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The possibilities of observing disentanglement of atomic and field states during their interaction are discussed in the framework of one-atom micromaser action. We find that, in certain cases, the atom can be in a pure state and the cavity field may be in an approximate number state.

We show the differences in the dynamics of a three-level and a two-level Rydberg atom interacting with two nondegenerate modes of frequencies ${\mathrm{\ensuremath{\omega}}}_{1}$ and ${\mathrm{\ensuremath{\omega}}}_{2}$ in an ideal cavity. In the case ${\mathrm{\ensuremath{\omega}}}_{1}$=${\mathrm{\ensuremath{\omega}}}_{0}$+\ensuremath{\epsilon} and ${\mathrm{\ensuremath{\omega}}}_{2}$=${\mathrm{\ensuremath{\omega}}}_{0}$-\ensuremath{\epsilon} (\ensuremath{\epsilon}\ensuremath{\ll}${\mathrm{\ensuremath{\omega}}}_{0}$), we present the time evolution of squeezing in the amplitudes (modulated at \ensuremath{\epsilon}) of waves of frequency ${\mathrm{\ensuremath{\omega}}}_{0}$.

We consider a system of $N$ two-level atoms (spins) interacting with the radiation field in a dispersive but high-$Q$ cavity. Under an adiabatic condition, the interaction Hamiltonian reduces to a function of spin operators which is capable of producing spin squeezing. For a bipartite system $(N=2)$, the expressions for spin squeezing get very simple, giving a clear indication of close to 100% noise reduction. We analyse this squeezing as a measure of bipartite entanglement.

We show that it is possible to improve the efficiency of a classical Otto-cycle heat engine by adding a high-Q microwave cavity and a laser system that can extract coherent laser energy from thermally excited ``exhaust'' atoms. This improvement does not violate the second law of thermodynamics, i.e., we show that a combined high-Q microwave cavity and a laser system does not improve the efficiency of a classical Carnot-cycle heat engine.

Using a quantum theory for an ensemble of three-level atoms $(\ensuremath{\Lambda})$ placed in an optical cavity and driven by electromagnetic fields, we show that the long-lived spin associated with the ground-state sublevels can be squeezed. Two kinds of squeezing are obtained: self-spin squeezing, when the input fields are coherent states and the atomic ensemble exhibits a large nonlinearity; squeezing transfer approaching 100%, when one of the incoming fields is squeezed.

The dynamical behavior of a two-level system in an intense frequency-modulated field is obtained without recourse to the weak-modulation assumption. Solutions to the optical Bloch equations are expressed in terms of continued fractions involving 2\ifmmode\times\else\texttimes\fi{}2 matrices. Such matrix-continued fractions are numerically evaluated to obtain a wide variety of absorption and fluorescence spectra in frequency-modulated fields. Results in various special cases involving combinations of weak fields, weak modulation, strong modulation, and strong fields are given. Analytical results for weak fields but with an arbitrary degree of modulation are also presented. The spectra exhibit additional resonances for strong modulation. The main resonance shifts and broadens considerably due to strong modulation and saturation effects.

The nonlinear response of a two-level system interacting with two pump beams of different frequencies is studied with a view to examine several recent experiments on nonlinear mixing of high orders, instabilities in homogeneously broadened lasers, and holes in homogeneous lines. Such a nonlinear response is calculated with use of the continued fractions given in our earlier work [J. Opt. Soc. Am. B1, 164 (1984)]. Saturation effects lead to the appearance of many structures at submultiples of the Rabi frequency. The origin of these subharmonics in nonlinear-response functions is explained. It is shown that collisions not only lead to hole burning at the line center for weak fields but can also lead in moderate fields to the appearance of structures at subharmonics of the Rabi frequency. Existence of collision-induced coherences similar to those in four-wave mixing is shown in six-wave mixing. Exact results for the degenerate nonlinear mixing of arbitrary order are presented for arbitrary values of field strengths. Saturating fields create holes at the line center of such nonlinear mixing signals. Gain profiles of two modes symmetrically displaced from line center are also given. Numerical results, with complete account of saturation and collisions, for a variety of nonlinear-response functions are presented.

A quantum statistical analysis of a two-photon laser is presented in a generalization of the one-photon laser. A two-photon loss mechanism is assumed by taking detailed-balance considerations into account. The expressions for the photon statistical distribution exhibit the exact influence of the Doppler parameter and other relaxation parameters. In addition, the photon statistics can be studied as a function of the detuning. Threshold conditions for the laser action are noticed. The peak photon number and half-width of the photon distributions are obtained. It is found that the photon distribution can be written as a ratio of the one-photon laser-photon distribution to the Poisson distribution for photons.