Fidelity of Quantum Teleportation for Single-Mode Squeezed State Light

The fidelity of quantum teleportation of a single-mode squeezed state of light is calculated based on the general theory of quantum-mechanical measurement in the Schrodinger picture. It is shown that the criterion for the nonclassical state teleportation is different from that for coherent state. F = 1/2 is no longer the rigorous boundary between classical and quantum teleportation for a squeezed state of light. When the quantum entanglement of an Einstein-Podolsky-Rosen （EPR） beam used for teleportation and the parameters of the system are given, the fidelity depends on the squeezing of the input squeezed state. The higher the squeezing is, the smaller the fidelity is, and the lower the classical limitation of fidelity is. The dependence of the optimum gain for teleporting a squeezed vacuum state upon the EPR entanglement is also calculated. The results obtained provide important references for designing experimental systems of teleporting a non-classical state and judging the quality of the teleported quantum state.     

Continuous-variable quantum teleportation of even and odd coherent states through varied gain channels

This paper has investigated quantum teleportation of even and odd coherent states in terms of the EPR entanglement states for continuous variables. It discusses the relationship between the fidelity and the entanglement of EPR states, which is characterized by the degree of squeezing and the gain of classical channels. It shows that the quality of teleporting quantum states also depends on the characteristics of the states themselves. The properties of teleporting even and odd coherent states at different intensities are investigated. The difference of teleporting two such kinds of quantum states are analysed based on the quantum distance function.     

Improving the fidelity of continuous-variable quantum teleportation by tuning displacement gain

The fidelity of teleportation of continuous quantum variables can be improved by tuning the local displacement gain. We investigate the optimization of the fidelity for the teleportation of Schrodinger cat states, and of coherent states. It is found that the gain corresponding to the maximum fidelity is not equal to one for the two input states in the case of the small squeezing degree of the entanglement resource, while unity displacement gain is the best choice for teleporting arbitrary quantum states in the case of large squeezing.     

Thermal entanglement and teleportation of a thermally mixed entangled state of a Heisenberg chain through a Werner state

The thermal entanglement and teleportation of a thermally mixed entangled state of a two-qubit Heisenberg XXX chain under the Dzyaloshinski Moriya （DM） anisotropic antisymmetric interaction through a noisy quantum channel given by a Werner state is investigated. The dependences of the thermal entanglement of the teleported state on the DM coupling constant, the temperature and the entanglement of tbe noisy quantum channel are studied }n detail for both the ferromagnetic and the antiferromagnetic cases. The result shows that a minimum entanglement of the noisy quantum channel must be provided in order to realize the entanglement teleportation. The values of fidelity of the teleported state are also studied for these two cases. It is found that under certain conditions, we can transfer an initial state with a better fidelity than that for any classical communication protocol.     

Entanglement and Teleportation of Pair Cat States in Amplitude Decoherence Channel

The dynamic behavior of the entanglement for the pair cat states in the amplitude decoherence channel is studied by adopting the entanglement of formation determined by the concurrence. Then, we consider the teleportation by using joint measurements of the photon-number sum and phase difference with the pair cat states as an entangle resource and discuss the influence of amplitude decoherence on the mean fidelity of the teleportation.     

Preparation and Decoherence of Two-Atom Entangled States in a Dissipative Cavity

We present a scheme for generating four pairs of two-atom Einstein Podolsky-Rosen （EPR） states using the simultaneous interaction of the two atoms with a single-mode cavity field under a large detuning condition. The influence of cavity dissipation on the prepared EPR states is investigated by means of the superoperator method and the state fidelity. It is shown that some kinds of the prepared EPR states are robust against cavity dissipation and the intensity of the field, and maintain their entanglement invariance, and the others are fragile and completely destroyed by the action of cavity dissipation and the intensity of the field in the long-time limit. Decoherence time of the fragile entangled states is extremely small for a typical cavity-QED experimental data.     

Realistic teleportation of coherent states using squeezed vacuum states

This paper presents a realistic scheme for the teleportation of coherent states in which a two-mode squeezed vacuum state serves as the quantum channel and the position-sum and momentum-difference of two local modes serve as the measuring observables. The average fidelity of the teleportation of coherent states is derived for finite squeezing parameters and it turns out that fidelity greater than 1/2 cannot be achieved by using a classical channel alone and the probability distribution of the measurement result is a Gaussian distribution around the unknown parameter of the input coherent state with a width given by the squeezing parameter.     

Entanglement and photon statistics of output fields from beam splitter for binomial state inputs

The entanglement properties are investigated based on linear entropy, and nonclassicalities are examined of output fields from a beam splitter for pure binomial state inputs. It is shown that the properties of the entanglement and the photon statistics of output fields are not only strongly dependent on the parameters of input binomial states but also quite involved with the nature of the beam splitter. The best entanglement can be obtained when the parameters of both input states and the beam splitter are chosen appropriately. Finally, we analyse briefly the distinguishability between the joint input state and the joint output state.     

Experimental Quantum Teleportation of Laser Beams

We experimentally demonstrate quantum teleportation for continuous variables by using squeezed-state entanglement. A fidelity expression for a real experimental system is presented, where all the imperfection factors are considered, including losses and phase fluctuations. The measured fidelity for input coherent states is 0.62 and the prospective result with our measured entanglement and efficiencies is 0.69. We will show the details of the quantum teleportation for continuous variable and discuss the problems for further improvement in this experiment.     

Multipartite Entanglement Transfer from Multi-Mode Coherent State to Spin Qubits

The multipartite entanglement transfer from continuous variable system to spin qubits is investigated. We select multi-mode coherent field as continuous variable field. It is found that the qubits can not gain tripartite entanglement for states of close to GHZ state from the multi-mode coherent field. Moreover, the ability of the qubits gain the tripartite entanglement for states close to W state and bipartite entanglement from the continuous variable system is depended on the phase of multi-mode coherent field.     

利用单个三粒子最大GHZ态或两个EPR态隐形传送任意三粒子GHZ态

提出利用单个三粒子最大Greenberger-Horne-Zeilinger (GHZ)态或两个Einstein-Podolsky-Rosen (EPR)态作为量子信道确定性隐形传送任意三粒子GHZ态的两个方案，并将方案推广至隐形传送任意n(n≥4)粒子GHZ态的情况.讨论了量子信道受噪声影响时隐形传态的保真度.研究发现，当作为量子信道的单个三粒子最大GHZ态受到噪声影响时，隐形传态的保真度仅与量子信道的纠缠度有关，而当作为量子信道的两个EPR态受到噪声影响时，隐形传态的保真度不仅与量子信道的纠缠度有关，还与待传送态的纠缠度有关.所提出的方案具有节省量子信道纠缠资源的特点. 关键词： 隐形传态 三粒子Greenberger-Horne-Zeilinger态 量子逻辑门 保真度     

Displacement gain dependent fidelity in quantum teleportation using entangled two-mode squeezed light

We study a scheme for quantum teleportation of a single-mode squeezed coherent state using entangled two-mode squeezed vacuum. We establish the analytic expression of displacement gain dependent fidelity in terms of the squeezing coherent parameter \(r\) and quantum channel parameter \(p\) . The dependence of the optimum displacement gain for teleporting a squeezed coherent state upon the EPR entanglement is discussed. It shows that the fidelity of teleportation can be improved by tuning the displacement gain. We find that the fidelity increases with the increase of EPR parameter, while it decreases with the increase of the squeezing coherent parameter of the signal. We get infinite squeezing as a resource is required for an ideal and perfect teleportation of unknown input states. We show that the nonclassical properties of an unknown state to be teleported can be preserved in the teleportation.     

Entanglement fidelity of the standard quantum teleportation channel

We consider the standard quantum teleportation protocol where a general bipartite state is used as entanglement resource. We use the entanglement fidelity to describe how well the standard quantum teleportation channel transmits quantum entanglement and give a simple expression for the entanglement fidelity when it is averaged on all input states.     

Entanglement Teleportation via One Dissipative Quantum Channel

Entanglement teleportation via one dissipative quantum channel composed by two identical spatially separated atoms in free space is investigated in detail. We mainly study the effects about the channel initial states and the interqubit distance on the entanglement of the output state C_out and the average fidelity F _a. It is shown that the magnitude of teleportated entanglement and the average fidelity is strongly dependent on the above factors. For different channel initial states with increasing input entanglement, the teleportated entanglement is zero initially, but at some finite values the teleportated entanglement emerges, and it then increase linearly as these finite input entanglement values are reached. We also obtain that the interqubit distance enhance the teleportated entanglement and the average fidelity peridicly, so we can find a threshold value of the interqubit distance which is most suitable for entanglement teleportation. Meanwhile, the values of the teleportated entanglement and the average fidelity are always zero when the value of the interqubit distance is zero.     

Some New Solutions of Jacobi Elliptic Functions to mBBM Equation

The modified mapping method is further improved by the expanded expression of u（ξ） that contains the terms of the first-order derivative of function f（ξ）. Some new exact solutions to the mBBM equation are determined by means of the method. We can obtain many new solutions in terms of the Jacobi elliptic functions of the equation.     

两个海森堡热纠缠信道中纠缠态的隐形传送

利用两个海森堡热纠缠信道,实现了一对量子纠缠态的隐形传送,求得输出的密度矩阵,进而算出隐形传送的保真度.分析外界环境（温度T和磁场B）对热纠缠及量子隐形传送的影响.发现在磁场较弱,温度很低的时候,以海森堡热纠缠混合态作为量子信道进行隐形传送优于经典信道.     

Continuous-Variable Entanglement and Wigner-Function Negativity via Adding or Subtracting Photons

The performance of adding or subtracting photons on two-mode squeezed thermal states via examining the Einstein–Podolsky–Rosen (EPR) correlation, the Hillery–Zubairy (HZ) correlation, the fidelity of teleportation, and the negativity of Wigner function is theoretically investigated. The normalization factors and the teleportation fidelity are related to Jacobi polynomials, and the (evolved) Wigner functions are simply associated with two-variable Hermite polynomials. Compared with the original squeezed thermal states, the EPR correlation and the teleportation fidelity can be enhanced by photon subtraction and basically weakened by photon addition symmetric operations, but they cannot be enhanced for both photon addition and subtraction asymmetric cases. Also, HZ correlation can provide a better option relative to the EPR correlation in detecting the entanglement, and the fidelity for teleporting a squeezed state with a large squeezing can also be enhanced via photon addition symmetric operations, in contrast to teleporting a coherent state. Additionally, the nonclassicality is discussed in terms of the negativity of the (evolved) Wigner functions, which shows that photon addition and subtraction and the squeezing cannot restrain the deteriorate of nonclassicality, and the evolved Wigner functions become Gaussian (corresponding to vacuum) with long decay times as a result of amplitude decay.     

利用非Bell基测量实现两粒子纠缠态的隐形传输

研究无Bell基测量的未知两粒子纠缠态的隐形传态方案。Alice需传送未知两原子纠缠态给Bob,以她和Bob的原子组成的最大纠缠GHZ态作为量子信道,通过两原子同时在一个强经典驱动场驱动下和一个单模腔场发生相互作用,产生态的演化,从而实现隐形传态。本方案可忽略腔场热作用和腔延迟作用的影响,传送成功的总几率为1。