# Stuttgart 2012 – wissenschaftliches Programm

## Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

# Q: Fachverband Quantenoptik und Photonik

## Q 32: Ultra-cold atoms, ions and BEC I

### Q 32.4: Vortrag

### Dienstag, 13. März 2012, 15:00–15:15, V7.02

**Quasi-Particle Theory for Strongly Interacting Lattice Bosons** — •Ulf Bissbort, Michael Buchhold, and Walter Hofstetter — Institut für Theoretische Physik, Goethe Universität Frankfurt a.M.

We develop a systematic quasi-particle theory for interacting bosons in optical lattices, which does not rely on a large condensate fraction and is valid for arbitrary interaction strengths. It is based upon the diagonalization of fluctuation operators on top of the bosonic Gutzwiller ground state and in the classical limit equivalent to the linearization of the time-dependent Gutzwiller equations of motion. The various collective modes, such as the sound and amplitude mode in the condensate, or the particle and hole mode in the Mott insulator emerge naturally from this unified formalism. It is valid beyond the realm of the latter, also being able to describe dynamics in the Mott insulator. For states in the vicinity of the respective Gutzwiller ground state, the system can be described as an ensemble of non-interacting quasi-particles, allowing for a direct treatment of time-dependent phenomena. Specifically, we calculate spectral functions and the dynamic structure factor for homogeneous systems in both the Mott insulator and condensate. The decay processes of the various quasi-particle modes induced by the higher order terms neglected in the quasi-particle Hamiltonian are identified, and the lifetimes are calculated. Furthermore we apply our theory to study quantum quenches and subsequent relaxation processes.