Fidelity decay in trapped Bose-Einstein condensates

The quantum coherence of a Bose-Einstein condensate is studied using the concept of quantum fidelity (Loschmidt echo). The condensate is confined in an elongated anharmonic trap and subjected to a small random potential such as that created by a laser speckle. Numerical experiments show that the quantum fidelity stays constant until a critical time, after which it drops abruptly over a single trap oscillation period. The critical time depends logarithmically on the number of condensed atoms and on the perturbation amplitude. This behavior may be observable by measuring the interference fringes of two condensates evolving in slightly different potentials.Comment: 4 pages, to appear in Physical Review Letters, February 200

Autoresonant control of the many-electron dynamics in nonparabolic quantum wells

The optical response of nonparabolic quantum wells is dominated by a strong peak at the plasmon frequency. When the electrons reach the anharmonic regions, resonant absorption becomes inefficient. This limitation is overcome by using a chirped laser pulse in the autoresonant regime. By direct simulations using the Wigner phase-space approach, the authors prove that, with a sequence of just a few pulses, electrons can be efficiently detrapped from a nonparabolic well. For an array of multiple quantum wells, they can create and control an electronic current by suitably applying an autoresonant laser pulse and a slowly varying dc electric field.Comment: 3 page

Bose-Einstein condensation of positronium: modification of the s-wave scattering length below the critical temperature

The production of a Bose-Einstein condensate made of positronium may be feasible in the near future. Below the condensation temperature, the positronium collision process is modified by the presence of the condensate. This makes the theoretical description of the positronium kinetics at low temperature challenging. Based on the quasi-particle Bogoliubov theory, we describe the many-body particle-particle collision in a simple manner. We find that, in a good approximation, the full positronium-positronium interaction can be described by an effective scattering length. Our results are general and apply to different species of bosons. The correction to the bare scattering length is expressed in terms of a single dimensionless parameter that completely characterizes the condensate

Hˉ+\bar {\sf {H}}^{+} ion production from collisions between antiprotons and excited positronium: cross sections calculations in the framework of the GBAR experiment

see also, Corrigendum: New J. Phys. 23 (2021) 029501International audienceIn the framework of the gravitational behaviour of antihydrogen at rest (GBAR) experiment, cross sections for the successive formation of $\bar {\sf {H}}$ and $\bar {\sf {H}}^{+}$ from collisions between positronium (Ps) and antiprotons ( $\bar p$ ) have been computed in the range 0-30 keV $\bar p$ energy, using the continuum distorted wavefinal state theoretical model in its three-body and four-body formulations. The effect of the electronic correlations in $\bar {\sf {H}}^{+}$ on the total cross sections of $\bar {\sf {H}}^{+}$ production has been studied using three different wave functions for $\bar {\sf {H}}$ (the matter equivalent of $\bar {\sf {H}}^{+}$). Ps excited states up to n$_p$ = 3, as well as $\bar {\sf {H}}$ excited states up to n$_h$ = 4, have been investigated. The results suggest that the production of $\bar {\sf {H}}^{+}$ can be efficiently enhanced by using either a fraction of Ps(2p) and a 2 keV ($\bar p$) beam or a fraction Ps(3d) and antiprotons with kinetic energy below 1 ke

Loschmidt echo in a system of interacting electrons

We study the Loschmidt echo for a system of electrons interacting through mean-field Coulomb forces. The electron gas is modeled by a self-consistent set of hydrodynamic equations. It is observed that the quantum fidelity drops abruptly after a time that is proportional to the logarithm of the perturbation amplitude. The fidelity drop is related to the breakdown of the symmetry properties of the wave function

The late winter diets of barren-ground caribou in North-Central Canada

Rumen samples from 104 barren-ground caribou (Rangifer tarandus groenlandicus) collected in March 1980 and 1981 at 18 sites on the winter range in south-central Northwest Territories (NWT) and northern Saskatchewan were examined microscopically for relative occurrence of plant fragments. The composition of plant fragments in the rumens of calves did not differ from that in older caribou. Samples were homogeneous within sites and among them. Therefore we analyzed composite samples for each site and then pooled the data. Terricolous fruticose and foliose lichens averaged 68.5 ± 1.5% (SE) ot tallied fragments at all 18 sites, followed by conifer needles (11.9 ± 1.2%), green leaves of Vactinium spp., Ledum spp., and other shrubs and iorbs (5.6 ± 0.6%), twigs and bark (5.5 ± 0.4%), bryophytes (4.9 ± 0.6%) and 3.6% unidentified. The lichen component consisted of 8.4 ± 1.5% Stereocaulon spp., 46.9 ± 2.6% other fruticose lichens (largely Cladina spp., Cladonia spp., and Cetraria spp.), and 13.2 ± 1.5% foliose lichens (largely Peltigera spp.). A comparison of rumen contents with the average relative abundance of plants found in feeding craters at 13 sites suggests that use of plant species was not always proportionate to their occurrence

Fragmentation Phase Transition in Atomic Clusters II - Coulomb Explosion of Metal Clusters -

We discuss the role and the treatment of polarization effects in many-body systems of charged conducting clusters and apply this to the statistical fragmentation of Na-clusters. We see a first order microcanonical phase transition in the fragmentation of $Na^{Z+}_{70}$ for Z=0 to 8. We can distinguish two fragmentation phases, namely evaporation of large particles from a large residue and a complete decay into small fragments only. Charging the cluster shifts the transition to lower excitation energies and forces the transition to disappear for charges higher than Z=8. At very high charges the fragmentation phase transition no longer occurs because the cluster Coulomb-explodes into small fragments even at excitation energy $\epsilon^* = 0$.Comment: 19 text pages +18 *.eps figures, my e-mail adress: [email protected] submitted to Z. Phys.

Ultrafast Magnetization Dynamics in Diluted Magnetic Semiconductors

We present a dynamical model that successfully explains the observed time evolution of the magnetization in diluted magnetic semiconductor quantum wells after weak laser excitation. Based on the pseudo-fermion formalism and a second order many-particle expansion of the exact p-d exchange interaction, our approach goes beyond the usual mean-field approximation. It includes both the sub-picosecond demagnetization dynamics and the slower relaxation processes which restore the initial ferromagnetic order in a nanosecond time scale. In agreement with experimental results, our numerical simulations show that, depending on the value of the initial lattice temperature, a subsequent enhancement of the total magnetization may be observed within a time scale of few hundreds of picoseconds.Comment: Submitted to PR

H-+ ion production from collisions between antiprotons and excited positronium: cross sections calculations in the framework of the GBAR experiment:

In the framework of the gravitational behaviour of antihydrogen at rest (GBAR) experiment, cross sections for the successive formation of (p) over bar and H-+ from collisions between positronium (Ps) and antiprotons ((p) over bar) have been computed in the range 0-30 keV (p) over bar energy, using the continuum distorted wave-final state theoretical model in its three-body and four-body formulations. The effect of the electronic correlations in H-+ on the total cross sections of H-+ production has been studied using three different wave functions for H- (the matter equivalent of H-+). Ps excited states up to n(p) = 3, as well as H- excited states up to n(h) = 4, have been investigated. The results suggest that the production of H-+ can be efficiently enhanced by using either a fraction of Ps(2p) and a 2 keV ((p) over bar) beam or a fraction Ps(3d) and antiprotons with kinetic energy below 1 keV