We evaluate the scattering functions of a gas of spin-polarized, noninteracting fermions confined in a quasi-one-dimensional harmonic trap at zero temperature. The main focus is on the inelastic scattering spectrum and on the angular distribution of scattered light from a mesoscopic atomic cloud as probes of its discrete quantum levels and of its shell structure in this restricted geometry. The dynamic structure factor is calculated and compared with the results of a local-density approximation exploiting the spectrum of a one-dimensional homogeneous Fermi gas. The elastic and inelastic contributions to the static structure factor are separately evaluated: the inelastic term becomes dominant as the momentum transfer increases, masking a small peak at twice the Fermi momentum in the elastic term but still reflecting the discrete quantum levels of the cloud. A fast and accurate numerical method is developed to evaluate the full pair distribution function for mesoscopic inhomogeneous clouds.

An alternative method is used to investigate the tunneling between two weakly linked Bose-Einstein condensates confined in double-well potential traps. The nonlinear interaction between the atoms in each well contributes to a finite chemical potential, which, with consideration of periodic instantons, leads to a remarkably high tunneling frequency. This result can be used to interpret the newly found macroscopic quantum self-trapping effect. Also an alternative kind of first-order crossover between different regions is predicted.

Here we study the collective excitations of a dilute spin-polarized Bose-Fermi mixture at zero temperature, considering, in particular, the features arising from the interaction between the two species. We show that a propagating zero-sound mode is possible for the fermions even when they do not interact among themselves.

We study a Nd-doped microchip glass laser that emits in two polarizations and in many longitudinal modes. Saturation of the inversion by standing waves causes spatial inhomogeneity of both the longitudinal and azimuthal distributions of the laser gain. These nonlinear inhomogeneities couple the modes and result in low-frequency oscillations (10–500 kHz) of the light flux in the individual laser modes. These oscillations are steadily driven by quantum noise and appear as 15% fluctuations of the power in each mode. In-phase fluctuations in the laser modes appear at the frequency of the main relaxation oscillation of the total laser power. Antiphase fluctuations appear at other frequencies in individual longitudinal and polarization laser modes only. The dominant frequency of these fluctuations is determined by the light power in the mode. Numerical simulations of rate equations, including Langevin forces, satisfactorily reproduce the experimental results. These phenomena must be taken into account when lasers are applied as stable coherent optical light sources, and also with sensitive absorption measurements in the laser cavity.

We report explicit analytical and numerical results for the polarization resolved intensity noise of vertical-cavity surface-emitting lasers operating in the fundamental transverse mode. We describe the fluctuations of the linear and circular polarization components of linearly polarized states on both sides of a nonthermal polarization switching. Our description is valid for small and large birefringence and arbitrary values of the spin flip rate, giving a complete description of the role of these parameters. Normalized cross-correlation functions for both linear and circular components are discussed in detail. They show different degrees of anticorrelated fluctuations in different frequency ranges.

Electromagnetically induced transparency (EIT) was observed in a mismatched-wavelength cascade system using a room temperature vapor cell and laser-cooled atoms. A cw probe laser beam monitored the cesium ${6S}_{1/2}\to {6P}_{3/2}$ transition while another cw laser coupled the ${6P}_{3/2}$ state to a higher excited state. The ratio of the observed Rabi frequencies for coupling to the ${6P}_{3/2}\to (11\mathrm{}–{13)D}_{3/2,5/2}$ transitions agreed closely with that predicted using the transition oscillator strengths. A comparison of the EIT signals obtained using cold atoms and the vapor cell is made.

We propose a generation method of Bell-type states involving light and the vibrational motion of a single trapped ion. The trap itself is supposed to be placed inside a high-$Q$ cavity sustaining a single mode, quantized electromagnetic field. Entangled light-motional states may be readily generated if a conditional measurement of the ion’s internal electronic state is made after an appropriate interaction time and a suitable preparation of the initial state. We show that all four Bell states may be generated using different motional sidebands (either blue or red), as well as adequate ionic relative phases.

We calculate the polarization bremsstrahlung spectra of electron–rare-gas atom collisions from 5000 to 40 000 K with a quantum-mechanical line-shape code. The electron-atom interaction is modeled by a Hartree-Fock-Slater plus polarization potential and for the induced dipole, a model consistent with the polarization potential is used. Compared to the previously calculated ordinary electron-neutral atom bremsstrahlung spectra, polarization radiation is significantly more intense at the lower temperatures and higher frequencies considered here, otherwise it is relatively unimportant.

Plasmas have been created with bulk temperatures $>~400$ eV and densities greater than $1\times {10}^{21}$ ${\mathrm{cm}}^{-3}$ in some regions by irradiating atomic clusters of argon with a 0.4 TW ultrashort (35 fs) laser pulse. An improved nozzle has been designed so that larger clusters can be formed, allowing the clusters to maintain high-density cores after the preplasma is formed due to the laser prepulse. Ar is the element with the highest atomic number, Z, for which the Lyman-α resonance line $\left({\mathrm{Ly}}_{\alpha }\right)$ has been observed in ultrashort $(<\mathrm{}100\mathrm{}$ fs) pulse laser experiments for any target. The unambiguous spectroscopic evidence, including high-resolution measurements of the ${\mathrm{Ar}}^{+17\mathrm{}}$ ${\mathrm{Ly}}_{\alpha }$ spectrum, is consistent with a theoretical two-temperature collisional-radiative model of irradiated atomic clusters incorporating the effects of highly energetic electrons $(\sim 5$ keV).

We propose a method for determining the time development of the position coordinates of a Rydberg wave packet using the sudden turn-on of a strong field (a “field step”). The feasibility of the technique is investigated using wave packets created by a half cycle pulse (HCP) that comprise a superposition of very-high-lying Rydberg states. The time evolution of the wave packet is measured using probe pulses that are applied following a variable time delay. The probe pulse ionizes a fraction of the atoms and the survival probability exhibits pronounced oscillations that are associated with the quasiperiodic evolution of the wave packet. Good agreement is found between the experimental data and the results of classical trajectory Monte Carlo simulations. Extraction of classical phase space coordinates from the data is discussed.

We demonstrate, analytically and numerically, that the ferromagnetic phase of the spinor Bose-Einstein condenstate may experience modulational instability of the ground state leading to a fragmentation of the spin domains. Together with other nonlinear effects in the atomic optics of ultracold gases (such as coherent photoassociation and four-wave mixing) this effect provides one more analogy between coherent matter waves and light waves in nonlinear optics.

A time for a quantum particle to traverse a barrier is obtained for stationary states by setting the local value of a “time” operator equal to a constant. This time operator, called the tempus operator because it is distinct from the time of evolution, is defined as the operator canonically conjugate to the energy operator. The local value of the tempus operator gives a complex time for a particle to traverse a barrier. The method is applied to a particle with a semiclassical wave function, which gives, in the classical limit, the correct classical traversal time. It is also applied to a quantum particle tunneling through a rectangular barrier. The resulting complex tunneling time is compared with complex tunneling times from other methods.

In the context of superluminal propagation of wave packets through potential barriers, the tunneling speed is usually characterized by the Wigner velocity. We propose an alternative speed that takes into account the interference between the incoming and the reflected waves and leads to a better estimation of arrival time for a wave packet entering the tunneling region. This arrival time is derived by an extrapolation from inside the barrier. The analytical theory is based on the stationary phase approximation whose validity is justified by a comparison with the numerical solution of the time-dependent Dirac equation.

We apply a general method for the estimation of completely positive maps to the one-to-two universal covariant cloning machine. The method is based on the maximum-likelihood principle, and makes use of random input states, along with random projective measurements on the output clones. The downhill simplex algorithm is applied for the maximization of the likelihood functional.

Deterministic extraction of Bell pairs from a finite number of partially entangled pairs is discussed. We derive the maximum number of Bell pairs that can be obtained with probability 1 by local operations and classical communication. It is proved that the optimal deterministic concentration needs only a two-pair collective manipulation in each step, and that a collective manipulation of all entangled pairs is not necessary. Finally, this scheme reveals an entanglement measure for the deterministic concentration.

We consider the quantum analogue of the pattern-matching problem, which consists of classifying a given unknown system according to certain predefined pattern classes. We address the problem of quantum template matching in which each pattern class ${\mathcal{C}}_i$ is represented by a known quantum state $g_i$ called a template state, and our task is to find a template that optimally matches a given unknown quantum state $\mathrm{f̂}.$ We set up a precise formulation of this problem in terms of the optimal strategy for an associated quantum Bayesian inference problem. We then investigate various examples of quantum template matching for qubit systems, considering the effect of allowing a finite number of copies of the input state $\mathrm{f̂}.$ We compare quantum optimal matching strategies and semiclassical strategies to demonstrate an entanglement assisted enhancement of performance in the general quantum optimal strategy.

In a recent paper, Bennett et al. [Phys. Rev. A 59, 1070 (1999)] have shown the existence of a basis of product states of a bipartite system with manifest nonlocal properties. In particular these states cannot be completely discriminated by means of bilocal measurements. In this paper we propose an optical realization of these states and we will show that they cannot be completely discriminate by means of a global measurement using only optical linear elements, conditional transformation, and auxiliary photons.

X-ray absorption in the region of the K edge measured on potassium vapor in a heat-pipe cell is analyzed. Excitation channels leading to single $1s$ vacancy as well as double $1s4s$ and $1s3p$ vacancies are identified by decomposition of spectral features and by comparison with excitation energies from a Dirac-Fock calculation. The analysis is relevant also for the interpretation of some features in the $\mathrm{Ar}1s3p$ excitation.

Breakup of an atomic particle into several charged fragments can be achieved by multiple photoionization or by collision processes. The threshold behavior of fragmentation cross sections is generally described by power laws, ${\sigma }_{\mathrm{fr}}\sim E^{\mu },$ where E is the excess energy above the breakup threshold. We evaluate threshold indices $\mu$ for four-fragment breakup of a large number of systems not considered before. All the fragments have different charges and (finite) masses with only one restriction imposed to limit the choice of systems considered: it is presumed that two of the fragments represent identical particles. Some previously suggested threshold laws are revised.

Based on the relativistic Dirac R-matrix method, we calculate angle-dependent and momentum-transfer cross sections for electron scattering by Rb, Cs, and Fr atoms at impact energies below 3 eV. Our results for momentum transfer for $e^{-}+\mathrm{Rb}$ and Cs collisions are compared with available data from swarm experiments. We find clear evidence for a ${\mathrm{Cs}}^{-}{(}^3{F}^o)$ shape resonance at 1.528 eV, in excellent agreement with angle-dependent electron-scattering measurements. We analyze and compare the ${}^3{F}^o$ shape resonance in $e^{-}+\mathrm{Rb},$ Cs, and Fr elastic collisions.