Figure 3

Average Uhlmann’s fidelity between legitimate response qubit \(\vert A \rangle _{i} = \mathcal{R}_{k_{AB}^{i}} ( {\pi} / {2} ) \vert \psi _{i} \rangle \) and response qubit estimated by Eve \(\vert A_{E} \rangle _{i} = \mathcal{R}_{E^{i}} ( {\pi} / {2} ) \vert \psi _{i} \rangle \) on (a) 3D and (b) 2D contour plot, where \(k_{AB}^{i} = ( \pi /4,0 )\). \(\theta _{E^{i}}\) and \(\phi _{E^{i}}\) are the polar and azimuthal angles of the secret key \(E^{i}\) estimated by Eve, respectively