American Journal of Physics
We describe a series of experiments used in a sophomore-level quantum physics course that are designed to provide students with a hands-on introduction to quantum mechanics. By measuring correlations, we demonstrate that a helium-neon laser produces results consistent with a classical model of light. We then demonstrate that a light source derived from a spontaneous parametric down-conversion process produces results that can only be described using a quantum theory of light, thus providing a (nearly) single-photon source. These single photons are then sent into a Mach–Zehnder interferometer, and interference fringes are observed whenever the path of the photons cannot be determined. These experiments are investigated theoretically using straightforward quantum-mechanical calculations.
Pearson, Brett J., and David P. Jackson. "A Hands-On Introduction to Single Photons and Quantum Mechanics for Undergraduates." American Journal of Physics 78, no. 5 (2010): 471- 484. https://aapt.scitation.org/doi/10.1119/1.3354986