We show the differences in the dynamics of a three-level and a two-level Rydberg atom interacting with two nondegenerate modes of frequencies ${\mathrm{\omega }}_1$ and ${\mathrm{\omega }}_2$ in an ideal cavity. In the case ${\mathrm{\omega }}_1$=${\mathrm{\omega }}_0$+ε and ${\mathrm{\omega }}_2$=${\mathrm{\omega }}_0$-ε (ε≪${\mathrm{\omega }}_0$), we present the time evolution of squeezing in the amplitudes (modulated at ε) of waves of frequency ${\mathrm{\omega }}_0$.

A new fourth-order interference experiment has been carried out and analyzed theoretically in classical and in quantum terms. Two photons produced in the process of parametric down-conversion provide the two inputs to a Mach-Zehnder type of interferometer, while two photodetectors coupled to a coincidence counter measure the output. The coincidence rate, after subtraction of accidentals, exhibits a cosine variation with the optical path difference, in agreement with quantum mechanics, but in disagreement with a classical analysis. By contrast, when two coherent light beams from a He:Ne laser are used as inputs to the interferometer, no fourth-order interference is observed.

We treat the scaling of thermal phase-noise effects and quantum fluctuations for solitons in optical fibers. The central result is that the size of the thermal noise relative to quantum noise is reduced in proportion to the soliton duration for solitons whose duration is less than the thermal correlation times, suggesting that squeezed quantum solitons should be realizable in optical fibers. The physical basis for this effect is largely the fact that squeezing, which is nonlinear, occurs more rapidly for shorter pulses.

A single trapped ion, laser cooled into its quantum ground state of motion, may be used as a very-low-temperature detector of radio-frequency signals applied to the trap end caps. If the signal source is a resonant oscillator of sufficiently high Q, the source may also be placed in its quantum ground state by coupling to the ion. Parametric couplings may be used to cool and detect source modes other than the mode directly coupled to the ion. A theoretical analysis of these cooling and detection processes is presented, and as an example, their application to single trapped electron and proton spectroscopy is examined. Squeezing and low noise detection of one quadrature component of the source oscillation are also discussed. The techniques discussed here may lead to radio-frequency measurements of improved accuracy and sensitivity. Cooling and detection of vibrations of macroscopic oscillators also appear possible.

The process of making a measurement on a quantum-mechanical system introduces quantum noise to that system. A quantum nondemolition measurement scheme seeks to make a measurement of an observable to better than this quantum limit, by feeding all the introduced noise into a conjugate variable to that under consideration. In this paper three quantitative criteria are suggested for the evaluation of nonideal quantum nondemolition measurements. The application of these criteria is illustrated using both a simple beam splitter and the ${\mathrm{\chi }}^3$ interaction in a Raman-active medium.

The intrinsic field errors of realistic wiggler structures degrade the quality of the electron beam as it propagates through the structure. In the following, we investigate the impact of the degraded-quality electron beam on the rate of conversion of beam energy into electromagnetic field energy. Specifically, we apply the linearized Vlasov theory to evaluate the expressions for free-electron-laser (FEL) gain in the low-gain regime and the growth rate in the high-gain regime. The analysis is both theoretical and computational and yields qualitative and quantitative agreement on the dominant physical processes. In addition, several figures of merit are identified that delineate conditions under which field errors have a negligible effect on the FEL growth rate.

The steady-state theory of degenerate four-wave mixing (DFWM) with broad-bandwidth lasers is extended to treat the time dependence of the interaction allowing calculation of the intensity dependence and saturation behavior of DFWM with pulsed lasers. An experimental study of this intensity dependence as a function of laser bandwidth is reported, showing qualitative agreement with the theory. The line shape of DFWM induced by broad-bandwidth pump fields, probed by a monochromatic probe, is shown to have a Doppler-broadened profile in agreement with the theoretical predictions.

We have performed experiments on germanium plasma irradiated with 0.53-μm laser light. A soft-x-ray amplification was observed. 2- and 2.4-${\mathrm{cm}}^{\mathrm{-}1}$ gains were measured for the two brightest lasing lines at 232.2 and 236.2 Å. A temporal analysis of lasing lines and gain is reported. Simulations by a series of computer programs compared favorably with the measured values and contributed to the clarification of some experimental results.

We demonstrate that atomic superposition states are sensitive to phase-dependent properties of radiation fields and that atoms prepared in such states can be employed as detectors. We concentrate on three-level detectors in two configurations, λ and ladder systems. λ systems prepared in a superposition state are shown to be sensitive to the relative phase between field modes and are relevant to measurements of fields produced by correlated-emission lasers. Ladder systems prepared in a superposition state are sensitive to the overall field phase and are relevant to measurements of fields generated in squeezing experiments. Such atomic-superposition-state detectors could be of value in detecting phase-dependent properties of microwave radiation in Rydberg atom masers and for investigating the properties of optical radiation generated in correlated-emission lasers.

An analytical study of the sideband correlations in a strongly driven three-level atom in the cascade configuration is presented. The quantum nature of the sidebands is discussed in terms of intensity-intensity correlations and photon statistics.

We give a general theory of the interaction of a large number of two-level atoms in an optical cavity driven by a broadband squeezed input of finite amplitude. No adiabatic elimination of atoms or field is made, and atomic and cavity loss and dispersion are fully incorporated in the theory. We calculate the optical and squeezing spectra that may be observed in transmission and reflection from the cavity; the latter exhibits a novel interference structure superimposed as a result of the squeezed input. Results presented indicate that it is possible to somewhat reduce the vacuum Rabi peaks in transmission, in the strong-coupling regime, with a moderately squeezed input. In the limit of a ‘‘bad cavity,’’ the characteristic triplet transmitted under conditions of saturation may have one of its sidebands suppressed and the other enhanced by a squeezed input. These signatures suggest new alternatives for the experimental study of the interaction of atoms with squeezed light.

It is shown that a three-level laser can become the first example of an optically active system to generate a squeezed-field state.

We study the effects of velocity-changing collisions (VCC’s) on nearly degenerate forward four-wave mixing (FWM) in the presence of a strong pump. The calculations include the effects of both VCC’s and phase-interrupting collisions. Explicit calculations and results for FWM in two-level systems for the case of strong collisions are presented in the Doppler limit. Effects of saturation on VCC-induced narrowing and those of VCC’s on strong-field-induced resonances are discussed in detail.

A binary gas mixture of a vapor of optically active particles and a buffer gas of comparable density is considered. This is the simplest system in which light-induced drift arises simultaneously with light-induced heat flux and pressure anisotropy. Explicit expressions are obtained for these fluxes and for the modified transport coefficients in a few complementary special situations.

We introduce an alternative approach to the study of multiphoton ionization. The approach is based on consideration of the relative frequency instead of the relative field strength of the applied laser field as a small parameter (or, equivalently, a large number of photons). The choice is based on the characteristics of present-day lasers. We apply our approach specifically to an electron bound by a δ-function potential. In order to show a simpler situation first, we start by applying our analysis to the time-independent tunneling problem from such a potential due to an external electrostatic field. For this problem, we derive from first principles the well-known ionization rate for tunneling. Next, we derive with the same general formalism an analytical formula, asymptotic in the number of photons, for the multiphoton ionization rate, under strong field conditions, of an electron confined by a δ-function potential. We also obtain the ionization rate from a numerical solution of the corresponding equations. The comparison with the analytical expression is very good, even for a small number of photons. Our approach puts the results of Perelomov, Popov, and Terentev (Zh. Eksp. Teor. Fiz. 50, 1393 (1966) [Sov. Phys. JETP 23, 924 (1966)]) on a rigorous basis as well as extending them to a wider range of parameters. To cover analytically the few-photon case, we also develop a perturbation theory in the relative field strength to calculate the ionization rate. This perturbative approach has the advantage over the conventional Rayleigh-Schrödinger theory in that it effectively takes into account the continuum without having to deal with it directly. The comparison with the numerical results is also very good.

The ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$ nuclear quadrupole resonance spectrum of a single crystal of sodium chlorate [R. Tycko, Phys. Rev. Lett. 58, 2281 (1987)] rotating about two axes reflects a non-Abelian gauge potential. This gauge potential is an example of Wilczek and Zee’s [Phys. Rev. Lett. 52, 2111 (1984)] generalization of Berry’s phase to the adiabatic transport of degenerate states.

A procedure based on the exact solutions of multiple-step recursion relations with successive coefficients is shown to provide upper bounds to the bound-state energies of a class of anharmonic-oscillator potentials. Any finite set of energy levels can thereby be estimated to any accuracy. The associated wave functions are guaranteed to be normalizable.

Quadrupole polarizabilities ${\mathrm{\alpha }}_{\mathit{q}}$ have been calculated using Ξa wave functions and the Sternheimer charge-perturbed differential equation procedure for ${\mathrm{F}}^{\mathrm{-}}$, ${\mathrm{Cl}}^{\mathrm{-}}$, and ${\mathrm{Br}}^{\mathrm{-}}$, respectively. It is shown that self-interaction correction with the proper choice of the exchange parameter, ${\mathit{a}}^{\mathrm{KLI}}$ (KLI is Kulback-Leibler information measure), the calculated ${\mathrm{\alpha }}_{\mathit{q}}$ values are close to the corresponding Hartree-Fock estimates.

The possible appearance of resonances in the partial cross sections of the inelastic collisions of positrons with lithium atoms at energies below 5 eV is investigated. It is assumed that only elastic and rearrangement channels are open, while excitation channels are closed. A coupled static formalism, in which the polarization potentials of the lithium and positronium are switched on, is employed. The basis set of Clementi and Roetti [At. Data Nucl. Data Tables 14, 177 (1974)] is used for describing the target model. Comparison between the resulting total cross sections and those obtained by other authors is presented.

The elastic and inelastic electron and positron scatterings from metastable hydrogen H(2s) are calculated by using the Wallace and Glauber approximations [Phys. Rev. Lett. 27, 622 (1971); Ann. Phys. (N.Y.) 78, 190 (1973); Lectures in Theoretical Physics, edited by W. F. Brittin (Interscience, N.Y. 1959), Vol. 1, pp. 315–414]. The general expressions for the Wallace amplitude, which are valid for any s-s and s-p collision process, are given. A comparison of the results of angular distributions for electron and positron scatterings from the metastable 2s state of hydrogen reveals some significant differences in their behavior when compared to the case of scattering from the ground 1s state.