April 17, 2025 -- Imagine the tiniest game of checkers in the world—one played by using lasers to precisely shuffle around ions across a very small grid.

That’s the idea behind a recent study published in the journal Physical Review Letters. A team of theoretical physicists from Colorado designed a new type of quantum “game” that scientists can play on a real quantum computer—or a device that manipulates small objects, such as atoms, to perform calculations.

The researchers even tested their game out on one such device, the Quantinuum System Model H1 Quantum Computer developed by the company Quantinuum. The study is a collaboration between scientists at the University of Colorado Boulder and Quantinuum, which is based in Broomfield, Colorado.

The findings highlight just a slice of what these devices may be capable of, said study co-author Rahul Nandkishore.

“Small-scale quantum devices are rapidly coming online,” said Nandkishore, associate professor in the Department of Physics at CU Boulder. “That really prompts the question: ‘What are they good for?’”

Why quantum?

The answer: A lot, potentially.

Scientists believe that quantum computers could one day perform a range of tasks with a speed that’s unheard of today—such as discovering new drugs to treat human illnesses or exploring how atoms and electrons interact at very small scales.

But building a quantum computer that works as desired isn’t an easy goal. Unlike your home laptop, which runs on bits, or switches that flip to either zero or one, quantum computers hinge on a concept called qubits. Qubits, which can be made from atoms or other small objects, take on values of zero, one, or through the strangeness of quantum physics, both simultaneously.

Qubits are also notoriously difficult to control, said study co-author David Stephen, a physicist at Quantinuum.

To explore a new way of lassoing these quantum entities, the research assembled a network of qubits into what physicists call a “topological” phase of matter—a bit like a clump of very small knots. That arrangement allowed the team to play a simple mathematical game without disrupting the quantum computer in the process, a major challenge for this kind of technology.

“In principle, there was nothing too surprising about this experiment. It worked exactly as we thought it would, in theory,” Stephen said. “But the fact that it did work so well can be seen as a benchmark for this quantum computer.”

Reading minds

Quantum games have been around for a long time, Nandkishore added, and even predate the world’s first quantum computer. They are mathematical exercises that allow scientists to explore some of the more out-there possibilities of quantum physics, which can also be tested experimentally.

Physicist David Mermin popularized the idea of quantum games in 1990. In a typical quantum game, two or more hypothetical human players receive prompts, then take turns filling out a grid with the numbers zero and one. (Picture something a little like sudoku). The players “win” the game if their arrangement of zeros and ones completes a certain mathematical pattern.

There’s just one problem, Nandkishore said. They players have to sit in different rooms. And they aren’t telepathic.

“They can agree on whatever strategy they want in advance, but they can’t communicate during the game,” said study co-author Oliver Hart, a postdoctoral associate in physics at CU Boulder. “It’s relatively straightforward to show that there’s no strategy that wins the game with certainty.”  

Which is where quantum physics comes in.

Mermin proposed that, in theory, you could give each player one of a collection of entangled particles. Entangled particles have interacted in such a way that measuring one will affect the outcome of measuring the other. That’s true even if the particles are separated, say in the next room (or next city) over. In a quantum game, players can use these correlations to coordinate their answers. It’s a feat so seemingly improbable that scientists nicknamed it quantum “pseudotelepathy.”

In practice, entangling particles inside a quantum computer, isn’t so simple.

Even the slightest disturbance, such as a minute increase in temperature, can snap the link between two particles. Those sorts of errors only stack up the more qubits you add to a quantum computer.

Quantum knotwork

Nandkishore and his colleagues wanted to play quantum games in a different way—one that might be easier to win in the real world.

To do that, the group turned to Quantinuum’s System Model H1. This device runs off a chip that can fit in the palm of your hand. It employs lasers to control a collection of as many as 20 qubits (in this case, ytterbium ions trapped above the surface of the chip).

In the current study, the researchers sent the computer commands online. They arranged the ytterbium ions into a two-dimensional grid so that they generated an unusual quantum structure: Instead of having just two or three ions that were entangled, the entire collection of ions exhibited an underlying pattern of entanglement, a “topological” order. It’s almost as if the qubits had tied themselves into knots.

And those knots, Nandkishore said, aren’t easy to unravel.

“We have order that's associated with this global pattern of entanglement across the whole system,” he said. “If you make a local disturbance, it shouldn’t mess it up.”

The researchers took on the role of quantum game players and experimented with making measurements of various qubits inside H1-1. They showed that they were able to achieve quantum pseudotelepathy, and win the game, roughly 95% of the time or more. The researchers were able to win the game consistently even when they added outside disturbances and additional hypothetical players measuring additional qubits.

Nandkishore noted that, on its own, the team’s game probably won’t solve any real-world problems. But it reveals that today’s quantum computers may already be able to grow bigger without losing their edge, at least in a few cases.

“This study is proof of principle that there is something that quantum devices can already do that outperforms the best available classical strategy, and in a way that’s robust and scalable,” he said.