Control of the optical multistability in a three-level ladder-type quantum well system

We theoretically investigated a hybrid absorptive-dispersive optical multistability (OM) behavior in a three-level ladder-type quantum well system inside a unidirectional ring cavity. We find that the frequency detuning of the control field and the electronic cooperation parameter as well as the total decay rates can affect the optical multistability behavior dramatically, which can be used to manipulate efficiently the threshold intensity and the hysteresis loop. The effect of the intensity of the control field on the OM is also studied. Our study is much more practical than its atomic counterpart due to its flexible design and the wide adjustable parameters. Thus it may provide some new possibilities for technological applications in optoelectronics and solid-state quantum information science.     

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.     

Supernarrow saturated absorption resonances in weakly coupled two resonant optical cavities

The advantages of the weakly coupled two resonant optical cavities (hereinafter referred to as three-mirror cavity) used for observation of the supernarrow saturated absorption resonances are shown. Among these advantages we can name: (a) the possibility to control the intensity in the cavity with the inside absorbing cell which is important when the gain and absorption saturation parameters differ significantly; (b) the resonances observation from the ‘passive’ side of the three-mirror cavity permits us to decrease drastically the influence of the reflected signal from the detector; (c) if instead of the absorbing cell an active system is put in (gain plus absorption), it is possible by tuning the operating mode of the active interferometer to obtain many-fold gain of the supernarrow resonance amplitude. Received: 11 January 2000 / Revised version: 20 June 2000 / Published online: 9 February 2001     

Squeezing by second-harmonic generation in a monolithic resonator

We have measured the intensity fluctuations of the second-harmonic mode generated in a MgO:LiNbO₃ external monolithic cavity pumped by a Nd:YAG laser. The cavity has mirror coatings for both the fundamental and the second-harmonic mode. We scan the cavity using the electro-optic effect of the crystal and observe that the second-harmonic beam of 2 mW exhibits a quantum noise reduction of 40(±5)%. In addition, we report on the active frequency stabilization of the monolithic device used in our squeezing experiments. Several fast tuning parameters such as the electro-optic effect, the photo-elastic effect, and the laser frequency have been investigated. With these tuning parameters the monolithic resonator can be locked on double-resonance at the phase-matching temperature, which is a prerequisit for observing squeezing in a cw-regime.     

Optical bistability via amplitude and phase control of a microwave field

We investigate the steady-state optical bistability behavior in a three-level Λ-type atomic system closed by a microwave field under the condition that the applied fields are in resonance with corresponding atomic transitions. It is shown that the bistable hysteresis cycles can be controlled by both the amplitude and the phase of the microwave field.     

Quantum nondemolition measurement by optomechanical coupling

 We show that a single-port optical cavity with a movable mirror can provide a quantum non-demolition measurement of the intensity of a light beam. Due to radiation pressure, the cavity length is sensitive to the light intensity and can be measured with a secondary light beam. Signal-meter correlations can be made very large even at non-zero temperature. We study these correlations when the moving mirror is a plane–convex crystal resonator and we show the importance of spatial matching between light and acoustic modes. Received: 12 June 1996/Revised version: 3 September 1996     

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.     

Generation of Two-Atom Cluster State via Cavity QED

We propose a physical scheme for generating a two-atom cluster state through the simultaneous interaction of two two-level atoms with a single-mode cavity field prepared initially in an odd-coherent state under a large-detuned limit. The influence of the dissipation constant, the intensity of the field and the imperfect manipulation on the preparation scheme are investigated. It is shown that when the intensity of the cavity is large enough, the influence of the cavity decay is ettlciently suppressed. The possible error in the implementation of the cluster state is negligible when the time difference between two atoms crossing the cavity axis is small. It is suggested that the scheme can be realized by current technologies.     

Role of spatial mode function in the presence of two-atom events in a micromaser

In this paper, we discuss the effects of spatial mode function in an one-photon micromaser in the presence of two-atom events. It is shown that two-atom events allow us a possibility to study the effects of different cavity eigenmodes in a micromaser. We find that squeezing properties of the radiation field depend upon the parity (odd or even) and order (lower or higher) of cavity eigenmodes. For example, squeezing can be obtained for odd-order cavity eigenmodes which completely vanishes for even-order modes. Our results also show that effects similar to self-induced transparency are never obtained in the presence of two-atom events. Finally, we consider the effect of pump fluctuations and cavity losses in our system.     

Conditional quantum-state engineering in repeated 2-photon down-conversion

The U(1,1) and U(2) transformations realized by three-mode interaction in the respective parametric approximations are studied in conditional measurement, and the corresponding non-unitary transformation operators are derived. As an application, the preparation of single-mode quantum states using an optical feedback loop is discussed, with special emphasis on Fock-state preparation. For that example, the influence of non-perfect detection and feedback is alsoconsidered. Received: 12 July 2000 / Revised version: 19 September 2000 / Published online: 30 November 2000     

Cavity-Induced Enhancement of Squeezing in Resonance Fluorescence of a V-Type Three-Level Atom

The quadrature squeezing spectra in the resonance fluorescence of a V-type three-level atom driven by a coherent field and coupled to a single-mode cavity is investigated. For weak excitation, the fluorescence field exhibit squeezing in the out-of-phase quadrature. The coupling between the atom and the cavity mode can greatly enhance the squeezing centred at the laser frequency. More importantly, for strong excitation, under the effect of the cavity-atom coupling, the in-phase quadrature of fluorescence can exhibit two-mode squeezing at the two inner sideband frequencies. By working in the dressed-state representation and hiring secular approximation, we give an analytical explanation for the effect. The result shows, under appropriate conditions, the squeezing can be greatly enhanced by appropriately tuning the cavity resonant frequency.     

Anomalous Effects of Driving Field Linewidth on a One-Atom Dressed-State Laser

We examine the effects of driving field linewidth on a one-atom dressed state laser. Unexpectedly, the linewidth leads to anomalous effects on the cavity field. The mean photon number of the cavity field is raised or the normalized variance is reduced to a certain degree as the linewidth increases for an appropriate range of parameters. The responsible mechanism is attributed to the fluctuation-induced modification of the electromagnetic reservoir where the atom stays.     

Bright entangled light from two-mode cascade laser

We show that a two-mode three-level cascade laser driven by external coherent fields generate intense entangled light. It turns out that external driving fields which are at resonance with the cavity modes substantially improve the intensity of the two-mode light in the cavity in a region where the squeezing and entanglement is significant making the system under consideration a viable source of bright squeezed as well as entangled light.     

The critical laser intensity of self-guided light filaments in air

The critical intensity inside plasma filaments generated in air by high-power, ultra-short laser pulses is estimated analytically and compared to recent experimental data. The result, I_crit≈4×10¹³ W/cm², is highly relevant for atmospheric applications. Received 18 August 2000 / Published online: 8 November 2000     

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.     

A degenerate three-level laser with a parametric amplifier

The aim of this paper is to study the squeezing and statistical properties of the light produced by a degenerate three-level laser whose cavity contains a degenerate parametric amplifier. In this quantum optical system the top and bottom levels of the three-level atoms injected into the laser cavity are coupled by the pump mode emerging from the parametric amplifier. For a linear gain coefficient of 100 and for a cavity damping constant of 0.8, the maximum intracavity squeezing is found at steady state and at threshold to be 93%.     

Generation of strongly squeezed states for a cavity field with a single atom

We propose a scheme to realize strong squeezing for a cavity field with a single three-level atom. In the scheme the atom is sent through the cavity initially filled with a coherent field. The atom dispersively interacts with the cavity field, which is displaced by a microwave resource during the interaction. Then, a selective measurement on the atom collapses the field to a superposition of an even coherent state with a vacuum state, which exhibits strong squeezing. The scheme can also be generalized to the two-mode case.     

Hysteresis in current transport in a GaAs diode containing self-assembled InAs quantum dots

We have observed hysteresis loops in current transport in a GaAs metal–semiconductor–metal diode containing InAs quantum dots. The dots in our structure are directly embedded under the GaAs–metal interface. The charging and discharging of electrons in the dots modulate the current and produce hysteresis. These processes are controlled by the applied voltages. The dots are charged by forward current flowing through the structure. The discharging of the electrons is dominated by the tunneling process under high reverse bias. The modulated currents are well fitted with an electron-trapping model considering both the ground states and the excited states of the quantum dots. Received: 5 October 2000 / Accepted: 12 December 2000 / Published online: 23 May 2001     

Noiseless amplification of images in a confocal cavity

We study the noiseless amplification of an optical image by means of a confocal cavity containing a parametric medium. We demonstrate, in the ideal situation, the possibility of preserving the signal-to-noise ratio while amplifying uniformly the entire image. Some specific effects, which may degrade the performances of the scheme, are taken into account. Received 23 March 2000     

Dynamics of a degenerate parametric oscillator in a squeezed reservoir

Dynamics of a cavity mode which, in addition to interacting to an outside field with squeezed fluctuations, is simultaneously submitted to linear and parametric amplification processes is discussed in the Markovian approximation. The master equation for a density matrix of the cavity field is solved analytically in the Heisenberg picture. Long time asymptotic properties of the cavity mode are studied in the whole range of the evolution parameters and the corresponding decoherence effects are reported. It is also shown that in an appropriate regime of the evolution parameters there exists a unique steady state such that all initial density matrices evolve towards it. This allows engineering cavity states with desired properties.