Oxford Physicists Use Hybrid Quantum Computer to Freeze a Simulated Particle With Quantum Interference

Physicists at the University of Oxford have used a hybrid quantum computer to recreate a strange quantum effect in which a particle responds to a magnetic field it never passes through. In their simulation, adding a simulated magnetic flux brought a particle's motion to a complete halt. The findings were published in Nature Physics.

The experiment reproduced the Aharonov-Bohm effect, predicted in 1959 by physicists Yakir Aharonov and David Bohm. They proposed that a charged particle could be affected by magnetic flux even if it traveled entirely outside the region containing the magnetic field. Instead of feeling a conventional magnetic force, the particle would undergo a change in its quantum phase. Phase describes an aspect of a particle's wave behavior that shapes how different possible paths interfere. It cannot be seen directly, but differences in phase produce measurable effects. The effect was later verified in experiments with real electrons.

The Oxford team wanted to explore how this phenomenon behaves in lattice gauge theories. These models describe how matter interacts with fields tied to fundamental forces, representing space as a grid in which matter sits at points and fields sit on the connections between them. They matter in particle and high-energy physics, but the mathematics becomes extraordinarily demanding as systems grow, and even powerful conventional computers can struggle. Quantum simulation offers an alternative: build a controllable quantum system that follows the same rules and watch how it behaves.

The project began in 2022, when lead author Dr. Sebastian Saner, Dr. Oana Bazavan and colleagues started developing a hybrid approach, in collaboration with Dr. Alejandro Bermudez of the Instituto de Física Teórica in Madrid. Their system used trapped ions, which are electrically charged atoms held in place by electromagnetic fields. Qubits encoded in the ions' internal states represented the gauge fields. Quantum oscillators, created by the vibrations of the same ions, represented matter.

With these ingredients the researchers built a simple loop, a basic building block of a lattice gauge theory. Two oscillators stood in for matter at two locations, and two qubits stood in for the fields connecting them. The researchers then placed the two qubits in an entangled state, which within their model represented magnetic flux passing through the center of the loop.

This design began as a workaround. The team had originally planned to introduce the flux as a fixed background condition, but doing so would have required capabilities their hardware lacked. Encoding the flux in the qubits instead made it part of the evolving quantum system. "For us, the exciting step was to encode the magnetic flux in a gauge field that was itself dynamical," said Saner. "Rather than having matter evolve in a fixed background, the matter and gauge field become part of the same quantum dynamics."

The researchers then watched how a matter particle moved between locations by quantum tunneling, a process that lets particles shift between states in ways classical physics forbids. Without magnetic flux, the particle tunneled freely around the loop. With the simulated flux, the result changed sharply. The particle had two possible paths around the loop, and the flux altered their relative quantum phases so that the paths interfered destructively, canceling each other out. Tunneling was completely suppressed, leaving the simulated particle frozen in its original state.

According to the researchers, this demonstrated the Aharonov-Bohm effect in a lattice gauge theory with a dynamical field, rather than only a particle moving around a fixed magnetic influence.

The work was published alongside a related study from the University of Maryland led by Professor Norbert Linke. That team also used a hybrid quantum system, but simulated the Yukawa potential, a mathematical description of an interaction relevant to nuclear and particle physics. The two groups developed their methods independently and later coordinated their submissions to Nature Physics. Together, the studies suggest hybrid quantum computers could become useful tools for investigating fundamental interactions that are hard to reproduce with classical simulations.

The source material points to clear limits. The Oxford setup is small, consisting of just two oscillators and two qubits, and it represents only a basic building block of a lattice gauge theory. The source does not describe specific plans for scaling up, but the researchers frame the experiment as an example of the potential of combining different types of quantum components so that simulations better reflect the physics under study.