title: Example of a quantum anomaly in the physics of ultracold gases.
abstract: In this Letter, we propose an experimental scheme for the observation of a quantum anomaly--quantum-mechanical symmetry breaking--in a two-dimensional harmonically trapped Bose gas. The anomaly manifests itself in a shift of the monopole excitation frequency away from the value dictated by the Pitaevskii-Rosch dynamical symmetry [L. P. Pitaevskii and A. Rosch, Phys. Rev. A 55, R853 (1997)]. While the corresponding classical Gross-Pitaevskii equation and the hydrodynamic equations derived from it do exhibit this symmetry, it is--as we show in our paper--violated under quantization. The resulting frequency shift is of the order of 1% of the carrier, well in reach for modern experimental techniques. We propose using the dipole oscillations as a frequency gauge.
authors.affiliation: Department of Physics, University of Massachusetts Boston, Boston Massachusetts 02125, USA.
authors.forename: Maxim
authors.initials: M
authors.lastname: Olshanii
authors.forename: Hélène
authors.initials: H
authors.lastname: Perrin
authors.forename: Vincent
authors.initials: V
authors.lastname: Lorent