Efficient Generation of Polarization-Entangled Photon Pairs with a Laser Diode Source

Abstract

Entanglement, as E. Schrodinger called it “the essence of quantum mechanics”, is not only an essential ingredient of quantum effects but it became also the most important resource of quantum information processing and communication. Entangled photon pairs, created initially by electron-positron annihilation and later in atomic cascade decays, were first used in distinctive comparisons of various concepts of quantum mechanics [1,2]. More recently, parametric fluorescence (spontaneous parametric down-conversion, SPDC) in nonlinear optical crystals as the source of entangled photon pairs [3–5] lead to a dramatic increase in count rates and experimental performance. This enabled a variety of experiments on the foundations of quantum mechanics [6–8] and the experimental realization of new concepts in quantum information [9–11]. In spite of that success, most of the experiments and potential applications still suffer from the low yield of the fluorescence process. When our new group joined the chair of Theodor Hansen about two years ago, it was thus the motivation for our work to optimize collection efficiency and thereby the available rate of polarization-entangled photon pairs from parametric down-conversion and to make polarization-entangled photon pairs useful for real applications.