Quantum Technologies Move A Step Closer With Demonstration Of An 'Entanglement' Filter

A team of physicists and engineers has demonstrated an optical device that filters two particles of light (or photons) based on the correlations between their polarisation that are only allowed in the seemingly bizarre quantum world. This so called "entanglement filter" passes the pair of photons only if they inhabit the same quantum state, without the user (or anything else) ever knowing what that state is. This device will have many important applications to quantum technologies, including computers, communication and advanced measurement.[...]