Minus state, |−⟩

The |−⟩ state is the equal superposition of |0⟩ and |1⟩ with opposite signs, written as a ket whose label is a minus. A Hadamard on the state certain to read 1 writes about +0.71 for 0 and −0.71 for 1, and the Z gate reaches the same pair by flipping the sign on the amplitude for 1 of a |+⟩ state.

Keith reads the minus as a penalty, a smaller chance of reading 1. The square of −0.71 is about a half, the same as the square of +0.71 beside it. A following Hadamard turns the opposite signs into a certain reading of 1.