Institute for Theoretical Physics

23/09/26

Theoretische Physik

FOR5522

Patrycja Lydzba

Memory of initial states in long-time dynamics revealed by non-Gaussianity

In quantum dynamics of observables in quadratic systems, information about the initial state is retained in long-time averages, as captured by the generalized Gibbs ensemble. Here, we show that this memory extends beyond the averages to the temporal fluctuations around them. By generating a manifold of non-Gaussian initial states and quantifying their non-Gaussianity through the binary entropy, we find that the magnitude of temporal fluctuations is a smooth function of the initial-state non-Gaussianity. This relation explains the qualitatively different scaling of fluctuations observed after quantum quenches: exponentially small fluctuations for non-Gaussian initial states and polynomially small fluctuations for Gaussian initial states. Our results establish non-Gaussianity as a measure of initial-state memory that persists in long-time dynamics.

Kontakt: Prof. Dr. Heidrich-Meisner

29/10/26

Theoretische Physik

Seminar Statistical Physics

Samuel Wilken

Self-assembled mesoscale mechanics: jamming and stiffening with DNA liquids

Living systems tune their mechanics across scales by coupling biochemistry to physical mechanisms that reconfigure and strengthen in response to their surroundings. We build controlled model systems from DNA nanostars, whose liquid-liquid phase separation (LLPS) harnesses nucleic acids' design power. First, dense packings of multiphase DNA droplets form a simple prototissue: same-species droplets coalesce, while different species repel like hard spheres. These packings undergo a solid-to-liquid unjamming transition, and simulations show its sharpness depends strongly on biomolecular diversity and stoichiometry. Second, DNA droplets occupying less than 10% of an entangled actin network stiffen it 25-fold, reversibly, far beyond the roughly 25% classical theory predicts. Actin penetrates the droplets, so network elasticity in turn sets droplet size, giving reciprocal control between matrix and inclusions. We attribute the stiffening to actin entrainment, which enlarges the effective inclusions until their contact network dominates the mechanics. Together, these results show that LLPS can control not only local composition but also mechanics, pointing toward design principles for adaptive materials.

Kontakt: Peter Sollich