Emergent hydrodynamics in a strongly interacting dipolar spin ensemble

TL;DR

This paper demonstrates how a disordered dipolar quantum spin system can exhibit emergent classical hydrodynamic behavior, such as controllable spin diffusion, bridging microscopic quantum laws and macroscopic classical phenomena.

Contribution

It introduces a solid-state spin platform showing emergent hydrodynamics from a disordered quantum Hamiltonian with tunable diffusion properties.

Findings

Observation of non-Gaussian diffusive spin dynamics

Control over spin diffusion coefficient via external fields

Emergence of classical hydrodynamics from quantum spin interactions

Abstract

Conventional wisdom holds that macroscopic classical phenomena naturally emerge from microscopic quantum laws. However, despite this mantra, building direct connections between these two descriptions has remained an enduring scientific challenge. In particular, it is difficult to quantitatively predict the emergent "classical" properties of a system (e.g. diffusivity, viscosity, compressibility) from a generic microscopic quantum Hamiltonian. Here, we introduce a hybrid solid-state spin platform, where the underlying disordered, dipolar quantum Hamiltonian gives rise to the emergence of unconventional spin diffusion at nanometer length scales. In particular, the combination of positional disorder and on-site random fields leads to diffusive dynamics that are Fickian yet non-Gaussian. Finally, by tuning the underlying parameters within the spin Hamiltonian via a combination of static and driven fields, we demonstrate direct control over the emergent spin diffusion coefficient. Our work opens the door to investigating hydrodynamics in many-body quantum spin systems.