Entangla

Meet Entangla, half of an entangled pair whose spin answers always come out opposite to her partner's.

The singlet state shown here describes two spin-½ particles. Neither particle has a definite spin direction on its own. Measure both along the same axis, though, and the results are always opposite: one up, one down. Tilt the two detectors at an angle and the correlation follows the cosine of that angle.

In 1935 Einstein, Podolsky and Rosen argued this meant quantum mechanics was incomplete. In 1964 John Bell showed that any theory with local hidden instructions limits certain correlations, and that quantum mechanics predicts violations of that limit. Experiments by John Clauser, Alain Aspect and others, and loophole-free tests in 2015, found the quantum predictions. Aspect, Clauser and Anton Zeilinger shared the 2022 Nobel Prize in Physics.

Entanglement is now a resource: it underlies quantum key distribution, quantum teleportation of states and quantum computing.

Each particle's own results look completely random, so entanglement cannot send a usable message faster than light.