Hadamard gate

From the state certain to read 0, one H writes two equal amplitudes of about +0.71. A second H returns the state certain to read 0, because the routes to a reading of 1 cancel.

The Hadamard gate, written H, turns the state certain to read 0 into the |+⟩ state, with equal amplitudes of the same sign. It turns the state certain to read 1 into the |−⟩ state, with equal amplitudes of opposite sign. A second H returns any qubit to the state it started from, because the extra routes cancel in pairs.

Keith’s sticker says “fair split” and covers only the first press of the button. Malcolm will tolerate the sticker if it also says that the second press undoes the first, which is the part the sticker usually omits.

Hadamard gate

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