NOTES 163 5 years agoPhotons test quantum paradox
Like Schrödinger’s cat, it was only supposed to be a thought experiment to elucidate the strange mathematics of quantum mechanics.
The theorem, first published in 1967 by the mathematicians Simon Kochen and Ernst Specker, shows that it is incorrect to assume, before measurements are made, that the results of a quantum mechanics experiment are already determined. That assumption is valid in classical physics; for example, the heat content of a cup of tea is unaffected by the thermometer measuring it. But it breaks down in quantum mechanics, where measurements change their subjects in ways that depend on what else is being measured — as if a set of thermometers conspired to create the heat that they measure.
This behaviour is called quantum contextuality. One example of the principle is ‘spooky action at a distance’, in which the quantum states of two particles are entangled such that measurements on one particle instantaneously influence the other, even if it is far away.
Testing contextuality for particles that are not entangled has been hard because the Kochen–Specker theorem is so complex: it considers the answers to a set of 117 measurements on a single quantum particle that can exist in three or more quantum states. Preparing photons or atoms in more than two quantum states has been possible only in the past few years.
