Figure 1

(a): Noisy measurement M̃ realized by a noisy unitary operation Ũ followed by a noiseless measurement in the standard basis. (b), (c): Noise models illustrated here for a single qubit on the Bloch sphere. (b) The depolarizing channel shrinks the Bloch vector. (c) Over- and under-rotation describes errors during a quantum gate where the rotation angle fluctuates according to a Gaussian distribution. The example shows an intended \(\pi /2\)-rotation about an axis in the xy-plane