We calculate the effects of perpendicular propagation through a dispersive and absorbing dielectric slab at arbitrary temperatures on specific nonclassical properties of an incident light field. The transmitted signal is assumed to be measured by a detector that receives radiation only from the direction normal to the slab surfaces. Squeezing and nonclassical counting statistics of the transmitted light are evaluated for continuous-wave squeezed states incident on both sides of the slab. The degree of second-order coherence is instead evaluated for an N-photon incident pulse, and the effects of transmission through the slab on its antibunching are calculated.

A path-integral formulation is developed to study the spectrum of radiation from a perfectly reflecting (conducting) surface. It allows us to study arbitrary deformations in space and time. The spectrum is calculated to second order in the height function. For a harmonic traveling wave on the surface, we find many different regimes in which the radiation is restricted to certain directions. It is shown that high-frequency photons are emitted in a beam with relatively low angular dispersion whose direction can be controlled by the mechanical deformations of the plate.

We use standard quantum laser theory to examine the linewidth of lasers with a four-level atomic gain medium as a function of the spontaneous emission rate into the lasing mode and the decay rates from the upper and lower lasing levels. We find that the laser linewidth ceases to exhibit the customary decrease with increased photon number when a critical photon number, proportional to the ratio of the decay rate from the lower lasing level to the rate of spontaneous emission into the lasing mode, is reached. This critical photon number would decrease as the size of the optical cavity is decreased. In addition we show that, in general, the laser linewidth depends critically on the ratio of the overall decay rates from the upper and lower lasing levels.

We report on the experimental demonstration of phase-dependent electromagnetically induced transparency (EIT). This effect is based on a quantum interference in closed-loop schemes of interaction of atoms with the radiation. It allows us to control optical properties of the medium by the phases of the laser fields. We discuss some of the possible applications of phase-dependent EIT.

We present a formulation of non-Markovian quantum trajectories for open systems from a measurement theory perspective. In our treatment there are three distinct ways in which non-Markovian behavior can arise: a mode-dependent coupling between the bath (reservoir) and system, a dispersive bath, and spectral detection of the output into the bath. In the first two cases the non-Markovian behavior is intrinsic to the interaction; in the third case the non-Markovian behavior arises from the method of detection. We focus in detail on the trajectories that simulate real-time spectral detection of the light emitted from a localized system. In this case the non-Markovian behavior arises from the uncertainty in the time of emission of particles that are later detected. The results of computer simulations of the spectral detection of the spontaneous emission from a strongly driven two-level atom are presented.

An interaction-free measurement system with a polarization-based Mach-Zehnder interferometer structure is analyzed for semitransparent objects. Here, it is shown that the interaction-free measurement of such objects with 100% detection efficiency is possible in principle if the system loss is negligible. The influence of two system imperfections, the system loss and the low quantum efficiency of the photon detectors, on the interaction-free measurement is also analyzed. Although the two system imperfections limit the maximal detection efficiency that can be achievable, the quantum efficiency of the photon detectors is less important when the system loss becomes small.

The resonance fluorescence from a four-level atom driven by two coherent fields is studied. If the dipole moments between the two upper levels and each of the two lower levels are parallel, the spontaneous emission paths from the upper levels to the lower levels will have strongly or even completely destructive quantum interference. We show that this quantum interference will result in a complete inhibition of the fluorescence when one of the driving fields is tuned at the middle point of the upper levels. The quantum interference will lead to the dependence of atomic populations at steady state on the initial condition, when both of the driving fields are tuned to the middle point of the upper levels. When the dipole moments are close to but not exactly parallel, or none of the driving fields is tuned at the middle point of the upper levels and there is a small difference between detunings of the two driving fields to the uppermost level, ultranarrow lines at the spectral center appear because of the destructive quantum interference.

We present quantum Maxwell-Bloch equations (QMBE) for spatially inhomogeneous semiconductor laser devices. The QMBE are derived from fully quantum mechanical operator dynamics describing the interaction of the light field with the quantum states of the electrons and the holes near the band gap. By taking into account field-field correlations and field-dipole correlations, the QMBE include quantum noise effects, which cause spontaneous emission and amplified spontaneous emission. In particular, the source of spontaneous emission is obtained by factorizing the dipole-dipole correlations into a product of electron and hole densities. The QMBE are formulated for general devices, for edge emitting lasers and for vertical cavity surface emitting lasers, providing a starting point for the detailed analysis of spatial coherence in the near-field and far-field patterns of such laser diodes. Analytical expressions are given for the spectra of gain and spontaneous emission described by the QMBE. These results are applied to the case of a broad area laser, for which the frequency and carrier density dependent spontaneous emission factor $\beta$ and the evolution of the far-field pattern near threshold are derived.

We theoretically investigate the quantum interference of entangled two-photon states generated in a nonlinear crystal pumped by femtosecond optical pulses. Interference patterns generated by the polarization analog of the Hong-Ou-Mandel interferometer are studied. Attention is devoted to the effects of the pump-pulse profile (pulse duration and chirp) and the second-order dispersion in both the nonlinear crystal and the interferometer’s optical elements. Dispersion causes the interference pattern to have an asymmetric shape. Dispersion cancellation occurs in some cases.

Pump–supercontinuum-probe (PSCP) spectroscopy with femtosecond time resolution is developed theoretically and experimentally. The connection to previous theoretical results on nonchirped probing is established. It is experimentally shown that the supercontinuum can be described as a single chirped pulse. A key problem of the technique—the precise time correction of transient spectra—is solved by monitoring the nonresonant electronic response from a pure solvent (liquids) or from a transparent substrate (solid films). This allows for an adequate characterization of the supercontinuum, in particular, for directly measuring the spectral dependence of the pump-probe cross correlation. For 50-fs pump pulses, a theoretical estimate gives an accuracy for the time correction of 10 fs, which is typically ≈1/30 of the supercontinuum pulse duration. Hence a time resolution of 10–20 fs can be experimentally realized. Contributions to the nonresonant transient signal from high-frequency Raman excitations and from low-frequency impulsive-stimulated Raman processes are discussed. The PSCP technique is illustrated by results from experiments with fused silica and several common solvents and with a chromophore in solution.

If an atom is able to exhibit macroscopic dark periods, or electron shelving, then a driven system of two atoms has three types of fluorescence periods (dark, single, and double intensity). We propose to use the average durations of these fluorescence types as a simple and easily accessible indicator of cooperative effects. As an example, we study two dipole-interacting V systems by simulation techniques. We show that the durations of the two types of light periods exhibit marked separation-dependent oscillations and that they vary in phase with the real part of the dipole-dipole coupling constant.

We investigate the photon statistics of the light transmitted from a driven optical cavity containing N two-level atoms, with emphasis on the weak driving field limit. This limit is of most interest from the point of view of quantum fluctuations. We find that various types of nonclassical behavior are possible, even with large numbers of atoms in the cavity, under conditions of strong atom-field coupling, which we refer to as the cavity quantum electrodynamics limit. We describe the system with a pure-state formalism valid for weak fields, and also use a Fokker-Planck equation obtained by a small fluctuation linearization. We examine the conditions under which the linearized theory is appropriate, and explore the sensitivity of nonclassical effects in the system to atom number, transit-time broadening, and detunings.

We propose a novel semiconductor microlaser, made by capturing the light emitted from a single InAs/GaAs quantum dot in the whispering-gallery mode of a glass microsphere. We demonstrate that such an arrangement allows the laser threshold condition to be satisfied. The corresponding threshold current should be several orders of magnitude lower than is currently possible in semiconductor lasers.

Chaotic spatiotemporal dynamics generated by a nonlinear set of coupled partial differential equations are synchronized via a scalar complex variable. Our results show that synchronization is robust to noise, and we demonstrate chaotic communication in a high-dimensional system. We have also discovered that the added dimensionality creates a new quasisynchronous state, enabling the transmission of multiple messages through a single scalar complex channel. The feasibility of these novel ideas is demonstrated on a realistic numerical model of chaotic semiconductor lasers.

Generalized single-atom Maxwell-Bloch equations for optically dense media are derived taking into account noncooperative radiative atom-atom interactions. Applying a Gaussian approximation and formally eliminating the degrees of freedom of the quantized radiation field and of all but a probe atom leads to an effective time-evolution operator for the probe atom. The mean coherent amplitude of the local field seen by the atom is shown to be given by the classical Lorentz-Lorenz relation. The second-order correlations of the field lead to terms that describe relaxation or pump processes and level shifts due to multiple scattering or reabsorption of spontaneously emitted photons. In the Markov limit a nonlinear and nonlocal single-atom density matrix equation is derived. To illustrate the effects of the quantum corrections, we discuss amplified spontaneous emission and radiation trapping in a dense ensemble of initially inverted two-level atoms and the effects of radiative interactions on intrinsic optical bistability in coherently driven systems.

The quantum statistics of damped optical solitons is studied using cumulant-expansion techniques. The effect of absorption is described in terms of ordinary Markovian relaxation theory, by coupling the optical field to a continuum of reservoir modes. After introduction of local bosonic field operators and spatial discretization, pseudo-Fokker-Planck equations for multidimensional s-parametrized phase-space functions are derived. These partial differential equations are equivalent to an infinite set of ordinary differential equations for the cumulants of the phase-space functions. Introducing an appropriate truncation condition, the resulting finite set of cumulant evolution equations can be solved numerically. Solutions are presented in a Gaussian approximation and the quantum noise is calculated, with special emphasis on squeezing and the recently measured spectral photon-number correlations [Spälter et al., Phys. Rev. Lett. 81, 786 (1998)].

We study the generation of coherence of a nonallowed transition by a Raman scattering process in a three-level system. We present analytical and numerical solutions of the density-matrix equations in steady state. We study the conditions for maximizing the coherence. We find that, when the system is far off resonance and the fields and the coupling are not too strong, the problem of coherence in the three-level system reduces to that in an effective two-level model, and the maximal coherence generated in steady state is limited by the steady-state two-level-model value $\pm 1/\left(2\sqrt{2}\right).\mathrm{}$ We show that when the amplitudes of the fields are sufficiently high that the system is far beyond the strong-coupling regime, the coherence of the nonallowed transition can reach its stationary maximum value $-1/2.$ We study the difference between the wave-vector shifts of the two fields, and examine the possibility of stationary induced transparency and matched pulses.

We discuss the generation of entangled states of two two-level atoms inside an optical resonator. When the cavity decay is continuously monitored, the absence of photon counts is associated with the presence of an atomic entangled state. In addition to being conceptually simple, this scheme can be demonstrated with presently available technology. We describe how such a state is generated through conditional dynamics, using quantum jump methods, including both cavity damping and spontaneous emission decay, and evaluate the fidelity and relative entropy of entanglement of the generated state compared with the target entangled state.

We present a study of factors that influence the feature width of nanostructures formed by atom-optical direct-write lithography. In this process, chromium atoms travel through a standing-wave laser light field and are deposited on a surface. Due to the atom-light interaction, the atoms are focused onto the surface in the standing wave nodes, producing a pattern of parallel chromium lines with widths as small as 28 nm and a spatial period of 212.78 nm. We present calculations and measurements of feature widths representing an exploration of the effects of laser power and laser-substrate separation. Strong qualitative agreement is seen between calculations and the measurements, but the observed feature widths are uniformly larger than theoretical predictions. Experiments in which the total amount of chromium deposited is varied indicate that this difference can be attributed to chromium growth behavior.

Quantum mechanically exact analytical solutions are obtained for a two-state exponential model, in which the exponent of diabatic coupling is one-half of that of the diabatic potential curve. A very simple and accurate semiclassical formula is found for the nonadiabatic transition probability. This gives a direct generalization of the Landau-Zener and Rosen-Zener formulas.