116 research outputs found
Evaporative cooling in a radio-frequency trap
A theoretical investigation for implementing a scheme of forced evaporative
cooling in radio-frequency (rf) adiabatic potentials is presented. Supposing
the atoms to be trapped by a rf field RF1, the cooling procedure is facilitated
using a second rf source RF2. This second rf field produces a controlled
coupling between the spin states dressed by RF1. The evaporation is then
possible in a pulsed or continuous mode. In the pulsed case, atoms with a given
energy are transferred into untrapped dressed states by abruptly switching off
the interaction. In the continuous case, it is possible for energetic atoms to
adiabatically follow the doubly-dressed states and escape out of the trap. Our
results also show that when the frequencies of the fields RF1 and RF2 are
separated by at least the Rabi frequency associated with RF1, additional
evaporation zones appear which can make this process more efficient.Comment: 12 pages, 11 figure
An Example of Quantum Anomaly in the Physics of Ultra-Cold Gases
In this article, we propose an experimental scheme for observation of a
quantum anomaly---quantum-mechanical symmetry breaking---in a two-dimensional
harmonically trapped Bose gas. The anomaly manifests itself in a shift of the
monopole excitation frequency away from the value dictated by the
Pitaevskii-Rosch dynamical symmetry [L. P. Pitaevskii and A. Rosch, Phys. Rev.
A, 55, R853 (1997)]. While the corresponding classical Gross-Pitaevskii
equation and the derived from it hydrodynamic equations do exhibit this
symmetry, it is---as we show in our paper---violated under quantization. The
resulting frequency shift is of the order of 1% of the carrier, well in reach
for modern experimental techniques. We propose using the dipole oscillations as
a frequency gauge.Comment: Misprints corrected, a discussion on damping added, text is polished
and shortened. 5 pages, 1 figur
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.
Rubidium-87 Bose-Einstein condensate in an optically plugged quadrupole trap
We describe an experiment to produce 87Rb Bose-Einstein condensates in an
optically plugged magnetic quadrupole trap, using a blue-detuned laser. Due to
the large detuning of the plug laser with respect to the atomic transition, the
evaporation has to be carefully optimized in order to efficiently overcome the
Majorana losses. We provide a complete theoretical and experimental study of
the trapping potential at low temperatures and show that this simple model
describes well our data. In particular we demonstrate methods to reliably
measure the trap oscillation frequencies and the bottom frequency, based on
periodic excitation of the trapping potential and on radio-frequency
spectroscopy, respectively. We show that this hybrid trap can be operated in a
well controlled regime that allows a reliable production of degenerate gases.Comment: 13 pages, 8 figure
Inhibition of electromagnetically induced absorption due to excited state decoherence in Rb vapor
The explanation presented in [Taichenachev et al, Phys. Rev. A {\bf 61},
011802 (2000)] according to which the electromagnetically induced absorption
(EIA) resonances observed in degenerate two level systems are due to coherence
transfer from the excited to the ground state is experimentally tested in a
Hanle type experiment observing the parametric resonance on the line of
Rb. While EIA occurs in the transition in a cell
containing only vapor, collisions with a buffer gas ( of )
cause the sign reversal of this resonance as a consequence of collisional
decoherence of the excited state. A theoretical model in good qualitative
agreement with the experimental results is presented.Comment: 8 pages, 7 figures, submitted to Physical Review
Bosons in cigar-shape traps: Thomas-Fermi regime, Tonks-Girardeau regime, and between
We present a quantitative analysis of the experimental accessibility of the
Tonks-Girardeau gas in the current day experiments with cigar-trapped alkalis.
For this purpose we derive, using a Bethe anzats generated local equation of
state, a set of hydrostatic equations describing one-dimensional
delta-interacting Bose gases trapped in a harmonic potential. The resulting
solutions cover the_entire range_ of atomic densities.Comment: 4 pages, 4 figure
Mortality Prediction after the First Year of Kidney Transplantation: An Observational Study on Two European Cohorts.
After the first year post transplantation, prognostic mortality scores in kidney transplant recipients can be useful for personalizing medical management. We developed a new prognostic score based on 5 parameters and computable at 1-year post transplantation. The outcome was the time between the first anniversary of the transplantation and the patient's death with a functioning graft. Afterwards, we appraised the prognostic capacities of this score by estimating time-dependent Receiver Operating Characteristic (ROC) curves from two prospective and multicentric European cohorts: the DIVAT (Données Informatisées et VAlidées en Transplantation) cohort composed of patients transplanted between 2000 and 2012 in 6 French centers; and the STCS (Swiss Transplant Cohort Study) cohort composed of patients transplanted between 2008 and 2012 in 6 Swiss centers. We also compared the results with those of two existing scoring systems: one from Spain (Hernandez et al.) and one from the United States (the Recipient Risk Score, RRS, Baskin-Bey et al.). From the DIVAT validation cohort and for a prognostic time at 10 years, the new prognostic score (AUC = 0.78, 95%CI = [0.69, 0.85]) seemed to present significantly higher prognostic capacities than the scoring system proposed by Hernandez et al. (p = 0.04) and tended to perform better than the initial RRS (p = 0.10). By using the Swiss cohort, the RRS and the the new prognostic score had comparable prognostic capacities at 4 years (AUC = 0.77 and 0.76 respectively, p = 0.31). In addition to the current available scores related to the risk to return in dialysis, we recommend to further study the use of the score we propose or the RRS for a more efficient personalized follow-up of kidney transplant recipients
Guiding Neutral Atoms
We demonstrate the guiding of neutral atoms by the magnetic fields due to
microfabricated current-carrying wires on a chip. Atoms are guided along a
magnetic field minimum parallel to and above the current-carrying wires. Two
waveguide configurations are demonstrated: one using two wires with an external
magnetic field, and a second using four wires without an external field. These
waveguide geometries can be extended to integrated atom optics circuits,
including beamsplitters.Comment: 11 pages, 4 figure
Broadband telecom to mid-infrared supercontinuum generation in a dispersion-engineered silicon germanium waveguide
We demonstrate broadband supercontinuum generation (SCG) in a dispersion-engineered silicon-germanium waveguide. The 3 cm long waveguide is pumped by femtosecond pulses at 2.4 μm, and the generated supercontinuum extends from 1.45 to 2.79 μm (at the −30 dB point). The broadening is mainly driven by the generation of a dispersive wave in the 1.5–1.8 μm region and soliton fission. The SCG was modeled numerically, and excellent agreement with the experimental results was obtained
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