Joint CEM & Condensed Matter Theory Seminar – Prof. Paul Kwiat

University of Illinois – Urbana-Champaign

“The End of Local Realism”

Ever since John Bell showed that quantum mechanics could give different predictions from a local realistic model in an appropriate experiment, there has been wide interest in carrying out such a test.  Unfortunately, to date no truly unambiguous test has ever been completed, due to the existence of two experimental loopholes: the “locality loophole” and the “detection loophole”.  Each of these has been closed individually in different experimental systems – photons, atoms, ions, and superconductors – but no system has simultaneously closed each of the loopholes.  Here we present a photon-based experiment that violates the Bell inequality, free of the detection loophole. We also discuss some rather subtle points in performing such an experiment, to ensure that new loopholes do not arise.  Our experiment has some “efficiency overhead”, but in its current form probably insufficient to perform a fully loophole-free test of local realism, which requires much larger separations between source and detectors. We discuss possible improvements, as well as the application to device-independent quantum communication, e.g., certified private random number generation. Time permitting, our efforts to turn undergraduates into Schrödinger cats will be discussed.