70 research outputs found
Dropping cold quantum gases on Earth over long times and large distances
We describe the non-relativistic time evolution of an ultra-cold degenerate
quantum gas (bosons/fermions) falling in Earth's gravity during long times (10
sec) and over large distances (100 m). This models a drop tower experiment that
is currently performed by the QUANTUS collaboration at ZARM (Bremen, Germany).
Starting from the classical mechanics of the drop capsule and a single particle
trapped within, we develop the quantum field theoretical description for this
experimental situation in an inertial frame, the corotating frame of the Earth,
as well as the comoving frame of the drop capsule. Suitable transformations
eliminate non-inertial forces, provided all external potentials (trap, gravity)
can be approximated with a second order Taylor expansion around the
instantaneous trap center. This is an excellent assumption and the harmonic
potential theorem applies. As an application, we study the quantum dynamics of
a cigar-shaped Bose-Einstein condensate in the Gross-Pitaevskii mean-field
approximation. Due to the instantaneous transformation to the rest-frame of the
superfluid wave packet, the long-distance drop (100m) can be studied easily on
a numerical grid.Comment: 18 pages latex, 5 eps figures, submitte
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