A new blueprint for a device, known as a time crystal, can theoretically continue to work as a computer even after the universe cools so the heat-death of the universe need not bring an end to the computing age, has brought its construction a step closer.
Ordinary crystals are three-dimensional objects whose atoms are arranged in regular, repeating patterns similar to table salt. They adopt this structure because it uses the lowest amount of energy possible to maintain.
Frank Wilczek, a theoretical physicist at the Massachusetts Institute of Technology, speculated that a similar structure might repeat regularly in the fourth dimension – time, earlier this year.
To translate the spatial symmetry of a regular crystal into the fourth dimension, the atoms in such a “time crystal” would have to continuously rotate and return to their original location.
Crucially, they would also have to be in their lowest possible energy state as they do so, meaning that they would naturally continue to rotate even after the universe has succumbed to entropy and cooled to a uniform temperature – a state known as heat-death.
While such behaviour would normally violate the laws of thermodynamics, nonstop rotation is allowed in the case of electrons in a superconductor, which flow without resistance.
Wilczek had originally suggested that a superconductive ring could serve as a time crystal if electrons could be made to flow separately rather than in a continuous stream, ensuring a repeating pattern, but he couldn’t figure out how to do so in practice.
Now Tongcang Li at the University of California, Berkeley, and colleagues at the University of Michigan in Ann Arbor and Tsinghua University in Beijing, China, have an alternative suggestion that may be possible to construct.
First you need an ion trap, a device which holds charged particles in place using an electric field.
This causes the ions to form a ring-shaped crystal, as ions trapped at extremely low temperatures repel each.
Next, you apply a weak static magnetic field, which causes the ions to rotate.
Quantum mechanics means that the rotational energy of the ions must be greater than zero, even when the ring is cooled to its lowest energy state.
In this state, the electric and magnetic fields are no longer needed to maintain the shape of the crystal and the spin of its constituent ions. The result is a time crystal – or indeed a space-time crystal, because the ion ring repeats in both space and time.
“I’m very pleased with it,” New Scientists quoted Wilczek as saying.
“They’ve really come up with something that looks like a realisable experimental design,” he added.