A method for generating macroscopically distinguishable superposition states via single atom dispersion was proposed by Savage et al. In that model, the atomic linewidth was not considered. However, including the atomic linewidth, we get two contradictory conditions for the generation of distinguishable superposition states. This shows that the atomic linewidth prevents the formation of macroscopically distinguishable superposition states by the proposed method.

We present an interesting theoretical prediction from semiclassical laser theory, namely, the quenching of laser action at high pump powers that results from the presence of excited-state absorption of pump photons. Experimental results are shown from an erbium-doped fiber laser that are consistent with our prediction.

We calculate the cavity photon statistics of conventionally pumped four-level lasers using a diagonal number state representation. The results are in agreement with those obtained from previous treatments using linearized Fokker-Planck equations and predict sub-Poissonian photon statistics at sufficiently high pump rates.

We discuss the conditions under which intensity squeezing is predicted to be observed in the output of conventionally pumped multilevel lasers.

Gordon and Mollenauer [Opt. Lett. 15, 1351 (1990)] have shown that the nonlinear Kerr effect limits the range of coherent communications systems using laser amplifiers. We show that parametric amplifiers avoid this limitation. Our method is novel in that we use quantum-optical master equations to model the communications systems. These are solved numerically for systems with either laser amplifiers or parametric amplifiers, with and without the nonlinear Kerr effect. Parametric amplifiers perform better because they preserve the signal-to-noise ratio and decrease the phase noise.

The noise properties of an LED with high quantum efficiency are investigated. Light with sub-Poissonian photon statistics is generated by driving the LED with a high impedance, well regulated current source. It is shown that it is necessary to distinguish between the measured total quantum efficiency and the optical quantum efficiency. In addition, the correlation between the fluctuations in the driving current and the fluctuations in the photocurrent is demonstrated, allowing a suppression of the shot noise after the measurement. The properties of this alternative noise reduction technique are discussed.

The quantum mechanical model of a dissipative system that is chaotic in its classical limit is solved numerically. The system is nonlinear optical second harmonic generation, and the model is the quantum optical master equation. The steady-state of the master equation is found and compared with the classical chaotic attractor. Computational methods appropriate for vector processors and for the connection machine are described.

Spatial variations of the laser mode and pumping rate are incorporated into the theory of conventionally pumped lasers that produce squeezed light. Both a quantum-mechanical theory and a heuristic statistical model are used. While variations in the laser mode are found to have a negligible effect on squeezing, variations in the pumping rate are significant. The maximum attainable squeezing is always reduced compared with the spatially uniform case. However, resonantly enhancing a low-power pump in a Fabry-Pérot cavity, rather than a ring cavity, may give better squeezing.

One-atom lasers are important because their governing equations can be solved exactly, even with a quantized field. Full abstract.

We find an upper bound for the sensitivity of Fabry-Pérot interferometric length measurements using inefficient photodetectors. Full abstract.

We calculate amplitude squeezing spectra for the light from a variety of conventionally pumped three- and fourlevel lasers. Hence we extend a recent prediction that a certain three-level laser can generate nonclassical light without the need for rigged pumping.

We calculate the amplitude squeezing in the output of a coherently pumped four-level laser and compare it with that from a similar incoherently pumped laser. We find that squeezing may be considerably enhanced by pumping with coherent light. The squeezing in both types of laser is explained by a simple statistical model.

We show that macroscopic quantum superpositions of the electromagnetic field can be generated through amplification of microscopic quantum superpositions prepared in a single atom. Our scheme has the advantage that dissipation is negligible, and hence the superpositions are not rapidly destroyed.
See Linewidth prevents macroscopic quantum superposition generation by single atom dispersion.

We investigate the effect of a spatially varying field mode on the squeezing generated by two-level atoms interacting with a single mode of an optical cavity. Full abstract.

The quantum mechanical master equation for a single two-level atom in a single-mode optical cavity is numerically solved in both the quantum and the semiclassical limits. The quantum limit of few cavity photons shows semiclassically forbidden behaviour such as steady state two-level population inversion. Qualitatively new fluorescent spectra, having sidebands broadened by the cavity interaction, also occur. The quantum theory of the single-atom laser with injected signal is presented. At the interface between its quantum and semiclassical dynamics we elucidate the signature of semiclassical limit cycles.

Squeezing a light beam incident on a cavity which is strongly coupled to a single atom is shown to change the width of the fluorescent sidebands of the atom. The sidebands are either broader or narrower than in the absence of squeezing depending on whether the driving field has excess or reduced amplitude fluctuations. Unlike previously reported effects the entire electromagnetic vacuum seen by the atom does not have to be squeezed for optimum effect. A single squeezed mode driving the cavity is sufficient.

The spectrum of the resonance fluorescence light from a single two-level atom in a small, high-quality, optical cavity is calculated. The coupling between the atom and cavity is made sufficiently strong compared to the dissipation that single quantum frequency splitting (vacuum Rabi splitting) occurs. Under high excitation qualitatively new fluorescent spectra are predicted. The usual three-peaked resonance fluorescence spectrum now has sidebands whose width is given by the Jaynes-Cummings atom-cavity coupling coefficient rather than by the system dissipation.

We describe a technique for modeling domain dynamics in the context of thermomagnetic magneto-optical recording. The new feature of our model is that no assumption of cylindrical symmetry is required. We illustrate the potential of our technique by applying it to domain erasure on a moving disk.

Dispersively bistable optical systems have two possible output states for certain ranges of their input parameters. We investigate this classical bistability in the context of quantised atoms and field. We find, in the small damping limit, that the classical bistable states appear as mixtures rather than as quantum superposition states.

A quantum mechanical analysis of a two-level atom in a coherently driven optical cavity is shown to predict steady-state atomic population inversion. Semi-classically this is forbidden because of the factorization of operator-product expectation values. The full quantum theory is much richer and different field states may be correlated with different atomic states. One consequence is that damping of the cavity field allows atomic polarization to be transferred from higher to lower field states and thus steady-state inversion becomes possible.

Absorptive optical bistability is shown to exist for a single two-level atom inside a resonant optical cavity. Solutions for the quantum-mechanical density operator are obtained numerically for a parameter regime at the interface between the quantum limit, in which quantum-mechanical noise invalidates the semiclassical prediction of bistability, and the classical limit, in which quantum noise is a negligible perturbation on semiclassical results. Bimodal photon number distributions and Q functions are obtained, and two-state transition rates are calculated

A two-level atom illuminated by a laser may be driven into a population-inverted steady state if it is coupled to a cavity. Full abstract.

We investigate quantum-mechanical second-harmonic generation for parameters such that classical electrodynamics predicts oscillations. Specifically we calculate the Q distribution function in a Gaussian approximation about the classical limit cycle. In the classical limit initial rapid collapse of the Q distribution into the neighborhood of the limit cycle is followed by diffusion around the limit cycle. The experimental significance of this quantum diffusion is discussed.

We have used a numerical model of thermomagnetic recording to investigate direct overwrite by domain destabilization in magneto-optical thin films. Our model includes a linear dependence of domain wall velocity on the net wall pressure due to the demagnetizing field and the wall energy density. Direct overwrite by domain destabilization can be accomplished in one step, without bias fields or prior reading or erasure.

We present a unified quantum analysis of parametric oscillators and intracavity four-wave mixers. The squeezing spectra below and above threshold for the degenerate cases are compared. Similarities between the systems are discussed and the optimum operating regimes identified.

Quantum tunneling times for the model of Drummond and Walls describing dispersive optical bistability are investigated for small cavity damping. Full abstract.

Tunneling times for absorptive optical bistability with a squeezed vacuum as input to the cavity are calculated. Using a squeezed input field to reduce the fluctuations in the critical quadrature, we show that the tunneling times may be increased. This may substantially improve the intrinsic stability of the device.

We derive and discuss the dissipative effects of a heat bath on a nonlinear oscillator, excluding very low temperatures [kT <(level width )] such that a Markovian master equation holds. For temperatures high enough for excited states of the oscillator to acquire noticeable thermal population we find the nonlinearity to have a drastic influence on transition rates and level shifts.

The squeezing spectrum for a cavity field mode interacting with an ensemble of three-level lambda-configuration atoms by an effective two-photon transition is calculated. Full abstract.

We use a Markovian master equation to solve for the dynamics of a free particle damped by the coupling of its coordinate to a bath of harmonic oscillators. Full abstract.

We solve the master equation for the coordinate-coordinate damped harmonic oscillator for initial superpositions of coherent states. Full abstract.

We undertake a detailed treatment of a Fabry-Perot cavity containing a degenerate parametric amplifier (DPA). Full abstract.

Instabilities leading to self-pulsing, period doubling and chaos are predicted to occur in two simple systems in nonlinear optics. Full abstract.

Numerical evidence is presented for period doubling and chaos at attainable laser powers in a model for optical tristability comprising two ring-cavity modes coupled via a J=1/2 to J=1/2 transition. Full abstract.

The steady state behaviour of two cavity modes of the electromagnetic field interacting with a three level atomic medium is studied. Full abstract.