5,874 research outputs found
Cold Collision Frequency Shift in Two-Dimensional Atomic Hydrogen
We report a measurement of the cold collision frequency shift in atomic
hydrogen gas adsorbed on the surface of superfluid 4He at T<=90 mK. Using
two-photon electron and nuclear magnetic resonance in 4.6 T field we separate
the resonance line shifts due to the dipolar and exchange interactions, both
proportional to surface density sigma. We find the clock shift Delta v_c =
-1.0(1)x10^-7 Hz cm^-2 x sigma, which is about 100 times smaller than the value
predicted by the mean field theory and known scattering lengths in the 3D case.Comment: 4 pages, 3 figure
Unconventional superfluidity of fermions in Bose-Fermi mixtures
We examine two dimensional mixture of single-component fermions and dipolar
bosons. We calculate the self-enregies of the fermions in the normal state and
the Cooper pair channel by including first order vertex correction to derive a
modified Eliashberg equation. We predict appearance of superfluids with various
non-standard pairing symmetries at experimentally feasible transition
temperatures within the strong-coupling limit of the Eliashberg equation.
Excitations in these superfluids are anyonic and follow non-Abelian statistics
The transverse breathing mode of an elongated Bose-Einstein condensate
We study experimentally the transverse monopole mode of an elongated rubidium
condensate. Due to the scaling invariance of the non-linear Schr\"odinger
(Gross-Pitaevski) equation, the oscillation is monochromatic and sinusoidal at
short times, even under strong excitation. For ultra-low temperatures, the
quality factor can exceed 2000, where and
are the mode angular frequency and damping rate. This value is much
larger than any previously reported for other eigenmodes of a condensate. We
also present the temperature variation of and .Comment: 4 pages, 4 figures, submitted to PR
Decoherence due to three-body loss and its effect on the state of a Bose-Einstein condensate
A Born-Markov master equation is used to investigate the decoherence of the
state of a macroscopically occupied mode of a cold atom trap due to three-body
loss. In the large number limit only coherent states remain pure for times
longer than the decoherence time: the time it takes for just three atoms to be
lost from the trap. For large numbers of atoms (N>10^4) the decoherence time is
found to be much faster than the phase collapse time caused by intra-trap
atomic collisions
1D model for the dynamics and expansion of elongated Bose-Einstein condensates
We present a 1D effective model for the evolution of a cigar-shaped
Bose-Einstein condensate in time dependent potentials whose radial component is
harmonic. We apply this model to investigate the dynamics and expansion of
condensates in 1D optical lattices, by comparing our predictions with recent
experimental data and theoretical results. We also discuss negative-mass
effects which could be probed during the expansion of a condensate moving in an
optical lattice.Comment: RevTeX4, 8 pages, 10 figures, extended and revised versio
Thermalization of an impurity cloud in a Bose-Einstein condensate
We study the thermalization dynamics of an impurity cloud inside a
Bose-Einstein condensate at finite temperature, introducing a suitable
Boltzmann equation. Some values of the temperature and of the initial impurity
energy are considered. We find that, below the Landau critical velocity, the
macroscopic population of the initial impurity state reduces its depletion
rate. For sufficiently high velocities the opposite effect occurs. For
appropriate parameters the collisions cool the condensate. The maximum cooling
per impurity atom is obtained with multiple collisions.Comment: 4 pages 6 figure
Dynamics of two colliding Bose-Einstein condensates in an elongated magneto-static trap
We study the dynamics of two interacting Bose-Einstein condensates, by
numerically solving two coupled Gross-Pitaevskii equations at zero temperature.
We consider the case of a sudden transfer of atoms between two trapped states
with different magnetic moments: the two condensates are initially created with
the same density profile, but are trapped into different magnetic potentials,
whose minima are vertically displaced by a distance much larger than the
initial size of both condensates. Then the two condensates begin to perform
collective oscillations, undergoing a complex evolution, characterized by
collisions between the two condensates. We investigate the effects of their
mutual interaction on the center-of-mass oscillations and on the time evolution
of the aspect ratios. Our theoretical analysis provides a useful insight into
the recent experimental observations by Maddaloni et al., cond-mat/0003402.Comment: 8 pages, 7 figures, RevTe
A Closed Class of Hydrodynamical Solutions for the Collective Excitations of a Bose-Einstein Condensate
A trajectory approach is taken to the hydrodynamical treatment of collective
excitations of a Bose-Einstein condensate in a harmonic trap. The excitations
induced by linear deformations of the trap are shown to constitute a broad
class of solutions that can be fully described by a simple nonlinear matrix
equation. An exact closed-form expression is obtained for the solution
describing the mode {n=0, m=2} in a cylindrically symmetric trap, and the
calculated amplitude-dependent frequency shift shows good agreement with the
experimental results of the JILA group.Comment: RevTex, 4 pages, 1 eps figure, identical to the published versio
Dynamics of a Bose-Einstein Condensate in an Anharmonic Trap
We present a theoretical model to describe the dynamics of Bose-Einstein
condensates in anharmonic trapping potentials. To first approximation the
center-of-mass motion is separated from the internal condensate dynamics and
the problem is reduced to the well known scaling solutions for the Thomas-Fermi
radii. We discuss the validity of this approach and analyze the model for an
anharmonic waveguide geometry which was recently realized in an experiment
\cite{Ott2002c}
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