title: Stable single-photon interference in a 1 km fiber-optic Mach-Zehnder interferometer with continuous phase adjustment.
abstract: We experimentally demonstrate stable and user-adjustable single-photon interference in a 1 km long fiber-optic Mach-Zehnder interferometer, using an active phase control system with the feedback provided by a classical laser. We are able to continuously tune the single-photon phase difference between the interferometer arms using a phase modulator, which is synchronized with the gate window of the single-photon detectors. The phase control system employs a piezoelectric fiber stretcher to stabilize the phase drift in the interferometer. A single-photon net visibility of 0.97 is obtained, yielding future possibilities for experimental realizations of quantum repeaters in optical fibers and violation of Bell's inequalities using genuine energy-time entanglement.
authors: Center for Telecommunication Studies, Pontifical Catholic University of Rio de Janeiro, R. Marquês de São Vicente 225, Gávea, 22451-900, Rio de Janeiro, Brazil. guix@opto.cetuc.puc‑rio.br
authors: G B
authors: GB
authors: Xavier
authors: J P
authors: JP
authors: von der Weid