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.     

Generation of Maximally Entangled States for Many Two-Level Atoms in a Thermal Cavity

We propose a scheme for generating maximally entangled states for two or more two-level atoms in a thermal cavity. The cavity frequency is large-detuned from the atomic transition frequency, so the Hamiltonian can be expressed as an effective form. The photon-number-dependent parts in the effective Hamiltonian are cancelled with the assistance of a strong classical field, thus the scheme is insensitive to both the cavity decay and the thermal field. The scheme can be used to generate multi-atom Bell-state and Greenberger-Horne-Zeiliner （GHZ） state.     

利用V形三能级原子与光场Raman相互作用制备多原子GHZ态

提出了一种利用V形三能级原子与光场Raman相互作用制备多原子GHZ态的方法. 关键词： GHZ态 Raman相互作用 V形三能级原子     

利用GHZ态实现多原子缠结态的量子隐形传态

提出一种利用GHZ态实现多原子缠结态的量子隐形传态方案.当作为量子通道的GHZ态含有一个单模高Q腔时,大大地简化了量子稳形传态中的联合测量过程.     

Preparation of Multi—Atom Entangled States with a Single Cavity in a Thermal State

A scheme is suggested for the generation of multi-atom maximally entangled states with a cavity in a thermal state,In this scheme several appropriately prepared two-level atoms are simultaneously sent through the nonresonant cavity.We divide the whole atom-cavity interaction time into two equal parts.At the end of the first part a π pulse is applied to the atome using a classical field.Then the photon-number-dependent shifts on the atomic states are cancelled and the atomic system finally evoloves to a maximally entangled state.     

基于腔QED的多用户间的多原子量子信道的建立

提出基于腔QED技术的多用户间的多原子W态和GHZ态量子信道的建立方案.在量子网络的空闲时段,各个用户和量子交换机共享EPR对.量子交换机通过原子和腔场的相互作用将两个EPR对制备成W态,再与另一个EPR对进行纠缠交换,经过直接测量后为用户建立三原子W态量子信道;同时讨论了四用户间的W态量子信道的建立方案.量子交换机对三个EPR对进行纠缠交换,将三个原子同时与腔场作用,经过直接测量后为用户建立三原子GHZ态量子信道;并将此方法推广到N个用户间的GHZ态量子信道的建立. 关键词： 腔QED 量子信道 量子交换机 纠缠交换     

Preparation of Multi-Atom Entangled States with a Single Cavity in a Thermal State

A scheme is suggested for the generation of multi-atom maximally entangled states with a cavity in a thermalstate. In this scheme several appropriately prepared two-level atoms are simultaneously sent through the nonresonantcavity. We divide the whole atom-cavity interaction time into two equal parts. At the end of the first part a π pulse isapplied to the atoms using a classical field. Then the photon-number-dependent shifts on the atomic states are cancelledand the atomic system finally evolves to a maximally entangled state.     

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.     

One-dimensional cluster state generated in one step via one cavity

A scheme to generate multi-atom one-dimensional cluster state via one microwave cavity with an additional driven classical field is proposed. According to the scheme, one-dimensional cluster state with 2k-atom can be prepared in one step via one cavity, one-dimensional cluster state with (2k-1)-atom can be generated by measuring the2kth-atom of an 2k-atom cluster state in a certain basis. This scheme avoids cavity-field induced decay and may achieve one-dimensional cluster states with ideal success probability.     

在热腔中产生多原子GHZ态的方法

我们提出了一个在热腔中产生多原子GHZ态的方法来检验量子非定域性。在这个方法中,三个原子被同时送入一个热腔中,它们初始时处于相同的态。这个方法既对腔的衰减不敏感又对热场不敏感,这为检验量子力学的基本方面提供了新的前景。     

Dense Coding with Multi-Atom Entanglement Channel in Cavity QED

Dense coding of multi-atom entangled states in cavity QED is studied. If the quantum channel is generalized GHZ states, dense coding can be directly realized in a simply way. As for the partially entangled pure states, we propose a feasible protocol for entanglement concentration, and the emciency of information transmitted is calculated. The schemes are insensitive to the cavity decay and the field state, due to the fact that the interaction here is a large-detuned one between atoms and the cavity.     

Generation and application of a controllable multi-atom entangled state

In this paper, we present a scheme to prepare a set of the multi-atom entangled states by the cavity quantum electrodynamics (QED) technology. The multi-atom entangled states have some particular entanglement properties. For example, the remaining reduced density matrices ρ_{ij} still retain entanglement or disentanglement when any N-2 atoms of the N atoms are traced out, which can be chosen freely according to our need, and the relative entanglement strength of any pair of atoms (measured by the concurrence) can be arbitrarily adjusted. In addition, they may be completely symmetric under the exchange of any two atoms, and perform certain quantum information tasks, such as telecloning, teleportation, secret sharing and so on.     

Entangled Fields in Multiple Cavities by Interaction with One Three-Level Atom

We present a scheme to entangle fields in multiple cavities. Our scheme is based on the resonant interaction of a Ξ-type three-level atom with the cavity fields for precalculated interaction time, which enables us to generate a quantum entangled Greenberger-Horn-Zeilinger (GHZ) state of fields in multiple cavities. In principle, the scheme can be also generalized to generate N-party GHZ state. The required experimental techniques are within the scope of what can be obtained in the microwave cavity QED set up.     

Remote atomic information concentration without Bell-state measurement

This paper proposes a scheme for information concentration of two remote two-level atoms in cavity QED. This scheme does not involve the Bell-state measurement. During the interaction between atom and cavity, the cavity frequency is large-detuned from the atomic transition frequency, thus the scheme is insensitive to both the cavity decay and the thermal field. This idea can directly be generalized in the case of multi-atom information concentration.     

利用双面腔制备n原子GHZ态

提出了一种利用双面腔制备多原子GHZ态的方法.当腔中囚禁原子处于特定态时,腔可能反射入射的单光子脉冲,也可能透射它.这个特性可以引起囚禁原子和输入腔肠的纠缠.数值模拟显示制备的多原子GHZ态具有很高的保真度和成功率.而且原子自发辐射等内禀噪声只对成功率有影响,而对保真度几乎没有影响.另外,对高Q腔和原子的L-D条件的不要求,提升了试验实现的可行性.     

Protocol for multi-party superdense coding by using multi-atom in cavity QED

We present a protocol for multi-party superdense coding by using multi-atom in cavity quantum electrodynamics (QED). It is shown that, with a highly detuned cavity mode and a strong driving field, the protocol is insensitive to both cavity decay and thermal field. It is even certain to identify GHZ states via detecting the atomic states. Therefore we can realize the quantum dense coding in a simple way in the multiparty system.     

Teleportation of an n-bit one-photon and vacuum entangled GHZ cavity-field state

A scheme for teleporting an arbitrary n-bit one-photon and vacuum entangled Greenberger-Horne-Zeilinger （GHZ） state is proposed. In this scheme, the maximum entanglement GHZ state is used as a quantum channel. We find a method of distinguishing four Bell states just by detecting the atomic states three times, which is irrelevant to the qubit number of the state to be teleported.     

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 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.     

Efficient scheme of quantum SWAP gate and multi-atom cluster state via cavity QED

In this paper, we propose a physical scheme to realize quantum SWAP gate by using a large-detuned single-mode cavity field and two identical Rydberg atoms. It is shown that the scheme can also be used to create multi-atom cluster state. During the interaction between atom and cavity, the cavity is only virtually excited and thus the scheme is insensitive to the cavity field states and cavity decay. With the help of our scheme it is very simple to prepare the N-atom cluster state with perfect fidelity and probability. The practical feasibility of this method is also discussed.