Critical slowing down in a bistable model with squeezed vacuum environment

Critical slowing down effect in a bistable model of a two-level atomic medium in a ring cavity and in contact with squeezed vacuum field is examined within the mean field approximations in the high-, low- and arbitrary-Q cavity cases. Depending on the squeezed vacuum field phase parameter, the time response to linear perturbation of the incident field near the swtiching-on point can be enhanced or reduced compared with the normal vacuum case. In the low-Q cavity case with atomic collisional broadening switching time is both increased and become insensitive to the phase of the squeezed vacuum field. Analytical expressions are given and analysed for the critical (extermal) values of the incident field. In the high-Q cavity, Gaussian field feature causes lesser-steep transition between the stable states in both the normal and squeezed vacuum cases.Received: 25 April 2004, Published online: 24 August 2004PACS: 42.65.Pc Optical bistability, multistability, and switching, including local field effects - 42.65.-k Nonlinear optics     

Optical bistability using quantum coherence in a microwave-driven four-level atomic system

The behavior of the optical bistability (OB) is investigated in an optical system which consists of a four-level atomic system with a microwave drive field and an optical cavity. It is found that the optical bistability can be accomplished by adjusting different physical parameters in both steady and transient process. Due to the existence of the microwave drive field, the optical bistability can be also obtained even under weak coherent coupling field condition. Since the intensity and phase of microwave drive field can be conveniently modulated, this optical system provides a new experimental method to test the optical bistability theory.     

Steady-state formulation of optical bistability for a Doppler-broadened medium in a Fabry-Perot

A two-level model for absorptive and dispersive bistability in a Fabry-Perot is described. Doppler broadening and the effects of atomic motion through the standing wave field are included. Numerical results illustrating saturation of the Doppler line are presented and bistable transmission characteristics are obtained for systems with varying degrees of Doppler broadening.     

Dynamical coupling between a Bose–Einstein condensate and a cavity optical lattice

A Bose–Einstein condensate is dispersively coupled to a single mode of an ultra-high finesse optical cavity. The system is governed by strong interactions between the atomic motion and the light field even at the level of single quanta. While coherently pumping the cavity mode the condensate is subject to the cavity optical lattice potential whose depth depends nonlinearly on the atomic density distribution. We observe optical bistability already below the single photon level and strong back-action dynamics which tunes the coupled system periodically out of resonance.     

非共振条件下∧型三能级原子系统光学双稳态和多稳态的控制

非共振条件下,我们理论研究了单向环形光腔中用一微波场驱动一个超精细低能态跃迁的∧型三能级原子系统光学双稳态和多稳态行为,结果表明原子介质双稳态的行为可以分别通过耦合场的强度和耦合场频率的失谐量控制,同时还发现微波场在实现多稳态过程中所起的重要作用.最后讨论了合作参数对光学多稳态阈值的影响.     

Concentration of Unknown Atomic Entangled States via Entanglement Swapping through Raman Interaction

We show that entanglement concentration of unknown atomic entangled states is achieved via the implementation of entanglement swapping based on Raman interaction in cavity QED. A maximally entangled state is obtained from a pair of partially entangled states probabilistically. Due to Raman interaction of two atoms with a cavity mode and an external driving field, the influence of atomic spontaneous emission has been eliminated. Because of the virtual excitation of the cavity mode, the decoherence of cavity decay and thermal field is neglected.     

Dynamic Equations and Nonlinear Dynamics of Cascade Two-Photon Laser

We derive equations and study nonlinear dynamics of cascade two-photon laser, in which the electromagnetic field in the cavity is driven by coherently prepared three-level atoms and classical field injected into the cavity. The dynamic equations of such a system are derived by using the technique of quantum Langevin operators, and then are studied numerically under different driving conditions. The results show that under certain conditions the cascade two-photon laser can generate chaotic, period doubling, periodic, stable and bistable states. Chaos can be inhibited by atomic populations, atomic coherences, and injected classical field. In addition, no chaos occurs in optical bistability.     

Influence of thermal photons on the fundamental model of quantum optics with a coherent pump

A quantum system consisting of a two-level atom interacting with a single field mode of a high-Qcavity under influence of a coherent pump is considered. The analytical solutions for the P and Q distribution functions are obtained in the limit of large Rabi frequencies. In the presence of thermal photons, the P distribution function loses its property of restriction by the range on the complex plane and becomes an analytical function. When the ratio of the atomic decay rate to the cavity mode damping rate is smaller than 4, the effect of phase bistability appears. Absorptive optical bistability is absent in this case. On the basis of the system of Fokker-Planck equations for the quasi-probabilities corresponding to the atom being on the upper and lower atomic levels, computer simulation of the stochastic trajectory of motion for the system is presented.     

Controlling the optical bistability and multistability in a two-level pumped-probe system

We study the behavior of the optical bistability (OB) and multistability (OM) in a two-level pumped-probe atomic system by means of a unidirectional ring cavity. We show that the optical bistability in a two-level atomic system can be controlled by adjusting the intensity of the pump field and the detuning between two fields. We find that applying the pumping field decreases the threshold of the optical bistability.     

Optical bistability without the rotating wave approximation

Optical bistability for two-level atomic system in a ring cavity is investigated outside the rotating wave approximation (RWA) using non-autonomous Maxwell-Bloch equations with Fourier decomposition up to first harmonic. The first harmonic output field component exhibits reversed or closed loop bistability simultaneously with the usual (anti-clockwise) bistability in the fundamental field component.     

在亚泊松泵浦统计和压缩真空条件下多单光子关联辐射光子双稳态

证明了亚泊松泵浦及原子的相干性可使多单光子双稳态的光场噪声降低，但不能产生光场的压缩效应，若向腔中注入压缩真空，可以双稳态的上支产生几乎完全挑子数压缩效应，同时还证明，双稳态临界合作与原子相干性及集居数都有关。     

Controlling the optical bistability via interacting dark-state resonances

We analyze the behavior of optical bistability in a four-level mercury atomic system driven by a cavity and two external coherent fields by means of a unidirectional ring cavity. We find that without interacting dark resonances and for large intensity of coupling field, the optical bistability disappears. So, the double dark resonances could significantly establish the optical bistability. Moreover, we demonstrate that the double dark resonances can dramatically reduce the threshold of optical bistability.     

Protocol for multi-party superdense coding by using multi-atom in cavity QED

We present a protocol for multi-party superdense coding by using multi-atom in cavity quantum electrodynamics (QED). It is shown that, with a highly detuned cavity mode and a strong driving field, the protocol is insensitive to both cavity decay and thermal field. It is even certain to identify GHZ states via detecting the atomic states. Therefore we can realize the quantum dense coding in a simple way in the multiparty system.     

Optical bistability via quantum interference from incoherent pumping and spontaneous emission

We theoretically investigate the optical bistability (OB) in a V-type three-level atomic system confined in a unidirectional ring cavity via incoherent pumping field. It is shown that the threshold of optical bistability can be controlled by the rate of an incoherent pumping field and by interference mechanism arising from the spontaneous emission and incoherent pumping field. We demonstrate that the optical bistability converts to optical multi-stability (OM) by the quantum interference mechanism.     

Optical bistability in a gaussian cavity mode

The mean field treatment of dispersive and absorptive bistability for two-level atoms in an optical cavity is extended to account for the gaussian envelope of the cavity mode. The principal modification to the plane wave cavity case is the raising of the critical threshold for absorptive bistability as compared to thresholds for dispersive bistability.     

Forces and spatial ordering of driven atoms in a resonator in the regime of fluorescence suppression

An atom in a high-Q cavity, which is coherently driven at the frequency of a cavity mode, exhibits strong suppression of fluorescence when the atomic decay rate exceeds the cavity linewidth. This effect is due to destructive interference of cavity and pump field, such that at the atomic position the total field intensity has a local minimum. For atomic ensembles the magnitude of the interference effect grows with atom number and depends on the relative atomic positions. It is strongest for a wavelength spaced array of atoms placed at the antinodes of the cavity mode. This suppresses fluorescence and enhanced collective scattering into the cavity mode. We analyze the mechanical forces in the regime where the interference condition is fulfilled. We show that the atomic pattern is mechanically stable whenever the driving frequency is red detuned with respect to the cavity frequency, irrespective of the atomic transition frequency. Hence atomic selforganization, as predicted in [6] can also occur in the parameter regime where superradiant scattering is suppressed by collective interference. PACS 32.80.Pj; 42.50.Pq; 42.50.Fx     

Observation of absorptive optical bistability in a fabry-perot cavity containing multiple atomic beams

Using an arrangement of highly collimated sodium atomic beams in a Fabry-Perot cavity absorptive optical bistability has been observed. The response of the optically bistable system was investigated on a time scale of the order of 100 times the characteristic time of the cavity. Even so a non steady state behaviour of the system was observed. Good qualitative agreement with the two-level atom mean field radiation theory has been obtained.     

Control of the switch between optical multistability and bistability in three-level V-type atoms

We theoretically investigated a hybrid absorptive-dispersive optical bistability and multistability behaviour in a three-level V-type system using a microwave field driving a hyperfine transition between two upper excited states inside a unidirectional ring cavity. We find that the intensity and the frequency detuning of the coupling field as well as the intensity of the microwave field can affect the OM behaviour dramatically, which can be used to control the transition from OM to OB or vice versa without need to resort the effect of the quantum interference. The effects of the phase, the quantum interference and the atomic cooperation parameter on the OM are also studied. Our scheme may be used for building more efficient all-optical switches and logic-gate devices for optical computing and quantum information processing.     

非相干泵浦过程对光学双稳的影响

研究了低能级偶极子的非相干泵浦过程环形腔中双稳行为的影响，结果表明，耦合系统的双稳机制为非相干泵浦过程的干涉性，双稳迟滞环与非相干泵浦场有严格的对应关系，在一定条件下，甚至出现多稳态，可以利用非相干泵浦的干步性能控制光学双稳。     

Theory of the magnon Kerr effect in cavity magnonics

We develop a theory for the magnon Kerr effect in a cavity magnonics system, consisting of magnons in a small yttrium iron garnet(YIG) sphere strongly coupled to cavity photons, and use it to study the bistability in this hybrid system. To have a complete picture of the bistability phenomenon, we analyze two different cases in driving the cavity magnonics system, i.e.,directly pumping the YIG sphere and the cavity, respectively. In both cases, the magnon frequency shifts due to the Kerr effect exhibit a similar bistable behavior but the corresponding critical powers are different. Moreover, we show how the bistability of the system can be demonstrated using the transmission spectrum of the cavity. Our results are valid in a wide parameter regime and generalize the theory of bistability in a cavity magnonics system.