Nonlocality of a Single Particle Demonstrated Without Objections

Detecting single-particle nonlocality: The yellow path is Hardy’s original scheme. The red path is part of the modified version, where a reference state is created in the “black box.” The reference state is split off by beam splitter 1 toward Alice, and the other part is reflected off a mirror and then split off by beam splitter 2 toward Bob. This ensures that Alice and Bob can consistently compare their measurement results, and that the nonlocality must stem from the original single-particle state. (Modified image from Dunningham and Vedral)