Darmstadt 2008 – wissenschaftliches Programm

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Q: Fachverband Quantenoptik und Photonik

Q 15: Quantengase (Gitter I)

Q 15.7: Vortrag

Dienstag, 11. März 2008, 15:30–15:45, 1C

AC-induced superfluidity — •André Eckardt and Martin Holthaus — Institut für Physik, Carl von Ossietzky Universität, 26111 Oldenburg

In previous work we have shown that it should be possible to coherently control the transition from a superfluid to a Mott insulator in the Bose-Hubbard model by an oscillating force through an effective modification of the tunneling matrix element [Eckardt et al., PRL 95, 260404 (2005)]. The effective tunnel modification has recently been observed experimentally by the Arimondo group in Pisa, without notable loss of coherence caused by the drive [Lignier et al., cond-mat/0707.0403 (2007)]. In this talk we will consider a Bose-Hubbard system that is subjected to a static potential tilt such that tunneling is strongly suppressed due to the localization of the Wannier-Stark states. We show that tunneling can be restored partially in a coherent way by resonantly driving the system at high frequencies (a few kHz for a typical experiment with Alkali atoms in an optical lattice). For integer filling, the interplay between interparticle repulsion and this kind of “photon”-assisted tunneling should give rise to a Mott-like transition, with (quasi) long-range order (i.e. superfluidity) being established by switching on the AC-drive [Eckardt & Holthaus, EPL 80, 50004 (2007)]. It is also possible to control the sign of the effective tunneling matrix element by varying the amplitude of the drive. We argue that an adiabatic passage of the system’s ground state through such a sign change is a many-body effect that relies on the existence of a Mott-insulator phase.