A team of researchers led by the University of Maryland reported the creation of an entirely new phase of matter, which they are calling a time crystal because the atoms move in a pattern that repeats in time rather than in space, according to an article on the University of Texas website.
Researchers have created the world's first time crystal, an exotic state of matter that combines the rigidity of
an ordinary crystal with a regular rhythm in time. (E. Edwards/JQI)
The atoms in the time crystal never settle into thermal equilibrium, where all the atoms have the same amount of heat, but settle into a nonequilibrium phase, which was predicted in 2012 but only proved possible this past fall.
An article from the MIT Technology Review in October explained the concept of a time crystal. It said, “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.”
The time crystals were formed from ions of ytterbium. According to the article, “By applying just the right electrical field, the researchers levitated 10 of these ions above a surface like a magician’s assistant.
“Next, they whacked the atoms with a laser pulse, causing them to flip head over heels. Then they hit them again and again in a regular rhythm. That set up a pattern of flips that repeated in time.”
The researchers saw that the pattern of atom flips repeated half as fast as the laser pulses, a quantum behavior that had been predicted prior to the experiment and denoted that the atoms were a time crystal. A second time crystal was formed at Harvard University a month later from a diamond.
The MIT article from October noted, “These guys discovered that after allowing the system to evolve, the interactions occurred at a rate that was twice the original period. Since there is no driving force with that period, the only explanation is that the time symmetry must have been broken, thereby allowing these longer periods. In other words, Monroe and co had created a time crystal.”
The theoretical work was published last year in Physical Review Letters. The experimental research was recently published in Nature. The abstract stated:
“Spontaneous symmetry breaking is a fundamental concept in many areas of physics, including cosmology, particle physics and condensed matter. An example is the breaking of spatial translational symmetry, which underlies the formation of crystals and the phase transition from liquid to solid.
“Using the analogy of crystals in space, the breaking of translational symmetry in time and the emergence of a ‘time crystal’ was recently proposed, but was later shown to be forbidden in thermal equilibrium. However, non-equilibrium Floquet systems, which are subject to a periodic drive, can exhibit persistent time correlations at an emergent subharmonic frequency. This new phase of matter has been dubbed a ‘discrete time crystal’.
“Here we present the experimental observation of a discrete time crystal, in an interacting spin chain of trapped atomic ions. We apply a periodic Hamiltonian to the system under many-body localization conditions, and observe a subharmonic temporal response that is robust to external perturbations.
“The observation of such a time crystal opens the door to the study of systems with long-range spatio-temporal correlations and novel phases of matter that emerge under intrinsically non-equilibrium conditions.”