167 research outputs found
Quantum Phase Slips: from condensed matter to ultracold quantum gases
Quantum phase slips are the primary excitations in one-dimensional
superfluids and superconductors at low temperatures. They have been well
characterized in most condensed-matter systems, and signatures of their
existence has been recently observed in superfluids based on quantum gases too.
In this review we briefly summarize the main results obtained on the
investigation of phase slips from superconductors to quantum gases. In
particular we focus our attention on recent experimental results of the
dissipation in one-dimensional Bose superfluids flowing along a shallow
periodic potential, which show signatures of quantum phase slips.Comment: 10 pages, 6 figure
Instabilities of a matter wave in a matter grating
We investigate the stability of Bloch waves for a Bose-Einstein condensate
moving through a periodic lattice created by another condensate modulated by an
optical lattice. We show that the coupling of phonon-antiphonon modes of the
two species give rise to a very rich structure of the regimes for dynamical
instability, with significant differences with respect to the case of a single
condensate in an optical lattice. We characterize the relative weight of each
condensate in the mixing and discuss an analytic limit that accounts for the
bare structure of the instability diagrams.Comment: 4 pages, 4 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
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
Feshbach resonances in ultracold K(39)
We discover several magnetic Feshbach resonances in collisions of ultracold
K(39) atoms, by studying atom losses and molecule formation. Accurate
determination of the magnetic-field resonance locations allows us to optimize a
quantum collision model for potassium isotopes. We employ the model to predict
the magnetic-field dependence of scattering lengths and of near-threshold
molecular levels. Our findings will be useful to plan future experiments on
ultracold potassium atoms and molecules.Comment: 7 pages, 6 figure
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
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