title: Detecting the drift of quantum sources: not the de Finetti theorem.
abstract: We propose and analyze a method to detect and characterize the drift of a nonstationary quantum source. It generalizes a standard measurement for detecting phase diffusion of laser fields to quantum systems of arbitrary Hilbert space dimension, qubits in particular. We distinguish diffusive and systematic drifts, and examine how quickly one can determine that a source is drifting. We show that for single-photon wave packets our measurement is implemented by the Hong-Ou-Mandel effect.
authors.affiliation: Department of Physics, Oregon Center for Optics, University of Oregon, Eugene, 97403, USA.
authors.forename: Lucia
authors.initials: L
authors.lastname: Schwarz
authors.forename: S J
authors.initials: SJ
authors.lastname: van Enk