Sensing intruders using entanglement: a photonic quantum fence

We describe the use of quantum-mechanically entangled photons for sensing intrusions across a physical perimeter. Our approach to intrusion detection uses the no-cloning principle of quantum information science as protection against an intruder's ability to spoof a sensor receiver using a 'classical' intercept-resend attack. Moreover, we employ the correlated measurement outcomes from polarization-entangled photons to protect against 'quantum' intercept-resend attacks, i.e., attacks using quantum teleportation. We explore the bounds on detection using quantum detection and estimation theory, and we experimentally demonstrate the underlying principle of entanglement-based detection using the visibility derived from polarization-correlation measurements.