Nonequilibrium dynamics and turbulence

Following dynamics in a single propagation

The entrance of the nonlinear medium suddenly switches photon–photon interactions on; the exit switches them off again. These interaction quenches make the propagation itself a controlled nonequilibrium experiment. By shaping the initial density and velocity fields and reconstructing the complex field at the output, we can study the formation of dispersive shock waves, solitons, vortices and correlated quasiparticles.

The same approach connects laboratory hydrodynamics to analogue spacetime. A time-dependent sound speed or flow profile changes the effective geometry seen by collective excitations, enabling optical analogues of expanding universes, horizons and curved spacetime.

Turbulence beyond the power spectrum

A spectrum or a variance describes typical fluctuations, but turbulence is often governed by intermittent, rare events. We therefore measure the full statistics of density and phase differences rather than stopping at two-point correlations. Higher-order cumulants reveal departures from Gaussian behaviour and test when a weakly interacting or Bogoliubov description ceases to be sufficient.

Large ensembles of full-field images let us connect energy transfer across scales to the local structures that carry it. We study how instabilities create vortices and solitons, how dissipation persists in the turbulent regime, and how the optical phase records intermittency that can remain hidden in intensity alone.

Thermalisation, universality and rare events

The same statistical toolbox applies from the earliest stage of a quench to its late-time state. Correlation functions track the growth of characteristic length scales, while the cumulant hierarchy tests whether information about the initial state survives thermalisation. In binary fluids, this programme extends to critical dynamics and domain coarsening across the miscible–immiscible transition.

Our goal is a quantitative account of nonequilibrium evolution that includes both its universal average behaviour and the exceptional events that control its extremes.

Associated publications