Quantum computers are on the edge of revealing new particle physics

Quantum computers are beginning to become powerful tools for studying some of the most fundamental forces in the universe – and some of the trickiest to understand. Two experiments have used them to pave a new way forward for nuclear and particle physics.

“We have this sort of grand scheme where we eventually want to do quantum computing for high-energy physics,” says Torsten Zache at the University of Innsbruck in Austria. “There’s a strong consensus that large-scale quantum computers will actually be able to solve problems that are otherwise intractable.”

He and his colleagues used a quantum computer to simulate how excited particles – those with lots of energy – behave in quantum fields, a situation akin to the conditions they experience in particle accelerators. Pedram Roushan at Google and his colleagues ran a similar simulation on a different quantum computer.

While conventional computers can typically only capture snapshots of particles’ behaviour, the new simulations show how they behave over time, a bit like making a movie.

Roushan says it all starts with quantum fields, which extend through space and exert forces on particles. His team wanted to simulate the electromagnetic field, but there was an added challenge of ensuring that the simulated field didn’t just apply everywhere, but also that it correctly affected particles when zooming in on just a few.

Roushan’s and Zache’s teams each simulated a version of this local structure based on a simplification of the standard model of particle physics – our best theory for how all particles and the forces acting upon them behave.

Zache and his colleagues used a quantum computer made from extremely cold atoms controlled by lasers and electromagnetic pulses, which was produced by the quantum computing firm QuEra. Roushan’s team worked with Google’s Sycamore quantum computer, which uses tiny superconducting circuits.

Both teams simulated two particles in the quantum field that were first confined to move in concert, and then broke away from each other. In that scenario, particles behave as if connected by a string of energy that vibrates and eventually snaps. Within the standard model, this string breaking is important for quarks, which make up the nuclei of atoms and are held together by the strong force. It is also key to matter and antimatter particle pairs.

While conventional computers can accurately simulate this phenomenon at one instance in time, or when energies are relatively low, they can only capture the whole process for very small systems. “For decades, we have been paying attention to static physics, but what if you want a dynamical situation? We visualised it for the first time,” says Roushan.

What they saw doesn’t contradict the standard model and is in line with state-of-the-art conventional computer simulations, but using only a slightly bigger quantum computer would push this work into unknown territory, says Jad Halimeh at the University of Munich in Germany. He says the new experiments bring quantum computers “neck and neck” with the best traditional computers.

Anthony Ciavarella at the Lawrence Berkeley National Laboratory in California says string-breaking for quarks is where there are the most open theoretical questions, and, just a few years ago, researchers could barely use quantum computing hardware to simulate the process.

But now, says Halimeh, quantum computers are slated to be “the major player” in understanding what happens in the hearts of particle colliders.

When very energetic ions get smashed together in a collider, they produce showers of particles that hit detectors – the data is like the last few frames of a movie, and physicists can use it to reverse engineer what happened in the frames before. But quantum computers could let us start with the collision and understand what happens next, he says.

“I absolutely believe in this [approach],” says Zache. “Eventually, I think it will become a tool that will play a very important role.”

To get there, researchers will have to run their simulations on larger quantum computers and in three instead of two spatial dimensions. Roushan says his team is working with the realities and limitations of some of the best existing quantum computers, and that there isn’t one magic trick that can fast-track their simulations – both the hardware and the way in which simulations are programmed must keep improving.

But for now, he says, simulations like these can also help researchers understand less extreme particle physics, such as the ways excited particles behave in exotic quantum materials.