Dissipative quantum North-East-Center model: steady-state phase diagram, universality and nonergodic dynamics

TL;DR

This paper investigates a dissipative quantum spin model combining kinetic constraints and chirality, revealing a phase diagram with bistable and normal phases, and explores nonergodic dynamics and stability near phase transitions.

Contribution

It introduces the dissipative quantum North-East-Center model with a cluster mean-field analysis, identifying phase behavior and nonergodic properties under novel dissipative conditions.

Findings

Two distinct steady-state phases: bistable and normal.

Emergence of instabilities at finite wavevectors near phase transition.

Minority spin islands are reabsorbed at constant velocity regardless of size.

Abstract

In this work we study the dissipative quantum North-East-Center (NEC) model: a two-dimensional spin-1/2 lattice subject to chiral, kinetically constrained dissipation and coherent quantum interactions. This model combines kinetic constraints and chirality at the dissipative level, implementing local incoherent spin flips conditioned by an asymmetric majority-vote rule. Through a cluster mean-field approach, we determine the steady-state phase diagram of the NEC model under different Hamiltonians, consistently revealing the emergence of two distinct phases, bistable and normal, across all cases considered. We further investigate the stability of the steady-state with respect to inhomogeneous fluctuations in both phases, showing the emergence of instabilities at finite wavevectors in the proximity of the phase transition. Next, we study the nonergodicity of the model in the bistable phase. We characterize the dynamics of minority islands of spins surrounded by a large background of spins pointing in the opposite direction. We show that in the bistable phase, the minority islands are always reabsorbed by the surrounding at a constant velocity, irrespectively of their size. Finally, we propose and numerically benchmark an equation of motion for the reabsorption velocity of the islands where thermal and quantum fluctuations act independently at linear order.