901 research outputs found

### How do sound waves in a Bose-Einstein condensate move so fast?

Low-momentum excitations of a dilute Bose-Einstein condensate behave as
phonons and move at a finite velocity v_s. Yet the atoms making up the phonon
excitation each move very slowly; v_a = p/m --> 0. A simple "cartoon picture"
is suggested to understand this phenomenon intuitively. It implies a relation
v_s/v_a = N_ex, where N_ex is the number of excited atoms making up the phonon.
This relation does indeed follow from the standard Bogoliubov theory.Comment: 6 pages, 2 figures (.eps), LaTeX2e. More introductory discussion
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### Analog model for an expanding universe

Over the last few years numerous papers concerning analog models for gravity
have been published. It was shown that the dynamical equation of several
systems (e.g. Bose-Einstein condensates with a sink or a vortex) have the same
wave equation as light in a curved-space (e.g. black holes). In the last few
months several papers were released which deal with simulations of the
universe.
In this article the de-Sitter universe will be compared with a freely
expanding three-dimensional spherical Bose-Einstein condensate. Initially the
condensate is in a harmonic trap, which suddenly will be switched off. At the
same time a small perturbation will be injected in the center of the condensate
cloud.
The motion of the perturbation in the expanding condensate will be discussed,
and after some transformations the similarity to an expanding universe will be
shown.Comment: Presented at the 4th Australasian conference on General Relativity
and Cosmology, Monash U, Melbourne, 7-9 January 200

### Measurement-induced Squeezing of a Bose-Einstein Condensate

We discuss the dynamics of a Bose-Einstein condensate during its
nondestructive imaging. A generalized Lindblad superoperator in the condensate
master equation is used to include the effect of the measurement. A continuous
imaging with a sufficiently high laser intensity progressively drives the
quantum state of the condensate into number squeezed states. Observable
consequences of such a measurement-induced squeezing are discussed.Comment: 4 pages, 2 figures, submitted to PR

### Bose-stimulated scattering off a cold atom trap

The angle and temperature dependence of the photon scattering rate for
Bose-stimulated atom recoil transitions between occupied states is compared to
diffraction and incoherent Rayleigh scattering near the Bose-Einstein
transition for an optically thin trap in the limit of large particle number, N.
Each of these processes has a range of angles and temperatures for which it
dominates over the others by a divergent factor as N->oo.Comment: 18 pages (REVTeX), no figure

### Quantum carpet interferometry for trapped atomic Bose-Einstein condensates

We propose an ``interferometric'' scheme for Bose-Einstein condensates using
near-field diffraction. The scheme is based on the phenomenon of intermode
traces or quantum carpets; we show how it may be used in the detection of weak
forces.Comment: 4 figures. Submitted to Phys. Rev.

### Velocity of sound in a Bose-Einstein condensate in the presence of an optical lattice and transverse confinement

We study the effect of the transverse degrees of freedom on the velocity of
sound in a Bose-Einstein condensate immersed in a one-dimensional optical
lattice and radially confined by a harmonic trap. We compare the results of
full three-dimensional calculations with those of an effective 1D model based
on the equation of state of the condensate. The perfect agreement between the
two approaches is demonstrated for several optical lattice depths and
throughout the full crossover from the 1D mean-field to the Thomas Fermi regime
in the radial direction.Comment: final versio

### In-situ velocity imaging of ultracold atoms using slow--light

The optical response of a moving medium suitably driven into a slow-light
propagation regime strongly depends on its velocity. This effect can be used to
devise a novel scheme for imaging ultraslow velocity fields. The scheme turns
out to be particularly amenable to study in-situ the dynamics of collective and
topological excitations of a trapped Bose-Einstein condensate. We illustrate
the advantages of using slow-light imaging specifically for sloshing
oscillations and bent vortices in a stirred condensate

### Interferometric detection of a single vortex in a dilute Bose-Einstein condensate

Using two radio frequency pulses separated in time we perform an amplitude
division interference experiment on a rubidium Bose-Einstein condensate. The
presence of a quantized vortex, which is nucleated by stirring the condensate
with a laser beam, is revealed by a dislocation in the fringe pattern.Comment: 4 pages, 4 figure

### Non-destructive, dynamic detectors for Bose-Einstein condensates

We propose and analyze a series of non-destructive, dynamic detectors for
Bose-Einstein condensates based on photo-detectors operating at the shot noise
limit. These detectors are compatible with real time feedback to the
condensate. The signal to noise ratio of different detection schemes are
compared subject to the constraint of minimal heating due to photon absorption
and spontaneous emission. This constraint leads to different optimal operating
points for interference-based schemes. We find the somewhat counter-intuitive
result that without the presence of a cavity, interferometry causes as much
destruction as absorption for optically thin clouds. For optically thick
clouds, cavity-free interferometry is superior to absorption, but it still
cannot be made arbitrarily non-destructive . We propose a cavity-based
measurement of atomic density which can in principle be made arbitrarily
non-destructive for a given signal to noise ratio

### Detecting Super-Counter-Fluidity by Ramsey Spectroscopy

Spatially selective Ramsey spectroscopy is suggested as a method for
detecting the super-counter-fluidity of two-component atomic mixture in optical
lattice.Comment: 3pages, no figures, replaced with revised version accepted by PRA.
Discussion of the Ramsey pattern specific for topological excitations is
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