Study On Teleportation Of An Entangled Coherent State And An Entangled Squeezed State By Optical Elements

Quantum information science,mainly including quantum communication and quantum computation,is a subject of the combination of quantum mechanics and information theory.With the use of quantum states as the cartier of information and with the adoption of quantum theory to investigate the information problems,quantum information has attracted extensive interests of the academic communities due to its unique advantage.Quantum teleportation,as a branch of quantum communication,has been paid a lot of attention of both theorists and experimenters since it was originally put forward in 1993.In the process of teleportation,an unknown quantum state can be transmitted from a sender to a remote receiver without transferring the carrier of the state. In this thesis,we proposed two kinds of schemes for teleporting continuous variable quantum states by optical devices.Optical schemes for the teleportation of entangled coherent state and of entangled squeezed vacuum state were presented here,respectively.The first scheme is to almost completely teleport a bipartite entangled coherent state by using a four-partite cluster-type entangled coherent state as the consumed quantum resource.The scheme is based on optical elements such as beam splitters,phase shifters and photon detectors.We also obtain the average fidelity of the teleportation process.It is shown that the average fidelity is quite close to unity if the mean photon number of the coherent state is not too small,for instance,F_av=0.967 at |α|=3.The second scheme is to teleport a two-particle four-component squeezed vacuum state by means of a pair of entangled squeezed vacuum states.The optical elements used are beam splitters and ideal photon number detectors capable of distinguishing between odd and even photon numbers.Our results show that only if all the photon detectors obtain odd photon numbers simultaneously,the teleportation of the initial two-particle squeezed vacuum state can be achieved with unity fidelity,and the corresponding success probability only depends on the squeezing amplitude.We believe that our schemes may be helpful to understand the applications of the cluster-type entangled coherent state and the squeezed vacuum state to quantum communication and quantum information processing.