Critical behavior helps to classify dynamic phase transitions

7 November 2023

Photo: Mathey group

The illustration shows the dynamics of the ultracold cloud with the spontaneous creation of vortex pairs (in red and blue). The time evolution of the system is shown schematically as a flow.

Researchers from Hamburg, Oxford and Hannover/Abu Dhabi have identified the universal behavior of a dynamic phase transition. In the renowned journal "Science", the scientists report on their findings, which could be of importance for the development of sensitive quantum sensors, for example.

Phase transitions occur in all fields of physics and are a central topic of many-body physics. Examples range from the simple transition of ice to water to the highly complex Bose-Einstein condensation of ultracold atomic gases. "Phase transitions occur in such a variety of systems that, at first glance, it seems impossible to organize them in a meaningful way," explains Prof. Ludwig Mathey of the Department of Physics at Universität Hamburg and a researcher in the Cluster of Excellence "CUI: Advanced Imaging of Matter." However, transitions can be divided into a small number of classes. These so-called universality classes include phase transitions in very different systems, from cold atom systems to neutron stars. What unites them in each case is their so-called critical behavior.

The researchers considered a "quench" scenario in a two-dimensional atomic cloud

The standard phase transitions are equilibrium transitions for which a classification could already be established. "We now asked ourselves whether non-equilibrium phase transitions could also be classified by their critical behavior," says Mathey. To this end, the researchers investigated a so-called "quench" scenario, in which a system parameter is changed rapidly, and the subsequent dynamics is detected.

Specifically, the researchers considered an atomic cloud in two dimensions undergoing a Kosterlitz-Thouless (BKT) transition and identified the universal behavior: They found that vortex pairs form from the fluctuations of the atomic cloud during this dynamic phase transition. Using the so-called real-time renormalization method, they then succeeded in describing the process and its time scale.

These findings are an important step towards a better understanding of many-body dynamics, in particular dynamical phase transitions. Some properties of these phase transitions could possibly be used to enhance certain effects, which would lead to increased sensitivity of, for example, a quantum sensor.

Citation:

Shinichi Sunami, Vijay Pal Singh, David Garrick, Abel Beregi, Adam J. Barker, Kathrin Luksch, Elliot Bentine, Ludwig Mathey, and Christopher J. Foot

“Universal scaling of the dynamic BKT transition in quenched 2D Bose gases”

Science 381, 443 (2023)

DOI: 10.1126/science.abq6753