2,764 research outputs found
Monte Carlo Study of the Inflation-Deflation Transition in a Fluid Membrane
We study the conformation and scaling properties of a self-avoiding fluid
membrane, subject to an osmotic pressure , by means of Monte Carlo
simulations. Using finite size scaling methods in combination with a histogram
reweighting techniques we find that the surface undergoes an abrupt
conformational transition at a critical pressure , from low pressure
deflated configurations with a branched polymer characteristics to a high
pressure inflated phase, in agreement with previous findings
\cite{gompper,baum}. The transition pressure scales with the system
size as , with . Below
the enclosed volume scales as , in accordance with the
self-avoiding branched polymer structure, and for our data
are consistent with the finite size scaling form ,
where .
Also the finite size scaling behavior of the radii of gyration and the
compressibility moduli are obtained. Some of the observed exponents and the
mechanism behind the conformational collapse are interpreted in terms of a
Flory theory.Comment: 20 pages + postscript-file, Latex + Postscript, IFA Report No. 94/1
Pulsed pumping of a Bose-Einstein condensate
In this work, we examine a system for coherent transfer of atoms into a
Bose-Einstein condensate. We utilize two spatially separate Bose-Einstein
condensates in different hyperfine ground states held in the same dc magnetic
trap. By means of a pulsed transfer of atoms, we are able to show a clear
resonance in the timing of the transfer, both in temperature and number, from
which we draw conclusions about the underlying physical process. The results
are discussed in the context of the recently demonstrated pumped atom laser.Comment: 5 pages, 5 figures, published in Physical Review
Achieving peak brightness in an atom laser
In this paper we present experimental results and theory on the first
continuous (long pulse) Raman atom laser. The brightness that can be achieved
with this system is three orders of magnitude greater than has been previously
demonstrated in any other continuously outcoupled atom laser. In addition, the
energy linewidth of a continuous atom laser can be made arbitrarily narrow
compared to the mean field energy of a trapped condensate. We analyze the flux
and brightness of the atom laser with an analytic model that shows excellent
agreement with experiment with no adjustable parameters.Comment: 4 pages, 4 black and white figures, submitted to Physical Revie
Approaching the Heisenberg limit in an atom laser
We present experimental and theoretical results showing the improved beam quality and reduced divergence
of an atom laser produced by an optical Raman transition, compared to one produced by an rf transition. We
show that Raman outcoupling can eliminate the diverging lens effect that the condensate has on the outcoupled
atoms. This substantially improves the beam quality of the atom laser, and the improvement may be greater
than a factor of 10 for experiments with tight trapping potentials. We show that Raman outcoupling can
produce atom lasers whose quality is only limited by the wave function shape of the condensate that produces
them, typically a factor of 1.3 above the Heisenberg limit
Observation of transverse interference fringes on an atom laser beam
Using the unique detection properties offered by metastable
helium atoms we have produced high resolution images of the transverse
spatial profiles of an atom laser beam. We observe fringes on the beam,
resulting from quantum mechanical interference between atoms that start
from rest at different transverse locations within the outcoupling surface
and end up at a later time with different velocities at the same transverse
position. Numerical simulations in the low output-coupling limit give good
quantitative agreement with our experimental data
Investigation and comparison of multi-state and two-state atom laser output-couplers
We investigate the spatial structure and temporal dynamics created in a
Bose-Einstein condensate (BEC) by radio-frequency (RF) atom laser
output-couplers using a one-dimensional mean-field model. We compare the
behavior of a `pure' two-state atom laser to the multi-level systems
demonstrated in laboratories. In particular, we investigate the peak
homogeneous output flux, classical fluctuations in the beam and the onset of a
bound state which shuts down the atom laser output.Comment: 9 pages, 8 figure
A detector for continuous measurement of ultra-cold atoms in real time
We present the first detector capable of recording high-bandwidth real time
atom number density measurements of a Bose Einstein condensate. Based on a
two-color Mach-Zehnder interferometer, our detector has a response time that is
six orders of magnitude faster than current detectors based on CCD cameras
while still operating at the shot-noise limit. With this minimally destructive
system it may be possible to implement feedback to stabilize a Bose-Einstein
condensate or an atom laser.Comment: 3 pages, 3 figures, submitted to optics letter
A multibeam atom laser: coherent atom beam splitting from a single far detuned laser
We report the experimental realisation of a multibeam atom laser. A single
continuous atom laser is outcoupled from a Bose-Einstein condensate (BEC) via
an optical Raman transition. The atom laser is subsequently split into up to
five atomic beams with slightly different momenta, resulting in multiple,
nearly co-propagating, coherent beams which could be of use in interferometric
experiments. The splitting process itself is a novel realization of Bragg
diffraction, driven by each of the optical Raman laser beams independently.
This presents a significantly simpler implementation of an atomic beam
splitter, one of the main elements of coherent atom optics
Nearly-zero transmission through periodically modulated ultrathin metal films
Transmission of light through an optically ultrathin metal film with a
thickness comparable to its skin depth is significant. We demonstrate
experimentally nearly-zero transmission of light through a film periodically
modulated by a one-dimensional array of subwavelength slits. The suppressed
optical transmission is due to the excitation of surface plasmon polaritons and
the zero-transmission phenomenon is strongly dependent on the polarization of
the incident wave.Comment: accepted by AP
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