The hype surrounding quantum computers is enormous but they’re still very much in their infancy. Google has been tinkering with one they’ve dubbed Sycamore and its biggest success to date was massively outperforming a conventional supercomputer in 2019, albeit in one task that was tailor-made to play to its strengths. Now, though, Google, along with collaborating researchers have announced that they’ve used their quantum computer to create a newly defined phase of matter: a time crystal.
Ordinary crystals like diamonds have their atoms arranged in repeating patterns in space. In 2012, physicist and Nobel Laureate Frank Wilczek wondered if an object could exist with a crystal-like pattern but instead of the pattern repeating physically, it repeated through time.
Wilczek wondered if an object could change and then revert back to its original state, flipping back and forth in regular intervals indefinitely with no energy input. A phase of matter locked in a self-sustained cycle of change. It’s a cool idea. There's just one problem: a Wilczekian time crystal basically achieves perpetual motion and that is a fundamental no-no.
A 2014 proof showed that this iteration of a time crystal was impossible. But physicists wouldn’t be deterred, and so they expanded the definition of what a time crystal could be. A so-called Floquet time crystal would flip back and forth like a Wilczekian one, but only if it’s being driven by an external source. Physicists have simulated Floquet time crystals in computers, imagining a row of particles with spins that flip up and down periodically when hit with a laser beam.
This time crystal needs the laser’s cycling light waves to flip, but it wouldn’t absorb any net energy from the laser to do so. Simulating a time crystal is one thing, but creating one is another. Actually… if we’re talking about quantum computers, then simulating a time crystal and creating one could actually be the same thing.
See, quantum computers use controllable quantum particles called qubits to perform their calculations. Using quantum particles means the system can simulate quantum phenomena much better than a classical computer can, which is what Google demonstrated back in 2019. After that, the Sycamore computer needed a new challenge. It was still too error-prone for applications like ultra-secure encryption, but researchers outside Google proposed Sycamore’s qubits were ideal for creating a time crystal. They joined forces and set to work.
The team used 20 qubits made of superconducting aluminum, each with two possible energy states which can represent up or down spins. The researchers set their spins up or down arbitrarily and randomized the interaction strength between the qubits, so they would interfere with each other and lock themselves into their assigned orientation.
When researchers hit the qubits with microwave pulses, their spins oscillated back and forth, but the system didn’t absorb or dissipate any net energy and the system’s entropy remained unchanged. To paraphrase one researcher, they evaded the second law of thermodynamics. At least for the milliseconds that the crystal lasted.
So, what’s next for quantum computer-made time crystals? Well, first and foremost, Google’s paper needs to make it through peer review. If it gets the thumbs up, then who knows? Maybe time crystals could be used as data storage for quantum computers. Maybe they could be used as a benchmark test that demonstrates a quantum computer’s level of control. Or maybe they’re just a strange novelty with applications that can only be teased out with further study. If you want to know more about how Sycamore achieved quantum supremacy, check out my video on that here. What do you think about time crystals? Promising future technology or obvious clickbait title?