Scheme for generating the singlet state of three atoms trapped in distant cavities coupled by optical fibers

An effective scheme is proposed to generate the singlet state with three four-level atoms trapped in three distant cavities connected with each other by three optical fibers, respectively. After a series of appropriate atom–cavity interactions, which can be arbitrarily controlled via the selective pairing of Raman transitions and corresponding optical switches, a three-atom singlet state can be successfully generated. The influence of atomic spontaneous decay, photon leakage of cavities and optical fibers on the fidelity of the state is numerically simulated showing that the three-atom singlet state can be generated with high fidelity by choosing the experimental parameters appropriately.     

Scheme for implementing quantum logic gates for two atomstrapped in different cavities

A scheme is presented for realizing quantum logic gates for two atoms localized in two distant optical cavities. Our scheme works in a regime in which the atom--cavity coupling strength is smaller than the cavity decay rate. Thus the requirement on the quality factor of the cavities is greatly relaxed. Furthermore, the fidelity of our scheme is not affected by detection inefficiency and atomic decay. These advantages are important in view of experiment.     

Long-distance quantum state transfer through cavity-assisted interaction

We propose a scheme for long-distance quantum state transfer between different atoms based on cavity-assisted interactions. In our scheme, a coherent optical pulse sequentially interacts with two distant atoms trapped in separated cavities. Through the measurement of the state of the first atom and the homodyne detection of the final output coherent light, the quantum state can be transferred into the second atom with a success probability of unity and a fidelity of unity. In addition, our scheme neither requires the high-Q cavity working in the strong coupling regime nor employs the single-photon quantum channel, which greatly relaxes the experimental requirements.     

Purification of entangled states for two atoms via cavity decay

In this paper a scheme is proposed for the purification of entangled states for two atoms trapped in two distant cavities via cavity decay. In the scheme, the atoms have no probability of being populated in the excited state and thus the atomic spontaneous emission is suppressed. This scheme is valid no matter when the cavity decay rate is larger or smaller than the effective atom-cavity coupling strength. The fidelity of the final state is not affected by the imperfection of the photodetectors.     

Quantum phase gate in decoherence-free subspace with cavity QED system

We demonstrate how to perform quantum phase gate with cavity QED system in decoherence-free subspace by using only linear optics elements and photon detectors. The qubits are encoded in the singlet state of the atoms in cavities among spatially separated nodes, and the quantum interference of polarized photons decayed from the optical cavities is used to realized the desired quantum operation among distant nodes. In comparison with previous schemes, the distinct advantage is that the gate fidelity could not only resist collective noises, but also immune from atomic spontaneous emission, cavity decay, and imperfection of the photodetectors. We also discuss the experimental feasibility of our scheme.     

Quantum state transfer between distant atoms via selectivity photon emission and absorption progresses

We proposed a simple scheme to deterministically generate three-dimensional (3D) quantum state transfer (QST) between two spatially atoms based on the selectivity photon emission and absorption progresses. In the present scheme, two M-type five-level atoms are trapped into two cavities connected by a fiber. By quantitatively discussing the evolution of system, we show that the effects of atom's spontaneous decay and photon leakage out of fiber can be suppressed in our scheme due to the presence of virtual excited processes in atom and fiber modes. Moreover, we also show that the present scheme can be extended to realize QST between distant nodes in a coupled array of optical cavity, which is very useful for the progress of the quantum information network.     

制备n原子GHZ类态

我们提出一个方案通过极化光子的干涉来制备囚禁在相距很远的腔中的n原子GHZ类态。在该方案中,原子腔耦合强度小于腔衰减率。因此对腔的品质因子的要求大大降低了,而且,该方案的保真度不受探测器效率和原子自发衰变的影响。 中文关键词：纠缠制备;GHZ类态;腔QED     

Deterministic Generation of W States for Any Number of Distant Atoms via Adiabatic Passage

We propose a deterministic scheme for preparing any number of distant atoms in a W state. The atoms are respectively trapped in spatially separated optical cavities connected by the fibers. Our scheme utilizes the adiabatic passage along dark state, and is robust against the atomic spontaneous emission and the decays of cavities. The numerical simulation of entanglement fidelity shows that the losses of fibers can be negligible under certain conditions. All of the advantages make the protocol more practical than previous ones.     

Dissipative preparation of entanglement in optical cavities

We propose a novel scheme for the preparation of a maximally entangled state of two atoms in an optical cavity. Starting from an arbitrary initial state, a singlet state is prepared as the unique fixed point of a dissipative quantum dynamical process. In our scheme, cavity decay is no longer undesirable, but plays an integral part in the dynamics. As a result, we get a qualitative improvement in the scaling of the fidelity with the cavity parameters. Our analysis indicates that dissipative state preparation is more than just a new conceptual approach, but can allow for significant improvement as compared to preparation protocols based on coherent unitary dynamics.     

Scheme for reliable realization of quantum logic gates for two atoms separately trapped in two distant cavities via optical fibers

An approach for realizing conditional phase gate for two atoms separately trapped in two distant cavities mediated by an optical fiber is proposed. Utilizing the adiabatic passage, the atomic spontaneous emission, and the decays of the fiber and cavities are avoided under certain condition. The effects of the losses in the fiber and cavities on the fidelity are analyzed. Moreover, our scheme is not restricted to Lamb-Dicke limit. We also generalize the approach to generate one-dimensional cluster state and entangled state for two collections of atoms.     

Establishment of Entanglement for Two Atoms Trapped in Two Distant Bad Cavities

A scheme is presented for generation of entangled states for two atoms trapped in two distant bad cavities. The scheme can work with bad cavities with the coupling strength smaller than the cavity decay rate, which is important from the viewpoint of experiment. In the scheme the atoms have no probability of being populated in the excited state and thus the atomic spontaneous emission is suppressed, which increases the probability of success. The fidelity of the entangled state is not affected by the detection eflciency. Furthermore, the scheme does not require the detection of the left-polarized photon and right-polarized photon at the same time.     

Arbitrary state controlled-unitary gate between two remote atomic qubits via adiabatic passage

We generalize the scheme of Lacour et al. [X. Lacour, N. Sangouard, S. Guerin, H.R. Jauslin, Phys. Rev. A 73 (2006) 042321] to the case of nonlocal qubits, which makes the resultant gate suitable for distributed quantum computation. In our scheme, two remote atomic qubits are separately trapped in two distant cavities connected by an optical fiber. Based on adiabatic passage, our scheme is immune to the decoherence due to spontaneous emission and to photon decay from the cavity modes and the fiber mode. Moreover, our scheme can work robustly beyond the Lamb–Dicke limit. It is shown that the minimum fidelity of the resultant gate operation for an arbitrary input state could be over 0.98.     

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.     

Deterministic generation of Greenberger-Horne-Zeilinger and W states for three distant atoms via adiabatic passage

We propose two schemes for generating Greenberger-Horne-Zeilinger and W states of three distant atoms.In the present schemes,the atoms are individually trapped in three spatially separated optical cavities coupled by two optical fibres.Performing an adiabatic passage along dark states,the population of cavities and fibres excited is negligible under certain conditions.In addition,the spontaneous decay of atoms is also efficiently suppressed based on our proposals.Furthermore,the discussion about the entanglement fidelity is given and we point out that our schemes work robustly with small fluctuations of experimental parameters.     

Approximate and Conditional Teleportation of?an?Unknown Atomic State with Dissipative Two-Photon Interaction in Cavity QED System

A scheme for approximate and conditional teleportation of an unknown atomic state via dissipative two-photon interaction in cavity QED is proposed. In our scheme, the dissipative two-photon interaction Jaynes-Cummings model is used to realize the approximate and conditional teleportation. We investigate analytically the influence of the cavity mode decay on the teleportation fidelity and show that the high fidelity teleportation can be implemented in dissipative case. Our scheme does not involve the Bell-state measurement and an additional atom, only requiring two atoms and one single-mode cavity. The scheme may be generalized to not only the teleportation of the state of a cavity mode to another mode by means of a single atom but also the teleportation of the state of a trapped ion.     

Approximate and Conditional Teleportation of an Unknown Atomic State with Dissipative Jaynes-Cummings Model

A scheme for approximately and conditionally teleporting an unknown atomic state in dissipative cavity QED is proposed. It is the extension of the scheme of [Phys. Rev. A 69 （2004） 064302], where the cavity mode decay has not been considered and only a time point of system evolution and the corresponding fidelity implementing the teleportation are given. In fact, the cavity mode decay exists really and must be delt with. In this paper, we investigate the influence from the cavity mode decay on the implementation of the approximate and conditional teleportation by means of the dissipative Jaynes Cummings model and then show the analytical expression of the fidelity of realization of the teleportation. Alternatively, our scheme does not involve an additional atom, only requiring two atoms and one single-mode cavity.     

Robust Generation of Three-Particle W State with Atoms Trapped in Separate Cavities

This paper presents a scheme for generating three-particle W state of remote atoms trapped in leaky cavities.The scheme uses cavity decay to inject photons into a setup of optical devices which consist of a series of beam splitters and photon detectors.Photon detection on the output mode projects the atomic state into the W state.In the condition of “weakly driven approach”,it shows that the scheme is robust and has high fidelity.It also points out that the scheme is scalable to generate multi-atomic W 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.     

通过绝热过程实现任意一原子态的隐形传态(英文)

我们利用腔场和激光相互作用,提出一个冗余的、对消相干不敏感的方案,来传输任意一个三能级原子的态.由于原子自发跃迁和腔延迟作用会造成信息丢失,通过用部分绝热过程和适当的原子场耦合的设计,信息丢失能够被有效的抑制,此方案传送成功的几率是0.5,保真度是1.     

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.