Quantum Gyroscope Navigation — Sagnac Interferometer Dead Reckoning

Drive a rover through a GPS-denied tunnel and watch two heading estimates fight for the truth: a quantum Sagnac-interferometer gyroscope, whose phase shift comes straight from counter-propagating light in a fiber coil and barely drifts, against a classical MEMS gyroscope, whose hidden bias random-walks over time. Both dead-reckon a trajectory from the same true speed and steering input — only the heading source differs — so the growing gap between the solid true path and the dashed estimated path is exactly the cost of sensor bias, made visible in real time alongside the live Sagnac phase-shift readout.