Large Deviation Functions of Open Quantum Systems with Strong Symmetries

Abstract

In open quantum systems with strong symmetries, the global rate function is typically non-convex and thus cannot be directly computed from the global scaled cumulant generating function (SCGF) via the Gartner-Ellis theorem. To overcome this limitation, we develop a framework that applies the theorem locally within each symmetry sector: local rate functions are computed for each sector, and the global rate function is subsequently reconstructed as the minimum envelope of these local functions. We illustrate our method using an exactly solvable model and an open Heisenberg chain with XXX interactions. For the latter system with continuous non-Abelian symmetries, our approach reveals sector-dependent fluctuations ranging from Poissonian to super-Poissonian statistics, together with emergent intermittency, demonstrating the broad applicability of our framework.