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Significant advances in nonequilibrium physics

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Publié le lundi 20 février 2023

Phase transitions are ubiquitous in Nature and manifest in the sudden changes in the state of matter when the external conditions are varied. Cooling a piece of iron can turn it into a ferromagnet and make a gas of alkali atoms form a Bose-Einstein condensate. The driving of phase transition leads to the formation of topological defects, excitations that are long-lived, being topologically protected. Examples include vortices in superfluids and superconductors, domain walls in ferromagnets, and the (elusive) cosmic strings that may have been formed in the early Universe. Universality is a powerful concept that provides a unified explanation of the behavior in all these different scenarios despite the vastly different energy scales.   

The dynamics across a phase transition, continuous or quantum, has long been known to be universal in the limit of slow driving. It is then described by the celebrated Kibble-Zurek mechanism (KZM), formulated independently by Tom W. Kibble and Wojciech H. Zurek in the ’70s and ’80s. This mechanism is one of the few universal paradigms available in nonequilibrium physics and finds applications ranging from material science to quantum computing. It predicts a universal power-law density of defects as a function of the quench rate. This key prediction has been the subject of exhaustive research sustained over four decades. By now, it has been studied using liquid crystals, colloids, superconducting systems, ultracold Bose and Fermi gases, ion chains, multiferroics, quantum simulators, quantum annealing devices, etc. However, its validity is limited to slow quenches and cannot explain the behavior under moderate and fast driving rates relevant to many applications.   

Prof. Adolfo del Campo at the Physics and Materials Science Department (DPhyMS) at the University of Luxembourg, in collaboration with Hua-Bi Zeng and Chuan-Yin Xia at the Center for Gravitation and Cosmology at Yangzhou University, has recently established the universality of critical dynamics for any driving rate, from the slow to the fast-quench limit. In their work, they show how the nonequilibrium dynamics, arbitrarily far from equilibrium, can be described in terms of equilibrium properties, both in the classical and quantum regimes. Their findings, reported in Physical Review Letters, constitute a significant advance in nonequilibrium physics of relevance to many experimental scenarios, away from the adiabatic limit. 

Proliferation of vortices in the density profile of a newborn Bose-Einstein condensate resulting from a fast thermal quench


DOI: 10.1103/PhysRevLett.130.060402