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Colloquium in Theoretical Physics

How do Rapidly Rotating Bose Gases Carry Angular Momentum?

Professor Gordon Baym
University of Illinois and Nordita

Wednesday, 16th February 2005, 10.30
Lecture hall (Sal) F, Sölvegatan 14

The energetically favored state of a rapidly rotating Bose condensed gas is, as observed, a triangular lattice of singly quantized vortices. What is the fate of the vortices when the rotation rate Ω is sufficiently rapid that the vortex cores would touch? Does a rotating Bose gas have a transition analogous to that observed in Type II superconductors at the upper critical magnetic field, Hc2? The problem is that while above Hc2 a Type II superconductor becomes normal, a low temperature bosonic system does not have a simple normal phase to which it can return. This talk will describe possible fates of the vortex lattice at large rotation in both harmonic and anharmonic traps. The vortex core sizes in a symmetric lattice approach a limiting fraction of the intervortex spacing, precluding a transition associated with core overlap. A system in a harmonic trap at Ω very close to the transverse trapping frequency becomes quasi two-dimensional and can ultimately enter a sequence of quantum Hall-like states. On the contrary, a system confined in a trap steeper than harmonic develops a hole along the rotation axis at sufficiently large Ω, and can, as numerical as well as variational calculations indicate, eventually make a transition to a multiply-quantized giant vortex state with the vorticity fully contained in the hole.

The Colloquia in Theoretical Physics are aimed for a general audience of students, teachers and researchers interested in physics and the laws of Nature. Coffee will be served before the Colloquium at 10.00.

Everybody is welcome!

Gösta Gustafson -- Theoretical physics
Sven Åberg -- Mathematical physics

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