9 research outputs found
A single measurement of a quantum many-body system of bosons
Here I propose an approximate way of simulating the outcomes of a
single-experiment density measurement that is performed on a state of N bosons.
The approximation is accurate if occupation of single-particle modes is
macroscopic.Comment: 4 pages, no figure
Mean field loops versus quantum anti-crossing nets in trapped Bose-Einstein condensates
We study a Bose-Einstein condensate trapped in an asymmetric double well
potential. Solutions of the time-independent Gross-Pitaevskii equation reveal
intrinsic loops in the energy (or chemical potential) level behavior when the
shape of the potential is varied. We investigate the corresponding behavior of
the quantum (many-body) energy levels. Applying the two-mode approximation to
the bosonic field operators, we show that the quantum energy levels create an
anti-crossing net inside the region bounded by the loop of the mean field
solution.Comment: 4 pages, 6 figures, version accepted for publication in European
Physical Journal
Quantum Chaotic Environments, The Butterfly Effect, And Decoherence
We investigate the sensitivity of quantum systems that are chaotic in a
classical limit, to small perturbations of their equations of motion. This
sensitivity, originally studied in the context of defining quantum chaos, is
relevant to decoherence in situations when the environment has a chaotic
classical counterpart.Comment: 4 pages, 3 figure
Quantum Depletion of an Excited Condensate
We analyze greying of the dark soliton in a Bose-Einstein condensate in the
limit of weak interaction between atoms. The condensate initially prepared in
the excited dark soliton state is loosing atoms because of spontaneous quantum
depletion. These atoms are depleted from the soliton state into single particle
states with nonzero density in the notch of the soliton. As a result the image
of the soliton is losing contrast. This quantum depletion mechanism is
efficient even at zero temperature when a thermal cloud is absent.Comment: 4 pages; version to appear in Phys.Rev.A; change in the title plus a
number of small changes in the tex
Images of the Dark Soliton in a Depleted Condensate
The dark soliton created in a Bose-Einstein condensate becomes grey in course
of time evolution because its notch fills up with depleted atoms. This is the
result of quantum mechanical calculations which describes output of many
experimental repetitions of creation of the stationary soliton, and its time
evolution terminated by a destructive density measurement. However, such a
description is not suitable to predict the outcome of a single realization of
the experiment were two extreme scenarios and many combinations thereof are
possible: one will see (1) a displaced dark soliton without any atoms in the
notch, but with a randomly displaced position, or (2) a grey soliton with a
fixed position, but a random number of atoms filling its notch. In either case
the average over many realizations will reproduce the mentioned quantum
mechanical result. In this paper we use N-particle wavefunctions, which follow
from the number-conserving Bogoliubov theory, to settle this issue.Comment: 8 pages, 6 figures, references added in version accepted for
publication in J. Phys.
Simple method for excitation of a Bose-Einstein condensate
An appropriate, time-dependent modification of the trapping potential may be
sufficient to create effectively collective excitations in a cold atom
Bose-Einstein condensate. The proposed method is complementary to earlier
suggestions and should allow the creation of both dark solitons and vortices.Comment: 8 pages, 7 figures, version accepted for publication in Phys. Rev.
A method for collective excitation of Bose-Einstein condensate
It is shown that by an appropriate modification of the trapping potential one
may create collective excitation in cold atom Bose-Einstein condensate. The
proposed method is complementary to earlier suggestions. It seems to be
feasible experimentally --- it requires only a proper change in time of the
potential in atomic traps, as realized in laboratories already.Comment: 4 pages, 4 figures; major revision, several references added,
interacting particles case adde
Breakdown of correspondence in chaotic systems: Ehrenfest versus localization times
Breakdown of quantum-classical correspondence is studied on an experimentally
realizable example of one-dimensional periodically driven system. Two relevant
time scales are identified in this system: the short Ehrenfest time t_h and the
typically much longer localization time scale T_L. It is shown that
surprisingly weak modification of the Hamiltonian may eliminate the more
dramatic symptoms of localization without effecting the more subtle but
ubiquitous and rapid loss of correspondence at t_h.Comment: 4 pages, 5 figures, replaced with a version submitted to PR