Birgitta Whaley
University of California at Berkeley
Tuesday, December 12, 2006
11:00 am in SPL 52
Note different room and time
Cat States and Bose Condensates in Double Well Potentials
Abstract: How macroscopic is a quantum superposition state in an interacting many-body system? Recent experiments claim to have observed quantum superposition states in near-macroscopic systems with very different physical constituents. How can we define the "size" of a superposition state in general, so as to allow comparison between diverse physical realizations? We propose a measure of size for such Schrödinger cat-like states that is based fundamentally on what measurements can be performed to probe and distinguish the different branches of the cat-state, allowing comparison of sizes of superposition states in very different physical systems. Applications to quantum superposition state of Bose gases trapped in a three-dimensional potential with a double well in one coordinate are described. We summarize the behavior of these condensates with both repulsive and attractive scattering lengths as a function of the strength of the interaction parameters and number of particles, using quantum Monte Carlo calculations to examine conditions under which superposition states are formed. The new measurement-based measure of cat size is evaluated explicitly for this system and compared with the effective size predicted by other measures such as disconnectivity.