Demonstration of the angular uncertainty principle for single photons

We present an experimental demonstration of a form of the angular uncertainty principle for single photons. Producing light from type I down-conversion, we use spatial light modulators to perform measurements on signal and idler photons. By measuring states in the angle and orbital angular momentum basis, we demonstrate the uncertainty relation of Franke-Arnold et al (2004 New J. Phys. 6 103). We consider two manifestations of the uncertainty relation. In the first we herald the presence of a photon by detection of its paired partner and demonstrate the uncertainty relation on this single photon. In the second, we perform orbital angular momentum measurements on one photon and angular measurements on its correlated partner exploring, in this way, the uncertainty relation through non-local measurements