The new study is the first experiment to simultaneously close both of these loopholes in a test of Bell's inequality. The scientists used a laser to make two specific electrons, each within a diamond located over 1km apart, to increase their energy and emit a particle of light (a photon), which was entangled with the state of the electron. The photons were then sent through an optical fibre to be united at a third location. If they arrived at just the same time, the photons would interact with each other and become entangled – meaning their remote electron buddies would become entangled too.