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Using an exactly soluble model for the radiative coupling of bound and autoionizing states, we explore the modification in the shape of the photoemission spectra and the total number of scattered photons (photon yield) resulting from finite interaction times. The photon yield studied as a function of the laser-field amplitude (Rabi frequency) or laser-atom detuning has a maximum. This maximum narrows and in certain circumstances shifts as the interaction time is. increased. Near the confluence of coherences the finite time spectra exhibit a rich structure; the heights and widths of the peaks, as well as their positions, are sensitively dependent on the interaction time. Moreover, the narrow central peak is accompanied by strong periodic wiggles, whose period is inversely proportional to the interaction time. The effects of laser broadening on the spectra are fully accounted for. Furthermore, the algebraic expressions for the ground-state occupation probability and the photon yield are considerably simplified from those of our previous analysis of the problem.

Above-threshold ionization photoelectron spectra are computed for an exactly solvable model. We predict that there will be no trapping or saturation of the bound–continuum transition and that the ionization rate is independent of the redistribution of the electron between the two continua. We find symmetric peaks about the ionization energy, and these peaks appear only during the ionization process.

Both, phase and amplitude fluctuations of a laser field are taken into account. A gaussian stochastic process describing the latter one is not assumed to be delta correlated. Apart from the modification of the damping constant, known before, a significant modification of the Rabi frequency is found.

We study, within a framework of the classical fields approximation, the static structure factor of a weakly interacting Bose gas at thermal equilibrium. As in a recent experiment [R. Schley et al., Phys. Rev. Lett. 111, 055301 (2013)], we find that the thermal distribution of phonons in a three-dimensional Bose gas follows the Planck distribution. On the other hand we find a disagreement between the Planck and phonon (calculated just as for the bulk gas) distributions in the case of elongated quasi-one-dimensional systems. We attribute this discrepancy to the existence of spontaneous dark solitons [i.e., thermal solitons as reported in T. Karpiuk et al., Phys. Rev. Lett. 109, 205302 (2012)] in an elongated Bose gas at thermal equilibrium. [ABSTRACT FROM AUTHOR]

A one-dimensional model of bosons with repulsive short-range interactions, solved analytically by Lieb and Liniger many years ago, predicts the existence of two branches of elementary excitations. One of them represents Bogoliubov phonons; the other, as suggested by some authors, might be related to dark solitons. On the other hand, it has been already demonstrated within the framework of the classical field approximation that a quasi-one-dimensional interacting Bose gas at equilibrium exhibits excitations which are phonons and dark solitons. By showing that for lower temperatures statistical distributions of dark solitons obtained within the classical field approximation are well represented by the distributions of quasiparticles of the second kind derived from fully quantum description, we demonstrate that type II excitations in the Lieb-Liniger model are, indeed, quantum solitons. [ABSTRACT FROM AUTHOR]

Interacting two-component Fermi gases are at the heart of our understanding of macroscopic quantum phenomena such as superconductivity. The changing nature of the interaction is expected to head to novel quantum phases. Here we study the ground state of a two-component fermionic gas in a harmonic potential with dipolar and contact interactions. Using a variational Wigner function we present the phase diagram of the system with equal but opposite values of the magnetic moment. We identify the second-order phase transition from paramagnetic to ferronematic phases. Moreover, we show the impact of the experimentally relevant magnetic field on the stability and magnetization of the system. We also investigate a two-component Fermi gas with large but almost equal values of the magnetic moment to study how the interplay between contact and dipolar interactions affects the stability properties of the mixture. To be specific we discuss experimentally relevant parameters for ultracold 161Dy. [ABSTRACT FROM AUTHOR]

We study a quasi-two-dimensional dipolar gas at finite, but ultralow, temperatures using the classical field approximation. The method, already used for a contact interacting gas, is extended here to samples with a weakly interacting long-range interatomic potential. We present statistical properties of the system for the current experiment with chromium [Millier, Billy, Henn, Kadau, Griesmaier, Jona-Lasinio, Santos, and Pfau, Phys. Rev. A 84, 053601 (2011)] and compare them with statistics for atoms with larger magnetic dipole moments. Significant enhancement of the third-order correlation function, relevant for the particle losses, is found. [ABSTRACT FROM AUTHOR]

We investigate separations of trapped balanced two-component atomic Fermi gases with repulsive contact interaction. Candidates for ground-state densities are obtained from the imaginary-time evolution of a nonlinear pseudo-Schrödinger equation in three dimensions, rather than from the cumbersome variational equations of the underlying energy density functional. With the employed hydrodynamical approach, gradient corrections to the Thomas-Fermi approximation are conveniently included and are shown to be vital for reliable density profiles. We provide critical repulsion strengths that mark the onset of phase transitions in a harmonic trap. We present transitions from identical density profiles of the two fermion species towards isotropic and anisotropic separations for various confinements, including harmonic and double-well-type traps. Our proposed method is suited for arbitrary trap geometries and can be straightforwardly extended to study dynamics in the light of ongoing experiments on degenerate Fermi gases. [ABSTRACT FROM AUTHOR]