Dissipative Cavity Research Articles

Dynamical behaviour of the entanglement between two spatially separated atoms under the influence of dissipation

We consider two two-level atoms, which are located in two independent dissipative cavities. The two atoms are initially prepared in the singlet state. We investigate the influence of dissipation on the entanglement between the two atoms. In the case of resonance the degree of the entanglement can fall abruptly to zero, which is the so-called sudden death of entanglement. It is noted that when two atoms are in a common environment, the singlet state is a decoherence-free state. When the dispersive limit is fulfilled, the degree of entanglement between the two atoms is oscillating at first, then it arrives at a steady value, which increases with the increase of the damping constant κ; when both fields are initially in the vacuum state, the entanglement between the two atoms will not decay.

Entanglement of Non-symmetric Two Charge Qubits Inducedby a Damped Cavity

Two charge qubits being coupled to a damped cavity withdifferent couplings are considered. The dynamical evolution of theentanglement between the two qubits is demonstrated analyticallyor numerically. It is found that with the cavity dissipation,the steady entanglement between the two qubits can be achieved.The two qubits being initially in the separable and most mixedstate can be easily induced to a steady entangled state, and therelative difference of the couplings can be used toenhance the steady entanglement between the two charge qubits.

Phase-space structure of two-dimensional excitable localized structures

In this work we characterize in detail the bifurcation leading to an excitable regime mediated by localized structures in a dissipative nonlinear Kerr cavity with a homogeneous pump. Here we show how the route can be understood through a planar dynamical system in which a limit cycle becomes the homoclinic orbit of a saddle point (saddle-loop bifurcation). The whole picture is unveiled, and the mechanism by which this reduction occurs from the full infinite-dimensional dynamical system is studied. Finally, it is shown that the bifurcation leads to an excitability regime, under the application of suitable perturbations. Excitability is an emergent property for this system, as it emerges from the spatial dependence since the system does not exhibit any excitable behavior locally.

Excitability Mediated by Localized Structures in Kerr Cavities

We characterize a scenario where localized structures in nonlinear optical cavities display an oscillatory behavior which becomes unstable leading to an excitable regime. Ex- citability emerges from spatial dependence since the system locally is not excitable. We show the existence of difierent mechanisms leading to excitability depending on the proflle of the pump fleld. DOI: 10.2529/PIERS060907134206 Localized structures (LS) in dissipative optical cavities arise as a consequence of the interplay between difiraction, nonlinearity, driving, and dissipation (1). These structures, also known as cavity solitons, are unique once the parameters of the system have been flxed. This fact makes this structures potentially useful in optical storage and processing of information (2,3). LS may develop a number of instabilities, for instance their amplitude can oscillate in time while remaining static in space. Here we report on a novel regime of excitability associated to the existence of localized structures in a nonlinear optical system (4,5). Excitability has been found in a variety of systems (6), including optical systems (7), and is characterized by a nonlinear response under applied external perturbation. Perturbations exceeding a certain threshold are able to elicit in the system a full and well deflned response. Furthermore after one perturbation the system cannot be excited again within a refractory period of time. Excitability is behind excitation waves in heart tissue and the existence of action potentials in neurons, and, so, may confer new computational capabilities to optical systems beyond information storage. In this paper we show the existence of difierent mechanisms leading to excitability depending on the proflle of the pump fleld. For a homogeneous pump the mechanism leading to excitable behavior is a saddle-loop bifurcation through which an stable oscillating LS collides with an unstable LS (4). For a system pumped by a localized Gaussian beam on top of homogeneous background the scenario is richer and one flnds two difierent mechanisms leading to excitability. One is based on a saddle- loop bifurcation as above while the other takes place through a saddle-node in the invariant circle (SNIC) bifurcation. This second mechanism has excitability threshold which can be much lower. We consider a ring cavity fllled with a nonlinear self-focusing Kerr medium pumped by an external fleld. In the mean fleld approximation, the dynamics of the electric fleld inside the cavity can be described by a single partial difierential equation for the scaled slowly varying amplitude E(~) (8) @tE = i(1 + iµ)E + ir 2 E + E0 + ijEj 2 E;

Linear entropy evolution in a dissipative system of two atoms and cavity field

Some investigations have been made on the evolution of the linear entropies of atom-field system, in which two identical two-level atoms simultaneously interact with a single-mode dissipative cavity field under large detuning. The effects of the initial atom states and the dissipative factors of the cavity on all linear entropies are also discussed. The results show that the influence of the cavity decay constant on different kinds of Bell states is completely different, and the state |Ψ〉12 is a robust entangled state against the decoherence while the state |Φ〉12 is a fragile entangled state.

Superposition of coherent states prepared in one mode of a dissipative bimodal cavity

We solve the problem of the temporal evolution of one of two modes embedded in the same dissipative environment and investigate the role of the losses after the preparation of a coherent state in only one of the two modes. Based on the current cavity QED technology, we present a calculation of the fidelity of a superposition of coherent states engineered in a bimodal high-Q cavity. Our calculation demonstrates that the engineered superposition retains coherence for large times when the mean photon number of the prepared mode is of the order of unity.

Generation of pure multipartite entangled vibrational states for ions trapped in a cavity

We propose schemes for the deterministic preparation of pure multipartite entangled vibrational states for $N$ ions trapped in a single-mode cavity. Through sequentially sending lasers with appropriate phases and amplitudes to drive the ions, two kinds of pure multipartite entangled continuous variable entangled states respectively suggested by van Loock and Braunstein [Phys. Rev. Lett. 84, 3482 (2000)] and Pfister et al. [Phys. Rev. A 70, 020302(R) (2004)] can be unconditionally prepared with the help of cavity dissipation.

Normal-mode coupling of rare-earth-metal ions in a crystal to a macroscopic optical cavity mode

We demonstrated coupling of rare-earth-metal ions in a crystal to a macroscopic cavity mode by observing optical bistability and normal-mode peaks due to sweeping-laser-induced population redistribution of the ions. The experimentally evaluated coupling constant between the individual ions and the single cavity mode is $15\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}$, which is comparable with or larger than the dissipation of the ions and will exceed the cavity dissipation with a narrowing of the mode waist of the cavity to the wavelength. The results advance the application of a coupled system of rare-earth-metal ions in a crystal and an optical cavity for quantum information processing.

Preparation of a 2n-qubit W state via entanglement transfer

Abstract We propose a scheme to generate a W state of n + n qubits trapped in two spatially separated cavities respectively by means of entanglement transfer. We find that the 2n qubits will be entangled in the W state periodically. The influence of cavity dissipation is also analytically demonstrated.

Deterministic generation of a pure continuous-variable entangled state for two ions trapped in a cavity

Two different schemes are proposed for deterministically generating a pure motion-entangled state for two well-separated ions trapped in a cavity. The first one is that through adjusting the amplitudes and the frequencies of transverse lasers, the two ions trapped in a bimodal cavity can unconditionally evolve into a two-mode squeezed vacuum state with the aid of the cavity dissipation. The second one is based on the interactions of two appropriate series of the driving laser pulses with the two ions trapped in a single-mode cavity, it allows us to produce a two-mode squeezed vacuum state for the trapped ions' center-of-mass motion.

INFORMATION TRANSFER IN LEAKY ATOM–CAVITY SYSTEMS

We consider a system of two enatangled cavities and a single two-level atom passing through one of them. A "monogamy" inequality for this tripartite system is quantitatively studied and verified in the presence of cavity leakage. Next, we consider the simultaneous passage of two-level atoms through both the cavities. Entanglement swapping is observed between the the two-cavity and the two-atom system. Cavity dissipation leads to the quantitative reduction of information transfer though preserving the basic swapping property.

Preparation and Decoherence of Two-Atom Entangled States in aDissipative Cavity

We present a scheme for generating four pairs of two-atomEinstein–Podolsky–Rosen (EPR) states using the simultaneousinteraction of the two atoms with a single-mode cavity field under alarge detuning condition. The influence of cavity dissipation on theprepared EPR states is investigated by means of the superoperatormethod and the state fidelity. It is shown that some kinds of theprepared EPR states are robust against cavity dissipation and theintensity of the field, and maintain their entanglement invariance, andthe others are fragile and completely destroyed by the action of cavitydissipation and the intensity of the field in the long-time limit.Decoherence time of the fragile entangled states is extremely small fora typical cavity-QED experimental data.

Stationary Entanglement of Two Charge Qubits Induced by aDamped and Driven Cavity

Two charge qubits located inside a damped driven cavity isconsidered. The dynamical evolution of the entanglement betweenthe two qubits is demonstrated analytically or numerically. It isfound that with the cavity dissipation, the steady entanglementbetween the two qubits is sensitive to the initial state of thequbits, but independent of the cavity field's initial state.The two qubits initially in the separable and most mixedstate can be more easily entangled. The external field can beused to enhance the steady entanglement between the two chargequbits.

The entanglement dynamics of two entangled atoms in the dissipative cavity

In this paper, we investigate the entanglement dynamics of two entangled two-level atoms interacting with a single-mode field in a dissipative cavity. The results show that the evolution properties of the entanglement degree of two entangled atoms depend on the initial atomic entanglement degree and form, the average photon number of the cavity field, and the cavity leakage rate. When the atoms are initially in a particular entangled state, the degree of entanglement can be amplified and not influenced by the dissipation of the cavity field.

Excitability Mediated by Localized Structures in a Dissipative Nonlinear Optical Cavity

We find and characterize an excitability regime mediated by localized structures in a dissipative nonlinear optical cavity. The scenario is that stable localized structures exhibit a Hopf bifurcation to self-pulsating behavior, that is followed by the destruction of the oscillation in a saddle-loop bifurcation. Beyond this point there is a regime of excitable localized structures under the application of suitable perturbations. Excitability emerges from the spatial dependence since the system does not exhibit any excitable behavior locally. We show that the whole scenario is organized by a Takens-Bogdanov codimension-2 bifurcation point.

Nonlocality and purity in atom–field coupling system

The effects of initial field state and thermal environment on quantum nonlocality and linear entropy in an atom–field coupling system are investigated. We found that if the cavity is lossless and the reservoir is in vacuum, the atom–field state can exhibit quantum nonlocality periodically and the linear entropies of the atom and the field also oscillate periodically with a period the same as that of quantum nonlocality. And if the cavity dissipation is very weak and the average photon number of the reservoir is very small, the quantum nonlocality will be lost and the linear entropies of the atom and the field oscillate with a decreasing amplitude. The rapidity of the loss of the quantum nonlocality depends on the amplitude of the initial squeezed coherent state, the cavity damping constant κ and the average photon number N of the thermal reservoir. The stronger the field and the larger the constant κ and the average photon number N could be, the more rapidly the nonlocality decreases.

Decay rate and decoherence control in coupled dissipative cavities

We give a detailed account of the derivation of a master equation for two-coupled cavities in the presence of dissipation. The analytical solution is presented and physical limits of interest are discussed. Firstly, we show that the decay rate of initial coherent states can be significantly modified if the two cavities have different decay rates and are weakly coupled through a wire. Moreover, we show that also decoherence rates can be substantially altered by manipulation of physical parameters. Conditions for experimental realizations are discussed.

Quantum Nonlocality in Atom-Field Coupling System viaDegenerate Raman Processes with Cavity Damping

The property of quantum nonlocality in the atom-field couplingsystem via degenerate Raman processes with cavity damping isinvestigated. It is found that if the cavity dissipation is veryweak, the atom-field state can exhibit quantum nonlocalityperiodically. The rapidity of the loss of the quantum nonlocalitydepends on the amplitude of the initial coherent state and thecavity damping constant. The stronger the field is and the largerthe damping constant could be, the more rapidly the nonlocality decreases.

Dynamics of nonlocality for atom–field entangled state in a cavity

The time evolution of nonlocality for atom-field entangled state in the system of a two-level atom interacting dispersively C with a single-mode field in a dissipative cavity is investigated. It is found that, if the cavity dissipation is very weak, the atom-field state can exhibits nonlocality periodically. The rapidity of the loss of the initial quantum nonlocality depends on the amplitude of the two coherent states and the cavity damping constant K. The stronger the field is and the larger the constant K, the more rapidly the nonlocality decreases. (C) 2001 Elsevier Science B.V. All rights reserved.

Atomic-state teleportation by using a quantum switch

We present a scheme of atomic-state teleportation by using a quantum switch (QS). Based on the principle of QS and the quantum interference effect, a controlled-NOT operation between atom and cavity is proposed and used to transform the joint measurement of the von Neumann type into the discrete measurements. A detection method using several atoms resonantly interacting with field state is also presented to read out the field state in a cavity. The fidelity due to cavity dissipation is discussed. In our scheme, since the transfer of quantum information between atom and cavity is achieved by nonresonant atom-cavity interaction, three-bit classical information is transmitted from Alice to Bob to complete teleportation.