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 Schrödinger 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.