Figure 13. Fidelity of the Grover search algorithm in the presence of an unknown static magnetic field that rotates every qubit by angle φ along the equator of the Bloch sphere.

Data is obtained in independent runs with marked element 00 for all fields giving rise to angles φ between 0 and 2π in steps of π/500. Noisy data is the fraction of an ensemble of agents that identifies the marked element correctly when performing all four measurements in Grover’s algorithm. Red (analytical) and orange (numerical, 3000 agents) curves give the success of the Grover search (all four measurements) without taking into account the field in the measurement direction. The light blue curve gives the success for an ensemble of 1000 agents that each have a perfectly trained projective simulator with 4 measurement directions, which has learned the external magnetic field before doing the measurements for the Grover search algorithm. The dark blue curve is an ensemble of 1000 agents that employs the glow mechanism to build a measurement direction that is adapted to the external magnetic field before using it to perform the Grover search.