What is quantum entanglement?

Entanglement is a strange feature of quantum physics, the science of the very small. It’s possible to link together two quantum particles – photons of light or atoms, for example – in a special way that makes them effectively two parts of the same entity. You can then separate them as far as you like, and a change in one is instantly reflected in the other. This odd, faster than light link, is a fundamental aspect of quantum science – Erwin Schrödinger, who came up with the name “entanglement” called it “the characteristic trait of quantum mechanics.” Entanglement is fascinating in its own right, but what makes it really special are dramatic practical applications that have become apparent in the last few years.