Using a semiclassical rescattering model, we have investigated the photoelectron spectra and angular distributions of the single and double ionization of helium in an intense ultrashort laser pulse. Through analyzing the spectrum structure we find that the photoelectrons emitted via double ionization are hotter than that via single ionization. Our calculations also reveal a significant correlation in the angular distributions of the two photoelectrons. These results have been compared with recent experiments.

We present a description of the behavior of a superfluid gas of fermions in the presence of a Feshbach resonance over the complete range of magnetic field detunings. Starting from a resonance Hamiltonian, we exploit a functional method to describe the continuous behavior from Bardeen-Cooper-Schrieffer to Bose-Einstein condensation type superfluidity. Our results show an ability for a resonance system to exhibit a high critical temperature comparable to the Fermi temperature. The results are derived in a manner that is shown to be consistent with the underlying microscopic scattering physics.

We determine the quantitative effect, in the maximum number of particles and other static observables, due to small anharmonic terms added to the confining potential of an atomic condensed system with negative two-body interaction. As an example of how a cubic or quartic anharmonic term can affect the maximum number of particles, we consider the trap parameters and the results given by Roberts et al. [Phys. Rev. Lett. $86,$ 4211 (2001)]. However, this study can be easily transferred to other trap geometries to estimate anharmonic effects.

Dynamic response of the $F=2\mathrm{}$ spinor Bose-Einstein condensate (BEC) under the influence of external magnetic fields is studied. A general formula is given for the oscillation period to describe population transfer from the initial polar state to other spin states. We show that when the frequency and the reduced amplitude of the longitudinal magnetic field are related in a specific manner, the population of the initial spin-0 state will be dynamically localized during time evolution. The effects of external noise and nonlinear spin-exchange interaction on the dynamics of the spinor BEC are studied. We show that while the external noise may eventually destroy the Rabi oscillations and dynamic spin localization, these coherent phenomena are robust against the nonlinear atomic interaction.

We present the tomographic reconstruction of the quantum state of the electromagnetic field emitted by an amplitude-squeezed semiconductor laser. The analysis of the field quadratures is performed by means of self-homodyning, where a frequency-dependent dephasing is accomplished by a Fabry-Pérot resonator. The Wigner function obtained clearly shows the nonclassical properties of the field.

The spectrum of quantum fluctuations in phase quadratures of resonance fluorescence of a three-level V-type atom driven by a coherent field is investigated. We find that quantum interference between two decay channels of the atom can greatly modify the spectrum. We show that for weak excitation, quantum interference can greatly enhance squeezing and change the phase quadrature in which the maximum squeezing occurs. We also show that for strong and far-off-resonance excitation two deeply squeezing peaks appear at the Rabi sideband frequencies and quantum interference broadens the squeezing peaks.

We discuss how the phase distribution of a Bose-Einstein condensate in an optical lattice may be measured directly using existing experimental techniques. We also demonstrate how a modification of this scheme may be able to resolve states, that are close to the Mott insulator state, much more accurately than present methods. This may be of interest for analyzing the quantum state of condensates in recent experiments.

In a close form without referring the time-dependent Hamiltonian to the total system, a consistent approach for quantum measurement is proposed based on Zurek’s triple model of quantum decoherence [W. Zurek, Phys. Rev. D 24, 1516 (1981)]. An exactly solvable model based on the intracavity system is dealt with in detail to demonstrate the central idea in our approach: by peeling off one collective variable of the measuring apparatus from its many degrees of freedom, as the pointer of the apparatus, the collective variable decouples with the internal environment formed by the effective internal variables, but still interacts with the measured system to form a triple entanglement among the measured system, the pointer, and the internal environment. As another mechanism to cause decoherence, the uncertainty of relative phase and its many-particle amplification can be summed up to an ideal entanglement or a Shmidt decomposition with respect to the preferred basis.

We analyze the dissipative quantum tunneling in the Caldeira-Leggett model by the nonperturbative renormalization-group method. We classify the dissipation effects by introducing the notion of effective cutoffs. We calculate the localization susceptibility to evaluate the critical dissipation for the quantum-classical transition. Our results are consistent with previous semiclassical arguments, but give considerably larger critical dissipation.

Exploiting an approach similar to the R-matrix theory, the diffusion Monte Carlo method is employed to compute phase shifts and threshold cross sections for the elastic scattering of positronium off light atoms. We briefly review the main ideas behind the use of quantum Monte Carlo techniques in scattering problems and, as applications, we present results for Ps-H and Ps-He. We find scattering lengths of 4.375(34) and 2.228(50) a.u. for the singlet and the triplet states of Ps-H, and of 1.4046(6) a.u. for Ps-He. A discussion of the agreement with other recent estimates for the same quantities is included. In particular, the scattering length for the Ps-H singlet agrees within $1\%$ with the stochastic variational minimization (SVM) estimate by Ivanov, Varga, and Mitroy [Phys. Rev. A $65,$ 32703 (2002)] and the R-matrix one by Blackwood, McAlinden, and Walter [Phys. Rev. A $65,$ 32517 (2002)]. The Ps-H triplet scattering length, which still shows good agreement $\mathrm{}(1\%)\mathrm{}$ with the SVM one, appears to be $10\%$ larger than the R-matrix value. As far as Ps-He is concerned, the calculation has been performed in a fully many-body framework. Comparison of the diffusion Monte Carlo scattering length with other estimates allows us to qualitatively and quantitatively assess the degree of approximation involved in other approaches.

Elastic scattering cross sections of 22.1-keV x rays by the elements Ti, V, Fe, Ni, Cu, Zn, Zr, Nb, Mo, Pd, Cd, In, Sn, Sm, Gd, Dy, Er, Yb, Au, and Pb have been measured at 90° with an overall error of 8–10 %. The 22.1-keV x rays were obtained from a Ag foil used as a secondary target in an x-ray fluorescence setup. Experimental cross sections have been compared with the nonrelativistic form factors (NFF), relativistic form factors, modified relativistic form factor (MRFF), relativistic form factor with anomalous scattering correction (RFFASF), modified relativistic form factor with anomalous scattering correction (MRFFASF), and the S matrix calculations. For low Z elements, experimental values are better represented by S matrix, RFFASF, and MRFFASF. For the elements Nb, Mo, and Pd whose K shell binding energies are very close to the exciting energy, the data are higher than all of the theoretical predictions. For higher Z elements, NFF and MRFF give a better agreement with the present data.

A fast and low power method is proposed and simulated for achieving substantial intramolecular dynamic nuclear polarization, as high as 50% for protons and 17% for deuterons, by means of simultaneous nuclear and allowed electronic magnetic resonance transitions.

We study the cavity-induced cooling of the center-of-mass motion of a transversally coherently pumped atom moving along the axis of a high-$Q$ multimode cavity. Including spontaneous emission and quantum fluctuations of the cavity field, we analytically calculate the linear friction and the diffusion coefficients. Efficient cavity-induced motional damping leads to steady-state temperatures well below the Doppler limit and lower than for an equivalent setup with direct cavity field pumping. The cooling process is strongly enhanced in the case of a multimode field, yielding a significantly lower temperature and a small number of spontaneous emissions per cooling time, which can even drop below 1.

Nonlinear coherent modes are the collective states of trapped Bose atoms, corresponding to different energy levels. These modes can be created starting from the ground-state condensate that can be excited by means of a resonant alternating field. A thorough theory for the resonant excitation of the coherent modes is presented. The necessary and sufficient conditions for the feasibility of this process are found. Temporal behavior of fractional populations and of relative phases exhibits dynamic critical phenomena on a critical line of the parametric manifold. The origin of these critical phenomena is elucidated by analyzing the structure of the phase space. An atomic cloud, containing the coherent modes, possesses several interesting features, such as interference patterns, interference current, spin squeezing, and massive entanglement. The developed theory suggests a generalization of resonant effects in optics to nonlinear systems of Bose-condensed atoms.

We investigate the dynamics of Bose-Einstein condensate bright solitons made of alkali-metal atoms with negative scattering length and under harmonic confinement in the transverse direction. Contrary to the one-dimensional (1D) case, the 3D bright soliton exists only below a critical attractive interaction that depends on the extent of confinement. Such a behavior is also found in multisoliton condensates with box boundary conditions. We obtain numerical and analytical estimates of the critical strength beyond which the solitons do not exist. By using an effective 1D nonpolynomial nonlinear Schrödinger equation, which accurately takes into account the transverse dynamics of cigarlike condensates, we numerically simulate the dynamics of the “soliton train” reported in a recent experiment [Nature (London) 417, 150 (2002)]. Then, analyzing the macroscopic quantum tunneling of the bright soliton on a Gaussian barrier, we find that its interference in the tunneling region is strongly suppressed with respect to nonsolitonic case; moreover, the tunneling through a barrier breaks the shape invariance of the matter wave. Finally, we show that the collapse of the soliton is induced by the scattering on the barrier or by the collision with another matter wave when the density reaches a critical value, for which we derive an accurate analytical formula.

The propagation of a band-limited light pulse through an atomic medium under a Λ excitation scheme is theoretically analyzed in this paper. We consider in particular the case where the light pulse is detected through the coherent microwave emission of the atomic ensemble (coherent population trapping maser). Significant differences are predicted with respect to the more usual optical detection (electromagnetically induced transparency signal) and found in agreement with the experimental results. Higher signal delays were observed in the microwave emission than in the optical signal with an equivalent group velocity of 6 m/s as well as highly superluminal propagation under a proper modulation scheme. The experiments were performed with a thermal ${}^{87}\mathrm{Rb}$ vapor in buffer gas.

The total cross sections for radiative charge transfer in ${\mathrm{H}}^{+}+\mathrm{Na}\mathrm{}\left(3s\right)\mathrm{}\to \mathrm{H}\mathrm{}\left(1s\right)+{\mathrm{Na}}^{+}$ and ${\mathrm{H}}^{+}+\mathrm{K}\mathrm{}\left(4s\right)\mathrm{}\to \mathrm{H}\mathrm{}\left(1s\right)+{\mathrm{K}}^{+}$ collisions at energies below 8 eV have been calculated using an optical potential method. The relevant molecular states and molecular potentials were obtained by full configuration interaction calculations using pseudopotentials for the ion cores of Na and K. From the calculated charge-transfer cross sections, the radiative charge-transfer rate coefficients were obtained for temperatures below 10 000 K. The rate coefficients for both systems are found to have broad maxima around 20 K with values of the order of ${10}^{-12}{\mathrm{cm}}^3{\mathrm{s}}^{-1}.$ The rate coefficient for $\mathrm{Na}+{\mathrm{H}}^{+}$ remains nearly constant below the maximum, but that for $\mathrm{K}+{\mathrm{H}}^{+}$ decreases at lower temperatures. Both the rate coefficients and the differences between them decrease as the temperature increases beyond 20 K.

Vacuum solutions of Maxwell equations in a rigidly rotating frame are derived in order to specify how the rotating observer would measure passing electromagnetic radiation. Approximate analytic solutions are found for the regions close to the light cylinder and the rotation axis, respectively. It is found that despite the singularity of the reference frame at the light cylinder, there is a subclass of solutions, which is regular at this distance. The results and their possible astrophysical applications are discussed.

A quantum processor is a device with a data register and a program register. The input to the program register determines the operation, which is a completely positive linear map, that will be performed on the state in the data register. We develop a mathematical description for these devices, and apply it to several different examples of processors. The problem of finding a processor that will be able to implement a given set of mappings is also examined, and it is shown that, while it is possible to design a finite processor to realize the phase-damping channel, it is not possible to do so for the amplitude-damping channel.

The one-loop Lamb shift is calculated for the ground state of the neutral alkali metals lithium through francium. The method used is Furry representation QED, defined in terms of a variety of local potentials. The method is exact in binding corrections, but is potential dependent. Significant differences with known Lamb shift results for lithium are found, and it is shown that large corrections result from a partial set of screening corrections. Comparison with other calculations is made.