We derive a quantum theory of evaporative cooling for a degenerate Fermi gas with two constituents and show that the optimum cooling trajectory is influenced significantly by the quantum statistics of the particles. The cooling efficiency is reduced at low temperatures due to Pauli blocking of available final states in each binary collision event. We compare the theoretical optimum trajectory with experimental data on cooling a quantum degenerate cloud of potassium-40, and show that temperatures as low as 0.3 times the Fermi temperature can now be achieved.

We have employed a second-order coherence function theory to study the effect of laser coherence on polarization beats in four-level system (PBFS). It is found that the temporal behavior of the beat signal depends on the stochastic properties of the lasers and transverse relaxation rate of the transition. The cases that pump beams have either narrow band or broadband linewidth are considered and it has been found that for both cases a Doppler-free precision in the measurement of the energy-level splitting between two excited states which are dipolar forbidden from the ground state can be achieved. We have also studied the asymmetric behavior of the polarization beats, and attributed this asymmetry to the shift of the zero time delay which is due to the dispersion of the optical components.

We examine the effect of electromagnetically induced transparency in a thin cell filled with a vapor of three-level $\Lambda$ atoms. We show that the absorption spectrum of the probe field and the fluorescence signal from the upper atomic level contain two sub-Doppler dips that have considerably different widths. The narrow dip corresponds to the effect of electromagnetically induced transparency, whereas the broader one results from the optical pumping of the external atomic states. Under the condition of exact resonance of the coupling field with the corresponding atomic transition, these two dips are superimposed on the frequency scale, while in the case of nonzero detuning of the coupling field, the two dips are shifted with respect to each other, which makes it possible to observe a competition between the two effects. In the frequency region where the absorption is low, large optical nonlinearities conditioned merely by the slow atoms having an effective 1 mK temperature are also found.

The second-order intensity correlation function of light transmitted out of a cavity QED system exhibits the nonclassical features and dynamics of the atom-field interaction. We present measurements of the intensity correlation to examine the size of the nonclassical features and the dependence on driving intensity, detuning, and the strength of the atom-field coupling. We use a model that takes into account experimental conditions to achieve a quantitative agreement with the observations.

A theory on spatial solitons in closed-circuit photorefractive-photovoltaic media is developed that gives rise to spatial solitons due to both the bulk photovoltaic effect and the spatially nonuniform screening of the external bias field. In case the photovoltaic effect can be neglected, these solitons are screening solitons. In case the external bias field is absent, these solitons are photovoltaic solitons in the closed-circuit case. We also show theoretically that the photovoltaic nonlinearity can be switched from self-defocusing to self-focusing by adding the external electric field. Under a strong bias condition, the photovoltaic nonlinearity can be switched from self-defocusing to self-focusing by changing the polarity of the external electric field or by rotating the polarization of the light.

The goal in this effort is twofold: (1) to develop an understanding of Casimir forces in geometries more complicated than the usual parallel-plate geometry and (2) to provide extensive numerical computations to elucidate quantitative and qualitative aspects of the vacuum fluctuation energy and Casimir forces for the rectangular cavity. We review geometries for which Casimir forces and vacuum energy have been computed, and point out some of the difficulties with the ideal-conductor boundary conditions and ideal-shape boundary conditions, e.g., infinitely sharp edges. We investigate the vacuum electromagnetic stress-energy tensor at 0 K for a perfectly conducting three-dimensional rectangular cavity with sides $a_1\times a_2\times a_3.$ The elements of the tensor are averaged over the appropriate spatial coordinates of the cavity. We first consider the average energy density $T^{00}=e\left(\mathit{a}\right)/V$ from the viewpoint of symmetry, where ${e(a}_1{,a}_2{,a}_3)=e(\mathit{a})$ is the finite change in the zero-point energy from the free-field case. The vacuum energy $e\left(\mathit{a}\right)$ and the total vacuum force on the wall normal to the i direction, $F_i=-\partial e/\partial a_i,$ are both homogeneous functions of the cavity dimensions. Because of this symmetry, the energy and forces are related by the equation $e\left(\mathit{a}\right)=\mathit{a}\cdot \mathit{F}\left(\mathit{a}\right).\mathrm{}$ We compute the vacuum forces and energy numerically for cavities with a broad range of dimensions. The implications of the perfect-conductor boundary conditions and the effects of the edges of the cavity are both considered. The $C_{3v}$ symmetry of the constant-energy surfaces is apparent. The zero-energy surface, which is invariant under dilations and therefore extends to infinity, separates the nested, concave, positive-energy surfaces from the open, negative-energy surfaces. The positive- (negative-) energy surfaces are mapped into each other by scale changes. The force $\mathit{F}\left(\mathit{a}\right)$ is normal to the constant-energy surface at $\mathit{a}.$ The surfaces corresponding to zero forces, ${\mathit{F}}_i\left(\mathit{a}\right)=0,$ are invariant under dilations and are therefore infinite. The zero-energy surface and the zero-force surfaces delineate the different geometries for which there are zero, one, or two negative (inward or attractive) forces on the cavity walls, along with the sign of the corresponding energy. There is no rectangular cavity geometry for which all forces are negative or zero; conversely, only geometries that are not too different from a cube have all positive (outward or repulsive) forces. Only for the last case is the energy $e\left(\mathit{a}\right)$ necessarily positive. To provide an intuitive feeling for these vacuum energies, comparisons are made to other forms of energy in small cavities. We consider the energy balance for changes in cavity dimensions.

The position-momentum quasidistribution obtained from an Arthurs and Kelly joint measurement model is used to obtain indirectly an “operational” time-of-arrival (TOA) distribution following a quantization procedure proposed by Kochański and Wódkiewicz [Phys. Rev. A 60, 2689 (1999)]. This TOA distribution is not time covariant. The procedure is generalized by using other phase-space quasidistributions, and sufficient conditions are provided for time covariance that limit the possible phase-space quasidistributions essentially to the Wigner function, which, however, provides a nonpositive TOA quasidistribution. These problems are remedied with a different quantization approach which, on the other hand, does not guarantee normalization. Finally, an Arthurs and Kelly measurement model for TOA and energy is worked out, valid also for arbitrary conjugate variables when one of the variables is bounded from below. The marginal TOA distribution so obtained, a distorted version of Kijowski’s distribution, is time covariant, positive, and normalized.

Measurements of low-energy electrons emitted by 4.5-keV ${\mathrm{Ne}}^{q+}$-ion impact on an Al surface are discussed for incident charge states $q=1\mathrm{}–6.$ Spectral structures found near 11 eV are attributed to the decay of bulk plasmons. A method is given to determine absolute values for the experimental electron yield from the plasmon decay. Absolute plasmon yields are studied as a function of the incidence angle of the projectile and the observation angle of the electron. A cosinelike angular distribution is found for the ejected electrons indicating that the plasmons decay well below the surface. The experimental data are compared with model calculations providing information about the plasmon production mechanisms.

We point out that the fermionic isotope ${}^{40}\mathrm{K}$ is a likely candidate for the formation of Cooper pairs in an ultracold atomic gas. Specifically, in an optical trap that simultaneously traps the spin states $|9/2,-9/2〉$ and $|9/2,-7/2〉,$ there exists a broad magnetic-field Feshbach resonance at ${B=196\mathrm{}}_{-21}^{+9\mathrm{}}$ G that can provide the required strong attractive interaction between atoms. An additional resonance, at ${B=191\mathrm{}}_{10}^{+5\mathrm{}}$ G, could generate p-wave pairing between identical $|9/2,-7/2〉$ atoms. A Cooper-paired degenerate Fermi gas could thus be constructed with existing ultracold-atom technology.

A scattering of short, weak, nonresonant laser pulses on a Bose-Einstein condensate is proposed as a tool for studying its statistical properties. We show in particular that the variance of the number of scattered photons may distinguish between the Poisson and microcanonical statistics.

We study the feasibility of preparing a Bose-Einstein condensed sample of atoms in a macroscopic quantum state that resembles a spin monopole. In this state, the atomic internal spins lie in the $x-y$ plane and point along the radial direction. The stability and dynamics of this structure are studied analytically in some cases and numerically in the more general situation. We find these structures to be stable objects giving rise to a nontrivial state of a Bose-Einstein condensate.

It is shown that diffusion of saturated gain (e.g., diffusion of population inversion in lasers) causes and/or enhances a modulational instability of the generated light field. In the case of a subcritical system (e.g., a laser with saturable absorber), the enhancement of the modulational instability stabilizes spatial solitons. These predictions are made for general nonlinear optical systems and are illustrated by numerical simulation of lasers with saturable absorbers.

We have studied an incoherently pumped laser operating with a Doppler-broadened three-level system placed in a doubly resonant cavity. This system generates two laser fields, one of them without population inversion. Both ladder and V-type three-level schemes are considered with a ratio $R={\omega }_{\alpha }/{\omega }_{\beta }$ of inversionless laser frequency ${\omega }_{\alpha }$ to ordinary laser frequency ${\omega }_{\beta }$ of $R=0.67\mathrm{}$ and $R=1.88,$ respectively. Dual-wavelength lasing extends up to Doppler-broadening values for optical transitions of atoms in a vapor cell. Some considerations for the practical realization of this dual-wavelength laser are discussed.

We report on recent experimental results of the dynamics of a laser-diode-pumped free-running ${\mathrm{N}\mathrm{d}:\mathrm{Y}\mathrm{V}\mathrm{O}}_4$ laser operating in a two-mode regime. We observe intrinsic quasiperiodic and chaotic oscillations as well as a locking of pulsation frequencies. We perform an asymptotic analysis of model rate equations in which an intensity-dependent cross-gain (i.e., nonlinear gain) mechanism of direct mode-mode coupling is introduced in addition to the coupling mechanism via cross saturation of population inversions. We show that the intrinsic instability originates from the nonlinear gain mechanism. The observed locking of pulsation frequencies is successfully reproduced by simulations based on the proposed rate equations.

We examine the effect of propagation on the resonance Rabi sideband of the four-wave mixing (FWM) spectrum, obtained when short temporally displaced pump and probe pulses interact with an optically thick medium of two-level atoms. We find that the dependence of the time-integrated FWM signal on the pump-probe delay is considerably altered by propagation. In particular, the logarithm of the FWM signal, for the case where the probe precedes the pump, deviates from linearity and may even increase over a range of values. An explanation is given in terms of the overlap of the pump envelope with the coherent response of the atomic system to the probe, both of which are modified on propagation.

We suggest a tunable optical device to synthesize Fock states and their superpositions starting from a coherent source. The scheme involves an avalanche-triggering photodetector and a ring cavity coupled to a traveling wave through a cross-Kerr medium. Low quantum efficiency at the photodetector improves the synthesizing quality at the expense of reducing the synthesizing rate.

We use a full density matrix framework and the propagation equation to study the electromagnetic field induced waveguide in an atomic vapor. We explain the experimental results of Truscott et al. [Phys. Rev. Lett. 82, 1438 (1999)] for waveguiding in Rb vapor.

A homogeneous gas of atoms with hyperfine spin $F=1\mathrm{}$ is considered below the critical temperature of the Bose-Einstein condensation. The general structure of the correlation functions (both for density and spin fluctuations) and their connection to the thermal Green’s functions are worked out. The damping of the modes is calculated in the random-phase approximation.

We study the first-order interference in spontaneous parametric down-conversion generated by two pump pulses that are well distinguishable in time. The observed modulation in the angular distribution of the signal photon can only be explained in terms of a quantum-mechanical description based on biphoton states. The condition for observing interference in the signal channel is shown to depend on the parameters of the idler photon.

In this paper we explore the mathematical and epistemological connections between the stochastic derivation of the Schrödinger equation and the one proposed by ourselves in previous papers. It will be shown that these connections are accomplished by means of the fluctuation-dissipation theorem, to which we may unambiguously relate the symbols and physical references of both approaches. As a by-product of our investigation, it will be possible to interpret the time-energy dispersion relation on sounder grounds. It will also be possible to discuss the superposition principle and to interpret it on a quite simple basis. The origin of the stochasticity and its relation to stability will be also addressed and the bridge to an axiomatic formulation of stochastic electrodynamics will be constructed.