Hierarchical hydrodynamics in long-range multipole-conserving systems

TL;DR

This paper explores the complex out-of-equilibrium hydrodynamics of long-range multipole-conserving systems, revealing diverse dynamical regimes and hierarchical behaviors relevant to experimental quantum systems.

Contribution

It introduces a hierarchical class of models with tunable local conservation of multipole moments and provides a unified analytical framework for their hydrodynamics.

Findings

Identification of regimes with subdiffusion, diffusion, and Lévy flights.

Development of an analytic reciprocal relationship for nested hydrodynamics.

Numerical validation with quantum simulations and experimental relevance.

Abstract

This work investigates the out-of-equilibrium dynamics of dipole and higher-moment conserving systems with long-range interactions, drawing inspiration from trapped ion experiments in strongly tilted potentials. We introduce a hierarchical sequence of multipole-conserving models characterized by power-law decaying couplings. Although the moments are always globally conserved, adjusting the power-law exponents of the couplings induces various regimes in which only a subset of multipole moments are effectively locally conserved. We examine the late-time hydrodynamics analytically and numerically using an effective classical framework, uncovering a rich dynamical phase diagram that includes subdiffusion, conventional diffusion, and L\'evy flights. Our results are unified in an analytic reciprocal relationship that captures the nested hierarchy of hydrodynamics in multipole conserving systems where only a subset of the moments are locally conserved. Moreover, we extend our findings to higher dimensions and explore the emergence of long-time scales, reminiscent of pre-thermal regimes, in systems with low charge density. Lastly, we corroborate our results through state-of-the-art numerical simulations of a fully quantum long-range dipole-conserving system and discuss their relevance to trapped-ion experimental setups.