Level 1, Curious

Measurement

Before the click the chances are 0.36 for 0 and 0.64 for 1. This drawing follows a click that returned 1, after which the amplitude for 1 is 1 and the amplitude for 0 is 0, so an immediate second click repeats the 1.

A measurement in the usual arrangement returns one bit, either 0 or 1, with chances given by the squared sizes of the amplitudes just before the click. Afterwards the qubit sits in the state you read, which is why a second measurement, done at once in the same arrangement, repeats that bit.

Keith calls the click a look at the answer. Malcolm calls it a new physical event in which the apparatus joins the description, and he has given up expecting the shorter name to die out.

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