**Colloquium in Theoretical Physics**
# How do Rapidly Rotating Bose Gases Carry Angular Momentum?

**Professor Gordon Baym**

University of Illinois and Nordita

Wednesday, 16^{th} 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, *H*_{c2}? The problem is that while above *H*_{c2} 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

Last modified: Feb 10 2004
Stefan Keppeler
(stefan.keppeler@matfys.lth.se)