New form of matter 'time crystals' created

 In a first, scientists have created time crystals - a new phase of matter that may have applications in quantum computers.

Just as crystals have an atomic structure that repeats in space, time crystals also have a structures that repeats in time. They are kicked periodically, sort of like tapping Jell-O repeatedly to get it to jiggle.

Norman Yao from University of California, Berkeley in the US found exactly how to make and measure the properties of such a crystal and even predicted what the various phases surrounding the time crystal should be - akin to the liquid and gas phases of ice.

Researchers from the University of Maryland and Harvard University in the US followed Yao's blueprint and have created the first-ever time crystals.

They are the first of a large class of new materials that are intrinsically out of equilibrium, unable to settle down to the motionless equilibrium of, for example, a diamond or ruby.

"This is a new phase of matter, period, but it is also really cool because it is one of the first examples of non-equilibrium matter," said Yao.

"For the last half-century, we have been exploring equilibrium matter, like metals and insulators. We are just now starting to explore a whole new landscape of non-equilibrium matter," he added.

The time crystal created by researchers at the University of Maryland employs a conga line of 10 ytterbium ions whose electron spins interact, similar to the qubit systems being tested as quantum computers.

To keep the ions out of equilibrium, they alternately hit them with one laser to create an effective magnetic field and a second laser to partially flip the spins of the atoms, repeating the sequence many times. Because the spins interacted, the atoms settled into a stable, repetitive pattern of spin flipping that defines a crystal.

Time crystals were first proposed in 2012 by Nobel laureate Frank Wilczek and last year theoretical physicists at Princeton University and UC Santa Barbara's Station Q in the US independently proved that such a crystal could be made.

According to Yao, the UC Berkeley group was "the bridge between the theoretical idea and experimental implementation."

From the perspective of quantum mechanics, electrons can form crystals that do not match the underlying spatial translation symmetry of the orderly, three-dimensional array of atoms, Yao said.

This breaks the symmetry of the material and leads to unique and stable properties we define as a crystal.

A time crystal breaks time symmetry. In this particular case, the magnetic field and laser periodically driving the ytterbium atoms produce a repetition in the system at twice the period of the drivers, something that would not occur in a normal system.
The study was published in the journal Physical Review Letters.