Relaxation dynamics in the alternating XY chain following a quantum quench

We investigate the relaxation dynamics of the fermion two-point correlation function C_mn(t)=⟨ψ(t)|c_m^†c_n|ψ(t)⟩ in the XY chain with staggered nearest-neighbor hopping interaction after a quench. We find that the deviation δ C_mn(t)=C_mn(t)-C_mn(∞) decays with time following the power law behavior t^-μ, where the exponent μ depends on whether the quench is to the commensurate phase (μ=1) and incommensurate phase (μ=1/2). This decay of δ C_mn(t) arises from the transient behavior of the double excited quasiparticle occupations and the transitions between different excitation spectra. Furthermore, we find that the steady value C_mn(∞), which is different from the ground state expectation value, only involves the average fermion occupation numbers (i.e. the average excited single particle). We also observe nonanalytic singularities in the steady value C_mn(∞) for the quench to the critical points of the quantum phase transitions (QPTs), suggesting its potential use as a signature of QPTs.