Scaling and Universality at Noise-Affected Non-Equilibrium Spin Correlation Functions

We investigate scaling and universality in nonequilibrium spin correlation functions in the presence of uncorrelated noise. In the absence of noise, spin correlation functions exhibit a crossover from monotonic decay at fast sweep velocities to oscillatory behavior at slow sweeps. We show that, under a stochastically driven field, the critical sweep velocity at which the spin correlation functions undergo an abrupt change decreases with increasing noise strength and scales linearly with the square of the noise intensity. Remarkably, when the noise intensity and sweep velocity are comparable, the excitation probability becomes locked to pk = 1/2 over a finite momentum window, signaling the emergence of noise-induced maximally mixed modes. This gives rise to a highly oscillatory region in the dynamical phase diagram, whose threshold sweep velocity increases with noise and likewise exhibits quadratic scaling with the noise strength. Finally, we identify a universal scaling function under which all boundary sweep-velocity curves collapse onto a single universal curve.

💡 Research Summary

The paper investigates how uncorrelated (white) noise influences the scaling behavior and universality of nonequilibrium spin‑spin correlation functions in a driven one‑dimensional XY spin chain. In the noiseless case, a linear ramp of the transverse field h₀(t)=vt drives the system through two quantum critical points at h_c=±1. The Landau‑Zener formula gives a momentum‑dependent excitation probability p_k=exp