Absorbing state phase transition with competing quantum and classical fluctuations

TL;DR

This paper investigates how quantum fluctuations influence non-equilibrium phase transitions in open quantum spin systems, revealing a shift from continuous to first-order transitions and identifying a unique bicritical point.

Contribution

It introduces a theoretical framework showing quantum fluctuations change the nature of absorbing state transitions, highlighting a bicritical point with novel universal properties.

Findings

Quantum fluctuations turn the transition first-order.

Existence of a bicritical point with distinct universal features.

Proposed experimental realization with Rydberg atom gases.

Abstract

Stochastic processes with absorbing states feature remarkable examples of non-equilibrium universal phenomena. While a broad understanding has been progressively established in the classical regime, relatively little is known about the behavior of these non-equilibrium systems in the presence of quantum fluctuations. Here we theoretically address such a scenario in an open quantum spin model which in its classical limit undergoes a directed percolation phase transition. By mapping the problem to a non-equilibrium field theory, we show that the introduction of quantum fluctuations stemming from coherent, rather than statistical, spin-flips alters the nature of the transition such that it becomes first-order. In the intermediate regime, where classical and quantum dynamics compete on equal terms, we highlight the presence of a bicritical point with universal features different from the directed percolation class in low dimension. We finally propose how this physics could be explored within gases of interacting atoms excited to Rydberg states.