Physicists at Oxford University and the Instituto de Física Teórica in Madrid have demonstrated the Aharonov-Bohm effect using a hybrid quantum computer, combining qubits and quantum oscillators to simulate a fundamental quantum phenomenon in a new setting. The 1959 prediction by Yakir Aharonov and David Bohm, that a charged particle circling a magnetic field experiences its influence even without direct contact, was observed within a lattice gauge theory, a complex area of physics challenging for classical computers.
“For us, the exciting step was to encode the magnetic flux in a gauge field that was itself dynamical,” says Dr. Sebastian Saner, lead author of the research published in Nature Physics, demonstrating a new capability for quantum simulation of matter and gauge field interactions.
Hybrid Quantum System Simulates Aharonov-Bohm Effect in Lattice Geometry
A loop constructed from qubits and quantum oscillators demonstrated the Aharonov-Bohm effect, a foundational quantum phenomenon, within a simulated lattice structure. The experiment, detailed in Nature Physics, used trapped ions to represent both matter and the forces acting upon it, creating a hybrid quantum system capable of modeling complex interactions. This simulation focused on lattice gauge theories, mathematical frameworks used to describe interactions between matter and gauge fields, which pose significant computational challenges for classical computers.
As these theoretical systems grow in complexity, the resources required to model them classically increase exponentially, prompting exploration of quantum simulation as an alternative. The team began developing this experiment in 2022, recognizing the potential of hybrid quantum systems to overcome these limitations and directly observe quantum behavior within these theoretical models.
Qubits served as the foundation for representing gauge fields, while the vibrational modes of the same trapped ions embodied the matter particles within the simulation. The core of the experiment involved constructing a fundamental loop, the basic building block of the lattice gauge theory, using two quantum oscillators representing matter at distinct points, connected by two qubits representing the intervening fields.
Preparing the qubits in an entangled state, a uniquely quantum phenomenon, corresponded to introducing a magnetic flux piercing the loop. Initially conceived as a practical solution to hardware limitations, encoding the flux in the qubits proved to be a more insightful approach.
Sebastian Saner stated, “Rather than having matter evolve in a fixed background, the matter and gauge field become part of the same quantum dynamics.” Researchers then observed a matter particle attempting to tunnel around the loop, a quantum mechanical process where particles can pass through barriers they classically shouldn’t. Without the magnetic flux, the particle tunneled freely, exhibiting expected quantum behavior. However, when the flux was present, the two possible paths around the loop interfered destructively, completely suppressing the tunneling and effectively freezing the particle in its initial state.
This suppression served as experimental confirmation of the Aharonov-Bohm effect occurring within the dynamically simulated lattice gauge theory. The observed interference pattern directly mirrored the predicted phase shift experienced by the particle due to the magnetic flux, even though the particle never directly interacted with a magnetic field.
This work appears alongside a complementary study from the University of Maryland led by Professor Norbert Linke, which used a similar hybrid quantum system to simulate the Yukawa potential, a fundamental interaction in nuclear and particle physics. The two research groups developed their approaches independently before coordinating their submissions to Nature Physics, highlighting a growing trend in the field. Both studies highlight the potential of hybrid quantum architectures to tackle classically intractable problems in fundamental physics.
The Oxford-Madrid team’s system, by dynamically encoding the magnetic flux, offers a new level of control and flexibility in simulating these complex interactions. The ability to simulate lattice gauge theories with increasing accuracy and scale holds significant promise for advancing our understanding of fundamental forces and particles.
While current quantum computers are still limited in size and complexity, this experiment demonstrates an important step towards building systems capable of tackling the most challenging problems in high-energy physics. The successful observation of the Aharonov-Bohm effect in this novel setting allows for further exploration of more complex lattice gauge theories and potentially uncovering new physics beyond the Standard Model.
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