The on-ramp to the all-optical quantum information processing highway

An optical waveguide circuit can be flexibly programmed with near-perfect fidelity [Also see Research Article by Carolan et al. ] Since the first formulations of quantum mechanics in the early 20th century, it became clear that the enormous complexity of quantum-mechanical systems presented intractable computational problems. Richard Feynman was the first to turn this problem on its head. He asked whether we could exploit this quantum complexity to construct a computer based on these same quantum mechanical principles, offering exponential algorithmic improvements, and whether such a computer could efficiently simulate quantum systems that our classical computers are unable to simulate. This challenge initiated the field of quantum computing and is today a major field of research in the physics and computer science communities. One hurdle has been to construct devices that match the flexible programmability of classical computers. On page 711 of this issue, Carolan et al. ( 1 ) present a step in that direction, a fully reconfigurable optical waveguide circuit that can be programmed to implement arbitrary linear optics transformations on up to six optical modes.