In a first, a quantum computer has simulated a high-energy particle physics experiment.
Physicists have long hoped to create computer models of these experiments. This would allow them to simply press “play” on a quantum computer and watch the experiment play out in real-time, a vision of Richard Feynman’s from 1982. High-energy particle physics experiments—like those being performed at the Large Hadron Collider at CERN—are expensive and can provide limited information.
Now, a team of Austrian physicists announced in Nature that they have taken a step in that direction, simulating the process by which a positron-electron pair are spontaneously created using a small quantum computer.
Elementary particles, such as electrons and positrons, are difficult to simulate because they are governed by quantum mechanics. Any simulation of their interactions needs to encode the complicated phenomenon of quantum entanglement, which describes the way all of the particles in a system interact collectively. It ends up being too much information for a standard computer—but not for a quantum computer.
The difference lies in the basic building blocks of the two machines. Classical computers process information as a series of bits, which are either 0 or 1. But quantum computers use qubits—a shortening of ‘quantum bit’—which can be in a so-called superposition. Just as Schrödinger’s cat can be alive, dead, or somewhere in between, a qubit can be in 0, 1, or somewhere in between—a superposition. This flexibility allows for vastly more computation power.
Today, quantum computers are largely a theoretical construct. Scientists pretty much understand how a quantum computer should work, but can’t quite overcome the engineering challenges to build a full-scale one. The most advanced quantum computers are still fairly small and rudimentary.
Esteban Martinez and Christine Muschik, the pair of physicists who led the recent experiments, used one of these basic quantum computers to simulate the mechanism by which energy is converted into two antiparticles, in this case, an electron and positron.
Here’s Davide Castelvecchi, writing for Nature News:
The team used a tried-and-tested type of quantum computer in which an electromagnetic field traps four ions in a row, each one encoding a qubit, in a vacuum. They manipulated the ions’ spins — their magnetic orientations — using laser beams. This coaxed the ions to perform logic operations, the basic steps in any computer calculation.
After sequences of about 100 steps, each lasting a few milliseconds, the team looked at the state of the ions using a digital camera. Each of the four ions represented a location, two for particles and two for antiparticles, and the orientation of the ion revealed whether or not a particle or an antiparticle had been created at that location.
The small-scale experiment was successful, but questions remain about whether the technique will scale up. It would take a larger quantum computer—the kind scientists don’t yet know how to build—to simulate more complicated particle interactions. But Martinez and his team have provided proof of concept, a valuable step toward realizing Feynman’s vision.
Scientists could learn a lot by simulating elementary particle interactions on a quantum computer, but it’s unlikely to ever replace the genuine discovery of experimentation. For now, the Large Hadron Collider’s job is safe.