70 research outputs found
Observation of Lasing Mediated by Collective Atomic Recoil
We observe the buildup of a frequency-shifted reverse light field in a
unidirectionally pumped high- optical ring cavity serving as a dipole trap
for cold atoms. This effect is enhanced and a steady state is reached, if via
an optical molasses an additional friction force is applied to the atoms. We
observe the displacement of the atoms accelerated by momentum transfer in the
backscattering process and interpret our observations in terms of the
collective atomic recoil laser. Numerical simulations are in good agreement
with the experimental results.Comment: 4 pages, 3 figure
Symmetry Aspects in Nonrelativistic Multi-Scalar Field Models and Application to a Coupled Two-Species Dilute Bose Gas
We discuss unusual aspects of symmetry that can happen due to entropic
effects in the context of multi-scalar field theories at finite temperature. We
present their consequences, in special, for the case of nonrelativistic models
of hard core spheres. We show that for nonrelativistic models phenomena like
inverse symmetry breaking and symmetry non-restoration cannot take place, but a
reentrant phase at high temperatures is shown to be possible for some region of
parameters. We then develop a model of interest in studies of Bose-Einstein
condensation in dilute atomic gases and discuss about its phase transition
patterns. In this application to a Bose-Einstein condensation model, however,
no reentrant phases are found.Comment: 8 pages, 1 eps figure, IOP style. Based on a talk given by R. O.
Ramos at the QFEXT05 workshop, Barcelona, Spain, September 5-9, 2005. One
reference was update
RF spectroscopy in a resonant RF-dressed trap
We study the spectroscopy of atoms dressed by a resonant radiofrequency (RF)
field inside an inhomogeneous magnetic field and confined in the resulting
adiabatic potential. The spectroscopic probe is a second, weak, RF field. The
observed line shape is related to the temperature of the trapped cloud. We
demonstrate evaporative cooling of the RF-dressed atoms by sweeping the
frequency of the second RF field around the Rabi frequency of the dressing
field.Comment: 7 figures, 8 pages; to appear in J. Phys.
Effective Potential and Thermodynamics for a Coupled Two-Field Bose Gas Model
We study the thermodynamics of a two-species homogeneous and dilute Bose gas
that is self-interacting and quadratically coupled to each other. We make use
of field theoretical functional integral techniques and evaluate the one-loop
finite temperature effective potential for this system considering the
resummation of the leading order temperature dependent as well as infrared
contributions. The symmetry breaking pattern associated to the model is then
studied by considering different values of self and inter-species couplings. We
pay special attention to the eventual appearance of reentrant phases and/or
shifts in the observed critical temperatures as compared to the monoatomic
(one-field Bose) case.Comment: 21 pages, 4 eps figure
STIRAP transport of Bose-Einstein condensate in triple-well trap
The irreversible transport of multi-component Bose-Einstein condensate (BEC)
is investigated within the Stimulated Adiabatic Raman Passage (STIRAP) scheme.
A general formalism for a single BEC in M-well trap is derived and analogy
between multi-photon and tunneling processes is demonstrated. STIRAP transport
of BEC in a cyclic triple-well trap is explored for various values of detuning
and interaction between BEC atoms. It is shown that STIRAP provides a complete
population transfer at zero detuning and interaction and persists at their
modest values. The detuning is found not to be obligatory. The possibility of
non-adiabatic transport with intuitive order of couplings is demonstrated.
Evolution of the condensate phases and generation of dynamical and geometric
phases are inspected. It is shown that STIRAP allows to generate the
unconventional geometrical phase which is now of a keen interest in quantum
computing.Comment: 9 pages, 6 figures. To be published in Laser Physics (v. 19, n.4,
2009
The Adiabatic Transport of Bose-Einstein Condensates in a Double-Well Trap: Case a Small Nonlinearity
A complete adiabatic transport of Bose-Einstein condensate in a double-well
trap is investigated within the Landau-Zener (LZ) and Gaussian Landau-Zener
(GLZ) schemes for the case of a small nonlinearity, when the atomic interaction
is weaker than the coupling. The schemes use the constant (LZ) and
time-dependent Gaussian (GLZ) couplings. The mean field calculations show that
LZ and GLZ suggest essentially different transport dynamics. Significant
deviations from the case of a strong coupling are discussed.Comment: 6 pages, 3 figures, to be published in Laser Physic
Strongly enhanced inelastic collisions in a Bose-Einstein condensate near Feshbach resonances
The properties of Bose-Einstein condensed gases can be strongly altered by
tuning the external magnetic field near a Feshbach resonance. Feshbach
resonances affect elastic collisions and lead to the observed modification of
the scattering length. However, as we report here, this is accompanied by a
strong increase in the rate of inelastic collisions. The observed three-body
loss rate in a sodium Bose-Einstein condensation increased when the scattering
length was tuned to both larger or smaller values than the off-resonant value.
This observation and the maximum measured increase of the loss rate by several
orders of magnitude are not accounted for by theoretical treatments. The strong
losses impose severe limitations for using Feshbach resonances to tune the
properties of Bose-Einstein condensates. A new Feshbach resonance in sodium at
1195 G was observed.Comment: 4 pages, 3 figure
Effect of anharmonicities in the critical number of trapped condensed atoms with attractive two-body interaction
We determine the quantitative effect, in the maximum number of particles and
other static observables, due to small anharmonic terms added to the confining
potential of an atomic condensed system with negative two-body interaction. As
an example of how a cubic or quartic anharmonic term can affect the maximum
number of particles, we consider the trap parameters and the results given by
Roberts et al. [Phys. Rev. Lett. 86, 4211 (2001)]. However, this study can be
easily transferred to other trap geometries to estimate anharmonic effects.Comment: Total of 5 pages, 3 figures and 1 table. To appear in Phys. Rev.
Coherent dynamics of Bose-Einstein condensates in high-finesse optical cavities
We study the mutual interaction of a Bose-Einstein condensed gas with a
single mode of a high-finesse optical cavity. We show how the cavity
transmission reflects condensate properties and calculate the self-consistent
intra-cavity light field and condensate evolution. Solving the coupled
condensate-cavity equations we find that while falling through the cavity, the
condensate is adiabatically transfered into the ground state of the periodic
optical potential. This allows time dependent non-destructive measurements on
Bose-Einstein condensates with intriguing prospects for subsequent controlled
manipulation.Comment: 5 pages, 5 figures; revised version: added reference
Exploring a quantum degenerate gas of fermionic atoms
We predict novel phenomena in the behavior of an ultra- cold, trapped gas of
fermionic atoms. We find that quantum statistics radically changes the
collisional properties, spatial profile, and off-resonant light scattering
properties of the atomic fermion system, and we suggest how these effects can
be observed.Comment: 5 pages, 3 figure
- …