Why biphoton but not two photons?
Dmitry Strekalov, T. B. Pittman, Morton H. Rubin, Yanhua H. Shih · Maryland Shared Open Access Repository (USMAI Consortium) · 1997
What is the difference between two-photon phenomena and phenomena involving two photons? We address this question by reporting two two-photon interference experiments. In the first experiment we show that two-photon interference does not require the “indistinguishability” of two photons, and hence is not interference of two photons.