Ice cubes are crystals with a nice, defined internal structure, but when they melt into water, the information of that structure is lost to the chaotic motion of the molecules. This is how it is with many actions in classical mechanics, but is it also true of those in quantum mechanics? According to researchers at the Vienna University of Technology, no, sometimes a quantum system can remember its original state, even as it decays into disorder.
The quantum system in question is a special one called a Bose-Einstein condensate. What makes it special is that every atom within it takes on the same wave function, so in effect the condensate behaves as though it were a single, giant atom. Condensates only exist under special conditions, including low temperature, so when one warms it 'melts' into a more traditional material, but it does not directly transition from the order to disorder. Instead a condensate will pause at a somewhat stable prethermalized state, and at this state it still remembers what it was like to be a condensate.
Beyond this unexpected memory, this discovery is very intriguing because of how long the prethermalized state seems to last. Instead of depending on temperature or pressure, the lifetime of this state is determined by previously unknown of length scale, which could have great significance in quantum mechanics as a whole.
Source: Vienna University of Technology