Crystals can exist in time as well as space Images Etc Ltd/Getty

It’s no longer just a wild theory. Two independent teams of physicists have followed a recipe to build the world’s first versions of an enigmatic form of matter – time crystals.

MIT physicist and Nobel laureate Frank Wilczek first speculated about the existence of time crystals in 2012, while teaching a class on ordinary crystals, such as salt, or snowflakes. In a typical crystal, the atoms or molecules are tightly arranged in regularly repeating patterns in three-dimensional space, resembling a lattice.

Wilczek thought it might be possible to create a similar crystal-like structure in time, which is treated as a fourth dimension under relativity. Instead of regularly repeating rows of atoms, a time crystal would exhibit regularly repeating motion.


Many physicists were sceptical, arguing that a time crystal whose atoms could loop forever, with no need for extra energy, would be tantamount to a perpetual motion machine – forbidden by the laws of physics.

Wilczek countered that a time crystal was more akin to a superconductor, in which electrons flow with no resistance, and in theory could do so forever without the need to add energy to the system. In a time crystal, electrons would travel in a loop rather than a line and occasionally bunch up rather than flow smoothly, repeating in time the way atoms in ordinary crystals repeat in space.

Crystal meth-odology

Now, in a paper published this week, Norman Yao at the University of California, Berkeley, and his colleagues have revealed a blueprint for making a time crystal. The recipe has already been followed by two teams.

For Yao’s time crystal, an external force – like the pulse of a laser – flips the magnetic spin of one ion in a crystal, which then flips the spin of the next, and so forth, setting the system into a repeating pattern of periodic motion.

There are two critical factors. First, after the initial driver, it must be a closed system, unable to interact with and lose energy to the environment. Second, interactions between quantum particles are the driving force behind the time crystal’s stability. “It’s an emergent phenomenon,” says Yao. “It requires many particles and many spins to talk to each other and collectively synchronise.”

Using Yao’s recipe as guidance, two groups have now created time crystals in the lab. Last September, a group headed by Chris Monroe of the University of Maryland in College Park built a time crystal out of a string of trapped ytterbium ions.

One month later, a team led by Harvard University’s Mikhail Lukin built a time crystal by exploiting defects formed in diamond. Both teams have submitted papers for publication.

History repeating

Both approaches yielded the telltale signature of a time crystal: the repeating pattern should be twice the period of the laser pulse used as the driver. But how could you tell if this was just because you were pushing it periodically with the laser pulse? The evidence is that the period the crystal settles into is different from that of the driving pulse that pushes it.

That means time crystals are more than just a curious oddity: they represent the simplest form of a new state of non-equilibrium matter that physicists have only begun to explore.

Spyridon Michalakis, a physicist at the California Institute of Technology, says Yao’s work “bridges the gap between theory and experiment by making concrete suggestions for experimental platforms”. Those suggestions have now been successfully implemented, and papers accepted for publication next month,

Time crystals could have enormous implications for building stable qubits for quantum computing. These devices rely on maintaining a state of entanglement among qubits to store information, but the slightest outside interference will destroy that entanglement, resulting in errors in the calculations.

One approach to combating this is to carefully isolate the qubits. But Microsoft’s Station Q group, among others, has been exploring the possibility of making building blocks that are inherently robust – braiding qubits into knots, for example. There are topological states analogous to time crystals that may one day prove useful for processing quantum information.

Journal reference: Physical Review Letters, DOI: 10.1103/PhysRevLett.118.030401