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.
Oh yeah.
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. So what do you think about time crystals?
Promising future technology or obvious clickbait title? Let us know in the comments, be sure
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and I'll see you next time on Seeker.