Entanglement And Non-classical Properties Of Gaussian And Non-gaussian States With Continuous-Variable

The quantum states with continuous variables have attracted much attention due to easy generation and manipulation compared to those with discrete variables. In addition, the non-Gaussian states generally possess more obvious nonclassical properties, higher entanglement and stronger fidelity of quantum teleportation than the Gaussian states, which shows that the non-Gaussian states can more effectively satisfy the needs of the application. In this paper, we introduce some new Gaussian and non-Gaussian states, generated by using Gaussian and non-Gaussian operations, then discuss their nonclassical properties and investigate the entanglement, quantum teleportation, so that we can further develop the extensive application and quantum state engineering.Firstly, we introduce a new non-Gaussian state which is Hermite polynomial excitation squeezed vacuum(SV)(?)? ? 0nH O S r with ??O ??a ??a. We investigate analytically the nonclassical properties according to Mandel’s Q parameter, second correlation function, squeezing effect and the negativity of Wigner function(WF). It is found that all these nonclassicalities can be enhanced by(?)nH O operation and adjustable parameters ? and ?. In particular, the optimal negative volumeopt? of WF can be achieved by modulating ? and? for n ?2, while ? is kept unchanged about 0.2131 for n ?1. Furthermore, the decoherence effect of phase-sensitive enviornment on this state is examined. It is shown that the nagative area gradually dissapears with the increases of n and ?t while increases with parameter M and the nagative volume ? with a bigger n diminishes more quickly than that with a lower n, which indicates that single-photon subtraction SV presents more roboustness. Parameter M of reservoirs can be effectively used to improve the nonclassicality.Secondly, we introcuce one- and two-mode combination squeezed thermal states(OTCSTS), a Gaussian state and investigate the property of entanglement in details. It is found that the OTCSTS possesses higher entanglement than the usual two-mode squeezed thermal states. It is shown that the teleportation fidelity can only be enhanced within a certain region of parameters by using the OTCSTS as an entangled channel, which is just the same as the condition exhibiting stronger squeezing in one quadrature. In addition, the condition realizing effective quantum teleportation(>1/2) is obtained analytically.Finally, a new entangled quantum state is introduced by applying local coherent superposition(?ra ?ta) of photon subtraction and addition to each mode of entangled coherent state(ECS) and the properties of entanglement are investigated. It is found that the Einstein-Podolsky-Rosen(EPR) inseparability of the ECS can be improved due to the coherent superposition operation. However, the degree of entanglement and the average fidelity of quantum teleportation can be enhanced only for the even ECS. The effects of improvement by coherent superposition operation is better than those by single(?a) and two-photon(? ?a b) addition under a small region of amplitude. In addition, the nonclassical properties are also discussed according to the negativity of WF.