07 Sep Greater precision in laser control of qubits
Trapped ions can serve as qubits in quantum computers, with their quantum states precisely manipulated using laser light. With a tightly focused laser beam, however, the strongest interaction with an ion does not necessarily occur where the light intensity is highest. This displacement, known as the optical Magnus effect, is particularly relevant to the precise laser control of ion qubits. If the lateral shift in the interaction is not taken into account, the optical Magnus effect can affect this control and contribute to errors.
Researchers from the Paul Scherrer Institute PSI, ETH Zurich and the University of Amsterdam have now directly demonstrated for the first time that the maximum of the light-ion interaction can be laterally displaced from the center of the laser beam.
Tight focusing changes the spatial structure of the laser beam’s electromagnetic field. As a result, the interaction with the ion is no longer strongest exactly at the center of the beam, but slightly to one side. This displacement is the optical counterpart of the Magnus effect known from classical mechanics.
Displacement of several hundred nanometers
For the experimental demonstration, the research team used a single calcium ion as a sensitive probe. The electrically charged atom was held nearly motionless at a defined position in an ion trap using electromagnetic fields. The researchers then investigated how strongly the ion interacted with the tightly focused laser light at different positions.
This allowed them to map the spatial structure of the laser light and detect a lateral displacement of several hundred nanometers. They also found that the magnitude of the displacement depends on the wavelength of the light, but not on how tightly the laser is focused.
Effect could couple qubits
According to the researchers, the effect could also be exploited deliberately. The resulting forces could be used to couple qubits, potentially enabling more complex quantum operations.
The optical Magnus effect had been theoretically predicted several years earlier by researchers at the University of Amsterdam. Using the trapped calcium ion, the team has now experimentally demonstrated the effect for the first time and characterized it in greater detail.
Original publication:
[Philip Leindecker et al.: Direct Observation of the Optical Magnus Effect with a Trapped Ion; Physical Review Letters, 06.08.2026 (online), DOI: 10.1103/kj5p-qqs5]
Source: www.psi.ch
Image: Paul Scherrer Institute PSI / Edgar Brucke
Caption: Ultra-high-vacuum chamber of a quantum computer at PSI that uses trapped ions. The experimental demonstration of the optical Magnus effect could help enable even more precise control of such quantum computers in the future.