Usually when physicists talk about nonlocality in quantum mechanics, they’re referring to the fact that two particles can have immediate effects on each other, even when separated by large distances. Einstein famously called the phenomena ‘spooky interaction at a distance’ because information about a particle seems to be traveling faster than the speed of light, violating the laws of causality. Although the idea is counterintuitive, nonlocality is now widely accepted by physicists, albeit almost exclusively for two-particle systems. So far, no experiment has sufficiently demonstrated the nonlocality of a single particle, although explanations have been proposed since 1991 (starting with Tan, Walls, and Collett). Since then, the issue has been strongly debated by physicists. In 1994, Lucien Hardy proposed a modified scheme of Tan, Walls, and Collett’s claim. However, others (notably Greenberger, Horne, and Zeilinger) objected to Hardy’s scheme, claiming that it was really a multi-particle effect in disguise, and could not be demonstrated experimentally. Now, Jacob Dunningham from the University of Leeds and Vlatko Vedral from the University of Leeds and the National University of Singapore have modified Hardy’s scheme, publishing their results in a recent issue of Physical Review Letters. By eliminating all unphysical inputs, […]