Generation of Entangled States of Multiple Superconducting Quantum Interference Devices in Cavity

We propose a scheme for generating the maximally entangled states of many superconducting quantum interference devices (SQUIDs) by using a quantized cavity field and classicalmicrowave pulses in cavity. In the scheme,the maximally entangled states can be generated without requiring the measurement and individual addressing of the SQUIDs.     

Generation of Greenberger-Horne-Zeilinger states for three atoms trapped in a cavity beyond the strong-coupling regime

A scheme is proposed for generating maximally entangled states for three atoms trapped in a two-mode cavity. The scheme is based on resonant atom-cavity interaction and linear optics elements. The fidelity of the entangled state is not affected by both the decoherence and detection inefficiencies. The scheme works beyond the strong-coupling regime, which is important for high-fidelity entanglement engineering under realistic conditions.     

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.     

Generation of Entangled Multi-atom Dicke States in Cavity Quantum Electrodynamics

We propose a scheme to generate two-atom maximally entangled state in cavity quantum electrodynamies （QED）. The scheme can 5e extended to generation of entangled multi-atom Dicke states if we control the interaction time of atoms with cavity modes. We use adiabatically state evolution under large atom-cavity detuning, so the scheme is insensitive to atomic spontaneous decay. The influence of cavity decay on fidelity and success probability is discussed.     

Production of three-dimensional entanglement for two atoms with a single resonant interaction

A scheme is proposed for generating three-dimensional maximally entangled states for two atoms. In the scheme the atoms are trapped in a two-mode cavity. The scheme only requires a single resonant interaction of the atoms with the cavity modes. Therefore, the scheme is very simple and required interaction time is very short, which is important in view of decoherence.     

Entanglement purification of gaussian continuous variable quantum states

We describe an entanglement purification protocol to generate maximally entangled states with high efficiencies from two-mode squeezed states or from mixed Gaussian continuous entangled states. The protocol relies on a local quantum nondemolition measurement of the total excitation number of several continuous variable entangled pairs. We propose an optical scheme to do this kind of measurement using cavity enhanced cross-Kerr interactions.     

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.     

Preparation of Entangled Atomic States Through Resonant Atom-Field Interaction

A scheme is proposed for the generation of two-atom maximally entangled states and multi-atom maximally entangled states of W class. The scheme is based on the simultaneous resonant interaction of atoms with a single-mode cavity field. It does not require accurate adjustment of the interaction time. The time needed to complete the generation does not increase with the number of the atom.     

Engineering three-dimensional maximally entangled states for two modes in a bimodal cavity

An alternative scheme is proposed for engineering three-dimensional maximally entangled states for two modes of a superconducting microwave cavity. In this scheme, an appropriately prepared four-level atom is sent through a bimodal cavity. During its passing through the cavity, the atom is coupled resonantly with two cavity modes simultaneously and addressed by a classical microwave pulse tuned to the required transition. Then the atomic states are detected to collapse two modes onto a three-dimensional maximally entangled state. The scheme is different from the previous one in which two nonlocal cavities are used. A comparison between them is also made.     

Scheme for Concentration of Unknown Greeberger-Horne-Zeilinger Entangled States via Cavity Decay

We present a scheme for entanglement concentration of an unknown atomic non-maximally entangled GHZ state via cavity decay. In the scheme, the atom trapped in a cavity is manipulated by laser field, so the maximally entangled GHZ state can be obtained by performing certain operation, which can be realized by illuminating the atom in a cavity. Our method is robust against spontaneous atomic decay.     

A Scheme for Generating Entangled Squeezed States Based on Cavity QED

We propose a scheme for generating entangled squeezed vacuum states of electromagnetical fields. The scheme is based on cavity QED. In this scheme, an atom interacts, successively, with a classical field, two quantum cavity fields, and another classical field. By detecting the final states of the atom, the two quantum cavity fields will be projected to an entangled state.     

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.     

利用纠缠交换制备原子-原子最大纠缠态

基于腔量子电动力学(QED)提出一种利用两对纠缠的级联型三能级原子与单模腔场系统制备原子-原子最大纠缠态的简单方案,最初两原子之间、两腔场之间互不纠缠,使其中一个原子与一个腔场发生作用,即纠缠交换,该过程仅需对单个腔场态测量就可实现从未有直接作用的两个原子之间的纠缠,精确控制原子与腔场的相互作用时间可获得具有最大保真度的纠缠态.该方案可以延长腔的有效泄漏时间,从而能有效克服光腔的消相干的影响,这样大大降低了系统对腔的品质的要求.     

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.     

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。     

Preparation of Multi-cavity Entangled States

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Preparation of Multi2cavity Entangled States

A scheme is proposed for the generation of maximally entangled field states in multiple cavities. In the scheme an appropriately prepared ladder-type multi-level atom is sent through the cavities initially in vacuum states. After resonant interactions the cavity system is prepared in a highly entangled state with the atom left in its lowest state.     

Scheme for Generation of Maximally Entangled States via Entanglement Swapping

Based on two atoms and two cavities initially in two pairs of atom-photon nonmaximally entangled states, we propose a relatively simple scheme to create maximally entangled photon-photon and atom-photon states via entanglement swapping using techniques of cavity QED inspired by the scheme proposed in [Phys. Rev. A 71 (2005)044302] and [Phys. Rev. A 71 (2005) 034312]. Our scheme does not involve the measurement in Bell basis, we only require detecting the states of atoms.     

Efficient scheme for two-atom entanglement and quantum information processing in cavity QED

A scheme is proposed for the generation of two-atom maximally entangled states and realization of quantum logic gates and teleportation with cavity QED. The scheme does not require the transfer of quantum information between the atoms and cavity. In the scheme the cavity is only virtually excited and thus the requirement on the quality factor of the cavities is greatly loosened.     

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.