Z gate

Z gate

Z leaves the amplitude for 0 alone and turns the amplitude for 1 red, which is the sign change. The lengths match before and after, so the chances of the two readings stay where they were.

The Z gate leaves the amplitude for 0 alone and flips the sign of the amplitude for 1. The chances of the two readings stay where they were, so a measurement straight after Z looks like a measurement straight before it.

The new sign becomes visible once another gate rotates it into those chances. Keith pressed Z six times, watched the chances sit still, and announced that the key had worn out, which is when Malcolm wrote the six sign changes down the margin and asked which of them a click was supposed to print.

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