8 research outputs found
Multi frequency evaporative cooling to BEC in a high magnetic field
We demonstrate a way to circumvent the interruption of evaporative cooling
observed at high bias field for Rb atoms trapped in the (F=2, m=+2)
ground state. Our scheme uses a 3-frequencies-RF-knife achieved by mixing two
RF frequencies. This compensates part of the non linearity of the Zeeman
effect, allowing us to achieve BEC where standard 1-frequency-RF-knife
evaporation method did not work. We are able to get efficient evaporative
cooling, provided that the residual detuning between the transition and the RF
frequencies in our scheme is smaller than the power broadening of the RF
transitions at the end of the evaporation ramp.Comment: 12 pages, 2 figure
Atomic Bose Gas with Negative Scattering Length
We derive the equation of state of a dilute atomic Bose gas with an
interatomic interaction that has a negative scattering length and argue that
two continuous phase transitions, occuring in the gas due to quantum degeneracy
effects, are preempted by a first-order gas-liquid or gas-solid transition
depending on the details of the interaction potential. We also discuss the
consequences of this result for future experiments with magnetically trapped
spin-polarized atomic gasses such as lithium and cesium.Comment: 16 PAGES, REVTEX 3.0, ACCEPTED FOR PUBLICATION IN PHYS. REV.
Spectral method for the time-dependent Gross-Pitaevskii equation with a harmonic trap
We study the numerical resolution of the time-dependent Gross-Pitaevskii
equation, a non-linear Schroedinger equation used to simulate the dynamics of
Bose-Einstein condensates. Considering condensates trapped in harmonic
potentials, we present an efficient algorithm by making use of a spectral
Galerkin method, using a basis set of harmonic oscillator functions, and the
Gauss-Hermite quadrature. We apply this algorithm to the simulation of
condensate breathing and scissors modes.Comment: 23 pages, 5 figure
Evidence of Bose-Einstein Condensation in an Atomic Gas with Attractive Interactions
Evidence for Bose-Einstein condensation of a gas of spin-polarized 7Li atoms is reported. Atoms confined to a permanent-magnet trap are laser cooled to 200 ÎĽK and are then evaporatively cooled to lower temperatures. Phase-space densities consistent with quantum degeneracy are measured for temperatures in the range of 100 to 400 nK. At these high phase-space densities, diffraction of a probe laser beam is observed. Modeling shows that this diffraction is a sensitive indicator of the presence of a spatially localized condensate. Although measurements of the number of condensate atoms have not been performed, the measured phase-space densities are consistent with a majority of the atoms being in the condensate, for total trap numbers as high as 2Ă—10Ë„5 atoms. For 7Li, the spin-triplet s-wave scattering length is known to be negative, corresponding to an attractive interatomic interaction. Previously, Bose-Einstein condensation was predicted not to occur in such a system
Adiabatic cooling of atoms by an intense standing wave
Lithium atoms channeled in the nodes of an intense standing-wave radiation field are cooled to near the recoil limit by adibatically reducing the radiation intensity. The final momentum distribution has a narrow component with a root-mean-squared momentum of 2ħk in one dimension, where ħk is the momentum of a radiation-field photon. The data are compared with the results of a Monte Carlo simulation using a two-level atom model. This process may be useful for cooling and increasing the phase-space density of atoms confined in a magnetic trap