Distant Cavities Research Articles

Implementation of a remote three-qubit controlled-Z gate for atoms separately trapped in cavities coupled by optical fibres

We propose a scheme for implementing a remote three-qubit controlled-Z gate with three atoms separately trapped in three distant cavities coupled by optical fibres. The influences of various decoherence processes, such as spontaneous emission of the atoms and photon leakage of the cavities and the optical fibres, on the fidelity are also investigated. It is found that the gate can be implemented with high fidelity even when these decoherence processes are considered. This scheme can be extended to the implementation of a remote N-qubit controlled-Z gate with N atoms separately trapped in N distant cavities coupled by optical fibres.

Quantum communication and entanglement between two distant atoms via vacuum fields

This paper proposes an efficient scheme for quantum communication between two atoms trapped in distant cavities which are connected by an optical fibre. During the operation, all the atomic system, the cavity modes and the fibre are not excited. The quantum state is mediated by the vacuum fields. The idea can be used to realize quantum entanglement between two distant atoms via vacuum.

Engineering atomic quantum reservoirs for photons

We present protocols for creating entangled states of two modes of the electromagnetic field by using a beam of atoms crossing microwave resonators. The atoms are driven by a transverse, classical field and pump correlated photons into (i) two modes of a cavity and (ii) the modes of two distant cavities. The protocols are based on a stochastic dynamics, characterized by random arrival times of the atoms and by random interaction times between atoms and cavity modes. The resulting effective model yields a master equation, whose steady state is an entangled state of the cavity modes. In this respect, the atoms act like a quantum reservoir, pulling the cavity modes into an entangled, Einstein-Podolski-Rosen state, whose degree of entanglement is controlled by the intensity and the frequency of the transverse field. This scheme is robust against stochastic fluctuations in the atomic beam, and it does not require atomic detection nor velocity selection.

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.

Shunts to Divert Aqueous Humor to Distant Epithelialized Cavities After Keratoprosthesis Surgery

Glaucoma is a frequent and often severe problem in patients needing keratoprosthesis (KPro) surgery. Standard glaucoma shunts in these cases often develop a very dense capsule that obstructs flow and causes intraocular pressure elevation. Therefore, we developed shunts that deliver aqueous to distant epithelialized cavities where an obstructing capsule is less likely to form. In this retroactive study of such shunts, the risk of postoperative infection (especially endophthalmitis) has been assessed. Ahmed shunts were connected with a tube to the lacrimal sac or ethmoid sinuses. In subsequent designs the polypropylene plate was eliminated, the valve was enclosed and a distal tube added (New World Medical Inc, Rancho Cucamonga, CA). The latter shunts were connected to the maxillary sinus or lower lid fornix. Between 2001 and 2005 the devices were implanted in 34 patients with very severe ocular disease. (31 had KPro implanted). Thus, the distal tube was led to the lacrimal sac (2 cases), to the ethmoid sinuses (6), to the maxillary sinus (16 cases), and to the lower lid fornix (10 cases). The patients were followed for cumulatively 145 shunt years, with a mean follow-up of 4 years and 3 months. They were instructed to administer low-dose topical antibiotics indefinitely. Only 1 case of acute bacterial endophthalmitis occurred, thus an incidence of 0.7% per shunt year. A slow-growing Mycobacterium was cultured in a disintegrating eye and 1 bacterial maxillary sinusitis occurred, both in autoimmune diseases. Three valves became exposed and had to be removed (1 replaced). Four eyes developed hypotony, probably from valve failure. The shunt arrangement, which connects the anterior chamber to potentially microbe-populated cavities or to the lower lid fornix and its flora, might be suspected to allow rapid retrograde invasion of infective agents, resulting in endophthalmitis. In this series of KPro patients, however, the incidence of severe infection was very low, in fact comparable to that after standard trabeculectomy.

Generation of two-mode squeezed states for two separated atomic ensembles via coupled cavities

We propose an efficient scheme for the generation of two-mode squeezed states for two separated atomic ensembles trapped in distant cavities. The scheme is based on selective couplings between the collective atomic modes and two linearly transformed common field modes mediated by an optical fiber or a third cavity. The quanta of the transformed atomic modes are exhausted due to the linear coupling with the transformed field modes, bringing the original atomic modes into the two-mode squeezed states. The experimental implementation of the scheme would be an important step toward quantum communication and networking with continuous variables.

Generation of entanglement of multiple atoms via distant cavities

A scheme is proposed for the generation of entangled states for three atoms trapped in three distant cavities connected by two identical single-mode fibers. Compared to the previous scheme, the significant advantage of the proposed scheme is that each cavity can interact with the other two directly, which is significant in distributed quantum computation and quantum communication.

Entanglement transfer between atoms in two distant cavities via an optical fibre

This paper presents a treatment of the entanglement transfer between atoms in two distant cavities coupled by an optical fibre. If the atoms resonantly and collectively interact with the local single-mode cavity fields and the dipole–dipole interaction between the atoms is neglected, then it shows that a complete transfer of entanglement from one pair of atoms to another can be deterministically realized. Furthermore, it also investigates the effects of dipole–dipole interaction on entanglement transfer on the condition that the interaction between the atoms and the cavity is much weaker than the coupling between the cavity and the fibre.

Entanglement generation between distant atoms by Lyapunov control

We show how to apply Lyapunov control design to the problem of entanglement creation between two atoms in distant cavities connected by optical fibers. The Lyapunov control design is optimal in the sense that the distance from the target state decreases monotonically and exponentially, and the concurrence increases accordingly. This method is far more robust than simple geometric schemes.

Generation of four-atom entangled decoherence-free states by interference of polarized photons

We propose a protocol to generate four-atom entangled decoherence-free states trapped in distant cavities by using the interference of polarized photons. The protocol uses the effects of quantum statistics of indistinguishable photons emitted by the atoms inside optical cavities. In the Lamb–Dicke limit, the protocol does not require the simultaneous click of detectors. This makes the protocol more realizable in experiments.

Transferring an N-atom state between two distant cavities via an optical fiber

This paper proposes a scheme for transferring an N-atom state between two distant cavities via an optical fiber. The scheme is based on adiabatic passage along a dark state. In the scheme, all the atoms are always in ground state, the field mode of the fiber remains in vacuum state, and the field mode of the cavities being excited can be negligible under certain conditions. Therefore, the scheme is very robust against decoherence. The successful probability of implementing the quantum state transfer increases with increasing number of atoms. Furthermore, the interaction time does not need to be accurately adjusted as long as the adiabaticity condition is fulfilled.

Preparation of a class of multiatom entangled states

We propose a protocol to generate a class of entangled states of N′Λ-type three-level atoms trapped in distant cavities by using interference of polarized photons. The proposed setup involves simple linear optical elements, cavities, and the conventional photon detectors that only distinguish the vacuum and the nonvacuum Fock number states.

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.

Generation of Greenberger-Horne-Zeilinger states for multiple atoms trapped in separated cavities

We propose a scheme for generating maximally entangled states for multiple atoms trapped in distant cavities connected by 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 that the cavities are excited is negligible. The scheme does not include projective measurement and the GHZ state is generated deterministically. Taking advantage of adiabatic passage, the entanglement fidelity is insensitive to fluctuation of experimental parameters.

Adiabatic passage scheme for entanglement between two distant microwave cavities interacting with single-molecule magnets

We propose a scheme for deterministically generating entanglement between two distant microwave cavities that interact with two single-molecule magnets (SMMs) and are connected by an optical fiber. In our scheme, the spontaneous decay of SMMs and photons damping in the fiber are efficiently suppressed via employing the stimulated Raman adiabatic passage (STIRAP). To check the experimental feasibility of our scheme, we numerically simulated the effects of some deviations of experimental parameters, and the numerical simulation shows that our scheme is robust with respect to those experimental parameters. We also discuss the effects of cavity damping, and as a result our proposal is good enough to demonstrate the generation of entanglement of microwave cavities within current experimental technology.

Scheme for implementing quantum logic gates for two atoms trapped 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.

Quantum state transfer between distant nodes of a quantum network via adiabatic passage

A scheme is presented to realize transfer of a three-dimensional quantum state between two atoms trapped in distant cavities connected by an optical fiber, whose mode is resonant with the polarization cavity modes. Performing an adiabatic passage along dark states, the fiber mode remains in the vacuum state and the population of the cavities being excited can be negligible under certain conditions. In addition, atomic transitions in our scheme are largely detuned from cavity modes. As a consequence, the atomic spontaneous emission and the fiber decay can be effectively eliminated. Furthermore, we give some discussions about the fidelity of our scheme.

Virtual-photon-induced quantum phase gates for two distant atoms trapped in separate cavities

We propose a scheme for implementing quantum gates for two atoms trapped in distant cavities connected by an optical fiber. The effective long-distance coupling between the two distributed qubits is achieved without excitation and transportation of photons through the optical fiber. Since the cavity modes and fiber mode are never populated and the atoms undergo no transitions, the gate operation is insensitive to the decoherence effect when the thermal photons in the environment are negligible. The scheme opens promising perspectives for networking quantum information processors and implementing distributed and scalable quantum computation.

Preparation of cluster states of four distant atoms by the interference of polarized photons

We propose a protocol to generate the cluster states of four A-type three-level atoms trapped in distant cavities by using the interference of polarized photons. The protocol uses the effects of the quantum statistics of indistinguishable photons emitted by the atoms inside optical cavities. This makes the protocol more realizable in experiments.

Robust Implementation of a Nonlocal N-Qubit Phase Gate by Interference of Polarized Photons

We propose a protocol to directly implement the nonlocal phase gate of N A-type three-level atoms trapped in distant cavities by using interference of polarized photons. The protocol uses the effects of quantum statistics of indistinguishable photons emitted by the atoms inside optical cavities.