Quantum Walks of Correlated Photon Pairs in Two-Dimensional Waveguide Arrays
Konstantinos Poulios, Robert Keil, Daniel Fry, Jasmin D. A. Meinecke, Jonathan C. F. Matthews, Alberto Politi, Mirko Lobino, Markus Gräfe, Matthias Heinrich, Stefan Nolte, Alexander Szameit, Jeremy L. O’Brien · Physical Review Letters · 2014
We demonstrate quantum walks of correlated photons in a two-dimensional network of directly laser written waveguides coupled in a "swiss cross" arrangement. The correlated detection events show high-visibility quantum interference and unique composite behavior: strong correlation and independence of the quantum walkers, between and within the planes of the cross. Violations of a classically defined inequality, for photons injected in the same plane and in orthogonal planes, reveal nonclassical behavior in a nonplanar structure.