Generation of Cluster States in Cavity QED

We propose two schemes for the generation of cluster states in the context of cavity quantum electrodynamics （QED）. In the first scheme, we prepare multi-cavity cluster states with information encoded in the coherent states. The second scheme is to generate multi-atom cluster states, where qubits axe represented by the states of cascade Rydberg atoms. Both the schemes axe based on the atom-cavity interaction and the atomic spontaneous radiation can be efficiently reduced since the cavity frequency is largely detuned from the atomic transition frequency.     

Schemes for preparing atomic qubit cluster states in cavity QED

Two schemes are proposed for generating atomic qubits cluster states in cavity quantum electrodynamics (QED). In the first scheme, only two-atom-cavity interactions are involved, and cluster states can be directly generated by using constructed two-qubit controlled phase gates. The second scheme needs the assistance of additional single-qubit rotations, but takes less time than the first one for two-atom operations in the cavity. In this scheme, two projective operators are constructed to prepare two-dimension or more complicated configurations of cluster states. Both schemes are insensitive to the cavity decay due to the fact that the cavity is only virtually excited during the interaction between atoms and the cavity. The idea can also be applied to the ion trap system.     

Generation of multiple-particle cluster state via cavity QED

This paper proposes schemes for generating multiple-photon and multiple-atom cluster states, respectively. The schemes are based on the cavity input-output process and atomic or photonic states measurement, and the successful probabilities approach unity in the ideal case. The numerical simulations show that the produced multiple-particle cluster states have high fidelity even if the Lamb-Dicke condition is not satisfied. Some practical imperfections, such as atomic spontaneous emission and output coupling inefficiency, only decrease the success probability but exert no influence on the fidelity of generated multiple-particle cluster states. From the experimental point of view, smaller operation number and lack of need for individual addressing keeps the schemes easy to implement. These schemes may offer a promising approach to the generation of a large-scale cluster state.     

Generation of multiple-particle cluster state via cavity QED

This paper proposes schemes for generating multiple-photon and multiple-atom cluster states, respectively. The schemes are based on the cavity input--output process and atomic or photonic states measurement, and the successful probabilities approach unity in the ideal case. The numerical simulations show that the produced multiple-particle cluster states have high fidelity even if the Lamb--Dicke condition is not satisfied. Some practical imperfections, such as atomic spontaneous emission and output coupling inefficiency, only decrease the success probability but exert no influence on the fidelity of generated multiple-particle cluster states. From the experimental point of view, smaller operation number and lack of need for individual addressing keeps the schemes easy to implement. These schemes may offer a promising approach to the generation of a large-scale cluster state.     

A Scheme for Generating Cluster States via Raman Interaction

A scheme for generating cluster states via Raman interaction is proposed. In the scheme, we firstly prepare cluster states of multi-cavities with information encoded in the coherent states and then generate cluster states of multiatoms, which encode the information in the ground states of A-type atoms. The advantages of our scheme are that the atomic spontaneous radiation can be efficiently reduced since the cavity frequency is largely detuned from the atomic transition frequency and the Hadamard gate operation of the coherent states is replaced by measuring the coherent states.     

Quantum Tasks with Non-maximally Quantum Channels via Positive Operator-Valued Measurement

By using a proper positive operator-valued measure (POVM), we present two new schemes for probabilistic transmission with non-maximally four-particle cluster states. In the first scheme, we demonstrate that two non-maximally four-particle cluster states can be used to realize probabilistically sharing an unknown three-particle GHZ-type state within either distant agent’s place. In the second protocol, we demonstrate that a non-maximally four-particle cluster state can be used to teleport an arbitrary unknown multi-particle state in a probabilistic manner with appropriate unitary operations and POVM. Moreover the total success probability of these two schemes are also worked out.     

Generation of Ising interaction and cluster states in a one-dimensional coupled resonator waveguide

We propose a scheme for realizing the Ising spin-spin interaction and atomic cluster states utilizing the trapped two-level atoms inside a one-dimensional coupled resonator waveguide. In the strong driving and large detuning conditions, an effective Ising spin-spin interaction can be generated through suitably tuning the parameters. Then atomic cluster states are produced by using this Ising interaction. This scheme need not initially prepare the superposition states of atoms, and is insensitive to cavity decay.     

Preparation of multi-atom cluster state and teleportation of arbitrary two-atom state via thermal cavity

We propose one cavity QED (CQED) scheme for generating an arbitrary 2-level-atom cluster state. Besides, by using a 4-atom cluster state as quantum channel, we propose another CQED scheme for teleporting any unknown two-atom state. In both schemes, the dynamics processes are essentially quite similar. The Rabi frequency of the classical driving field is much bigger than the detuning between the atoms and the cavity. Hence both schemes are insensitive to the cavity decay. The necessary time for implementation is much shorter than the Rydberg-atom lifespan, therefore atom decays do not need to be considered. Moreover, in the teleportation scheme the discrimination of the 16 mutually orthogonal 4-atom cluster states is transformed into the discrimination of single-atom product states, consequently the discrimination difficulty is degraded and the scheme is more easily implemented.     

Preparation of Cluster States of Atomic Qubits in Cavity QED

We propose an optical scheme to generate cluster states of atomic qubits, with each trapped in separate optical cavity, via atom-cavity-laser interaction. The quantum information of each qubit is encoded on the degenerate ground states of the atom, hence the entanglement between them is relatively stable against spontaneous emission. A single-photon source and two classical fields are employed in the present scheme. By controlling the sequence and time of atom-cavity-laser interaction, we show that the atomic cluster states can be produced deterministically.     

Scheme for Entanglement Concentration of Unknown Multiparticle Greenberger-Horne-Zeilinger or W Class States

We present two schemes for concentrating unknown nonmaximally entangled Greenberger-Horme-Zeilinger (GHZ) or W class states. The first scheme for concentrating the nonmaximally entangled GHZ state is based on linear optical devices. The second scheme for concentrating the W class states can be applied to a wide variety of atomic state. Both of our schemes are not postselection ones and are within the current technologies.     

Robust schemes for the generation of multipartite entanglement for remote atoms with cross-Kerr nonlinearity

Based on the interference effect of indistinguishable polarized photons leaking out of separated cavities with each atom trapped in separate cavity, using quantum nondemolition detection, we propose the robust schemes for the generation of N-atom GHZ state, three-atom W state and four-atom cluster state with a certain success probability. In Lamb-Dicke limit, the schemes do not require the simultaneous click of the photon-detectors. These made the schemes more realizable in experiments. Meanwhile, the advantage of the scheme is that the fidelity of the entangled states is not affected by the atomic spontaneous, cavity decay, and imperfection of the photodetectors. The schemes would be useful steps towards long-distance quantum communication.     

Preparation of Arbitrary Four-Qubit W State with Atomic Ensembles via Rydberg Blockade

The generation of various entangled states is an essential task in quantum information processing. Recently, a scheme （PRA 79, 022304） has been suggested for generating Greenberger-Horne-Zeilinger state and cluster state with atomic ensembles based on the Rydberg blockade. Using similar resources as the earlier scheme, here we propose an experimentally feasible scheme of preparing arbitrary four-qubit W class of maximally and non- maximally entangled states with atomic ensembles in a single step. Moreover, we carefully analyze the realistic noises and predict that four-qubit W states can be produced with high fidelity （F - 0.994） via our scheme.     

Generation of Atomic Cluster State via Adiabatic Evolution of Dark Eigenstates

We propose a scheme to generate atomic cluster states of arbitrary configuration in the cavity quantum electrodynamics (QED) system. The process is achieved via adiabatic evolution of dark states, which only requires adiabatically increasing or decreasing Rabi frequencies of laser. Thus it allows the robust implementation of entanglement against certain types of errors. Our scheme is relatively decoherence-free in the sense that excited atomic states are never populated and excited cavity photon states can be made negligible in certain conditions.     

Preparation of Entanglement of Atoms and of Photons via Cavity Input-Output Process

We propose a method to prepare multipartite entangled states such as cluster states and graph states based on the cavity input-output process and single photon measurement. Two quantum gates, a controlled phase gate and a fusion gate between two atoms trapped in respective cavities, are proposed to prepare atomic cluster states and graph states with one and two dimensions. We also introduce a scheme that can generate an arbitrary multipartite photon duster state which uses two coherent states as a qubit basis.     

Possible Realization of Cluster States and Quantum Information Transfer in Cavity QED via Raman Transition

We present a scheme to generate cluster states with many scheme, no transfer of quantum information between the atoms in cavity QED via Raman transition. In this atoms and cavities is required, the cavity fields are only virtually excited and thus the cavity decay is suppressed during the generation of cluster states. The atoms are always populated in the two ground states. Therefore, the scheme is insensitive to the atomic spontaneous emission and cavity decay. We also show how to transfer quantum information from one atom to another.     

Generation of GHZ state and cluster state with atomic ensembles via the dipole-blockade mechanism

This paper proposes scalable schemes to generate the Greenberger-Horne-Zeilinger (GHZ) state and the cluster state with atomic ensembles via the dipole blockade mechanism on an atom chip, where the qubit is not carried by a single atom but an atomic ensemble. In the protocols, multiqubit entangled states are determinately prepared. Needlessness for single-photon source further decreases the complexity of the experiment. Based on the present laboratory technique, the schemes may be realized. The achieved results reveal a prospect for large-scale quantum communication and quantum computation.     

Teleportation of Unknown Atomic Entangled States Using GHZ Class States

We propose two physical schemes, which can teleport unknown atomic entangled states from user A （Alice） to user B （Bob） via GHZ class states as quantum channel The two schemes are both based on cavity QED techniques. In the two schemes, teleportation and distillation procedures can be realized simultaneously. The second teleportation scheme is more advantageous than the first one.     

光腔耦合阵列中四模方形Cluster态的制备

提出一种四模方形cluster态的制备方案,方案选用四个分别包含一个原子系综的独立单模光腔,光腔之间用短光纤实现耦合.讨论证明在合适外加激光脉冲的驱动下,可确定性的制备得到稳定的四模方形cluster态.通过调节驱动激光的频率和相位,该方案可以拓展到多模和其他形cluster态的制备.     

光腔耦合阵列中四模方形Cluster态的制备

提出一种四模方形cluster态的制备方案,方案选用四个分别包含一个原子系综的独立单模光腔,光腔之间用短光纤实现耦合.讨论证明在合适外加激光脉冲的驱动下,可确定性的制备得到稳定的四模方形cluster态.通过调节驱动激光的频率和相位,该方案可以拓展到多模和其他形cluster态的制备.     

Deterministic Joint Remote Preparation of an Arbitrary Two-Qubit State Using the Cluster State

Recently, deterministic joint remote state preparation (JRSP) schemes have been proposed to achieve 100% success probability. In this paper, we propose a new version of deterministic JRSP scheme of an arbitrary two-qubit state by using the six-qubit cluster state as shared quantum resource. Compared with previous schemes, our scheme has high efficiency since less quantum resource is required, some additional unitary operations and measurements are unnecessary. We point out that the existing two types of deterministic JRSP schemes based on GHZ states and EPR pairs are equivalent.