Quantum Time Crystals
Channel: Civil Disturbia
Date: 08/02/2017

Physicists Create World’s First Time Crystal.

SOURCE: https://www.technologyreview.com/s/602541/physicists-create-worlds-first-time-crystal/

Time crystals were first predicted in 2012. Now researchers have created time crystals for the first time and say they could one day be used as quantum memories.

Chris Monroe at the University of Maryland in College Park and a few pals, who have created a time crystal in their laboratory for the first time.

The basic process for making time crystals is straightforward. The idea is to create a quantum system, such as a group of ions arranged in a ring, and cool them until they are in their lowest energy state. In these circumstances, the laws of physics would suggest that the ring should be perfectly stationary.

But if time symmetry were broken, then the ring could vary periodically in time. In other words, it would rotate. Of course, it would never be possible to extract energy from this motion, that would violate the conservation of energy. But the temporal symmetry breaking would manifest itself in this repeating motion in time, just as spatial symmetry breaking manifests itself as repeating patterns in space.

That’s the theory, but in the real world, things are not quite as simple. The main problem is that the quantum world is not governed by time dependent variables, so time symmetry cannot be broken on this scale. So in ordinary circumstances, cooling a ring of ions to their lowest energy state would leave them stationary.

But there are circumstances in which quantum systems do evolve over time. Munro and co have focused on these: quantum systems that are not in equilibrium. Their quantum system is a line of ytterbium ions with spins that interact with each other. 

That interaction leads to a special kind of behavior. One of the strange features of quantum particles is that they do not usually exist in specific locations. Instead they are smeared out in space with the chances of them appearing anywhere governed by the laws of probability.

But in some circumstances this can change. For example, a single electron inside a material can interfere with itself in a way that forces it to appear in a single location. This is known as Anderson localization, after the physicist who predicted it in the 1950s.