2,357 research outputs found
Obtaining Atomic Matrix Elements from Vector Tune-Out Wavelengths using Atom Interferometry
Accurate values for atomic dipole matrix elements are useful in many areas of
physics, and in particular for interpreting experiments such as atomic parity
violation. Obtaining accurate matrix element values is a challenge for both
experiment and theory. A new technique that can be applied to this problem is
tune-out spectroscopy, which is the measurement of light wavelengths where the
electric polarizability of an atom has a zero. Using atom interferometry
methods, tune-out wavelengths can be measured very accurately. Their values
depend on the ratios of various dipole matrix elements and are thus useful for
constraining theory and broadening the application of experimental values.
Tune-out wavelength measurements to date have focused on zeros of the scalar
polarizability, but in general the vector polarizability also contributes. We
show here that combined measurements of the vector and scalar polarizabilities
can provide more detailed information about the matrix element ratios, and in
particular can distinguish small contributions from the atomic core and the
valence tail states. These small contributions are the leading error sources in
current parity violation calculations for cesium.Comment: 11 pages, 3 figure
Optical detection of a BCS phase transition in a trapped gas of fermionic atoms
Light scattering from a spin-polarized degenerate Fermi gas of trapped
ultracold Li-6 atoms is studied. We find that the scattered light contains
information which directly reflects the quantum pair correlation due to the
formation of atomic Cooper pairs resulting from a BCS phase transition to a
superfluid state. Evidence for pairing can be observed in both the space and
time domains.Comment: 8 pages, 4 figures, revte
Growth and Collapse of a Bose Condensate with Attractive Interactions
We consider the dynamics of a quantum degenerate trapped gas of Li-7 atoms.
Because the atoms have a negative s-wave scattering length, a Bose condensate
of Li-7 becomes mechanically unstable when the number of condensate atoms
approaches a maximum value. We calculate the dynamics of the collapse that
occurs when the unstable point is reached. In addition, we use the quantum
Boltzmann equation to investigate the nonequilibrium kinetics of the atomic
distribution during and after evaporative cooling. The condensate is found to
undergo many cycles of growth and collapse before a stationary state is
reached.Comment: Four pages of ReVTeX with four postscript figure
Stabilizing an Attractive Bose-Einstein Condensate by Driving a Surface Collective Mode
Bose-Einstein condensates of Li have been limited in number due to
attractive interatomic interactions. Beyond this number, the condensate
undergoes collective collapse. We study theoretically the effect of driving
low-lying collective modes of the condensate by a weak asymmetric sinusoidally
time-dependent field. We find that driving the radial breathing mode further
destabilizes the condensate, while excitation of the quadrupolar surface mode
causes the condensate to become more stable by imparting quasi-angular momentum
to it. We show that a significantly larger number of atoms may occupy the
condensate, which can then be sustained almost indefinitely. All effects are
predicted to be clearly visible in experiments and efforts are under way for
their experimental realization.Comment: 4 ReVTeX pages + 2 postscript figure
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