Ars Technica: One test of the wave–particle duality of quantum objects is a class of experiments, in which a measurement made on one photon determines the wave-like or particle-like behavior of its entangled partner. However, this type of experiment has only been conducted in single laboratories, which leaves open the possibility that the photon detectors might have interacted, leading to spurious results. Xiao-Song Ma of the University of Vienna and colleagues have now conducted the experiment by separating the entangled photons over 144 km, between two labs in the Canary Islands. After entangling two photons in one lab, they sent one of them through the open air to the other facility and into a device that determines the photon’s polarization, a state correlated with that of its entangled partner. The device was randomly switched between two modes to measure either circular polarization or linear polarization. If the distant device detected a photon that was circularly polarized, then the photon that passed through a polarizing beam-splitter in the original location would behave like a wave; if the distant device detected linear polarization, then the photon in the original lab would behave like a particle.