmax(N)=(1-1/2N)exp(-??)for all the three TISs,where Wqmax(N)is the maximum value of the quantum-witness when N times intermediate measurements are applied.Secondly,quantumness of the photon-added two-mode squeezed coherent state is studied.The? and ?1 phase,the photon-added number,displacement parameters,and squeezing parameter are respectively considered.The quantumness is quantified by the minimum of degree of the sum squeezing Smin.Numerical results show that when the photon-added number is relatively larger,displacement parameters of two modes are equal and they are relatively larger,the squeezing parameters are relatively larger,it is good for photon-added two-mode squeezed coherent state to remain nonclassicality.Finally,the quantum Shannon information entropy of a family of one-dimensional nearest-neighbor tight-binding models is studied.The Shannon information entropy in position space Sx and the Shannon information entropy in momentum space Sp obey the entropy uncertain relationship.They are complementary.To a certain extent,they can quantitatively measure wavelike and particlelike properties.Numerical results show that for extended states,Sx>Sp,while for localized states,Sx<Sp It reflects complementary relationship of Shannon information entropy in position space Sx and the Shannon information entropy in momentum space Sp.The mobility edges reflected from these quantities are same as analytical values.