Session H4 - Optical Lattices of Ultra Cold Atoms.
INVITED session, Tuesday morning, March 04
Ballroom E, Austin Convention Center
An intriguing aspect of quantum mechanics is that even at absolute zero temperature quantum fluctuations prevail in a system, whereas all thermal fluctuations are frozen out. These quantum fluctuations are able to induce a macroscopic phase transition in the ground state of a many body system, when the ratio of two competing terms in the underlying Hamiltonian is varied across a critical value. When atoms with repulsive interactions forming a Bose-Einstein condensate are transferred into a three-dimensional optical lattice potential, they will undergo such a quantum phase transition from a Superfluid to a Mott Insulator as the ratio between the interaction strength and the tunnel coupling is varied. In the talk I will present the observation of such a transition and the measurement of the characteristic gap in the excitation spectrum. Recently we also observed that ultracold collisions between atoms lead to a collapse and revival of the macroscopic matter wave field of a Bose-Einstein condensate.
With these experiments we are able to enter a new field of physics with ultracold quantum gases. In this strongly correlated regime interactions between atoms dominate the behavior of the many-body system, such that it cannot be described anymore by the usual theories for weakly interacting Bose gases. This novel quantum system offers the unique possibility to experimentally address fundamental questions of modern solid state physics, atomic physics and quantum optics, some of which I will address in my presentation.