H ZBINDEN, J BRENDEL, W TITTEL and N GISIN

Group of Applied Physics, University of Geneva, 1211 Geneva 4, Switzerland

Abstract.

Entanglement, one of the most important features of quantum mechanics, is at the core of the famous Einstein--Bohr philosophical debate [1]  and is the principal resource for quantum information processing [2].   We report on new experimental investigations of the properties of entangled photon pairs with emphasis on the tension between quantum mechanics and relativity [3,4]. Entangled photons are sent via an optical fiber network to two villages near Geneva, separated by more than 10 km where they are analyzed by interferometers [5].  The photon pair source is set as precisely as possible in the center so that the two photons arrive at the detectors within a time interval of less than 5 ps (corresponding to a path length difference of less than 1 mm). This sets a lower bound on the `speed of quantum information' to 10⁷ times the speed of light. Next, one detector is set in motion [6]  so that both detectors, each in its own inertial reference frame, are first to do the measurement! The data always reproduces the quantum correlations.

Keywords: Quantum information processing; quantum communication.

Pacs Nos. 03.67.Lx; 03.65.Bz