Schemes for Probabilistic Teleportation of a Three-Atom GHZ Class State via Cavity QED

Using a quantum channel composed of a two-atom and a three-atom nonmaximally entangled states, we present two schemes to teleport a three-atom GHZ class state via entanglement swapping in cavity QED with different success probabilities. The schemes can be respectively realized with the large-detuned vacuum cavities and with the large-detuned thermal cavities by separate atomic measurements after we choose appropriate atom-cavity-field interaction time.     

Schemes for Probabilistic Teleportation of a Three-Atom GHZ Class State via Cavity QED

Using a quantum channel composed of a two-atom and a three-atom nonmaximally entangled states,we present two schemes to teleport a three-atom GHZ class state via entanglement swapping in cavity QED with different success probabilities. The schemes can be respectively realized with the large-detuned vacuum cavities and with the large-detuned thermal cavities by separate atomic measurements after we choose appropriate atom-cavity-field interaction time.     

远距离三原子量子纠缠特性与其应用

三原子分别被束缚在用光纤环形连接单侧泄漏微光学腔场中,在微腔中输入激光驱动场和施加局域激光场,利用输入-输出技术及绝热近似理论,推导出一维Ising链模型的有效哈密顿量,该哈密顿量表明该系统会诱导出三原子中的任意两原子纠缠及三原子纠缠,用伴随数(concurrence)度量两原子纠缠,用内禀纠缠度量三原子纠缠,通过数值计算,给出两原子和三原子纠缠随时间演化曲线,通过适当调控激光驱动场和局域激光场,在远距离三原子中任意两原子实现未知量子态的隐形传送。     

Theory of surface recombination of spin-polarized hydrogen

A theory is presented, based on the Faddeev equations, for direct two-body recombination of hydrogen atoms on a liquid helium surface. The equations developed are applicable to hydrogen or deuterium atoms in any spin state, but are applied in particular to dipolar recombination ofb state hydrogen atoms. The equations yield terms corresponding to one- and two-step processes. These terms are calculated for low temperatures (T-0.1 to 1.1 K) and high field strengths (B=4 to 14 T). The one-step term increases slowly withB, while the two-step term is rapidly decreasing. While the overall rate is quite small (5×10^–18 cm²/s) compared to recombination by two-body spin-relaxation, the results have important consequences in understanding the experimentally measured three-atom dipolar surface recombination rates. In three-atom recombination, where the role of spin-relaxation and the two-atom one-step processes are repressed, the role of the underlying two-atom, two-step process is enhanced. The field dependence of the process relevant to the three-atom system is calculated and found to be in fairly good agreement with the experimental three-atom data. The role of possible liquid excitations in enhancing the contribution of the two-step processes is also discussed.     

Engineering Two-Atom Thermal Entanglement via Two-Photon Process

We study that two atoms simultaneously interact with a single mode thermal field via different couplings and different spontaneous emission rates when two-photon process is involved. It is found that we indeed can employ the different couplings to produce the two-atom thermal entanglement in two-photon process. The different atomic spontaneous emission rates are also utilizable in generating thermal entanglement. We also investigate the effect of the cavity leakage. To the initial atomic state $| eg\rangle$, a slight leakage can relieve the restriction of interaction time so that we can obtain a strong and steady entanglement.     

Environment induced entanglement in cavity-QED

The effects of dissipative dynamics on the magnitude of entanglement generated In atom-photon interactions inside cavities is studied. We present some concrete examples of environment Induced entanglement in alom-photon interactions. We consider various dissipative atom-cavity systems and show that their collective dynamics can be used to maximize entanglement for intermediate values of the cavity leakage parameter κ. We first consider the interaction of a single two-level atom with one of two coupled microwave cavities and show analytically that the atom-cavity entanglement increases with cavity leakage. We next consider a system of two atoms passing successively through a cavity and derive the expression for the maximum value of in terms of the Rabi angle gt, for which the two-atom entanglement can be Increased. Finally, numerical investigation of micromaser dynamics also reveals the increase of two-atom entanglement with stronger cavity-environment coupling for experimentally attainable values of the micromaser parameters.     

Revisiting “Quantum State Sharing of an Arbitrary Two-Atom State by Using a Six-Atom Cluster State in Cavity QED”

In Nie et al. (Int. J. Theor. Phys. 50: 2526, 2011), authors put forward a cavity QED scheme for deterministic quantum state sharing (QSTS) of an arbitrary two-atom state. They claimed that, the quantum channel of the QSTS scheme is a six-atom cluster state. After simple calculation, one can see that the quantum channel they used is a direct product of two three-atom GHZ states. In this paper, we propose a cavity QED scheme for QSTS of an arbitrary two-atom state via a six-atom cluster state channel. In our scheme, two two-atom Bell state measurements are transformed into the discrimination of single-atom product states. Moreover, the two-atom unitary operation is changed to single-qubit unitary operations. Our scheme is insensitive to the cavity decay. The necessary time for the scheme is much shorter than the Rydberg-atom lifespan, therefore atom decays do not need to be considered.     

Influence of selective atomic measurement on the entanglement properties of a two-atom outside cavity

Considering three two-level atoms initially in the W or Greenberger--Horne--Zeilinger (GHZ) state, one of the three atoms is put into an initially coherent light cavity and made to resonantly interact with the cavity. The two-atom entanglement evolution outside the cavity is investigated. The influences of state-selective measurement of the atom inside the cavity and strength of the light field on the two-atom entanglement evolution outside the cavity are discussed. The results obtained from the numerical method show that the two-atom entanglement outside the cavity is strengthened through state-selective measurement of the atom inside the cavity. In addition, the strength of the light field also influences the two-atom entanglement properties.     

A Position-Dependent Two-Atom Entanglement in Real-Time Cavity QED System

We study a special two-atom entanglement case in assumed cavity QED experiment in which only one atom effectively exchanges a single photon with a cavity mode. We compute two-atom entanglement under position-dependent atomic resonant dipole-dipole interaction （RDDI） for large interatomic separation limit. We show that the RDDI, even t, hat which is much smaller than the maximal atomic Rabi frequency, can induce distinct diatom entanglement. The peak entanglement reaches a maximum when RDDI strength can compare with the Rabi frequency of an atom.     

原子的选择测量对原子纠缠特性和场熵的影响*

考虑初始处于W态的三个二能级原子,将其中两个原子同时注入处于真空态的单模腔中,并与光场发生共振相互作用的情况。采用数值计算方法,通过对是否进行原子态选择性测量情况下,腔内原子间的纠缠性质和场熵的比较,讨论了对腔外原子的态选择性测量对腔内原子间的纠缠性质和场熵演化的影响。研究结果表明：对腔外原子的选择性测量,可增强腔内原子间的纠缠,但会减弱腔內原子与光场的关联。     

Bell态原子与双模纠缠相干光场相互作用的纠缠特性

运用Negativity熵研究了Bell态原子与双模纠缠相干光场相互作用系统中两个全同二能级原子之间的纠缠演化特性.分析了光场强度、光场纠缠度及原子间相互作用强度对纠缠的影响.结果表明:原子处于|β11〉时,两原子始终处于最大纠缠态;原子处于|β00〉时,初始纠缠的两原子始终较长时间处于退纠缠状态;原子处在|β10〉时,增大双模光场的平均光子数可以明显增大两原子之间的纠缠度并保持较大的纠缠状态;原子初态处在|β01〉时,原子间的相互作用强度对双原子间纠缠度有较显著的非线性调制作用.     

Thermal Entanglement in a Two-Qubit Heisenberg XXZ Spin Chain Under a Single Pulse Magnetic Field

The thermal entanglement in a two-qubit Heisenberg XXZ spin chain is investigated under a single pulse magnetic field Bsinθ. The paper shows that the greater the contribution of the inhomogeneity on the exchange interaction, the higher thermal entanglement will be attained at the fixed temperature except the case that $\theta=2k\pi+\frac{3}{2}\pi$ . J _z  significantly disturb the thermal entanglement in uniform case. When the structure of the spin system are given, changing the external magnetic field B can induce controllable entanglement. Our study may provide a useful tool to change the entanglement of spin chain system.     

Remote State Preparation of a Two-Atom Entangled State in Cavity QED

A physical scheme for remotely preparing a diatomic entangled state based on the cavity QED technique is presented in this paper. The quantum channel is composed of a two-atom entangled state and a three-atom entangled W state. The non-resonant interaction between two atoms and cavity is utilized at sender’s side to distribute the information among the quantum channel, and the original state can be transmitted to either one of the two receivers. It shows that an extra cavity and an atom are needed at the final receiver’s side as an auxiliary system if the non-maximally entangled states are worked as the quantum channel. The total success probabilities for the two receivers are not equal to each other except that the states of the quantum channel are maximally entangled.     

The Controlled Teleportation of an Arbitrary Two-Atom Entangled State in Driven Cavity QED

In this paper, we propose a scheme for the controlled teleportation of an arbitrary two-atom entangled state |φ〉₁₂=a|gg〉₁₂+b|ge〉₁₂+c|eg〉₁₂+d|ee〉₁₂ in driven cavity QED. An arbitrary two-atom entangled state can be teleported perfectly with the help of the cooperation of the third side by constructing a three-atom GHZ entangled state as the controlled channel. This scheme does not involve apparent (or direct) Bell-state measurement and is insensitive to the cavity decay and the thermal field. The probability of the success in our scheme is 1.0.     

远程控制原子的纠缠特性

考虑初始处于GHZ态的三个二能级原子,将其中两个原子同时注入处于真空态的单模腔中,并与光场发生共振相互作用的情况.利用全量子理论和采用数值计算方法,研究了腔内原子的纠缠性质.通过对是否进行腔外原子态选择性测量和腔外原子旋转操作情况下,腔内原子间的纠缠性质的比较,讨论了对腔外原子的旋转操作和测量对腔内原子间纠缠性质的影响.研究结果表明：若没有对腔外原子进行旋转操作,腔内两原子是分离的|若对腔外原子进行旋转操作和选择性测量,腔内两原子是纠缠的.另一方面,腔内两原子间的纠缠性质随旋转角的变化具有对称性,其对称轴为θ=π/2,可通过控制旋转角度的大小来控制腔内原子间的纠缠度.     

远程制备双原子纠缠态

提出一种远程制备双原子纠缠态的方案,该方案基于两个原子与单模腔场的同时非共振相互作用.由于双粒子纠缠态比三粒子纠缠态容易制备,方案用两对双原子纠缠态作为量子通道.Alice 拥有的两个相同原子同时与一单模腔场非共振相互作用.Alice已知她要制备的纠缠态,她选择适当的相互作用时间、测量她所拥有的两个原子并通过经典通道通知Bob.Bob引入一个相同的辅助原子和一个单模腔场来实现方案.方案对腔场状态和腔损耗不敏感,基于当前的腔QED 技术,方案能在实验上实现.该方案有望在量子信息过程中有重要的应用价值.     

On the dipole moment of three identical spherical atoms

Martin's perturbation theory result [2] for the dipole moment of three identical spherical atoms at large separations is shown to simplify: There are two contributions to this three-atom dipole and the strength of each factors into a product of the dipole polarizability of one atom and a two-atom average of dipole and quadrupole matrix elements. The simplified results are used to obtain an improved evaluation of the three-atom dipole of three He atoms, employing extensive pseudo-spectral representations of the dipole and quadrupole excitations.     

Tavis-Cummings模型中两纠缠原子纠缠的演化特性

研究了两个纠缠的两能级原子与单模粒子数场进行相互作用系统中两原子的纠缠演化.结果表明：两个原子之间的纠缠呈现出周期性的演化特性，初始两原子的状态、原子之间的偶极相互作用和粒子数场对腔中两个原子的纠缠有着显著的影响.发现适当选择原子的初态，两原子会永远处于最大纠缠态. 关键词： 量子纠缠 偶极-偶极相互作用 部分转置矩阵负本征值 纠缠原子     

Entanglement in Three-Atom Tavis-Cummings Model Induced by a Thermal Field

The explicit form of the evolution operator for the three-atom Tavis-Cummings model is given. The atoms can be entangled through their interaction with a thermal field. The degree of entanglement depends on the mean photon number of the thermal field and the initial state of the atoms.     

腔外原子操作控制腔内原子的纠缠特性

考虑初始处于W态的三个二能级原子,将其中两个原子同时分别注入处于真空态的两个腔中并发生共振相互作用的情况.采用数值计算方法,研究了对腔外原子的旋转操作和测量对腔内原子纠缠性质的影响.研究结果表明,通过对腔外原子的旋转操作和选择性测量可控制腔内原子的纠缠性质.