Atomic N00N state generation in distant cavities by virtual excitations

A general scheme of generating N00N states of virtually-excited 2N atoms is proposed. The two cavities are fibre-connected with N atoms in each cavity. Although we focus on the case of N=2, the system can be extended to a few atoms with N>2. It is found that all 2N atoms can be entangled in the form of N00N states if the atoms in the first cavity are initially in the excited states and atoms in the second cavity are all in the ground states. The feasibility of the scheme is carefully discussed, it shows that the N00N state with a few atoms can be generated with good fidelity and the scheme is feasible in experiment.     

Entangling Mesoscopic Squeezed Vacuum States and Fock States in Dissipative Cavity QED System

A scheme is proposed for generating the mesoscopic entanglement between the mesoscopic squeezed vacuum states and Fock states {|0〉,|2〉} by considering both the two-photon interaction of N two-level atoms in cavities with high quality factor assisted by a strong driving field. Moreover, we derive the dissipative interaction models for two-photon interaction. The corresponding analytical expressions of the fidelities can be given. Our scheme can be realized in the current techniques on the cavity QED.     

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.     

Generation of Quantum States for Atomic Ensemble via Cavity QED

A scheme is proposed for generating quantum states of atomic ensemble. In this scheme, a beam of three-level atoms in the Λ configuration is trapped in a cavity, then squeezed vacuum state and squeezed coherent state of the atomic ensemble are prepared by choosing different initial states of the system. The scheme is based on the off-resonant interaction between the atom and cavities, so the high-level of the atom is eliminated adiabatically.     

A single atom-based generation of Bell states of two cavities

A new conditional scheme for generating Bell states of two spatially separated high-Q cavities is reported. Our method is based on the passage of one atom only through the two cavities. A distinctive feature of our treatment is that it incorporates from the very beginning the unavoidable presence of fluctuations in the atom-cavity interaction times. The possibility of successfully implementing our proposal against cavity losses and atomic spontaneous decay is carefully discussed. Received 31 July 2001 and Received in final form 9 October 2001     

Implementation of quantum search scheme by adiabatic passage in a cavity--laser--atom system

This paper proposes a scheme for implementing the adiabatic quantum search algorithm of different marked items in an unsorted list of N items with atoms in a cavity driven by lasers. N identical three-level atoms are trapped in a single-mode cavity. Each atom is driven by a set of three pulsed laser fields. In each atom, the same level represents a database entry. Two of the atoms are marked differently. The marked atom has an energy gap between its two ground states. The two different marked states can be sought out respectively starting from an initial entangled state by controlling the ratio of three pulse amplitudes. Moreover, the mechanism, based on adiabatic passage, constitutes a decoherence-free method in the sense that spontaneous emission and cavity damping are avoided since the dynamics follows the dark state. Furthermore, this paper extends the algorithm with m (m>2) atoms marked in an ideal situation. Any different marked state can be sought out.     

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.     

Robust scheme to generate N-atom W state in two distant cavities

We propose a scheme to realize W states for N-atoms trapped in two distant cavities connected by an optical fiber. In the scheme, the cavity modes and fiber mode are not excited during the process. The quantum information is encoded in two degenerate ground states, so the atom's spontaneous emission can be omitted approximately. Moreover, the operation speed increases with the number of the atoms without a limitation and thus the scheme is extremely robust against decoherence.     

多能级原子与多模光场的相互作用机理研究

研究了多能级原子与多模光场的相互作用.探讨了旋波近似下N能级原子与(N-1)模光场相互作用演化规律，给出了相互作用绘景中其相应的Schrdinger方程的解析通式，分析了三能级原子、四能级原子分别与双模、三模光场相互作用的演化规律.研究结果表明：当原子初始时刻处于基态时，三能级原子与四能级原子的基态概率幅具有相同的变化规律. 关键词： 多能级原子 多模光场 旋波近似     

Probabilistic Teleportation of an Arbitrary Two-mode <Emphasis Type="Italic">N</Emphasis>-photon Entangled State in Cavity QED

We propose a scheme for teleportation of an arbitrary two-mode N-photon entangled states in cavity QED. The scheme is based on the resonant interaction between Λ-type atoms and two-mode cavity fields. In contrast to all the theoretical schemes proposed previously in cavity QED for teleportation of two-mode cavity field states, in the present scheme, the established entanglement for the quantum channel is the type of the multi-dimensional entanglement between the symmetric multi-atom Dicke states and two-mode N-photon states. Therefore, the scheme extends the scope of the theoretical study of the teleportation.     

Efficient generation of N-photon binomial states and their use in quantum gates in cavity QED

A high-fidelity scheme to generate N-photon generalized binomial states (NGBSs) in a single-mode high-Q cavity is proposed. A method to construct superpositions of exact orthogonal NGBSs is also provided. It is then shown that these states, for any value of N, may be used for a realization of a controlled-NOT gate, based on the dispersive interaction between the cavity field and a control two-level atom. The possible implementation of the schemes is finally discussed.     

A Cavity-QED-Based Scheme for Generating Multi-photon NOON State

We present a scheme for generating a multi-photon NOON state within the context of cavity QED. In the present scheme, an N-atom entangled state between two separated cavities is established based on atomic Bragg scattering firstly, and then the entanglement is transferred from atoms to the fields of the two cavities via stimulated Raman adiabatic passage. With the photons emitting from the cavities along two different directions, the maximally path-entangled optical NOON state is obtained.     

利用原子-腔场喇曼相互作用制备纠缠压缩真空态

提出了利用量子态腔场与原子的喇曼相互作用制备纠缠压缩真空态的方案.在该方案中,一个初始制备在基态的原子被依次送入几个初始制备在压缩真空态的微腔中.通过控制原子的运行速度,使原子与每一个腔具有相同的相互作用时间.当原子与腔场发生相互作用,原子与腔场产生纠缠之后,进行原子的测量.当原子被测量处于基态或激发态时,按照量子力学波包塌缩原理,腔场态将塌缩到相应的纠缠压缩真空态.对纠缠压缩真空态的纠缠性质也进行了简略的讨论.     

偶数个多原子Greenberger-Horne-Zerlinger态的制备

提出了一种制备偶数个多原子Greenberger-Horne-Zerlinger态的方案,它是基于原子-腔场相互作用.首先n个分离的腔初始时处于真空态,通过双光子转移,把n个腔制备成数态|2>和真空态|o>的缠结态.随后,与腔场发生共振相互作用的2n个等同的原子被分别送入n个腔,通过相互作用后,2n个原子处于GHZ态,而n个腔仍然处于真空态.     

Resonance fluorescence of a two-level atom excited by a superposition of coherent states, and the instability of the average atomic dipole moment

We find the evolution of average atomic variables in the resonance fluorescence of a two-level atom excited by a superposition of coherent states shifted in phase by π. A new effect is predicted, the quantum instability of the average atomic dipole moment, with a strong correlation between atom and field being the reason. We propose different ways of verifying the effect in experiments involving high-Q optical and microwave cavities. Zh. éksp. Teor. Fiz. 111, 1174–1189 (April 1997)     

Teleportation of a Superposition of Three Orthogonal States of an Atom via Photon Interference

We propose a scheme to teleport a superposition of three states of an atom trapped in a cavity to a second atom trapped in a remote cavity. The scheme is based on the detection of photons leaking from the cavities after the atom-cavity interaction.     

Teleporting <Emphasis Type="Italic">N</Emphasis>-qubit unknown atomic state by utilizing the V-type three-level atom

Realizing the teleportation of quantum state, especially the teleportation of N-qubit quantum state, is of great importance in quantum information. In this paper, Raman-interaction of the V-type degenerate three-level atom and single-mode cavity field is studied by utilizing complete quantum theory. Then a new scheme for teleporting N-qubit unknown atomic state via Raman-interaction of the V-type degenerate three-level atom with a single-mode cavity field is proposed, which is based upon the complete quantum theory mentioned above.     

Teleportation of a Superposition of Three Orthogonal States of an Atom via Photon Interference

We propose a scheme to teleport a superposition of three states of an atom trapped in a cavity to a second atom trapped in a remote cavity. The scheme is based on the detection of photons leaking from the cavities after the atom-cavity interaction.     

A Confined Hydrogen Atom in Higher Space Dimensions

We compute ground state energies for the N-dimensional hydrogen atom confined in an impenetrable spherical cavity. The obtained results show their dependence on the size of the cavity and the space dimension N. We also examine the value of the critical radius of the cavity in different dimensions. Furthermore, the number of bound states was found for a given radius S, in different space dimensions. .