“Share one to entangle them all”

The delocalized addition of a single photon entangles two separate laser pulses containing an average of up to 60 photons each. Our recent results have just appeared in a paper on PRL.

Quantum particles can be in two different places at the same time. If a single particle of light, a photon, is shared between two distinct laser beams, some quantum entanglement (the ‘spooky’ correlation that Einstein did not believe possible) can be established between them, independently of their intensity. In this work, we have experimentally verified that the delocalized addition of a single photon does indeed entangle in a measurable way two weak laser pulses containing up to 60 photons each, on average. Creating such quantum correlations between macroscopic objects is a fascinating goal that may help us understand how quantum mechanics blends into classical physics and provide new tools for enhanced measurement precision.