17 research outputs found
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
Cooling Atoms in an Optical Trap by Selective Parametric Excitation
We demonstrate the possibility of energy-selective removal of cold atoms from a tight optical trap by means of parametric excitation of the trap vibrational modes. Taking advantage of the anharmonicity of the trap potential, we either selectively remove the most energetic trapped atoms or excite those at the bottom of the trap by tuning the parametric modulation frequency. This process, which had been previously identified as a possible source of heating, also appears to be a robust way for forcing evaporative cooling in anharmonic traps
-enhanced grey molasses on the transition of Rubidium-87 atoms
Laser cooling based on dark states, i.e. states decoupled from light, has
proven to be effective to increase the phase-space density of cold trapped
atoms. Dark-states cooling requires open atomic transitions, in contrast to the
ordinary laser cooling used for example in magneto-optical traps (MOTs), which
operate on closed atomic transitions. For alkali atoms, dark-states cooling is
therefore commonly operated on the transition . We show that, for , thanks to the large hyperfine
structure separations the use of this transition is not strictly necessary and
that quasi-dark state cooling is efficient also on the line, . We report temperatures as low as K and an increase of almost an order of magnitude in the phase space
density with respect to ordinary laser sub-Doppler cooling
Decay of persistent currents in annular atomic superfluids
We investigate the role of vortices in the decay of persistent current states
of annular atomic superfluids by solving numerically the Gross-Pitaevskii
equation, and we directly compare our results with experimental data from Ref.
[1]. We theoretically model the optical phase-imprinting technique employed to
experimentally excite finite-circulation states in Ref. [1] in the
Bose-Einstein condensation regime, accounting for imperfections of the optical
gradient imprinting profile. By comparing simulations of this realistic
protocol to an ideal imprinting, we show that the introduced density
excitations arising from imperfect imprinting are mainly responsible for
limiting the maximum reachable winding number in the
superfluid ring. We also investigate the effect of a point-like obstacle with
variable potential height onto the decay of circulating supercurrents.
For a given obstacle height, a critical circulation exists, such that for
an initial circulation larger than the supercurrent decays through
the emission of vortices, which cross the superflow and thus induce phase
slippage. Higher values of the obstacle height further favour the
entrance of vortices, thus leading to lower values of . Furthermore, the
stronger vortex-defect interaction at higher leads to vortices that
propagate closer to the center of the ring condensate. The combination of both
these effects leads to an increase of the supercurrent decay rate for
increasing , in agreement with experimental observations.
[1]: G. Del Pace, et al., Phys. Rev. X 12, 041037 (2022
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
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
Universal Spin Transport in a Strongly Interacting Fermi Gas
Transport of fermions is central in many elds of physics. Electron transport runs modern technology,
de ning states of matter such as superconductors and insulators, and electron spin, rather
than charge, is being explored as a new carrier of information [1]. Neutrino transport energizes
supernova explosions following the collapse of a dying star [2], and hydrodynamic transport of the
quark-gluon plasma governed the expansion of the early Universe [3]. However, our understanding
of non-equilibrium dynamics in such strongly interacting fermionic matter is still limited. Ultracold
gases of fermionic atoms realize a pristine model for such systems and can be studied in real time
with the precision of atomic physics [4, 5]. It has been established that even above the super
uid
transition such gases
ow as an almost perfect
uid with very low viscosity [3, 6] when interactions
are tuned to a scattering resonance. However, here we show that spin currents, as opposed to
mass currents, are maximally damped, and that interactions can be strong enough to reverse spin
currents, with opposite spin components reflecting off each other. We determine the spin drag coefficient, the spin di usivity, and the spin susceptibility, as a function of temperature on resonance and
show that they obey universal laws at high temperatures. At low temperatures, the spin di usivity
approaches a minimum value set by ħ/m, the quantum limit of di usion, where ħ is the reduced
Planck's constant and m the atomic mass. For repulsive interactions, our measurements appear to
exclude a metastable ferromagnetic state [7{9].National Science Foundation (U.S.)United States. Office of Naval ResearchUnited States. Army Research Office (DARPA OLE programme)Alfred P. Sloan FoundationUnited States. Air Force Office of Scientific Research. Multidisciplinary University Research InitiativeUnited States. Army Research Office. Multidisciplinary University Research InitiativeUnited States. Defense Advanced Research Projects Agency. Young Faculty AwardDavid & Lucile Packard Foundatio
Shielding of optical pulses on hydrodynamical time scales in laser-induced breakdown of saline water
Pulse shielding in Laser-Induced Breakdown of saline water on hydrodynamic time scales is experimentally characterized. Pairs of pulses from a Nd:YAG laser are focused into saline water with a controlled time delay between them. The Laser-Induced Breakdown produced by the first pulse creates a cavitation bubble that later collapses generating a plume of bubbles that evolves on hydrodynamic time scales. When the second pulse arrives, the light is scattered by this plume with a consequent reduction in the intensity at the focal spot resulting in a lower breakdown efficiency of this pulse. By means of acoustic measurements, we determine the breakdown energy threshold for the first pulse and characterize the shielding of the second pulse as a function of the salinity of the solution, the energy of the pulse, and the inter-pulse interval. A model for the blocking process that takes into account both linear and nonlinear absorption along the path is developed which satisfactorily explains the observations. © 2014 AIP Publishing LLC.We acknowledge technical support from Dr. Luca Furfaro (U. du Franche-Compté), and funding from the Direcció General de Recerca, Desenvolupament Tecnològic i Innovació de la Conselleria d'Innovació, Interior i JustÃcia del Govern de les Illes Balears co-funded by the European Union FEDER funds. J.J. acknowledges financial support from the Ramon y Cajal fellowship. F. Marino acknowledges partial financial support from UIBPeer Reviewe