Quantum Vicsek Model for Active Matter

Abstract: We propose a quantum analog of the Vicsek model, consisting of an ensemble of overdamped spin$-1/2$ particles with ferromagnetic couplings, driven by a uniformly polarized magnetic field. The spontaneous magnetization of the spin components breaks the $SO(3)$ (or $SO(2)$) symmetry, inducing an ordered phase of flocking. We derive the hydrodynamic equations, similar to those formulated by Toner and Tu, by applying a mean-field approximation to the quantum analog model up to the next leading order. Our investigation not only establishes a microscopic connection between the Vicsek model and the Toner-Tu hydrodynamics for active matter, but also aims to inspire further studies of active matter in the quantum regime.