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 $^{87}$Rb. While EIA occurs in the $F=1\to F^{\prime}=2$ transition in a cell containing only $Rb$ vapor, collisions with a buffer gas ($30 torr$ of $Ne$) 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