Researchers at the Paul Scherrer Institute and ETH Zurich have experimentally confirmed the optical Magnus effect, a subtle quantum phenomenon where a tightly focused laser beam interacts most strongly with an atom slightly off-center from the beam itself — not dead-center as long assumed.
The team used a single calcium ion, held nearly motionless in an electromagnetic trap, as an ultra-sensitive probe. By nudging the ion through different points of a focused laser beam and measuring the interaction strength at each position, they detected a sideways shift of just hundreds of nanometers. The size of the shift depends only on the light's wavelength, not on how tightly the beam is focused, matching a theoretical prediction made years earlier by researchers at the University of Amsterdam.
The effect matters for quantum computing: lasers are widely used to control individual atoms as qubits with extreme precision, and this hidden displacement could be a source of unwanted errors, or decoherence. But the researchers say the same effect might instead be harnessed as a new tool for coupling qubits together. The work was published in Physical Review Letters, with Philip Leindecker as lead author.