Walter H. Aschbacher
On the emptiness formation probability in quasi-free states
(222K, latex 2e with 1 eps figure)

ABSTRACT.  We study the behavior of the emptiness formation probability for large spin strings in translation invariant quasi-free states on the CAR algebra on the discrete line and establish a simple criterion on the one-particle density matrix of the quasi-free state which ensures exponential decay. As an illustration, we treat the example of the XY spin chain out of equilibrium, in thermal equilibrium, in the ground state, and in the chaotic state.