A matterless double slit

Double slits provide incoming particles with a choice. Those that survive passage through the slits have chosen from two possible paths, which interfere to distribute them in a wave-like manner. Such wave-particle duality1 continues to be challenged(2-5) and investigated in a broad range of disciplines with electrons6, neutrons7, helium atoms(8), C-60 fullerenes(9), Bose-Einstein condensates(10) and biological molecules(11). All variants have hitherto involved material constituents. We present a matterless doubleslit scenario in which photons generated from virtual electronpositron pair annihilation in head-on collisions of a probe laser field with two ultra-intense laser beams form a double-slit interference pattern. Such electromagnetic fields are predicted to induce material-like behaviour in vacuum, supporting elastic scattering between photons(12,13). Our double-slit scenario presents, on the one hand, a realizable method with which to observe photonphoton scattering and, on the other hand, demonstrates the possibility of both controlling light with light and non-locally investigating features of the quantum vacuum structure.