Fig. 4: Single-instance verification with artificially added phase noise.
From: Verifiable measurement-based quantum random sampling with trapped ions
Root infidelity estimate \(\sqrt{1-F}\) (hexagons) and empirical total-variation distance dTV (stars) of a 2 × 2 cluster state with artificially introduced local (pink) and global (green) phase noise—Z-rotations with rotation angle drawn from a Gaussian distribution with variance σ2—before and after Mølmer-Sørensen gate applications as a function of the noise strength σ, see Methods for details. Solid (dashed) lines show simulated root infidelity (total-variation distance) for the respective types of noise. The experimental data (top axis) is shifted with respect to the simulations (bottom axis) due to the fact that there is residual noise when no artificial noise is introduced. The value of the relative shift given by 0.045π (dashed vertical line) provides an estimate for the natural noise strength. Colored error bars represent the 3σ interval of the statistical error. The systematic measurement error of the fidelity estimate is represented by gray error bars.
