Controlled Entanglement Source for Quantum Cryptography

Abstract

Proposes upgrading an entanglement source with access control, by phase-randomising the optical pump according to a string that only authorised users can decode from a pre-shared seed. A proportion of the emitted states are mixed and carry no key information; users who can decode the modulation string discard those rounds, while an attacker holding the raw outcomes cannot tell which rounds were correlated and so derives a wrong key even though the error correction and privacy amplification methods are public. Presented as a practical countermeasure against the memory attack on device-independent QKD at negligible cost, and demonstrated with off-the-shelf components: a 2.5 GHz phase-modulated pump into a silicon waveguide chip producing time-bin entanglement, read out on superconducting nanowire single-photon detectors.