Niels Bohr Institutet > Kalender - det sker på NBI > 2009 > Many-Body Excitations ...

Many-Body Excitations and their Decay in a BEC

The study of excitations and decay in Bose-Einstein Condensates provides insight into fundamental phenomena in many-body quantum systems. We use Bragg spectroscopy as a sensitive tool for creating and probing these excitations and their dynamics. In this talk I will present experimental and theoretical work on quantum interference effects, which appear for low momentum excitations, and short-time non-exponential decay of excitations for a BEC loaded into a 1D opticallattice.

In a Bose-Einstein condensate, the excitation of a Bogoliubov phonon with low momentum is strongly suppressed due to destructive interference between two indistinguishable excitation pathways. Here we show that scattering of this sound excitation into a double-momentum mode is strongly enhanced due to constructive interference. We further show that due to parity considerations, this effect is extended to higher-order excitations.

Relaxation and decoherence of excited quantum states, caused by their coupling to the environment, is a ubiquitous phenomenon. For a BEC loaded into a 1D optical lattice, we observe strong enhancement of the decay compared to the Golden Rule (long-time limit) results. This enhancement of decay increases with the lattice depth. It indicates that the description of decay in this system must take into account short-time, non-exponential contributions