ABSTRACT
This chapter focuses on the strange properties of a single photon and considers the interplay of the wave and particle properties. It shows how bizarre is the quantum mechanical notion of a single photon. The chapter also shows that photons are unreal — they do not exist independently of the machines we use to observe them and they are uncertain — measurements on a photon can produce completely unpredictable outcomes. It provides the case that the photon is nonlocal more strongly — that is, the photon can have a wave-like existence spread over lightyears, but a particle-like existence is concentrated at a single detector. The chapter discusses the experiments which can be explained by dumping quantum theory and invoking unknown hidden-variable arguments. A workhorse for the quantum theory of light is a particular device called a balanced Mach-Zehnder interferometer, named after the two physicists who thought it up.
