Interfering entangled photons of different colors
Todd S. Larchuk, Richard A. Campos, John Rarity, P. R. Tapster, Eric Jakeman, Bahaa E. A. Saleh, Malvin Carl Teich · Physical Review Letters · 1993
We have observed unusual second- and fourth-order interference patterns when entangled photons with center-wavelength differences \ensuremath{\approxeq}40 nm are mixed together at single or dual Mach-Zehnder interferometers. The difference frequency of the photons appears directly in the spectrum of the coincidence rate. This phase-sensitive behavior can reveal center-frequency differences from zero to hundreds of THz.