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.     

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.     

Entanglement and Teleportation via Thermally Entangled State of Anisotropic Heisenberg XYZ Chain with Inhomogeneous External Magnetic Field

In this paper we study the entanglement in a two-qubit spin in the XYZ model, and teleport a two-qubit entangled state using this spin chain in the condition of the thermal equilibrium as a quantum channel. We investigate the effects of the interaction of z-component Jz, the inhomogeneous magnetic field b, the anisotropy γ and the temperature T on the entanglement and fidelity. In order to characterize the quality of the teleported state, we research the average fidelity Fα. High average fidelity of the teleportation is obtained when the temperature is very low. Under some condition, we also find that when innomogeneity increases to a certain value, the average fidelity can exhibit a larger revival than that for less values of b.     

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.     

The decoherence of quantum entanglement and teleportation in Bell-diagonal states

We study the dynamics of entanglement and teleportation in Bell-diagonal states. Using the concepts of concurrence and fidelity, the analytical expressions of the entanglement, the output entanglement and the average fidelity with decoherence are obtained for this model. We discover a class of initial states in which the output entanglement and the average fidelity are destroyed by decoherence. The quality of teleportation depends on the system parameters and time.     

伊辛模型中量子的热纠缠和保真度

研究了伊辛模型中两个粒子在均匀和非均匀磁场中的热纠缠以及利用它作为量子信息传输的通道的传输保真度.计算出纠缠度的度量Concurrence,以及在不同种情况下呈现出来的纠缠度的表现形为.与均匀磁场相反,我们发现在非均匀磁场中传输的保真度能够得到增强,同时我们发现保真度还与耦合系数和温度有关.我们通过图形清楚地表示它们的性质,从图形中我们得出,第一:在其它条件相同的情况下,无论磁场方向是相同还是相反,它们的纠缠度都是相同的;但是当磁场方向相反时,平均保真度比均匀磁场具有更大的值.第二:为了提高纠缠和平均保真度我们可以通过选择适当的磁场强度、耦合系数和降低温度来实现.     

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.     

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.     

Entanglement Teleportation Via a Two-qubit Heisenberg Chain under a Nonuniform Magnetic Field

By introducing the nonuniform magnetic field, we investigate the entanglement teleportation via two-qubit Heisenberg chain. We show that for ferromagnetic chain, the opposite direction magnetic field on the two-qubit chain can excite the teleported entanglement C _out, while the uniform magnetic field can not do it. The effect of the uniform magnetic field B and the nonuniform magnetic field b on the threshold temperature T _c is also plotted. Our study on the average fidelity of this quantum channel system shows that the magnetic field in opposite direction can result in the ideal average fidelity no matter whether the chain is ferromagnetic or antiferromagnetic.     

Teleportation and thermal entanglement in two-qubit Heisenberg X Y Z spin chain with the Dzyaloshinski-Moriya interaction and the inhomogeneous magnetic field

This paper studies the average fidelity of teleportation and thermal entanglement for a two-qubit Heisenberg X Y Z chain in the presence of both an inhomogeneous magnetic field and a Dzyaloshinski-Moriya interaction. It shows that for a fixed Dz, the increase of bz will broaden the critical temperature at the cost of decreasing the thermal entanglement. And it can modulate the inhomogeneous magnetic field and the Dzyaloshinski-Moriya interaction for the average fidelity of teleportation to be optimal.     

Short-Distance Teleportation of an Arbitrary Two-Qubit State Via a Bell State

We propose a scheme for teleportation of an arbitrary two-qubit state by using a Bell state as the quantum channel working together with an auxiliary qubit. Our scheme needs less entanglement resource, but at the cost of shortening teleportation distance. This is because that in order to successfully recover the teleported state, both sender and receiver need to implement quantum-gate operations on the shared auxiliary qubit. So, the auxiliary qubit must be close to both sender and receiver. Otherwise, the sender and receiver cannot carry out quantum-gate operations on it. Thus, our scheme is invalid for long-distance teleportation. But for short-distance teleportation, our scheme is an optimal choice because it requires less entanglement resource. From a practical point of view, our scheme is very promising for application in quantum teleportation on chip.

     

Thermal entanglement and teleportation in a two-qubit Heisenberg XXZ chain with different Dzyaloshinskii-Moriya interactions

We study the thermal output entanglement and teleportation in a two qubit Heisenberg XXZ chain with different Dzyaloshinskii-Moriya (DM) interactions. The analytical expressions of the output entanglement and the average fidelity are obtained for this model. We find the entanglement of replica states will be induced by some large value of D_z and the output entanglement exists for the case of J_z < − 1. The influences of the different DM interactions on the fidelity of teleportation are studied. We show that by introducing the x-component DM interaction, the average fidelity F_A can reach its maximum value 1.     

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.     

Teleportation via thermally entangled states of a two-qubit Heisenberg XXZ chain

We investigate quantum teleportation as a tool to study the thermally entangled state of a two-qubit Heisenberg XXZ chain. Our work is mainly to investigate the characteristics of a Heisenberg XXZ chain and get some analytical results of the fully entangled fraction. We also consider the entanglement teleportation via a two-qubit Heisenberg XXZ chain.     

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.     

Entanglement and quantum teleportation in a nonlinear spin channel

The ground state and thermal entanglement of a two-qubit spin system in the presence of the nonlinear coupling interaction is investigated. It is found that the nonlinear coupling interaction can excite and enhance the entanglement both for ferromagnetic chain and anti-ferromagnetic ones even at the higher temperature. The entanglement teleportation via the quantum channel constructed by this system is also discussed, and the influence of the nonlinear coupling interaction on the fidelity of the teleportation is studied. The results show that both the entanglement of the output state and the fidelity can be increased by inducing a proper nonlinear coupling interaction.     

Entanglement Teleportation Via Two-Qubit Channel Under the Non-Markovian Environment

Entanglement teleportation via a two-qubit quantum channel under the non-Markovian environment is investigated in detail. We mainly concentrate on the effects about the channel initial states and decoherence environment on the entanglement of the output state C _out and the average fidelity F _a. It is shown that for different channel initial states with increasing noise environment parameters the teleportated entanglement is initially decreased from the maximum value to a minimum value and then undergoes a increasing tendency finally to be one constant nonzero value. The average fidelity is strongly dependent on the channel initial states and the Non-Markovian environment, tuning these parameters can make the average fidelity larger than the maximum value of classical communication 2/3. Moreover, there is a threshold time t _c , when t<t _c the average fidelity is always superior to 2/3, tuning the environment parameters and channel initial states not only can make F _a superior to 2/3 but also can broaden the region where F _a is larger than 2/3. We also obtain the analytic solution values of t _c in the limit case of γ→∞ where the non-Markovian environment reduced to the Markovian one.     

Teleportation via thermally entangled states of a two-qubit Heisenberg XXZ chain

We investigate quantum teleportation as a tool to study the thermally entangled state of a twoqubit Heisenberg XXZ chain.Our work is mainly to investigate the characteristics of a Heisenberg XXZ chain and get some analytical results of the fully entangled fraction.We also consider the entanglement teleportation via a two-qubit Heisenberg XXZ chain.     

Teleportation of a Coherent Superposition State Via a nonmaximally Entangled Coherent Xhannel

We investigate the problemm of teleportation of a superposition coherent state with nonmaximally entangled coherent channel. Two strategies are considered to complete the task. The first one uses entanglement concentration to purify the channel to a maximally entangled one. The second one teleports the state through the nonmaximally entangled coherent channel directly. We find that the probabilities of successful teleportations for the two strategies are depend on the amplitudes of the coherent states and the mean fidelity of teleportation using the first strategy is always less than that of the second strategy.