Quantum Teleportation Through a Two-Qubit Heisenberg XXZ Chain

We consider a two-qubit Heisenberg XXZ chain as a resource for quantum teleportation via the standard teleportation protocol To. The effects of anisotropic on teleportation fidelity and entanglement are studied in detail. We find anisotropic not only improves the criticM temperature Tc and criticM magnetic field Bc, beyond which quantum teleportation is inferior to classicM communication protocol, but also enhances the fidelity for fixed magnetic field B and temperature T. For entanglement teleportation, the effects of magnetic field on average fidelity and output entanglement are studied.     

Standard Teleportation of One-Qubit State and Partial Teleportation of Two-Qubit State via X-States

In this article,we derive the explicit entanglement and fidelity expressions for a larger class of two-qubit states,namely,a seven-parameter family of so called X-states.The analytical expressions of the entanglement,the output entanglement and the average fidelity are obtained for this general model by using the concept of concurrence and average fidelity.We study the relations between quantum entanglement,the output entanglement,and the average fidelity for standard teleportation of one-qubit and partial teleportation of two-qubit state.We discover that the average fidelity and entanglement is not a simple dependence relation.The higher entangled system is helpful for teleportation.     

Entanglement Teleportation via a Two-Qubit System with Anisotropic Couplings under a Different Nonuniform Magnetic Field

We examine entanglement teleportation,characterized by average fidelity,of two-qubit XY Z spin chain under different nonuniform magnetic field.The entanglement teleportation and the fidelity of entanglement teleportation are investigated separately.We show explicitly that the fidelity of entanglement teleportation can be enhanced by changing the direction of the magnetic field.This means that we can always get optimal fidelity by choosing the directions of magnetic field in the process of quantum teleportation.Moreover,the results show that in some cases the ferromagnetic chain also is a qualified candidate in the process of teleportation protocol.     

Quantum teleportation via a two-qubit Heisenberg <Emphasis Type="Italic">XXZ</Emphasis> chain – effects of anisotropy and magnetic field

We study quantum teleportation via a two-qubit Heisenberg XXZ chain under an inhomogeneous magnetic field. We first consider entanglement teleportation, and then focus on the teleportation fidelity under different conditions. The effects of anisotropy and the magnetic field, both uniform and inhomogeneous, are discussed. We also find that, though entanglement teleportation does require an entangled quantum channel, a nonzero critical value of minimum entanglement is not always necessary.     

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.     

Quantum Entanglement and Teleportation in a Vertical Quantum Dot

We study the thermal entanglement and teleportation using quantum dot as the quantum channel. We firstly investigate the evolution of entanglement in the vertical quantum dot, then focus on the effects of the important parameters of the system on the teleported fidelity under different conditions. We obtain the critical temperature of suddenly dead entanglement. Based on Bell measurements in two subspaces, the isotropy and anisotropy subspaces, we can find that the anisotropy measurements always overmatch the isotropy ones. Moreover, we obtain the high-fidelity teleportation for quantum dot as quantum channel when the parameters are adjusted. The possible applications of quantum dot are expected in quantum teleportation     

High-fidelity teleportation beyond the no-cloning limit and entanglement swapping for continuous variables

We experimentally demonstrate continuous-variable quantum teleportation beyond the no-cloning limit. We teleport a coherent state and achieve the fidelity of 0.70 +/- 0.02 that surpasses the no-cloning limit of 2/3. Surpassing the limit is necessary to transfer the nonclassicality of an input quantum state. By using our high-fidelity teleporter, we demonstrate entanglement swapping, namely, teleportation of quantum entanglement, as an example of transfer of nonclassicality.     

Entanglement and teleportation through thermal equilibrium state of spins in the XXZ model

We study the pairwise entanglement of a three-qubit spins in the XXZ model, and teleport an unknown state using the spin chain in the thermal equilibrium as a quantum channel. The effects of coupling strength, magnetic field, the anisotropy and temperature on the entanglement and fidelity are investigated. We find that the ferromagnetic spin chain is suitable for quantum teleportation, while the anti-ferromagnetic one is not. We give the maximal average fidelity, and the condition under which the maximal average fidelity is obtained. In addition, the relation between the entanglement and fidelity is studied, and we find that the considered entanglement cannot completely reflect the fidelity.     

Quantum Teleportation via Completely Anisotropic Heisenberg Chain in Inhomogeneous Magnetic Field

The quantum teleportation with the entangled thermal state is investigated based on the completely anisotropic Heisenberg chain in the presence of the externally inhomogeneous magnetic field. The effects of the anisotropy and magnetic field for the quantum fidelity are studied in detail. The zero temperature limit and the features of the nonzero temperature for this nonclassical fidelity are obt8ained. We find that the quantum teleportation demands more stringent conditions than the thermal entanglement of the resource by investigating the threshold temperature of the thermal concurrence and the critical temperature of the maximal teleportation fidelity. The useful quantum teleportation should avoid the point of the phase transition of the system and the anisotropy of the chain and the external magnetic field can control the applicability of the resource in the quantum teleportation.     

Optimal teleportation with a mixed state of two qubits

We consider a single copy of a mixed state of two qubits and derive the optimal trace-preserving local operations assisted by classical communication such as to maximize the fidelity of teleportation that can be achieved with this state. These optimal local operations turn out to be implementable by one-way communication and always yield a teleportation fidelity larger than 2/3 if the original state is entangled. This maximal achievable fidelity is an entanglement measure and turns out quantifying the minimal amount of mixing required to destroy the entanglement in a quantum state.     

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     

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.     

海森堡模型中量子隐形传递的研究

通过对海森堡模型中量子热纠缠的研究,进而研究以海森堡热纠缠混合态为信道的量子隐形传递,计算出纠缠度和保真度,分析外界环境(温度、磁场等)对热纠缠及隐形传递的影响.     

Enhancing teleportation fidelity by means of weak measurements or reversal

The enhancement of teleportation fidelity by weak measurement or quantum measurement reversal is investigated. One qubit of a maximally entangled state undergoes the amplitude damping, and the subsequent application of weak measurement or quantum measurement reversal could improve the teleportation fidelity beyond the classical region. The improvement could not be attributed to the increasing of entanglement, quantum discord, classical correlation or total correlation. We declare that it should be owed to the probabilistic nature of the method.     

Quantum teleportation of one－ and two－photon superposition states

Quantum teleportation of one- and two-photon superposition states based on EPR entanglement of continuous-wave two-mode squeezed state is discussed. The fidelities of teleportation axe deduced for two different input quantum states. The dependence of the fidelity on the parameters of EPR entanglement and the gain of the classical channels are shown numerically. Comparing with the teleportation of Fock state and coherent state, it is pointed out that for given EPR entanglement and classical gain, the higher the nonclassicality of the input state, the lower the accessible fidelity of teleportation.     

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.     

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.     

Quantum Teleportation via a Two-Qubit Ising Heisenberg Chain with an Arbitrary Magnetic Field

The quantum teleportation via a two-qubit Ising Heisenberg chain in the presence of an external magnetic field with an arbitrary direction are investigated. The effect of the orientation of an external magnetic field on the entanglement teleportation has been analyzed numerically. It is found that the teleported thermal concurrence and average fidelity can be maximized by rotating the magnetic field (with fixed magnitude) to an optimal direction. The ferromagnetic channel is not suitable to teleportation. A minimal entanglement of the thermal state is needed to realize the entanglement teleportation for antiferromagnetic channel. It is also found that the entanglement of the channel cannot completely reflect the teleported concurrence and average fidelity. There exist double-value phenomena between them.     

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.     

Equivalence between entanglement and the optimal fidelity of continuous variable teleportation

We devise the optimal form of Gaussian resource states enabling continuous-variable teleportation with maximal fidelity. We show that a nonclassical optimal fidelity of N-user teleportation networks is necessary and sufficient for N-party entangled Gaussian resources, yielding an estimator of multipartite entanglement. The entanglement of teleportation is equivalent to the entanglement of formation in a two-user protocol, and to the localizable entanglement in a multiuser one. Finally, we show that the continuous-variable tangle, quantifying entanglement sharing in three-mode Gaussian states, is defined operationally in terms of the optimal fidelity of a tripartite teleportation network.