Amplitude

Amplitude

The left pair are the amplitudes, +0.60 for a reading of 0 and −0.80 for a reading of 1. The right pair are the squares, 0.36 and 0.64, so the taller amplitude is the likelier click and the minus has dropped out of the chance.

An amplitude is the number a qubit carries for one outcome, so a single qubit has an amplitude for 0 and an amplitude for 1. The chance of reading that outcome is the square of the size of its amplitude, so a larger size means a likelier click, and a minus sign on its own does not change the chance.

Keith wanted to rename them weights, on the grounds that weights sound friendlier at a party. Malcolm kept the sterner word, because the square is the part a newcomer forgets and a friendly name was not going to save it.

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