An ‘impossible’ time-crystal system may hold the secret to the quantum computing revolution

In a seemingly physics-defying experiment, scientists have created the first-ever time-crystal two-body system — and it could have incredible implications for the future of quantum computing.

In a paper published today in the journal Nature Communications, researchers from the UK, Russia and Finland described how they created two time crystals inside a superfluid – in this case, an isotope rare helium, cooled to about a ten-thousandth of a degree from absolute zero – and brought them together to touch, creating a coupled system that is not based on classical physics, but on quantum rules.

“It turns out that the combination of two of them works wonders,” explained Dr. Samuli Autti, member of the EPSRC and lead author of the study. “Even though time crystals shouldn’t exist in the first place.”

“Time Crystals” can look like something a IndianaJones movie, but they’re actually so much more awesome than that. They are one of those strange quantum phenomena that baffle scientists a bit – their existence was only proposed in 2012, and for a long time they were supposed to be purely theoretical.

Imagine the scientific community’s collective surprise, then, when two separate research teams announced the discovery of real-time crystals in 2017. Since then, the mysterious little objects have appeared everywhere – from state-of-the-art quantum computers technology. to an everyday child’s toy.

But what exactly are time crystals? Depending on how you think about it, they are either exactly what they sound like or none of that. You see, a normal, non-temporal crystal – something like an emerald or a snowflake – is defined by its regular, repeating atomic structure. A diamond, for example, looks like this under the microscope:

Image credit: posmguys/Shutterstock.com

It’s extremely symmetrical – no matter where you are in the space of the structure, the pattern will be the same. And time crystals are the same – except the pattern doesn’t repeat in space, but in time.

This is how we understand temporal crystals where their name takes on its full meaning: they are the temporal analogue of a normal crystal. The slightly more confusing aspect comes when you try to imagine what it actually looks like.

“Let’s say you took pictures of a planet and its orbiting moon every time it completes its orbit over a period of time with the Hubble Telescope,” explained Google Quantum AI researchers Pedram Roushan and Kostyantyn Kechedzhi, who did not participate in the research. “These images would all look the same with the moon repeating its orbit over and over again.”

But “what if there was a system of one planet and many moons where the moons could periodically repeat their orbits, without ever increasing entropy?” They continue. “This configuration – obviously difficult to achieve – would be considered a time crystal.”

In other words, a time crystal isn’t really a crystal at all – at least not the way we’re used to thinking of them. It is a new phase of matter, both stable and constantly changing at the same time, and always returning periodically to the same pattern.

And that…shouldn’t make sense. “Everyone knows that perpetual motion machines are impossible,” Autti said. “However, in quantum physics, perpetual motion is acceptable as long as we keep our eyes closed.”

“By sneaking through this fissure, we can create time crystals,” he explained.

But creating a time-crystal two-body system is more than just a way to cheat the laws of physics. The basic building block of a quantum computer – widely considered the next big step forward in computation – is what is called a “two-level system”: a quantum system that exists in a superposition of two states independent quantum. And that’s exactly what the researchers constructed: “In our experiments, two coupled time crystals made of spin-wave quasiparticles… form a macroscopic two-level system,” the paper explains.

“Both levels evolve over time as determined intrinsically by nonlinear feedback, allowing us to construct spontaneous two-level dynamics,” the authors continue. “[The] magnon time crystals allow access to all aspects and details of coherent quantum interactions in a single run of the experiment.

And that opens up exciting possibilities for the future. Generally speaking, quantum computers rely on extremely cold temperatures – Google’s, for example, is kept below 50 millikelvins, which is literally colder than the coldest place in the universe.

But “we already know [time crystals] also exist at room temperature,” Autti said — and so finding this two-body system may provide a way to make quantum computers that can operate without supercooling.

And that… would be extremely exciting.

Sherry J. Basler