Recently, Dr. Chao Gao in the Discipline of Physics cooperated with Prof. Hui Zhai, Postdoc. Sun Mingyuan from Tsinghua University, and Prof. Zhang Peng from Renmin University of China make a progess in research about ultracold atomic gas dynamics far from equilibrium state. The related achievements published in the international top Physical academic journal Physical Review Letters. The paper titled the Universal dynamics of a degenerate Bose gas quenched to unitarity (see 10.1103 / PhysRevLett. 124.040403).
A gas of neutral atoms exhibits quantum properties at very low temperatures. For example, at temperatures below millkelvin, the equilibrium state of weakly interacting Bose atomic gas is a Bose Einstein condensate (BEC) with superfluid properties . Previous studies have revealed that the ultra-cold atomic gas has universality in equilibrium state, that is, it does not depend on the type of atoms and the microscopic interaction. And one of the frontiers in the field is about does universality persist far from equilibrium? If so, in what form?
An experimental study published in Nature in 2018  found that the subsequent evolution of a cloud of BEC gas is universal if the atomic interaction is quenched to its maximum, or unitary limit. Specifically, its momentum distribution will reach a preheating stage, that is, it will not change with time. And it's going to be exponential over a certain interval. This exponential behavior had not been predicted in previous theoretical studies. The study of Gao et al. provides important theoretical understanding of this phenomenon from the perspective of two-body and multi-body. For the corresponding version of the diatomic system, they show that the system will reach steady state in the long time limit and give a strict correspondence between the initial state and the final state. For the multi-atomic system, they found that the time average of momentum distribution does conform to the exponential form and semi-quantitatively conforms to the experimental observation over a long period of time by using the time-dependent method. They also showed correlations between two-body and multi-body results. Their work provides important insights into the non-equilibrium dynamics of quantum systems. It is worth noting that this study takes advantage of the scale invariance of the system in unitary limits. In an earlier study  Gao et al. used scale invariance to predict that the dynamics of another class of systems would take on a fractal structure, also in Physical Review Letters.
Published by the American Physical Society, Physical Review Letters is the most authoritative journal in physics. It is a comprehensive report on the latest and most important physical research results of research groups around the world and has a wide impact on the entire field of scientific research. The first author of this paper is Dr. Chao Gao, and the co-corresponding authors are Dr. Chao Chao and Prof. Hui Zhai.
Gao Chao, obtianed Ph.D from Tsinghua University, Master's Supervisor, joined ZJNU in 2016. His main research area is ultra-cold quantum gas.
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Article: Gao Xianlong, Translation: Wan.