Distant Cavities Research Articles

The Influences of the Selective Atomic Measurement on Entanglement Properties in the System of Three Atoms Trapped in Two Distant Cavities Connected by an Optical Fiber

Three two-level atoms are trapped in two initially empty cavities connected by an optical fiber. The entanglement evolution between two atoms in the same cavity and the entanglement evolution between two cavities are investigated. The influence of the state-selective measurement of the atom trapped in the other cavity on the entanglement and that of fiber-cavity coupling coefficient on the entanglement are discussed. The results obtained show that atom-atom entanglement property is strengthened, and cavity-cavity entanglement property is weakened with increasing of the cavity-fiber coupling coefficient. On the other hand, the results also show that the entanglement between two cavities and that between two atoms in the same cavity can be strengthened through the state-selective measurement on the atom trapped in the other cavity.

High fidelity and flexible quantum state transfer in the atom-coupled cavity hybrid system

We investigate a system composed of N coupled cavities (linear array) and two-level atoms interacting one at a time. Adjusting appropriately the atom-field detuning, and making the hopping rate of photons between neighboring cavities, A, greater than the atom-field coupling g (i.e. A ? N 3/2 g), we can eliminate the interaction of the atom with the non-resonant normal modes reducing the dynamics to the interaction of the atom with only a single-mode. As an application of this interaction, we propose a two-step protocol for quantum communication of an arbitrary atomic quantum state between distant coupled cavities. In the ideal case, the coupled cavities system acts as a perfect quantum bus and we obtain a flexible and perfect quantum communication for any N. Considering the influence of dissipation, an interesting parity effect emerges and we still obtain a high fidelity quantum state transfer for an appreciable number of cavities with current experimental parameters. We also studied important sources of imperfections during the procedure.

Coherent cavity networks with complete connectivity

When cavity photons couple to an optical fiber with a continuum of modes, they usually leak out within a finite amount of time. However, if the fiber is about 1 m long and linked to a mirror, photons bounce back and forth within the fiber on a much faster time scale. As a result, dynamical decoupling prevents the cavity photons from entering the fiber. In this paper, we use the simultaneous dynamical decoupling of a large number of distant cavities from the fiber modes of linear optics networks to mediate effective cavity–cavity interactions in a large variety of configurations. Coherent cavity networks with complete connectivity can be created with potential applications in quantum computing and in the simulation of the complex interaction Hamiltonians of biological systems.

Creation of four-mode weighted cluster states with atomic ensembles in high-Q ring cavities

Two schemes for the preparation of weighted continuous variable cluster states with four atomic ensembles are proposed. In the first scheme, the four separated atomic ensembles inside a two-mode ring cavity are driven by pulse laser fields. The basic idea of the scheme is to transfer the ensemble bosonic modes into suitable linear combinations that can be prepared in a pure cluster state by a sequential application of the laser pulses with the aid of the cavity dissipation. In the second one, we take two separate two-mode cavities, each containing two atomic ensembles. The distant cavities are coupled by dissipation in a cascade way. It has been found that the mixed cluster state can be produced. These schemes may contribute towards implementing continuous variable quantum computation, quantum communication and networking based on atomic ensembles.

Remote on-chip coupling

Scientists have demonstrated strongly coupled photon states between two distant high-Q photonic crystal cavities connected by a photonic crystal waveguide. Remote dynamic control over the coupled states could aid the development of delay lines, optical buffers and qubit operations in both classical and quantum information processing.

Entangling Two Atomic Ensembles Trapped in Separated Cavities

We propose a scheme for the generation of two collections of atoms trapped in distant cavities connected by an optical fiber. The virtual photon exchange leads to the entanglement between these two atomic ensembles. During the operation the atomic system, cavity modes, and fiber are not excited, which is important in view of decoherence.

Generation of N-atom and 2N-atom W states in distant cavities via adiabatic passage

N-atom W state and 2N-atom W state are generated in atom-cavity system linked by optical fibers via adiabatic passage. Numerical results including the non-adiabatic effects such as atomic spontaneous emission and cavity dissipation are also included. The W state generating schemes are robust against atomic emission and cavity decay under adiabatic condition.

Quantum repeaters based on deterministic storage of a single photon in distant atomic ensembles

Quantum repeaters hold the promise to prevent the photon losses in communication channels. Most recently, the serious efforts have been applied to achieve scalable distribution of entanglement over long distances. However, the probabilistic nature of entanglement generation and realistic quantum memory storage times make the implementation of quantum repeaters an outstanding experimental challenge. We propose a quantum repeater protocol based on the deterministic storage of a single photon in atomic ensembles confined in distant high-finesse cavities and show that this system is capable of distributing the entanglement over long distances with a much higher rate as compared to previous protocols, thereby alleviating the limitations on the quantum memory lifetime by several orders of magnitude. Our scheme is robust with respect to phase fluctuations in the quantum channel, while the fidelity imperfection is fixed and negligibly small at each step of entanglement swapping.

Creation of entanglement of two atoms coupled to two distant cavities with losses

We present a model to generate atomic entanglement with atoms located at distant cavities. It consists of two cavities connected by an optical fibre, where each cavity interacts with a single two-level atom. For certain atom–cavity and cavity–fibre coupling parameters, we find a wide time plateau for the concurrence between the atoms. An increase of the atom–cavity detuning gives rise to a linear increase of the width of the plateau, but at the same time, when losses are included in the model, it also decreases the value of the concurrence and increases the response time to reach the maximum.

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.

SCHEME FOR GENERATION OF GREENBERGER-HORNE-ZEILINGER STATES OF REMOTE ATOMS TRAPPED IN SEPARATE OPTICAL CAVITIES

We propose a scheme for generating maximally entangled states for three atoms trapped in three distant cavities connected by two identical single-mode fibers. During the operation, neither the atomic system nor the fibers are excited, which is important in view of decoherence. Under certain conditions, the probability of the excited cavities can be negligible. Taking advantage of adiabatic passage, the GHZ state can be generated deterministically, and the fidelity of entanglement is insensitive to fluctuation of experimental parameters. Compared to the previous schemes, the significant advantage of the proposed scheme is that each cavity can interact with the other two directly, which can avoid the effect of indirect interaction brought about using only local quantum operator and nonlocal resources.

Fault tolerant analogue search algorithm within a quantum network

We investigate how to implement an analogue search algorithm by adiabatic passage in distant cavities. Any atom with a mark can be found by adjusting the classical fields according to the search condition. The decoherence due to the spontaneous emission of excited states and the decay of fibre modes is efficiently suppressed. In the presence of cavity decay, the fidelity for performing the search algorithm is improved by quantum feedback control.

Generation of Wn state with three atoms trapped in two remote cavities coupled by an optical fibre

We propose two schemes for the generation of the Wn state with three atoms separately trapped in two distant cavities coupled by an optical fibre. One is implemented by controlling the interaction time, the other is implemented via the adiabatic passage. The influence of various decoherence processes, such as spontaneous emission of the atoms and photon leakages of the cavities and the optical fibre, on the fidelity is also investigated. It is found that the Wn state can be generated with high fidelity even when these decoherence processes are present.

Generation of NOON Sates for Two Atomic Samples Trapped in Two Distant Cavities

A scheme is proposed for generating NOON states for two atomic samples trapped in two distant cavities connected by a third cavity and optical fibers. In the scheme, all the atoms are always populated in the two degenerate ground states, so the atoms’ spontaneous emission can be omitted approximately. During the operation neither the cavity modes nor fiber modes are excited, which is important in view of decoherence. The scheme does not include projective measurement and the NOON state is generated deterministically.

Deterministic generation of multiparticle entanglement in a coupled cavity-fiber system

We develop a one-step scheme for generating multiparticle entangled states between two cold atomic clouds in distant cavities coupled by an optical fiber. We show that, through suitably choosing the intensities and detunings of the fields and precisely tuning the time evolution of the system, multiparticle entanglement between the separated atomic clouds can be engineered deterministically, in which quantum manipulations are insensitive to the states of the cavity and losses of the fiber. The experimental feasibility of this scheme is analyzed based on recent experimental advances in the realization of strong coupling between cold 87Rb clouds and fiber-based cavity. This scheme may open up promising perspectives for implementing quantum communication and networking with coupled cavities connected by optical fibers.

Distributed qutrit–qutrit entanglement via quantum Zeno dynamics

A scheme is proposed to generate a three-dimensional entangled state for two atoms trapped in two distant cavities via quantum Zeno dynamics. We study such system in the regime of resonant atom–field interactions, which makes the scheme work very fast. We also investigate the influence of dissipation, due to atomic spontaneous emission and photon leakage, on the qutrit–qutrit entanglement.

The entanglement properties in the system composed of a -type atom and a V-type atom trapped in two distant cavities connected by an optical fiber

We consider a system consisting of a -type atom and a V-type atom, which are individually trapped in two spatially separated cavities that are connected by an optical fiber. The evolution of the state vector of the system is given. We investigate the temporal evolution in the entanglement between atoms and that between cavities. We discuss the influence of cavity-fiber coupling coefficient on entanglement. The results obtained by the numerical method show that the entanglement between atoms and the entanglement between cavities have the same evolution regularities. On the other hand, the entanglement between atoms and that between cavities are strengthened with the increase of cavity-fiber coupling coefficient.

Generating single-mode behavior in fiber-coupled optical cavities

We propose to turn two resonant distant cavities effectively into one by coupling them via an optical fiber which is coated with two-level atoms [Franson et al., Phys. Rev. A 70, 062302 (2004)]. The purpose of the atoms is to destructively measure the evanescent electric field of the fiber on a time scale which is long compared to the time it takes a photon to travel from one cavity to the other. Moreover, the boundary conditions imposed by the setup should support a small range of standing waves inside the fiber, including one at the frequency of the cavities. In this way, the fiber provides an additional decay channel for one common cavity field mode but not for the other. If the corresponding decay rate is sufficiently large, this mode decouples effectively from the system dynamics. A single non-local resonator mode is created.

Quantum SWAP gate with atomic ensembles in two distant cavities

A scheme is presented to realize remote quantum SWAP gate with atomic ensembles. During the process, the fiber mode is only virtually excited. The quantum information is encoded in two degenerate ground states, so the atoms' spontaneous emission can be omitted approximately. Moreover, the time needed to complete the gate is proportional to the inverse of the number of atoms and thus the gate is greatly speeded up as the number of atoms increases.

Multi-Atom Entanglement Engineering in Distant Cavities via Resonant Interaction

We propose a scheme for the generation of entangled states for multiple atoms trapped in three distant cavities connected by two identical single-mode fibers. Compared with the previous schemes, the distinct advantages of the proposed scheme are: First, all the cavities in the proposed protocol can interact with each other freely, which is important in quantum communication and distributed quantum computation. Secondly, in the scheme, the atoms, cavities, and fiber mode are in resonance. Thus, the required interaction time is short, which is important in view of decoherence. In principle, the proposed scheme can be extended to generate n atoms entangled states.