158 research outputs found
Quantum Zeno suppression of three-body losses in Bose-Einstein condensates
We study the possibility of suppressing three-body losses in atomic
Bose-Einstein condensates via the quantum Zeno effect, which means the delay of
quantum evolution by frequent measurements. It turns out that this requires
very fast measurements with the rate being determined by the spatial structure
of the three-body form factor, i.e., the point interaction approximation
is not adequate. Since the molecular binding
energy provides a natural limit for the measurement rate, this
suppression mechanism can only work if the form factor possesses certain
special properties.Comment: 4 pages, 2 figure
Quantum simulation of cosmic inflation in two-component Bose-Einstein condensates
Generalizing the one-component case, we demonstrate that the propagation of
sound waves in two-component Bose-Einstein condensates can also be described in
terms of effective sonic geometries under appropriate conditions. In comparison
with the one-component case, the two-component setup offers more flexibility
and several advantages. In view of these advantages, we propose an experiment
in which the evolution of the inflaton field, and thereby the generation of
density quantum fluctuations in the very early stages of our universe during
inflation, can be simulated, realizing a {\em quantum simulation via analogue
gravity models}.Comment: 8 pages of RevTex4, 1 figure; added explanatory material, to appear
in Physical Review
Quantum radiation by electrons in lasers and the Unruh effect
In addition to the Larmor radiation known from classical electrodynamics,
electrons in a laser field may emit pairs of entangled photons -- which is a
pure quantum effect. We investigate this quantum effect and discuss why it is
suppressed in comparison with the classical Larmor radiation (which is just
Thomson backscattering of the laser photons). Further, we provide an intuitive
explanation of this process (in a simplified setting) in terms of the Unruh
effect.Comment: 4 pages, 3 figure
Propagation of quantum correlations after a quench in the Mott-insulator regime of the Bose-Hubbard model
We study a quantum quench in the Bose-Hubbard model where the tunneling rate
is suddenly switched from zero to a finite value in the Mott regime. In
order to solve the many-body quantum dynamics far from equlibrium, we consider
the reduced density matrices for a finite number (one, two, three, etc.) of
lattice sites and split them up into on-site density operators, i.e., the mean
field, plus two-point and three-point correlations etc. Neglecting three-point
and higher correlations, we are able to numerically simulate the time-evolution
of the few-site density matrices and the two-point quantum correlations (e.g.,
their effective light-cone structure) for a comparably large number of lattice sites
On the feasibility of a nuclear exciton laser
Nuclear excitons known from M\"ossbauer spectroscopy describe coherent
excitations of a large number of nuclei -- analogous to Dicke states (or Dicke
super-radiance) in quantum optics. In this paper, we study the possibility of
constructing a laser based on these coherent excitations. In contrast to the
free electron laser (in its usual design), such a device would be based on
stimulated emission and thus might offer certain advantages, e.g., regarding
energy-momentum accuracy. Unfortunately, inserting realistic parameters, the
window of operability is probably not open (yet) to present-day technology --
but our design should be feasible in the UV regime, for example.Comment: 7 pages RevTeX, 4 figure
Emergence of coherence in the Mott--superfluid quench of the Bose-Hubbard model
We study the quench from the Mott to the superfluid phase in the Bose-Hubbard
model and investigate the spatial-temporal growth of phase coherence, i.e.,
phase locking between initially uncorrelated sites. To this end, we establish a
hierarchy of correlations via a controlled expansion into inverse powers of the
coordination number . It turns out that the off-diagonal long-range order
spreads with a constant propagation speed, forming local condensate patches,
whereas the phase correlator follows a diffusion-like growth rate.Comment: 4 page
O(N) symmetry-breaking quantum quench: Topological defects versus quasiparticles
We present an analytical derivation of the winding number counting
topological defects created by an O(N) symmetry-breaking quantum quench in N
spatial dimensions. Our approach is universal in the sense that we do not
employ any approximations apart from the large- limit. The final result is
nonperturbative in N, i.e., it cannot be obtained by %the usual an expansion in
1/N, and we obtain far less topological defects than quasiparticle excitations,
in sharp distinction to previous, low-dimensional investigations.Comment: 6 pages of RevTex4-1, 1 figure; to be published in Physical Review
Tunneling-induced damping of phase coherence revivals in deep optical lattices
We consider phase coherence collapse and revival in deep optical lattices,
and calculate within the Bose-Hubbard model the revival amplitude damping
incurred by a finite tunneling coupling of the lattice wells (after sweeping
from the superfluid to the Mott phase). Deriving scaling laws for the
corresponding decay of first-order coherence revival in terms of filling
factor, final lattice depth, and number of tunneling coupling partners, we
estimate whether revival-damping related to tunneling between sites can be or
even has already been observed in experiment.Comment: 4+epsilon pages of RevTex4; Rapid Communication in Physical Review
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