**Cat States and Bose Condensates in Double Well Potentials** - Birgitta Whaley

How macroscopic is a quantum superposition state in an interacting
many-body system, and how can we define the ``size'' of a superposition
state most generally, to allow comparison between diverse physical
realizations? We describe such a general measure of size for these
SchrÃ¶dinger cat-like states that is based on what measurements can be
performed to distinguish the different branches of the state.
Applications to Bose gases trapped in a three-dimensional potential
with a double well in one coordinate are described. Quantum Monte Carlo
calculations are used to determine conditions under which superposition
states are formed. The new measurement-based measure of cat size is
evaluated explicitly for this system and seen to show significantly
smaller effective sizes than predicted by previously discussed measures.