Abstract
Extending the understanding of Bose–Einstein condensate (BEC) physics to new geometries and topologies has a long and varied history in ultracold atomic physics. One such new geometry is that of a bubble, where a condensate would be confined to the surface of an ellipsoidal shell. Study of this geometry would give insight into new collective modes, self-interference effects, topology-dependent vortex behavior, dimensionality crossovers from thick to thin shells, and the properties of condensates pushed into the ultradilute limit. Here we propose to implement a realistic experimental framework for generating shell-geometry BEC using radiofrequency dressing of magnetically trapped samples. Such a tantalizing state of matter is inaccessible terrestrially due to the distorting effect of gravity on experimentally feasible shell potentials. The debut of an orbital BEC machine (NASA Cold Atom Laboratory, aboard the International Space Station) has enabled the operation of quantum-gas experiments in a regime of perpetual freefall, and thus has permitted the planning of microgravity shell-geometry BEC experiments. We discuss specific experimental configurations, applicable inhomogeneities and other experimental challenges, and outline potential experiments.
Highlights
The study of quantum-degenerate ultracold atomic gases has historically been guided by explorations of geometry, dimensionality, topology, and interaction
We present modeling related to proposed experiments with bubble-geometry Bose–Einstein condensate (BEC) aboard the NASA Cold Atom Laboratory (CAL), currently in operation aboard the International Space Station (ISS)
The rf frequency would be ramped upwards, forcing the condensate in the uppermost adiabatic potential into a shell geometry. The timescale of this ramp (~100 ms anticipated) would be enforced by mechanical adiabaticity of the BEC deformation and technical limits on the graining of the rf signal; timescales associated with motion perpendicular to the local shell surface are satisfied, but adiabaticity with respect to motion around the shell remains an open question
Summary
The study of quantum-degenerate ultracold atomic gases has historically been guided by explorations of geometry, dimensionality, topology, and interaction. Field amplitude, could have some weak spatial dependence) serves the twofold purpose of controlling the potential curvature of the local bubble minimum and ensuring (through sufficiently large magnitude) stability against Landau–Zener-type nonadiabatic losses in this dressed-state picture These losses have been explored in the context of magnetic traps[31] and are connected to the stability of condensates in rf-dressed spindependent optical lattices.[32,33]. Heating.[43] A key capability to begin dressed-atom experiments with CAL is the generation of traps of lower density and aspect ratio; a trap expansion protocol that does not incur unwanted center-of-mass motion is desired Such paths have been developed in the context of shortcuts to adiabiaticity with drop-tower missions[44] and in planning for CAL; in a semiclassical approach we have developed expansion ramps roughly in the form of a hyperbolic tangent, following the formalism of ref. Such paths have been developed in the context of shortcuts to adiabiaticity with drop-tower missions[44] and in planning for CAL; in a semiclassical approach we have developed expansion ramps roughly in the form of a hyperbolic tangent, following the formalism of ref. 39
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