Coherent control of optical bistability in tunnel-coupled double quantum wells

We analyze optical bistability (OB) behavior based on intersubband transitions in an asymmetric coupled-quantum well (CQW) driven coherently by a probe laser field and a control laser field by means of a unidirectional ring cavity. We demonstrate that OB can be controlled by tuning the energy splitting between two tunnel-coupled electronic levels, the intensity of the control field, and the frequency detuning of the probe and control fields. The influence of the electronic cooperation parameter on the OB behavior is also discussed. This investigation may be used for optimizing and controlling the optical switching process in the CQW solid-state system, which is much more practical than that in atomic system because of its flexible design and the controllable interference strength.     

Optical bistability in a triple semiconductor quantum well structure with tunnelling-induced interference

We study the behavior of optical bistability (OB) in a triple semiconductor quantum well structure with tunnelling-induced interference, where the system is driven coherently by the probe laser inside the unidirectional ring cavity. The results show that we are able to control efficiently the bistable threshold intensity and the hysteresis loop by tuning the parameters of the system such as laser frequency and tunnelling-induced frequency splitting. This investigation can be used for the development of new types of nanoelectronic devices for realizing switching process.     

Entanglement via tunable Fano-type interference in asymmetric semiconductor quantum wells

Entanglement is realized in asymmetric coupled double quantum wells (DQWs) trapped in a doubly resonant cavity by means of Fano-type interference through a tunneling barrier, which is different from the previous studies on entanglement induced by strong external driven fields in atomic media. We investigate the generation and evolution of entanglement and show that the strength of Fano interference can influence effectively the degree of the entanglement between two cavity modes and the enhanced entanglement can be generated in this DQW system. The present investigation may provide research opportunities in quantum entangled experiments in the DQW solid-state nanostructures and may result in a substantial impact on the technology for entanglement engineering in quantum information processing.     

Effect of Quantum Interference from Incoherent Pumping Field and Spontaneous Emission on Controlling the Optical Bistability and Multi-Stability

Optical bistability (OB) and optical multi-stability (OM) of a four-level Λ-type atomic system with two fold lower levels inside a unidirectional ring cavity is investigated. The effect of quantum interference arising from spontaneous emission and incoherent pumping on OB and OM is discussed. It is found that the threshold of OB and OM can be controlled by quantum interference mechanisms. In addition intensity of coupling field and the rate of an incoherent pumping field on behavior of OB and OM are then discussed.     

Observation of Fano-Type Interference in a Coupled Cavity-Atom System

We present the experimental observation of the Fano-type interference in a coupled cavity-atom system by confining the laser-cooled ~(85)Rb atoms in an optical cavity.The asymmetric Fano profile is obtained through quantum interference in a three-level atomic system coherently coupled to a single mode cavity field.The observed Fano profile can be explained by the interference between the intra-cavity dark state and the polariton state of the coupled cavity-atom system.The possible applications of our observations include all-optical switching,optical sensing and narrow band optical filters.     

Optical bistability and multi-stability in a four-level atomic scheme

We investigate the optical bistability (OB) and optical multi-stability (OM) in a four-level Y-type atomic system. It is found that the optical bistability can strongly be affected by intensity and frequency detuning of coupling and probe fields. The effect of spontaneously generated coherence on phase control of the OB and OM is then discussed. It has also been shown that the optical bistability can be switched to optical multi-stability just by the quantum interference mechanism and relative phase of applied fields.     

基于可调谐Fano干涉的超快全光开关

简要介绍了量子相干和干涉效应的研究动态和一项最新理论研究进展.设计了一个存在Fano类型隧穿感应量子干涉的GaAs/A lxGa1-xAs非对称量子阱结构.在该量子阱中,可通过一束控制光抑制量子干涉,进而调制信号光的传播特性.这一现象可用来实现一个宽带超快全光开关.     

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.     

Controllable optical bistability in a three-mode optomechanical system with a membrane resonator

We study the optical bistability(OB) in a three-mode cavity optomechanical system, where an oscillating membrane of perfect reflection is inserted between two fixed mirrors of partial transmission. By investigating the behavior of steady state solutions, we find that the left and right cavities will exhibit the bistable behavior simultaneously in this optomechanical system by adjusting the left and right coupling fields. In addition, one can control the OB threshold and the width of the OB curve via adjusting the coupling strength, the detuning, and the decay rate. Moreover, we further illustrate the OB appearing in the cavity by the effective potential as a function of the position.     

Optical bistability in a defect slab with a negative refractive quantum dot nanostructure

We demonstrate optical bistability (OB) in a defect slab doped V-type four-level InGaN/GaN quantum dot nanostructure in the negative refraction frequency band. It has been shown that the OB behavior of such a quantum dot nanostructure system can be controlled by the amplitude of the driving fields and a new parameter for controlling the OB behavior as thickness of the slab medium in the negative refraction band. Meanwhile, we show that the negative refraction frequency band can be controlled by tuning electric permittivity and magnetic permeability by the amplitude of the driving fields and electron concentration in the defect slab doped. Under the numerical simulations, due to the effect of quantum coherence and interference, it is possible to switch bistability by adjusting the optimal conditions in the negative refraction frequency band, which is more practical in all-optical switching or coding elements, and technology based nanoscale devices.     

Optical bistability and multistability in a parametric region

We study the optical bistability (OB) and optical multistability (OM) behaviors in a five-level $\Lambda $ -type parametric region atomic system by two-photon resonant transitions. We find that the intensity threshold of OB and switching from OB to OM or vice versa can be controlled via quantum interference between different two-photon transitions pathways.     

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.     

Controllable Optical Bistability and Multistability in a Four-Level Atomic System with Closed-Loop Configuration

We theoretically investigate optical bistability （OB） and multistability （OM） behaviour of a closed-loop configuration atomic system driven by a degenerate coupling- field and a degenerate probe field inside a unidirectional ring cavity. It is found that the OB and OM behaviour can be controlled by adjusting- the intensity and the frequency detuning of the coupling- field, respectively. Interestingly, our numerical results show that it is easy to realize the transition from OB to OM or vice versa by adjusting- the intensity of the coupling- field under a appropriate frequency detuning. The effect of the atomic cooperation parameter on the OB behaviour is also discussed.     

Bistable behaviour in squeezed vacua: I. Stationary analysis

A time-independent theoretical and numerical analysis of an optical bistable model of two-level atoms in a ring cavity, driven by a coherent field and in contact with a squeezed vacuum field is presented in the two cases of absorptive and dispersive optical bistability (OB). In the former case, a suitable choice of the phase of the squeezed vacuum field reduces the threshold for OB to occur compared with the normal vacuum case. In the latter case, regions of OB are identified as one or two disconnected simple closed curves depending on the cooperation parameter [0pt] : is the maximum possible value of the critical value of C at fixed values of the squeezed vacuum field parameters. Phase switching effects between different (output) states of the system is investigated in detail. In the absorptive case, one- or two-way optical switching is possible depending on [0pt] . We also present results which demonstrate more complicated switching behaviour in the dispersive case. Received 12 March 1999 and Received in final form 20 August 1999     

Optical bistability in low-dimensional semiconductor heterostructures under cw pump laser and infrared pulse signals

We have investigated theoretically the optical bistability (OB) and optical multistability in quantum-well (QW) semiconductor heterostructures. The effect of a cw pump laser field and a control infrared pulse signal on OB is discussed. It is found that the OB threshold can be controlled by varying the strength of applied fields. It is also shown that OB can be switched to optical multistability or vice versa just using an appropriate relative phase of applied fields. This investigation may open up some new possibilities for applications in all-optical switching in quantum-well structures.     

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 and multi-stability via voltage-controlled and the rate of incoherent pump in a quantum dot nanostructure

The optical bistability (OB) and optical multi-stability (OM) in a four-level quantum dot molecule are investigated. The effect of tunnel coupling and the rate of incoherent pump on OB are then discussed. It is found that the OB threshold can be controlled via tunnel coupling and the rate of incoherent pump. We demonstrate that the voltage-controlled detuning can significantly affect the behavior of OB and OM, therefore the OM converts to OB only by the rate of incoherent pump. The results obtained can be used for the development of new types of nanoelectronic devices for realizing switching process.     

Optical bistability and multistability via amplitude and phase control in a Duplicated two-level system

We investigate the optical bistability(OB) in a duplicated two-level system contained in a ring cavity.The atoms are driven by two orthogonally polarized fields with a relative phase.The OB behavior of such a system can be controlled by the amplitude and the relative phase of the coupling field,and it is possible to switch between bistability and multistability by adjusting the relative phase.     

Coherence properties of a Bose-Einstein condensate in an optical superlattice

We study the effect of a one dimensional optical superlattice on the superfluid properties (superfluid fraction, number squeezing, dynamic structure factor) and the quasi-momentum distribution of the Mott-insulator. We show that due to the secondary lattice, there is a decrease in the superfluid fraction and the number fluctuation. The dynamic structure factor which can be measured by Bragg spectroscopy is also suppressed due to the addition of the secondary lattice. The visibility of the interference pattern (the quasi-momentum distribution) of the Mott-insulator is found to decrease due to the presence of the secondary lattice. Our results have important implications in atom interferometry and quantum computation in optical lattices.     

Controlling the optical bistability via quantum interference in a four-level N-type atomic system

We investigate the optical bistability (OB) and optical multi-stability (OM) in a four-level N-type atomic system. The effect of spontaneously generated coherence (SGC) on OB and OM is then discussed. It is found that SGC makes the medium phase dependent, so the optical bistability and multi-stability threshold can be controlled via relative phase between applied fields. We realize that the frequency detuning of probe and coupling fields with the corresponding atomic transition plays an important role in creation OB and OM. Moreover, the effect of laser coupling fields and an incoherent pumping field on reduction of OB and OM threshold is then discussed.