Spin correlation functions of the ground-state quenched XY model


We obtain exact expressions for the magnetizations and spin correlation functions for the ground-state quenched spin-1/2 XY model with both anisotropy and transverse magnetic field as quench parameters. The spin correlation functions were evaluated by Pfaffians of matrices with spinless fermionic operator correlations as elements. The transverse magnetization is obtained in the thermodynamic limit by the computation of a time-dependent density matrix. Non-analyticities in these quantities at some critical times are indicative of dynamical quantum phase transitions.