A particle does not have to pass through a magnetic field to be influenced by it. That surprising feature of quantum physics has now been recreated by researchers at the University of Oxford, who used a hybrid quantum computer to demonstrate how an invisible magnetic influence can bring a simulated particle’s movement to a complete stop.
The experiment reproduced a phenomenon known as the Aharonov-Bohm effect, in which a charged particle traveling around a region containing magnetic flux experiences a measurable change in its quantum state, even though its path never takes it through the magnetic field itself.
The Oxford team achieved this using a quantum system that combines qubits, the basic units of quantum information, with quantum oscillators, which represent vibrating motion. Their findings, published in Nature Physics, demonstrate how this combination could help scientists investigate fundamental interactions between matter and fields that are increasingly difficult to simulate using conventional computers.
A Strange Quantum Effect Predicted in 1959
In everyday physics, a charged particle responds to the electric and magnetic fields it encounters. Quantum mechanics, however, reveals that particles can behave in ways that have no straightforward counterpart in our ordinary experience.
In 1959, physicists Yakir Aharonov and David Bohm predicted that a charged particle could be affected by magnetic flux even if it traveled entirely outside the region containing the magnetic field. Rather than experiencing a conventional magnetic force along its path, the particle would undergo a change in its quantum phase.
Quantum phase describes an aspect of a particle’s wave behavior that influences how different possible paths interfere with one another. Although the phase itself is not directly visible, differences in phase can produce measurable effects.
The prediction became known as the Aharonov-Bohm effect and was eventually verified in experiments involving real electrons. It remains one of the clearest demonstrations that the quantum world operates according to rules that go beyond the familiar laws of classical physics.
Researchers are now exploring how this phenomenon behaves in more complex theoretical systems known as lattice gauge theories.
These theories describe how matter interacts with fields associated with fundamental forces. They represent space as a grid, with matter located at individual points and fields associated with the connections between them. Such models are particularly important in particle physics and high-energy physics, where scientists study the basic particles and interactions that make up the universe.
The challenge is that the mathematics becomes extraordinarily demanding as these systems grow more complicated. Even powerful conventional computers can struggle to calculate how all the interacting components evolve.
Quantum computers offer a different approach. Instead of attempting to calculate every aspect of a quantum system using classical computing methods, scientists can construct another quantum system that follows the same underlying rules. They can then observe its behavior directly, an approach known as quantum simulation.
How Scientists Built the Quantum Experiment
The Oxford project began in 2022, when lead author Dr. Sebastian Saner, Dr. Oana Bazavan, and their colleagues started developing a way to simulate lattice gauge theories using a hybrid quantum system. They collaborated with Dr. Alejandro Bermudez of the Instituto de FÃsica Teórica in Madrid.
Their experimental design relied on two different quantum components that performed separate functions.
The first consisted of qubits encoded in the internal states of trapped ions, which are electrically charged atoms held in place using electromagnetic fields. These qubits represented the gauge fields in the theoretical model.
The second component used quantum oscillators, created by the vibrations of those same trapped ions. These oscillators represented matter.
By combining the two, the researchers constructed a simple loop that served as a basic building block of a lattice gauge theory. Two oscillators represented matter at two different locations, while two qubits represented the fields connecting those locations.
Although the arrangement was small, it was sufficient to reproduce an important interaction between matter and magnetic flux.
Quantum Entanglement Creates a Surprising Solution
The researchers next placed the two qubits into an entangled quantum state. Entanglement is a phenomenon in which quantum systems become linked in ways that cannot be fully explained by classical physics.
Within the team’s simulated lattice gauge theory, this entangled state represented magnetic flux passing through the center of the loop.
Initially, the researchers had planned to introduce the magnetic flux as a fixed background condition. However, creating the necessary interaction would have required capabilities that their quantum hardware did not possess.
Encoding the flux directly into the qubits provided a practical alternative. More importantly, it allowed the magnetic flux to become part of the evolving quantum system rather than remaining an unchanging external influence.
“For us, the exciting step was to encode the magnetic flux in a gauge field that was itself dynamical,” says Dr. Saner. “Rather than having matter evolve in a fixed background, the matter and gauge field become part of the same quantum dynamics.”
What began as a technical workaround ultimately enabled the researchers to explore a more interesting version of the phenomenon, one in which matter and the field could participate together in the quantum dynamics.
A Quantum Effect That Stops Particle Motion
With their simulated loop in place, the scientists examined how a matter particle moved between locations through a process known as quantum tunneling.
Quantum tunneling allows particles to move between states in ways that would not be possible under ordinary classical rules.
When the researchers ran their simulation without magnetic flux, the particle could tunnel freely around the loop.
Introducing the simulated flux produced a strikingly different result.
The particle had two possible paths around the loop, but the magnetic flux changed their relative quantum phases. As a result, the two paths interfered destructively, meaning their quantum contributions canceled each other out.
This interference completely suppressed the tunneling, leaving the simulated particle frozen in its original state.
The outcome demonstrated the Aharonov-Bohm effect within a lattice gauge theory containing a dynamical field. Rather than simply reproducing the familiar behavior of a particle moving around a fixed magnetic influence, the experiment showed how the phenomenon can emerge when matter and the field are both represented by interacting quantum components.
A New Tool for Exploring Fundamental Physics
The Oxford findings were published alongside a related study by researchers at the University of Maryland, led by Professor Norbert Linke.
The Maryland team also used a hybrid quantum system, but their experiment focused on simulating the Yukawa potential, a mathematical description of an interaction relevant to nuclear and particle physics.
Although the two research groups developed their methods independently, they later coordinated the submission of their studies to Nature Physics.
Together, the experiments demonstrate how hybrid quantum computers could become valuable tools for investigating fundamental interactions that are difficult to reproduce using classical simulations.
By combining different types of quantum components, researchers can build systems in which matter and fields are represented in ways that more closely reflect the physics they want to study.
The Oxford experiment provides an example of that potential. A phenomenon first predicted in 1959 and later observed with electrons has now been recreated in a quantum simulator where the field itself participates in the dynamics, offering scientists another way to explore the unusual rules governing the quantum world.
