November 3, 2016
For systems near continuous phase transitions, the details don’t matter. In principle, a universal theory can be applied to understand continuous phase transitions whether they occur in biological cell membranes, magnets, liquid crystals, or even in the entire early universe! But while the universal theory of static systems near continuous phase transitions has been generally successful, the degree to which the dynamics of crossing such transitions can be universally explained presents an exciting new frontier.
Recent work by the Chin group uncovers these universal features in the dynamics of ultracold atoms in a shaking optical lattice. When the researchers shake the lattice they find that atoms undergo a continuous, quantum phase transition, after which they must choose between two new ground states with either leftward or rightward momentum. This causes the gas to split into domains with atoms in one momentum state or the other, which can then be observed using a microscope. The researchers found that the details are indeed irrelevant: the growth of domains over time and their pattern across space are independent of the rate at which the transition is crossed, once they account for a simple power-law scaling of space and time. These findings support the universal scaling symmetry of phase transition dynamics, which provides a simple, powerful prediction for the behavior of a huge variety of systems when they cross continuous phase transitions.