Seminarium Advances in Nanoengineering – 13 października 2026

We cordially invite you to Advances in Nanoengineering seminar, which will be held on October 13, 2026 at 13.15 in room 321, building A-1, where

Dr Abel Beregi
from Department of Physics and Astronomy, Bates College, USA & Clarendon Laboratory, University of Oxford, UK
will deliver a lecture titled:
Superfluid behaviour of 2D Bose gases in flat and curved geometries

Please find an abstract below.
 
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Superfluidity is an extraordinary state of matter that is relevant to phenomena ranging from the microscopic to the astrophysical scale. Two-dimensional (2D) systems are particularly interesting due to the competition between ordering and thermal fluctuations, leading to the celebrated Berezinskii-Kosterlitz-Thouless (BKT) transition between a superfluid and a normal fluid phase. Thanks to reliable sample preparation and a high degree of static and dynamic control, ultracold quantum gas experiments are ideally suited to studying these systems.
In the first part of my talk, I will present recent experimental progress on probing the equilibrium and out-of-equilibrium behaviour of 2D superfluids using ultracold Bose gases. This is enabled by the development of a precisely controllable bilayer trap and a spatially selective matter-wave interferometry readout scheme. Using this experimental protocol, it is possible to reconstruct the statistics of order-parameter fluctuations over repeated measurements, thereby probing higher-order correlations in the system. In the low-temperature regime, the measured statistics converge to a universal non-Gaussian extreme-value distribution, in good agreement with theoretical predictions and simulations. Across the superfluid transition, the order-parameter distribution is characterised through its first two relevant moments and the Binder cumulant, which show distinct crossover behaviour.
The same approach is used to study the relaxation dynamics of a novel out-of-equilibrium state, initialised by the coherent splitting of a single-layer 2D gas. This quenches the system across the BKT critical point from the superfluid into the normal-fluid regime. Previous measurements have shown that following the quench the relaxation of two-point correlation functions and vortex density follow universal scaling laws, in good agreement with real-time renormalisation group theory and numerical simulations. I will extend the analysis of this out-of-equilibrium superfluid by order parameter statistics measurements, which point towards parameter-independent scaling dynamics of higher-moment observables that are distinctly different to equilibrium systems.
The second part of my talk will focus on NASA’s Cold Atom Laboratory, an experimental platform aboard the International Space Station. I will discuss its main scientific objectives, with an emphasis on the realisation of ultracold gases trapped along the surface of a bubble. Such systems, enabled by the microgravity environment, are notable for being topologically distinct from samples realised on Earth. Owing to their unique geometry, the numerical simulation of these systems is particularly challenging. I will introduce an efficient numerical simulation scheme to solve the Gross-Pitaevskii equation in such geometries in experimentally relevant conditions. Furthermore, I will present results of finite-temperature simulations to study the superfluid behaviour of thin-shell Bose gases on the surface of a bubble.