  Fiber optic gyroscopes (FOG) based on the Sagnac effect are a valuable tool
in sensing and navigation and enable accurate measurements in applications
ranging from spacecraft and aircraft to self-driving vehicles such as
autonomous cars. As with any classical optical sensors, the ultimate
performance of these devices is bounded by the standard quantum limit (SQL).
Quantum-enhanced interferometry allows us to overcome this limit using
non-classical states of light. Here, we report on an entangled-photon gyroscope
that uses path-entangled NOON-states (N=2) to provide phase supersensitivity
beyond the standard-quantum-limit.
