The musical Mach-Zehnder interferometer

The phenomenon of interference lies at the heart of quantum physics, and is responsible for many of the unusual aspects of quantum behaviour that deviate from our everyday expectations. Though classical physics allows for waves (e.g. of sound) to interfere, quantum theory allows for interference effects also to affect single particles. One device that demonstrates this experimentally is the Mach–Zehnder interferometer: here a single particle (e.g. a photon) travels down one of two possible paths, and quantum interference between the two paths affects the final position where the particle arrives. In this article, I propose a mechanism to musically demonstrate quantum single-particle interference: the musical Mach–Zehnder interferometer. This new quantum musical instrument makes use of two independently operated electronic keyboards, whose outputs are interfered according to the rules of the Mach–Zehnder interferometer. I discuss the musical possibilities this instrument enables, and outline a method to construct it via software simulation.