Novel entanglement source for high-speed quantum networks

The ability to efficiently generate and control entangled photons has led to remarkable progress in our understanding of quantum physics. Sources of entangled photons are also an enabling resource in quantum technology, and pushing the limits of generation rate and quality of entanglement are necessary pre-requisites towards practical application. On this topic, researchers in the group of Rupert Ursin at IQOQI, together with other collaborators, published the recent the journal paper "Polarization Entanglement by Time-Reversed Hong-Ou-Mandel Interference" on Physical Review Letters. Here, they present an ultra-bright source of polarization-entangled photon pairs that uses Hong-Ou-Mandel interference on a polarization beam splitter to separate indistinguishable photons into two spatial modes (typically this requires the photons to be distinguishable in some degree of freedom, e.g. wavelength distinguishability or non-collinear emission angles). Their source yields high-fidelity polarization entanglement and high pair-generation rates without any requirement for active interferometric stabilization, which makes it an ideal candidate for a variety of applications, in particular those requiring indistinguishable photons.