QLV was conceived as a hardware upgrade, fully compatible with existing optical communication infrastructure and data security measures, which adds quantum-assured capabilities for sensing and alerting its users of an eavesdropping attack.

QLV exploits the fact that light is fundamentally quantum. QLV employs a pair of indistinguishable photons—the fundamental particles of light.

One photon (the home photon) is retained in a delay loop at the trusted entry to the link, which we refer to as the home node.  The second photon (the field photon) is combined with the classical communication; sent to the field node and returned.  Thus it is used to test the physical pathway of the comms link.

After being reflected to the home node, both photons undergo quantum interference.  When the delay at the home node matches the link length, the interference is at its maximum and verifies a fully secured link.

Any attempt by an eavesdropper to intercept the link—partially or in whole—unavoidably affects the second photon, changing the quantum interference and showing that the link is not secure, thus revealing the eavesdropper.  QLV relies on well-documented, tested and verified concepts.  The quantum interference—Hong-Ou-Mandel (HOM) Interference—was first observed in 1987, and more recently, long-distance HOM Interferences have been demonstrated.  Routing techniques that allow co-propagation of classical and quantum signals in shared communication channels are now part of commercial quantum communication systems.