# Hannover 2010 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 24: Quantum Gases: Mixtures and Spinor Gases

### Q 24.2: Vortrag

### Mittwoch, 10. März 2010, 10:45–11:00, E 001

**Parametric amplification of quantum spin fluctuations in a spinor Bose-Einstein condensate** — •Gebremedhn Gebreyesus^{1}, Philipp Hyllus^{2}, Frank Deuretzbacher^{1}, and Luis Santos^{1} — ^{1}Institut für Theoretische Physik, Leibniz Universität Hannover, Appelstraße 2, 30167, Germany — ^{2}BEC-INFM, Dipartimento di Fisica, Università di Trento, Via Sommarive 14, I-38050 Povo, Italy

In this presentation we analyze the spinor dynamics in spinor condensates (with particular emphasis on the Rb87 F=2 case). Starting from an initial condensate in the Zeeman state m=0, the initial stages of the dynamics are characterized by a correlated pair-creation into m=+1 and -1 which closely resembles parametric amplification in quantum optics. This coherent dynamics is induced by spin-changing collisions, but, as we shall show in detail, the actual amplification gain largely depends on the interplay between these collisions, quadratic Zeeman effect, and external confinement. In particular, the magnetic-field dependence of the amplification (which presents a striking multiresonant character) is shown to map the instability of the corresponding spin excitations. We analyze also in detail the triggering mechanism showing that under proper conditions the systems is basically insensitive against spurious seeding, being purely driven by quantum spin fluctuations. In the last part of this presentation we shall discuss recent results on the number statistics of the parametrically amplified clouds in m=+1 and -1.