Researchers at the University of Maryland's Joint Quantum Institute have created the world's first time crystals.
Atoms in a time crystal are arranged in a stable, repeating pattern throughout time. By trapping ions, 12 university researchers have created these crystals in a lab, publishing their findings in the journal Nature March 9.
To do this, a JQI research group called Trapped Ion Quantum Information, manipulated ions — individual atoms with a positive charge — so they satisfied the conditions of being a time crystal.
"We saw that it was interesting physics that no one has done yet and we could sort of easily do it in our system. So, why not do it?" said Antonios Kyprianidis, a physics graduate student and JQI experimenter.
Patrick Becker, a physics graduate student and experimenter at JQI, said the researchers can use lasers to make ions spin from their normal states. As time goes on, the ions switch states and repeat the pattern, he said.
Similar to time crystals, space crystals are solids made up of atoms arranged in a repeating pattern in space, such as table salt or diamonds, said Christopher Monroe, a JQI fellow and distinguished physics professor at this university. The ions researched at the JQI were made to repeat themselves over time in a pattern "robust to perturbation," or its 'up-down-up-down' movement was resistant to the researchers' attempts to change it, Becker said.
When the lasers were changed to make the ions spin in a different pattern, they continued in their original repeating pattern, just like how the ions in a salt crystal repeat themselves in space.
"If we start from 'up' and we try to make it 'down-but-not-quite-down,' and then 'up-but-not-quite-up,' we see some sort of magical jumping to the position it was expected to be," Kyprianidis said.
The ions' consistent repeating, despite researchers' attempts to keep the pattern from continuing, is what makes their discovery novel, Monroe said. This separates the ions in the lab from other objects that repeat in patterns over time, like a pendulum in a grandfather clock, which wouldn't return to its movement spontaneously if something made it stop, Becker said.
The pattern of the ions they observed, however, isn't affected by outside forces, satisfying the qualifications to be a time crystal.
Frank Wilczek, a Nobel Prize-winning theoretical physicist, first proposed the concept of time crystals in 2012, saying these crystals are like coins that spontaneously flip from heads to tails in a set pattern over time, despite attempts to disturb it, Becker said. In 2013, Patrick Bruno, a theorist at the European Synchrotron Radiation Facility in France, proved it is impossible for a system in equilibrium to exhibit this kind of behavior, saying in a research paper that time crystals couldn't exist.
But in 2016, University of California, Berkeley physics professor Norman Yao proposed while time crystals were impossible to exist in equilibrium, they could be observed in an out-of-equilibrium system, saying time crystals could exist if a system of trapped ions were made to spin in a pattern with lasers. His work served as the basis of the JQI researchers' work, Kyprianidis said.
"That in-equilibrium model of the universe that we have isn't necessarily accurate," Becker said. "It's an excellent approximation, but if you really want to know what's happening sometimes you need to consider out-of-equilibrium physics."
The JQI normally deals with trapped ions to research quantum computing, but it didn't take many modifications for the lab to carry out Yao's theory, Monroe said. It only took a couple of months to set up the lab to perform the experiments, which took only a few days to finish, he said.
The institute is one of a few labs worldwide that can do something like this due to the necessary equipment and setup for the experiment, Monroe said. It took a combination of the lab's highly accurate ultraviolet lasers, low-pressure vacuums and microwave radiation to observe time crystals without the ions heating up and melting, he said.
The Intelligence Advanced Research Projects Activity, the Department of Defense and the National Science Foundation fund JQI's research, with about half of the funding coming from IARPA, Monroe said. The program's funding lasts until Jan. 31, 2021, according to the Federal Business Opportunities website.
Monroe's group is trying to trap ions using electromagnetic fields and store information within each ion for uses such as quantum computing, he said. Using trapped ions in quantum computing, which uses atoms to perform tasks, "could eclipse the performance of conventional computers" by increasing computer efficiency, according to Monroe's website.
The discovery of time crystals helps researchers understand how trapped ions behave, which can help make quantum computing a reality, Becker said.