189 research outputs found
Capillary-gravity waves: a "fixed-depth" analysis
We study the onset of the wave-resistance due to the generation of
capillary-gravity waves by a partially immersed moving object in the case where
the object is hold at a fixed immersion depth. We show that, in this case, the
wave resistance varies continuously with the velocity, in qualitative
accordance with recent experiments by Burghelea et al. (Phys. Rev. Lett. 86,
2557 (2001)).Comment: 7 pages, 3 figures, submitted to Europhysics Letter
An Atom Faucet
We have constructed and modeled a simple and efficient source of slow atoms.
From a background vapour loaded magneto-optical trap, a thin laser beam
extracts a continuous jet of cold rubidium atoms. In this setup, the extraction
column that is typical to leaking MOT systems is created without any optical
parts placed inside the vacuum chamber. For detailed analysis, we present a
simple 3D numerical simulation of the atomic motion in the presence of multiple
saturating laser fields combined with an inhomogeneous magnetic field. At a
pressure of mbar, the moderate laser power of
10 mW per beam generates a jet of flux atoms/s with a
mean velocity of 14 m/s and a divergence of mrad.Comment: Submitted to EPJD. 1 TeX file (EPJ format), 7 picture
Achieving one-dimensionality with attractive fermions
In this article we discuss the accuracy of effective one-dimensional theories
used to describe the behavior of ultracold atomic ensembles confined in quantum
wires by a harmonic trap. We derive within a fully many-body approach the
effective Hamiltonian describing this class of systems and we calculate the
beyond-mean field corrections to the energy of the ground state arising from
virtual transitions towards excited state of the confining potential. We find
that, due to the Pauli principle, effective finite-range corrections are one of
magnitude larger than effective three-body interactions.By comparing to exact
solutions of the purely 1D problem, we conclude that a 1D effective theory
provides a good description of the ground state of the system for a rather
large range of interaction parameters
Boltzmann equation simulation for a trapped Fermi gas of atoms
The dynamics of an interacting Fermi gas of atoms at sufficiently high
temperatures can be efficiently studied via a numerical simulation of the
Boltzmann equation. In this work we describe in detail the setup we used
recently to study the oscillations of two spin-polarised fermionic clouds in a
trap. We focus here on the evaluation of interparticle interactions. We compare
different ways of choosing the phase space coordinates of a pair of atoms after
a successful collision and demonstrate that the exact microscopic setup has no
influence on the macroscopic outcome
Exact vortex nucleation and cooperative vortex tunneling in dilute BECs
With the imminent advent of mesoscopic rotating BECs in the lowest Landau
level (LLL) regime, we explore LLL vortex nucleation. An exact many-body
analysis is presented in a weakly elliptical trap for up to 400 particles.
Striking non-mean field features are exposed at filling factors >>1 . Eg near
the critical rotation frequency pairs of energy levels approach each other with
exponential accuracy. A physical interpretation is provided by requantising a
mean field theory, where 1/N plays the role of Planck's constant, revealing two
vortices cooperatively tunneling between classically degenerate energy minima.
The tunnel splitting variation is described in terms of frequency, particle
number and ellipticity.Comment: 4 pages,4 figure
Counter-flow instability of a quantum mixture of two superfluids
We study the instability of a mixture of two interacting counter-flowing
superfluids. For a homogeneous system, we show that superfluid hydrodynamics
leads to the existence of a dynamical instability at a critical value of the
relative velocity . When the interspecies coupling is small the
critical value approaches the value , given by the sum of the
sound velocities of the two uncoupled superfluids, in agreement with the recent
prediction of [1] based on Landau's argument. The crucial dependence of the
critical velocity on the interspecies coupling is explicitly discussed. Our
results agree with previous predictions for weakly interacting Bose-Bose
mixtures and applies to Bose-Fermi superfluid mixtures as well. Results for the
stability of transversally trapped mixtures are also presented.Comment: 5 pages, 2 figue
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