Single-atom setup settles Einstein–Bohr challenge with new clarity

A research team at the University of Science and Technology of China (USTC), led by Pan Jianwei, has experimentally realized a century-old thought experiment originally proposed by Albert Einstein in 1927, which challenged the foundations of quantum mechanics. Using a highly sensitive single-atom interferometer with a trapped rubidium atom cooled near absolute zero, they recreated Einstein’s idea of detecting a photon’s path by measuring the recoil of a movable slit. Their results confirmed Niels Bohr’s counterargument: attempting to determine the photon’s trajectory destroys the interference pattern, demonstrating the fundamental incompatibility of certain quantum properties in a single measurement. This experiment provides one of the clearest modern validations of Bohr’s interpretation of quantum mechanics. Beyond settling this historic debate, the experiment offers a precise platform to explore more subtle quantum phenomena such as coherence loss and entanglement with the environment. By controlling the atom’s confinement and thus the photon’s momentum uncertainty, the team could tune the visibility of interference fringes, aligning