419 research outputs found
Laser cooling of new atomic and molecular species with ultrafast pulses
We propose a new laser cooling method for atomic species whose level
structure makes traditional laser cooling difficult. For instance, laser
cooling of hydrogen requires single-frequency vacuum-ultraviolet light, while
multielectron atoms need single-frequency light at many widely separated
frequencies. These restrictions can be eased by laser cooling on two-photon
transitions with ultrafast pulse trains. Laser cooling of hydrogen,
antihydrogen, and many other species appears feasible, and extension of the
technique to molecules may be possible.Comment: revision of quant-ph/0306099, submitted to PR
Adiabatically changing the phase-space density of a trapped Bose gas
We show that the degeneracy parameter of a trapped Bose gas can be changed
adiabatically in a reversible way, both in the Boltzmann regime and in the
degenerate Bose regime. We have performed measurements on spin-polarized atomic
hydrogen in the Boltzmann regime demonstrating reversible changes of the
degeneracy parameter (phase-space density) by more than a factor of two. This
result is in perfect agreement with theory. By extending our theoretical
analysis to the quantum degenerate regime we predict that, starting close
enough to the Bose-Einstein phase transition, one can cross the transition by
an adiabatic change of the trap shape.Comment: 4 pages, 3 figures, Latex, submitted to PR
Evanescent-wave trapping and evaporative cooling of an atomic gas near two-dimensionality
A dense gas of cesium atoms at the crossover to two-dimensionality is
prepared in a highly anisotropic surface trap that is realized with two
evanescent light waves. Temperatures as low as 100nK are reached with 20.000
atoms at a phase-space density close to 0.1. The lowest quantum state in the
tightly confined direction is populated by more than 60%. The system offers
intriguing prospects for future experiments on degenerate quantum gases in two
dimensions
A high-flux 2D MOT source for cold lithium atoms
We demonstrate a novel 2D MOT beam source for cold 6Li atoms. The source is
side-loaded from an oven operated at temperatures in the range 600<T<700 K. The
performance is analyzed by loading the atoms into a 3D MOT located 220 mm
downstream from the source. The maximum recapture rate of ~10^9 /s is obtained
for T=700 K and results in a total of up to 10^10 trapped atoms. The recaptured
fraction is estimated to be 30(10)% and limited by beam divergence. The
most-probable velocity in the beam (alpha_z) is varied from 18 to 70 m/s by
increasing the intensity of a push beam. The source is quite monochromatic with
a full-width at half maximum velocity spread of 11 m/s at alpha_z=36 m/s,
demonstrating that side-loading completely eliminates beam contamination by hot
vapor from the oven. We identify depletion of the low-velocity tail of the oven
flux as the limiting loss mechanism. Our approach is suitable for other atomic
species.Comment: 13 pages,9 figures, submitted to Phys.Rev.
Continuous loading of a non-dissipative atom trap
We study theoretically a scheme in which particles from an incident beam are
trapped in a potential well when colliding with particles already present in
the well. The balance between the arrival of new particles and the evaporation
of particles from the trapped cloud leads to a steady-state that we
characterize in terms of particle number and temperature. For a cigar shaped
potential, different longitudinal and transverse evaporation thresholds can be
chosen. We show that a resonance occur when the transverse evaporation
threshold coincides with the energy of the incident particles. It leads to a
dramatic increase in phase space density with respect to the incident beam.Comment: 7 pages, 2 figure
RR Lyrae Variables in the Globular Cluster M55. The First Evidence for Non Radial Pulsations in RR Lyr Stars
We present the results of a photometric study of RR Lyrae variables in the
field of the globular cluster M55. We have discovered nine new RR Lyrae stars,
increasing the number of known variables in this cluster to 15 objects. Five of
the newly discovered variables belong to Bailey type RRc and two to type RRab.
Two background RRab stars are probable members of the Sagittarius dwarf galaxy.
Fourier decomposition of the light curves was used to derive basic properties
of the present sample of RR Lyrae variables. From an analysis of the RRc
variables we obtain a mean mass of , luminosity , effective temperature K, and helium
abundance . Based on the colors, periods and metallicities
of the RRab stars we estimate the value of the color excess for M55 to be equal
to . Using this value we derive the colors of the blue and
red edges of the instability strip in M55. The blue edge lies at
mag and the red edge lies at mag. We estimate the values of the
visual apparent and dereddened distance moduli to be and
, respectively. The light curves of three of the RRc variables
exhibit changes in amplitude of over 0.1 mag on the time scale of less than a
week, rather short for the Blazhko effect, but with no evidence for another
radial pulsational frequency. However we do detect other periodicities which
are clearly visible in the light curve after removing variations with the first
overtone radial frequency. This is strong evidence for the presence of
non-radial pulsations, a behavior common for Scuti stars but not yet
observed among RR Lyr variables.Comment: submitted to Astronomical Journal, 33 pages with 11 figure
Spin-Polarized Atomic Deuterium: Stabilization, Limitations on Density, and Adsorption Energy on Helium
Influence of nearly resonant light on the scattering length in low-temperature atomic gases
We develop the idea of manipulating the scattering length in
low-temperature atomic gases by using nearly resonant light. As found, if the
incident light is close to resonance with one of the bound levels of
electronically excited molecule, then virtual radiative transitions of a pair
of interacting atoms to this level can significantly change the value and even
reverse the sign of . The decay of the gas due to photon recoil, resulting
from the scattering of light by single atoms, and due to photoassociation can
be minimized by selecting the frequency detuning and the Rabi frequency. Our
calculations show the feasibility of optical manipulations of trapped Bose
condensates through a light-induced change in the mean field interaction
between atoms, which is illustrated for Li.Comment: 12 pages, 1 Postscript figur
Evaporative cooling of trapped fermionic atoms
We propose an efficient mechanism for the evaporative cooling of trapped
fermions directly into quantum degeneracy. Our idea is based on an electric
field induced elastic interaction between trapped atoms in spin symmetric
states. We discuss some novel general features of fermionic evaporative cooling
and present numerical studies demonstrating the feasibility for the cooling of
alkali metal fermionic species Li, K, and Rb. We also
discuss the sympathetic cooling of fermionic hyperfine spin mixtures, including
the effects of anisotropic interactions.Comment: to be publishe
Hydrodynamic behavior in expanding thermal clouds of Rb-87
We study hydrodynamic behavior in expanding thermal clouds of Rb-87 released
from an elongated trap. At our highest densities the mean free path is smaller
than the radial size of the cloud. After release the clouds expand
anisotropically. The cloud temperature drops by as much as 30%. This is
attributed to isentropic cooling during the early stages of the expansion. We
present an analytical model to describe the expansion and to estimate the
cooling. Important consequences for time-of-flight thermometry are discussed.Comment: 7 pages with 2 figure
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