CQD Special Seminar

2. October 2018 09:30

Seminarraum 2.403, Kirchhoff-Institut für Physik, INF 227

Quantum butterfly effect in critical systems: instability vs. chaos

Benjamin Geiger
Theoretische Physik, Universität Regensburg

The investigation of the scrambling of information in interacting quantum systems has recently attracted a lot of attention as a manifestation of quantum chaos. To capture the effect, one can make use of the so-called out-of-time-ordered correlators (OTOCs) whose short-time behavior can be directly related to the instability of a corresponding classical chaotic system with characteristic sensitivity to initial conditions given by the Lyapunov exponent. We show that local instability of the mean-field dynamics can be sufficient to reproduce the short-time behavior of the OTOCs as expected for chaotic systems, where the classical stability exponent takes the role of the Lyapunov exponent. We further investigate the transition from integrability to chaos in a hallmark system. We find that the onset of chaos strongly affect the long-time behavior of the OTOC while the short-time behavior remains dominated by criticality.

CQD Colloquium

12. November 2025 16:30 Uhr

INF 226, K1-3 (Goldbox)

tba

Dr Rob Smith, University of Oxford

PreTalk: Andreea Oros, KIP, Heidelberg University

CQD Special Seminar

7. November 2025 13:30 Uhr

INF 226, K1-3 (Goldbox)

Scale invariance and universal probability distribution of an order parameter across a continuous phase transition

Prof David Clément , Institut d'Optique Graduate School, Laboratoire Charles Fabry, France

Scale invariance lies at the foundation of modern statistical physics and underpins the description of continuous phase transitions. Its most striking manifestation is the universal probability distribution function (PDF) of the order parameter, which encapsulates the complete statistical structure of critical fluctuations—beyond what traditional quantities such as averages or critical exponents can reveal. However, this universal distribution is exceptionally challenging to measure, as it reflects the non-Gaussian and scale-invariant nature of critical fluctuations.

We will report on the experimental study of the statistics of the condensate order parameter across the superfluid–Mott transition in a gas of 3D lattice bosons, making use of single-atom-resolved detection in momentum space [1]. First, we observe non-Gaussian statistics of the order parameter near the transition, distinguished by non-zero and oscillating high-order cumulants [2]. We provide direct experimental evidence that these oscillations are universal. Second, crossing the Mott transition for various entropies and collapsing the cumulant oscillations, we obtain the non-universal coefficients required to reconstruct the universal PDF [3]. Finally, this universal scaling function determined experimentally is shown to yield algebraic scaling laws whose exponents are consistent with the critical exponents of the (expected) 3D XY universality class.

contact

Prof. Dr. M. Weidemüller
Physikalisches Institut
Im Neuenheimer Feld 226
69120 Heidelberg

06221-54 19470

Ferman Alkasari