Constraints on stability and renormalization group flows in nonequilibrium matter

TL;DR

This paper establishes quantum information-based constraints on the stability and RG flows of nonequilibrium matter, linking CMI properties to phase stability and transitions.

Contribution

It introduces a non-perturbative stability criterion based on CMI monotonicity along RG flows and bounds CMI for mixtures, applying these to various nonequilibrium phenomena.

Findings

CMI scaling function is monotonic along RG flow.

Bound on CMI of mixed states in terms of components.

Constraints applied to decoherence, symmetry breaking, and phase transitions.

Abstract

We derive constraints on renormalization group (RG) flows and stability of phases in nonequilibrium systems using quantum information inequalities. These constraints involve conditional mutual information (CMI), which quantifies correlations between spatially separated regions not mediated by their surroundings. First, assuming CMI is UV finite, we show that the scaling function associated with CMI is monotonic along the RG flow. This implies a non-perturbative stability criterion: a fixed point with smaller CMI cannot be destabilized toward one with larger CMI. Second, we bound the CMI of a convex mixture of states in terms of the CMI of individual components. We use this inequality to infer perturbative stability of spontaneous symmetry breaking states against quantum channels that explicitly break symmetry. We illustrate these constraints through several examples, including decoherence-driven transitions in classical symmetry-broken states, strong-to-weak symmetry breaking criticality in two dimensions, and even transitions in pure quantum states. We also discuss implications for classical nonequilibrium steady states.