Time crystal: Physics taken to a whole new level

9 Mar 2017

Image: GiroScience/Shutterstock

A new form of matter has been discovered after two groups of scientists took predictions of elusive physical properties and, individually, went and proved them.

Time crystal sounds like a fantasy crime thriller that gets cancelled after one optimistic, yet ultimately poorly executed, midweek TV series.

In reality, it is a new form of matter – solid, but not quite. The key difference is that the atoms in time crystals never settle into what’s called a ‘thermal equilibrium’.

In normal solids, all atoms are the same temperature; in time crystals, they are not. This is new, and it has physicists excited.

It’s one of the first examples of a broad new class of matter called non-equilibrium phases. These have been predicted but, until now, have remained out of reach.

The physics field has had a storming start to 2017. Earlier this month, for example, MIT physicists created a ‘supersolid’, replicating the viscosity-free, endless flowing attributes of superfluids.

Time crystals can move without using any energy, which was theoretically impossible prior to their (a) prediction in 2012 and (b) proof in 2017.

Back in 2012, Nobel Prize-winning theoretical physicist Frank Wilczek predicted an object that could achieve everlasting movement while in its ground state.

This would be done by switching the alignment of atoms inside the crystal over and over again – in and out of the ground state.

A team of scientists led by the University of Maryland, and another at Harvard, have helped to prove the new forms this year, with their discoveries pioneering a new strand of physics.

Interestingly, they both went about their projects in wildly different ways. While the Harvard study looked at diamonds in getting to this stage, the former used ytterbium ions.

“This opens the door to a whole new world of non-equilibrium phases,” said Andrew Potter, an assistant professor of physics at the University of Texas at Austin, who worked on the ytterbium ions project.

Potter’s team applied an electrical field to 10 ions, levitating them above a surface. Next, they whacked the atoms with a laser pulse, causing them to flip. They hit them again and again in a regular rhythm, setting up a pattern of flips that repeated in time.

However, the ions only flipped half as fast as the laser pulses hit them – a tell-tale sign of time crystals.

The Harvard team packed diamonds with significant amounts of nitrogen impurities through nitrogen atoms, and they turned black. They hit them with a microwave pulse, and the resulting spin was similar to the ytterbium project.

“We’ve taken these theoretical ideas that we’ve been poking around for the last couple of years and actually built it in the laboratory,” said Potter. “Hopefully, this is just the first example of these, with many more to come.”

Both papers feature in Nature, here and here.

Gordon Hunt was a journalist with Silicon Republic