A.R. Its. B.-Q. Jin and V.E.Korepin
Entanglement in XY Spin Chain
(541K, PS)

ABSTRACT.  We consider the ground state of the XY model on an infinite chain at zero 
temperature. Following Bennett, Bernstein, Popescu, and Schumacher we use entropy of a sub-system as a measure of entanglement. Vidal, Latorre, 
Rico and Kitaev conjectured that von Neumann entropy of a large block of 
neighboring spins approaches a constant as the size of the block increases. We evaluated this limiting entropy as a function of anisotropy and transverse magnetic field. 
We used the methods based on integrable Fredholm 
operators and Riemann-Hilbert problem.