The atoms in a time crystal never settle down into a thermal equilibrium, a state in which they all have the same amount of heat. According to the researchers, it is one of the first examples of a new class of matter, called nonequilibrium phases, that have been predicted but until now have remained out of reach.
"This opens the door to a whole world of nonequilibrium phases," says assistant professor Andrew Potter at the University of Texas at Austin. "We've taken these theoretical ideas and actually built it in the laboratory. Hopefully, this is just the first example of these, with many more to come."
The team created the time crystal from ions of the element ytterbium. By applying the right electrical field, the researchers levitated 10 of these ions above the surface.
Next, they beamed the atoms with a laser pulse, causing them to flip. They created a regular rhythm by hitting the atoms with a laser pulse again and again. That set up a pattern of flips that repeated in time.
The team noted the pattern of atom flips repeated only half as fast as the laser pulses. This quantum behaviour helped confirm that the result was indeed a time crystal.
A team at Harvard University created a second time crystal from a diamond a month after the first team.