CQD Special Seminar

23. May 2019 09:00

Seminarraum, Institut für Theoretische Physik, Philosophenweg 16

Far-from-equilibrium dynamics of molecules in 4He nanodroplets: a quasiparticle perspective

Dr. Giacomo Bighin
IST Austria, Klosterneuburg, Austria

Angular momentum plays a central role in a plethora of quantum processes, from nuclear collisions to decoherence in quantum dots to ultrafast magnetic switching. Here we consider a single molecule embedded in a superfluid Helium nanodroplet as a prototype of a fully controllable many-body system in which to reveal angular momentum dynamics: an ultrashort, high-intensity laser pulse can induce molecular axis alignment, creating extreme out-of-equilibrium conditions, while imaging of molecular fragments after Coulomb explosion allows to obtain time-resolved measurements of molecular alignment [1].

The rotational dynamics of a molecule in superfluid Helium cannot be simply understood in terms of interference of rotational molecular states due to the strong interactions with many-body environment: we show that this scenario can be described in terms of the angulon quasiparticle [2,3]—a quantum rotor dressed by a field of many-body excitations—with a very good agreement with experimental data [4] for several molecular species and across a wide range of laser fluences. The dynamical theory we develop contributes to advancing the understanding of angular momentum dynamics in a many-body environment, with applications ranging from ultracold molecules to condensed matter.

1. D. Pantlehner et al., Phys. Rev. Lett. 110, 093002 (2013).

2. R. Schmidt and M. Lemeshko, Phys. Rev. Lett. 114, 203001 (2015).

3. M. Lemeshko, Phys. Rev. Lett. 118, 095301 (2015).

4. I.N. Cherepanov, G. Bighin, L. Christiansen, A.V. Jørgensen, R. Schmidt, H. Stapelfeldt, M. Lemeshko, submitted

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