Introducing quantum mechanics with a two-mode Mach–Zehnder interferometer.

As an early teaching tool in QM, we propose to use a single-photon Mach–Zehnder interferometer. We demonstrate experimentally several properties associated with the concept of single photons in quantum optics and use them to introduce the quantum formalism and postulates in a more intuitive way. Editor's Note: Recent progress in laser optics, high-speed electronics, and low-noise photon counting has significantly simplified what used to be either thought experiments or state-of-the-art quantum optics experiments. In this paper, the authors take advantage of this progress to present a Mach–Zehnder interferometer operated at the single-photon counting level in order to introduce undergraduate students to quantum concepts, building upon their previous knowledge of wave optics. The simplicity of the Mach–Zehnder configuration allows for an easy introduction to the formalism of quantum states in two-dimensional Hilbert spaces. Anyone teaching introductory quantum mechanics should have a look at this paper, either to perform such experiments or simply to discuss them in class. [ABSTRACT FROM AUTHOR]