Three photons entangled, not just two
Crystals split light while linking its properties
By Andrew Grant
A process that works once in every quadrillion attempts has produced trios of entangled photons.
Particles with properties that are entangled share an extraordinary connection: Measuring the properties for one particle immediately determines the properties for the other, no matter the distance between particles (SN: 11/20/10, p. 22).
Physicists routinely create entangled pairs of photons. But confirming the entanglement of more than two photons can be done only after measuring the particles, which destroys their delicate entanglement state.