Generation of Multi-ion Graph States with Trapped Ions in Thermal Motion

We propose a scheme for generating multi-ion graph states using many trapped ions in thermal motion. Our generation scheme is insensitive to external state since the interaction between ions and laser fields does not involve the external degree of freedom. The scheme can be well realized within the current experimental technique.     

Feasible Scheme for Teleportation of an Arbitrary N-Atom State with Thermal Cavity

We present a scheme for teleportation of an arbitrary cavity QED, and show the feasibility in experiment. thermal field, and the fidelity of teleportation is only the success probability reaches 1.0. N-atom state without Bell state measurement in thermal Our scheme is also insensitive to both cavity decay and slightly affected by the experimental errors. In addition,     

Implement a measurement of GHZ entanglement for a multipartite system via cavity QED

We propose a scheme for implementing a measurement of GHZ entanglement for a multipartite system via cavity QED. In the scheme the atoms interact simultaneously with a highly detuned cavity mode with the assistant of a classical field. The scheme is insensitive to the cavity decay and the thermal field. A set of GHZ states can be exactly distinguished via detecting atomic state in a simple way.     

Scheme for implementing controlled teleportation and dense coding with genuine pentaqubit entangled state in cavity QED

We present a simple scheme for implementing perfect controlled teleportation and dense coding with the genuine pentaqubit entangled state proposed by [I.D.K. Brown, S. Stepney, A. Sudbery, S.L. Braunstein, J. Phys. A: Math. Gen. 38 (2005) 1119]. In cavity QED, we have proposed to prepare the Brown state and demonstrated the feasibility of this scheme. The distinct feature of this scheme is that it is insensitive to both the cavity decay and the thermal field, which is of importance in view of experiment.     

Control Chaos in Hindmarsh--Rose Neuron by Using Intermittent Feedback with One Variable

The mechanism of the famous phase compression is discussed, and it is used to control the chaos in the Hindmarsh-Rose （H-R） model. It is numerically confirmed that the phase compression scheme can be understood as one kind of intermittent feedback scheme, which requires appropriate thresholds and feedback coeffcient, and the intermittent feedback can be realized with the Heaviside function. In the case of control chaos, the output variable （usually the voltage or the membrane potential of the neuron） is sampled and compared with the external standard signal of the electric electrode. The error between the sampled variable and the external standard signal of the electrode is input into the system only when the sampled variable surpasses the selected thresholds. The numerical simulation results confirm that the chaotic H-R system can be controlled to reach arbitrary n-periodical （n = 1, 2, 3, 4, 5, 6,...） orbit or stable state even when just one variable is feed backed into the system intermittently. The chaotic Chua circuit is also investigated to check its model independence and effectiveness of the schemes and the equivalence of the two schemes are confirmed again.     

Simultaneous implementation of n SWAP gates using superconducting charge qubits coupled to a cavity

Based on superconducting quantum interference devices (SQUIDs) coupled to a cavity, we propose a scheme for implementing n SWAP gates simultaneously. In our scheme, the SQUID works in the charge regime, the quantum logic gate operations are performed in the subspace spanned by two charge states |0〉 and |1〉. The interaction between the qubits and the cavity field can be achieved by turning the gate voltage and the external flux. Especially, the gate operation time is independent of the number of the qubits, and the gate operation is insensitive to the initial state of the cavity mode. We also analyze the experimental feasibility that the conditions of the large detuning can be achieved by adjusting the frequency of the cavity mode, and the operation time satisfies the requirement for the designed experiment by choosing suitable detuning and the quality factor of the cavity. Based on the simple operation, our scheme may be realized in this solid-state system, and our idea may be realized in other systems.     

Selecting molecules in the vibrational and rotational ground state by deflection

A beam of diatomic molecules scattered off a standing wave laser mode splits according to the rovibrational quantum state of the molecules. Our numerical calculation shows that single state resolution can be achieved by properly tuned, monochromatic light. The proposed scheme allows for selecting non-vibrating and non-rotating molecules from a thermal beam, implementing a laser Maxwell's demon to prepare a rovibrationally cold molecular ensemble. Received 23 August 2000 and Received in final form 17 November 2000     

Teleportation of an Arbitrary Two-Atom Entangled State via Thermal Cavity

We present an experimentally feasible scheme for teleportation of an arbitrary unknown two-atom entangled state by using two-atom Bell states in driven thermal cavities. In this scheme, the effects of thermal field and cavity decay can be all eliminated. Moreover, the present scheme is feasible according to current technologies.     

Generation of four-atom cluster states in thermal cavity and implementing remote controlled not gate

We propose an experimentally feasible scheme for preparing a four-atom cluster state in a thermal cavity. In the scheme, the cavity field is only virtually excited and the photon-number-dependent part in the effective Hamiltonian is cancelled so that the system is insensitive to the cavity decay and the thermal field. At the same time, the scheme can be generalized to prepare n-atom cluster states with the success probability 100\%. In addition, using the four-atom cluster state, we also propose a simpler scheme for implementing a remote--controlled not gate (CNOT) without the Bell states measurement.     

Abrupt turn-on and hysteresis in a VCSEL with frequency-selective optical feedback

The emission characteristics of a vertical-cavity surface-emitting laser (VCSEL) operated in a single-transverse mode and coupled to an external cavity with a diffraction grating as a frequency-selective element are analyzed experimentally, numerically and analytically. The experiments yield a rather abrupt turn-on of the VCSEL to a high-amplitude emission state and hysteresis phenomena. The experimental results are explained by numerical simulations and analytical calculations demonstrating the possibility of bistability between lasing and non-lasing states close to threshold. Hence, the scheme might be useful in all-optical photonic switching applications. A detailed bifurcation analysis near threshold is given by superimposing the numerical results with analytical steady-state curves. The mode selection and switching behavior obtained in the simulations can be interpreted from the point of view of the preference of states with the minimal total losses.     

Controlled Dense Coding Through a Genuine Five-Atom Entangled State in Cavity QED

We present an experimentally feasible scheme for implementing controlled dense coding through a genuine five-atom entangled state in cavity QED. The scheme is insensitive to both the cavity decay and the thermal field. In the scheme that four-atom entangled states can be exactly distinguished with detecting the atomic state, and the controlled dense coding can be realized in a simple way.     

Concentration of Unknown Atomic Entangled States via Entanglement Swapping through Raman Interaction

We show that entanglement concentration of unknown atomic entangled states is achieved via the implementation of entanglement swapping based on Raman interaction in cavity QED. A maximally entangled state is obtained from a pair of partially entangled states probabilistically. Due to Raman interaction of two atoms with a cavity mode and an external driving field, the influence of atomic spontaneous emission has been eliminated. Because of the virtual excitation of the cavity mode, the decoherence of cavity decay and thermal field is neglected.     

Controlled Quantum State Transfer with Separate Measurements in Cavity QED

An experimental scheme on controlled quantum state transfer is proposed in cavity quantum electrodynamics (QED) without joint Bell-state measurement (BSM). A quantum state can be transferred 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 is insensitive to the cavity decay and the thermal field. The probability of the success in our scheme is 1.0.     

Schemes for Generating Cluster States via Cavity Systems

We propose a scheme for generating an N-atom cluster state via cavity quantum electrodynamics （ CQED）. In our scheme, there is no transfer of quantum information between the atoms and the cavity, i.e., the cavity is always in the vacuum state, so the cavity decay can be suppressed. Also, the generated cluster state is the entanglement of the ground states, so the atomic spontaneous emission can be avoided. Therefore, the cluster state generated in our scheme has a longer lifetime. Furthermore, the requirement on the quality factor of the cavity greatly loosened for the cavity is only virtually excited.     

外场驱动下腔QED中实现任意两原子态的隐形传送方案

提出了一种外场驱动下在腔QED中实现任意两原子态隐形传送的方案.在隐形传送的过程中.以两原子最大纠缠态作为量子通道,不用考虑腔场耗散和外界热场环境的影响.在传送过程中包含着对原子的Bell基测量,但不需要直接进行Bell基测量,而且最终能成功实现传送的几率为1.0.同时这种方案也可以用来传送未知的三原子GHZ态,传送的几率也为1.0.     

Splitting an Arbitrary Three-Qubit State via a Five-Qubit Cluster State and a Bell State

Quantum information splitting (QIS) provides an idea for transmitting the quantum state through a classical channel and a preshared quantum entanglement resource. This paper presents a new scheme for QIS based on a five-qubit cluster state and a Bell state. In this scheme, the sender transmits the unknown three-qubit secret state to two agents by the quantum channel with the Bell basis measurement three times and broadcasts the measurement results to the agents through the classical channel. The agent who restores the secret state can successfully recover the initial information to be transmitted through the appropriate unitary operation with the help of the other party. Firstly, our scheme’s process can be accurately realized by performing the applicable Bell basis measurement, single-qubit measurement, and local unitary operation instead of a multiparticle joint measurement. The splitting process of quantum information is realized through a convenient operation. Secondly, compared with some previous schemes, the efficiency of the total scheme has been improved in principle, and the qubit consumption is reduced. Finally, the security of the quantum information splitting scheme is analyzed from the perspectives of external attacks and participant attacks. It is proved that our scheme can effectively resist internal participant attacks and external eavesdropper attacks.     

Distributed quantum computing in decoherence-free subspace via adiabatic passage

A scheme is proposed to implement distributed quantum computation in decoherence-free subspaces (DFSs) via adiabatic passage. The logical single-qubit is encoded in two atoms trapped in a single-mode cavity and the cavities are connected by an optical fiber. Our scheme is immune from the decoherence due to dephasing in virtue of encoding scheme and the decoherence due to spontaneous emission from excited states as the system in our scheme evolves along a dark state. Furthermore, the decoherence due to photon decay is greatly suppressed since the fiber mode remains in a vacuum state and the populations of the cavities’ modes being excited can be negligible under certain condition. It is shown that the minimum fidelity of the resultant gate operation for an arbitrary input state could be over 0.97.     

Teleportation for an Ionic Entangled Internal State by Entanglement Swapping

We present an effective scheme to teleport an unknown ionic entangled internal state via trapped ions without joint Bell-state measurement. In the constructed quantum channel process, we adopt entanglement swapping to avoid decrease of entanglement during the distribution of particles. Thus our scheme provides new prospects for quantum teleportation over longer distance. The distinct advantages of our scheme are that our scheme is insensitive to heating of vibrational mode and can be generalized to teleport an N-ion electronic entangled GHZ class state. Furthermore, in our scheme the success probability can reach 1.     

Electric field effects on the states of an exciton in square cross-section quantum well wires

The Letter studies the role of the external electric field on the binding energy of the exciton states in square cross-section quantum well wires. Using the effective-mass approximation within a variational scheme and expanding the wave function into Fourier series, we calculate the binding energies of the ground state as well as that of the excited states as the functions of the geometry and the strength of the applied electric field. In the presence of an electric field, it is found that for the ground state the Stark effect is redshift, and for the first and the second excited state the binding energy are split into two levels which will change in contrary situation along with the increasing of the strength of the applied electric field.     

Statistical Properties of Thermal State Under Quantum Hadamard Transform

We study a new type of thermal state which is obtained by operating Hadamard operator on a thermal field. We call this new thermal state as quantum Hadamard’s thermal state (QHTS). The normally ordered form of QHTS is derived by using Weyl-ordering invariance under the similarity transformation and the Weyl correspondence scheme. We find that QHTS can be considered as squeezed state under certain conditions. The statistical properties of QHTS is also discussed.