82 research outputs found
Realization of a high power optical trapping setup free from thermal lensing effects
Transmission of high power laser beams through partially absorbing materials
modifies the light propagation via a thermally-induced effect known as thermal
lensing. This may cause changes in the beam waist position and degrade the beam
quality. Here we characterize the effect of thermal lensing associated with the
different elements typically employed in an optical trapping setup for cold
atoms experiments. We find that the only relevant thermal lens is represented
by the crystal of the acousto-optic modulator exploited to adjust the
laser power on the atomic sample. We then devise a simple and totally passive
scheme that enables to realize an inexpensive optical trapping apparatus
essentially free from thermal lensing effects
Direct evaporative cooling of 39K atoms to Bose-Einstein condensation
We report the realization of Bose-Einstein condensates of 39K atoms without
the aid of an additional atomic coolant. Our route to Bose-Einstein
condensation comprises Sub Doppler laser cooling of large atomic clouds with
more than 10^10 atoms and evaporative cooling in optical dipole traps where the
collisional cross section can be increased using magnetic Feshbach resonances.
Large condensates with almost 10^6 atoms can be produced in less than 15
seconds. Our achievements eliminate the need for sympathetic cooling with Rb
atoms which was the usual route implemented till date due to the unfavourable
collisional property of 39K. Our findings simplify the experimental set-up for
producing Bose-Einstein condensates of 39K atoms with tunable interactions,
which have a wide variety of promising applications including
atom-interferometry to studies on the interplay of disorder and interactions in
quantum gases.Comment: 7 pages, 6 figure
A Bose-Einstein condensate in an optical lattice with tunable spacing: transport and static properties
In this Letter we report the investigation of transport and static properties
of a Bose-Einstein condensate in a large-spaced optical lattice. The lattice
spacing can be easily tuned starting from few micrometers by adjusting the
relative angle of two partially reflective mirrors. We have performed in-situ
imaging of the atoms trapped in the potential wells of a 20 micrometers-spaced
lattice. For a lattice spacing of 10 micrometers we have studied the transport
properties of the system and the interference pattern after expansion,
evidencing quite different results with respect to the physics of BECs in
ordinary near-infrared standing wave lattices, owing to the different length
and energy scales.Comment: 11 pages, 7 figures, revised version (modified figures, extended
text
Velocity-dependent quantum phase slips in 1D atomic superfluids
Quantum phase slips are the primary excitations in one-dimensional
superfluids and superconductors at low temperatures but their existence in
ultracold quantum gases has not been demonstrated yet. We now study
experimentally the nucleation rate of phase slips in one-dimensional
superfluids realized with ultracold quantum gases, owing along a periodic
potential. We observe a crossover between a regime of temperature-dependent
dissipation at small velocity and interaction and a second regime of
velocity-dependent dissipation at larger velocity and interaction. This
behavior is consistent with the predicted crossover from thermally-assisted
quantum phase slips to purely quantum phase slips.Comment: 7 pages, 6 figure
Accurate near-threshold model for ultracold KRb dimers from interisotope Feshbach spectroscopy
We investigate magnetic Feshbach resonances in two different ultracold K-Rb
mixtures. Information on the K(39)-Rb(87) isotopic pair is combined with novel
and pre-existing observations of resonance patterns for K(40)-Rb(87).
Interisotope resonance spectroscopy improves significantly our near-threshold
model for scattering and bound-state calculations. Our analysis determines the
number of bound states in singlet/triplet potentials and establishes precisely
near threshold parameters for all K-Rb pairs of interest for experiments with
both atoms and molecules. In addition, the model verifies the validity of the
Born-Oppenheimer approximation at the present level of accuracy.Comment: 9 pages, 7 figure
Collisions of self-bound quantum droplets
We report on the study of binary collisions between quantum droplets formed
by an attractive mixture of ultracold atoms. We distinguish two main outcomes
of the collision, i.e. merging and separation, depending on the velocity of the
colliding pair. The critical velocity that discriminates between the two
cases displays a different dependence on the atom number for small and
large droplets. By comparing our experimental results with numerical
simulations, we show that the non-monotonic behavior of is due to the
crossover from a compressible to an incompressible regime, where the
collisional dynamics is governed by different energy scales, i.e. the droplet
binding energy and the surface tension. These results also provide the first
evidence of the liquid-like nature of quantum droplets in the large limit,
where their behavior closely resembles that of classical liquid droplets
Optical frequency comb assisted laser system for multiplex precision spectroscopy.
A laser system composed of two lasers phase-locked onto an Optical Frequency Comb Synthesizer (OFCS), operating around 1083 nm, was developed. An absolute frequency precision of 6x10(-13) at 1s, limited by the OFCS, was measured with a residual rms phase-noise of 71 mrad and 87 mrad for the two phase-locks, respectively. Multiplex spectroscopy on 1083 nm Helium transitions with this set-up is demonstrated. Generalization of this system to a larger number of OFCS assisted laser sources for wider frequency separations, even in other spectral regions, is discussed. (C) 2011 Optical Society of Americ
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