2,734 research outputs found
Evolution of a collapsing and exploding Bose-Einstein condensate in different trap symmetries
Based on the time-dependent Gross-Pitaevskii equation we study the evolution
of a collapsing and exploding Bose-Einstein condensate in different trap
symmetries to see the effect of confinement on collapse and subsequent
explosion, which can be verified in future experiments. We make prediction for
the evolution of the shape of the condensate and the number of atoms in it for
different trap symmetries (cigar to pancake) as well as in the presence of an
optical lattice potential. We also make prediction for the jet formation in
different cases when the collapse is suddenly terminated by changing the
scattering length to zero via a Feshbach resonance.Comment: 8 pages, 11 ps figures, Physical Review
Nonlinear effects for Bose Einstein condensates in optical lattices
We present our experimental investigations on the subject of dynamical
nonlinearity-induced instabilities and of nonlinear Landau-Zener tunneling
between two energy bands in a Rubidium Bose-Einstein condensate in an
accelerated periodic potential. These two effects may be considered two
different regimes (for small and large acceleration) of the same physical
system and studied with the same experimental protocol. Nonlinearity introduces
an asymmetry in Landau-Zener tunneling; as a result, tunneling from the ground
state to the excited state is enhanced whereas in the opposite direction it is
suppressed. When the acceleration is lowered, the condensate exhibits an
unstable behaviour due to nonlinearity. We also carried out a full numerical
simulation of both regimes integrating the full Gross-Pitaevskii equation; for
the Landau-Zener effect we also used a simple two-level model. In both cases we
found good agreement with the experimental results.Comment: 9 pages, 7 figures. Submitted to Laser Physic
Instabilities of a Bose-Einstein condensate in a periodic potential: an experimental investigation
By accelerating a Bose-Einstein condensate in a controlled way across the
edge of the Brillouin zone of a 1D optical lattice, we investigate the
stability of the condensate in the vicinity of the zone edge. Through an
analysis of the visibility of the interference pattern after a time-of-flight
and the widths of the interference peaks, we characterize the onset of
instability as the acceleration of the lattice is decreased. We briefly discuss
the significance of our results with respect to recent theoretical work.Comment: 7 pages, 3 figures; submitted to Optics Express (Focus Issue on Cold
Atomic Gases in Optical Lattices
Dynamics and phase evolution of Bose-Einstein condensates in one-dimensional optical lattices
We report experimental results on the dynamics and phase evolution of
Bose-Einstein condensates in 1D optical lattices. The dynamical behaviour is
studied by adiabatically loading the condensate into the lattice and
subsequently switching off the magnetic trap. In this case, the condensate is
free to expand inside the periodic structure of the optical lattice. The phase
evolution of the condensate, on the other hand, can be studied by
non-adiabatically switching on the periodic potential. We observe decays and
revivals of the interference pattern after a time-of-flight.Comment: 6 pages, 5 figures; submitted to the Proceedings of the 11th Laser
Physics Workshop, Bratislava 200
Rydberg excitation of a Bose-Einstein condensate
We have performed two-photon excitation via the 6P3/2 state to n=50-80 S or D
Rydberg state in Bose-Einstein condensates of rubidium atoms. The Rydberg
excitation was performed in a quartz cell, where electric fields generated by
plates external to the cell created electric charges on the cell walls.
Avoiding accumulation of the charges and realizing good control over the
applied electric field was obtained when the fields were applied only for a
short time, typically a few microseconds. Rydberg excitations of the
Bose-Einstein condensates loaded into quasi one-dimensional traps and in
optical lattices have been investigated. The results for condensates expanded
to different sizes in the one-dimensional trap agree well with the intuitive
picture of a chain of Rydberg excitations controlled by the dipole-dipole
interaction. The optical lattice applied along the one-dimensional geometry
produces localized, collective Rydberg excitations controlled by the
nearest-neighbour blockade.Comment: 7 pages, 7 figures, Laser Physics in press. arXiv admin note: text
overlap with arXiv:1103.423
Full counting statistics and phase diagram of a dissipative Rydberg gas
Ultra-cold gases excited to strongly interacting Rydberg states are a
promising system for quantum simulations of many-body systems. For off-resonant
excitation of such systems in the dissipative regime, highly correlated
many-body states exhibiting, among other characteristics, intermittency and
multi-modal counting distributions are expected to be created. So far,
experiments with Rydberg atoms have been carried out in the resonant,
non-dissipative regime. Here we realize a dissipative gas of rubidium Rydberg
atoms and measure its full counting statistics for both resonant and
off-resonant excitation. We find strongly bimodal counting distributions in the
off-resonant regime that are compatible with intermittency due to the
coexistence of dynamical phases. Moreover, we measure the phase diagram of the
system and find good agreement with recent theoretical predictions. Our results
pave the way towards detailed studies of many-body effects in Rydberg gases.Comment: 12 pages, 5 figure
De-excitation spectroscopy of strongly interacting Rydberg gases
We present experimental results on the controlled de-excitation of Rydberg
states in a cold gas of Rb atoms. The effect of the van der Waals interactions
between the Rydberg atoms is clearly seen in the de-excitation spectrum and
dynamics. Our observations are confirmed by numerical simulations. In
particular, for off-resonant (facilitated) excitation we find that the
de-excitation spectrum reflects the spatial arrangement of the atoms in the
quasi one-dimensional geometry of our experiment. We discuss future
applications of this technique and implications for detection and controlled
dissipation schemes.Comment: 6 pages, 5 figure
Resonant nonlinear quantum transport for a periodically kicked Bose condensate
Our realistic numerical results show that the fundamental and higher-order
quantum resonances of the delta-kicked rotor are observable in state-of-the-art
experiments with a Bose condensate in a shallow harmonic trap, kicked by a
spatially periodic optical lattice. For stronger confinement,
interaction-induced destruction of the resonant motion of the kicked harmonic
oscillator is predicted.Comment: amended version, new Fig.
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