Locating a photon: Position observables and an uncertainty relation

This paper is written in celebration of Kamil A. Valiev's 75th birthday and 50-year career. His wide-ranging work includes running workshops on quantum information science at the Academy's Institute of Physics and Technology, events that invariably attract experts and beginners alike. He often gives thought-provoking talks in which issues of quantum mechanics are considered from an unusual angle. A series of lectures on the theory of the photon provided a basis for the present theoretical study dealing with the long-standing question of how to locate a photon. This topic has acquired a new dimension with the task of manipulating photons, individually or collectively, for the purposes of quantum cryptography. © Pleiades Publishing, Inc. 2006.