Transformation of bipartite non-maximally entangled states into a tripartite W state in cavity QED

We present two schemes for transforming bipartite non-maximally entangled states into a W state in cavity QED system, by using highly detuned interactions and the resonant interactions between two-level atoms and a single-mode cavity field. A tri-atom W state can be generated by adjusting the interaction times between atoms and the cavity mode. These schemes demonstrate that two bipartite non-maximally entangled states can be merged into a maximally entangled W state. So the scheme can, in some sense, be regarded as an entanglement concentration process. The experimental feasibility of the schemes is also discussed.     

通过原子与腔场共振相互作用制备三原子的W态

提出了一种简单、可行的三原子W态制备方案，它是基于三个二能级原子与一个单模腔场共振相互作用实现的。通过控制原子与腔场相互作用时间和耦合参数，无需对腔场态的探测，就可获得三原子的W态。此外，讨论了在现有实验技术下本方案实现的可能性。     

Generation of four-photon W state via cavity QED

This paper proposes an alternative scheme for generating four-photon W state via cavity QED. The scheme bases on the resonant interaction of a A-type three level atom with two bimodal cavities. The detection of atom collapses the cavity to the desired state. Comparing with previous schemes, the advantage of this scheme is that the interaction time can be greatly shortened since it uses the resonant interaction between atom and cavities. Moreover, the proposed scheme is more experimentally feasible than the previous ones.     

A simple scheme for generating multi-atom GHZ state via cavity QED

This paper proposes a simple scheme for generating a three-atom GHZ state via cavity quantum electrodynamics (QED). The task can be achieved through the interaction between two EPR states, which can be prepared easily with current technology. In this scheme, the cavity field is only virtually excited during the interaction process, and no quantum information transfer between the atoms and the cavity is required. Thus it greatly prolongs the efficient decoherent time. Moreover, this scheme is also applicable for generating an N-atom GHZ state.     

利用腔QED概率传送未知原子纠缠态

利用V型三能级原子与双模腔场的共振相互作用,通过调节原子与光场的相互作用时间,并对待传送的原子态进行选择性探测,从而实现未知双原子纠缠态的隐形传送。该方案的特点是不需要进行Bell基测量,其成功几率为1/16。     

A scheme for transferring an unknown atomic entangledstate via cavity quantum electrodynamics

In this paper, we propose a scheme for transferring an unknown atomic entangled state via cavity quantum electrodynamics (QED). This scheme, which has a successful probability of 100 percent, does not require Bell-state measurement and performing any operations to reconstruct an initial state. Meanwhile, the scheme only involves atom--field interaction with a large detuning and does not require the transfer of quantum information between the atoms and cavity. Thus the scheme is insensitive to the cavity field states and cavity decay. This scheme can also be extended to transfer ring an entangled state of $n$-atom.     

Entanglement Concentration for Three-Atom W State via Introducing an Auxiliary Atom in Cavity QED

We present two physical schemes for concentrating three-atom W state based on the same interaction model which involves two three-level atoms, a cavity field and a classical field. Both schemes introduce only one auxiliary atom. The first scheme involves only one measurement. There is one more measurement on the auxiliary atom in the second scheme, but the interaction time is simple in form and there is no single-qubit operation on the auxiliary atom. Moreover, both schemes are insensitive to cavity decay and within the current cavity quantum electrodynamics (QED) technique.     

利用双光子J-C模制备三原子的W纠缠态

提出了利用双光子J-C模制备三原子W纠缠态的方案。阐明了通过控制原子腔场的相互作用时间便能获得所制备的态。还指出利用这个模型制备W态比制备GHZ态更优越。此外，就腔QED技术对方案的实验实现作了分析。     

Generation of a four-atom entangled cluster state in cavity QED

We propose a method of generating a four-atom entangled cluster state by considering two kinds of the atoms–cavity field interaction in cavity QED. During the preparation the cavity is only virtually excited no quantum information will be transferred from the atoms to the cavity and thus the scheme is insensitive to the cavity field states and cavity decay. The scheme can also be used to generate the cluster state for the trapped ions.     

A novel scheme of hybrid entanglement swapping and teleportation using cavity QED in the small and large detuning regimes and quasi-Bell state measurement method

We outline a scheme for entanglement swapping based on cavity QED as well as quasi-Bell state measurement(quasiBSM) methods. The atom–field interaction in the cavity QED method is performed in small and large detuning regimes.We assume two atoms are initially entangled together and, distinctly two cavities are prepared in an entangled coherent–coherent state. In this scheme, we want to transform entanglement to the atom-field system. It is observed that, the fidelities of the swapped entangled state in the quasi-BSM method can be compatible with those obtained in the small and large detuning regimes in the cavity QED method(the condition of this compatibility will be discussed). In addition, in the large detuning regime, the swapped entangled state is obtained by detecting and quasi-BSM approaches. In the continuation,by making use of the atom–field entangled state obtained in both approaches in a large detuning regime, we show that the atomic as well as field states teleportation with complete fidelity can be achieved.     

利用三原子W类纠缠态在腔量子电动力学体系中实现单原子态的远程制备

提出了两个利用三原子W类纠缠态作为量子通道.在腔量子电动力学(QED)体系中实现单原子态的远程制备方案:一个是接收者借助于原子与单模腔场之间的大失谐相互作用实现初始态重建,另一个则是接受者利用原子与单模腔场之间的共振相互作用完成远程态制备.两方案中都涉及到了一位发送者和两位接收者,发送者可以将被传送态远程制备到两位接收者中的任何一位的手中,而另一位接受者必须为其提供必要的协助.表明利用原子与腔场之间的大失谐相互作用的方法可以很好地克服腔场的消相干,降低对腔品质因子的要求;而利用共振相互作用的方法则无需引入辅助原子,操作简便.但不论采用何种方法,实现单原子远程态制备的总成功概率是相同的.     

Scheme for generation of four-atom Greenberger-Horne-Zeilinger states in an optical cavity

We propose a scheme for generating maximally GHZ state for four atoms trapped in a two-mode optical cavity via combination of cavity QED and linear optics system. The GHZ state can be not only generated deterministically with a single resonant interaction in cavity QED, but also can be prepared probabilistically based on cavity QED and linear optics elements. The fidelity of the entangled states is not affected by the atomic spontaneous, cavity decay, and imperfection of the photon-detectors. Finally, we briefly analyze and discuss the experimental feasibility of the proposed scheme.     

Generation of quantum switch and nonlocal fields with an external field in a high quality dispersive cavity

We present a scheme to prepare an optical “quantum switch”, a superposition of “open” and “closed” states. The scheme is based on the interaction of an Λ-type three-level atom with a single-mode of quantized cavity field and an external classical driving field, in the regime where the atom and fields are highly detuned. We show how this interaction can be used to generate coherent states of the cavity field in contrast to the usual method used in microwave cavity QED of injecting a coherent state into a cavity. A combination of switches could be used to prepare a quantum superposition of coherent field states located simultaneously in two cavities. Compared with previous proposals, our scheme is simplified due to economizes the Ramsey zone and the time required for the state generation is short.     

Scheme for Implementing Controlled Dense Coding with Six-Atom Cluster State in Cavity QED

We propose an experimentally feasible protocol for implementing controlled dense coding with a six-atom cluster state in cavity QED. In the scheme, we investigate that the atoms interact simultaneously with the highly detuned single-mode cavity and the strong classical driving field, and thus our scheme is not sensitive to both the cavity decay and the thermal field. In addition, the four-atom entangled states can be exactly distinguished by performing the single-atom measurements in cavity QED, therefore our scheme might be implemented in a simple way.     

Teleportation of two-atom entangled state in resonant cavity quantum electrodynamics

An alternative scheme is presented for teleportation of a two-atom entangled state in cavity quantum electrodynamics (QED). It is based on the resonant atom--cavity field interaction. In the scheme, only one cavity is involved, and the number of the atoms needed to be detected is decreased compared with the previous scheme. Since the resonant atom--cavity field interaction greatly reduces the interaction time, the decoherence effect can be effectively suppressed during the teleportation process. The experimental feasibility of the scheme is discussed. The scheme can easily be generalized to the teleportation of N-atom Greeninger--Horne--Zeilinger (GHZ) entangled states. The number of atoms needed to be detected does not increase as the number of the atoms in the GHZ state increases.     

利用双模腔场与V型三能级原子共振作用隐形传送腔场纠缠态

提出了一种利用双模腔场与V型三能级原子共振相互作用隐形传送腔场纠缠态的方案。该方案不需要进行Bell基测量,成功几率为1/16.     

利用双模腔场与V型三能级原子共振作用隐形传送腔场纠缠态

提出了一种利用双模腔场与V型三能级原子共振相互作用隐形传送腔场纠缠态的方案.该方案不需要进行Bell基测量,成功几率为1/16.     

Quantum dense coding using a peculiar tripartite entangled state

Following a recent proposal ( Phys. Lett. A 346 (2005) 330) about quantum dense coding using a tripartite entangled GHZ state and W state, this paper proposes an experimentally feasible scheme for dense coding in cavity QED by using another peculiar tripartite entangled state. In the scheme the atoms interact simultaneously with a highly detuned cavity mode with the assistance of a classical field, the successful probability of dense coding scheme with this peculiar tripartite entangled state equals 1.     

利用双模腔场与V型三能级原子共振作用隐形传送未知原子态

给出了双模腔场与V型三能级原子共振相互作用下系统态矢的演化公式.利用V型三能级原子与双模腔场的相互作用,通过控制原子与光场的相互作用时间,并对待传送的原子态进行选择性探测,从而实现未知双原子纠缠态的隐形传送.该方案不需要进行Bell基测量,其成功几率为1/16.     

Alternative Scheme for Teleportation of Two-Atom Entangled State in Cavity QED

We have proposed an alternative scheme for teleportation of two-atom entangled state in cavity QED. It is based on the degenerate Raman interaction of a single-mode cavity field with a A-type three-level atom. The prominent feature of the scheme is that only one cavity is required, which is prior to the previous one. Moreover, the atoms need to be detected are reduced compared with the previous scheme. The experimental feasibility of the scheme is discussed. The scheme can easily be generalized for teleportation of N-atom GHZ entangled states. The number of the atoms needed to be detected does not increase as the number of the atoms in GHZ state increases.