Non-local emergent hydrodynamics in a long-range quantum spin system

Understand

Generic short-range interacting quantum systems with a conserved quantity exhibit universal diffusive transport at late times.

• We employ non-equilibrium quantum field theory and semi-classical phase-space simulations to show how this universality is replaced by a more general transport process in a long-range XY spin chain at infinite temperature with couplings decaying algebraically with distance as $r^{-\alpha}$.
• While diffusion is recovered for $\alpha>1.5$, longer-ranged couplings with $0.5<\alpha\leq 1.5 $ give rise to effective classical L\'evy flights; a random walk with step sizes drawn from a distribution with algebraic tails.
• We find that the space-time dependent spin density profiles are self-similar, with scaling functions given by the stable symmetric distributions.