 Using an Oak Ridge National Laboratory technology, inspectors of containers of nuclear material will be able to know with unprecedented confidence whether an intruder has tampered with a seal. The system uses a light source of entangled photons to verify the continuity of a fiber-based seal, according to Travis Humble, who led the development team. Entanglement is a feature of quantum physics that describes how two spatially disparate systems exhibit strong correlations in otherwise independent behaviors. The work, sponsored by the Defense Threat Reduction Agency, is vital to ensure compliance with nonproliferation treaties because inspectors must confirm the uninterrupted containment and surveillance of any nuclear material.