George Musser in Quanta Magazine:
When an ice cube melts and attains equilibrium with the liquid, physicists usually say the evolution of the system has ended. But it hasn’t — there is life after heat death. Weird and wonderful things continue to happen at the quantum level. “If you really look into a quantum system, the particle distribution might have equilibrated, and the energy distribution might have equilibrated, but there’s still so much more going on beyond that,” said Xie Chen, a theoretical physicist at the California Institute of Technology.
Chen, Swingle and others think that, if an equilibrated system looks boring and blah, we’re just not looking at it in the right way. The action has moved from quantities that we can see directly to highly delocalized ones that require new measures to track. The favorite measure, at the moment, is known as circuit complexity. The concept originated in computer science and has been appropriated — misappropriated, some have grumbled — to quantify the blossoming patterns in a quantum system. The work is fascinating for the way it brings together multiple areas of science, not just black holes but also quantum chaos, topological phases of matter, cryptography, quantum computers, and the possibility of even more powerful machines.
More here.