Hybrid ququart-encoded quantum cryptography protected by Kochen-Specker   contextuality
  Quantum cryptographic protocols based on complementarity are nonsecure against attacks in which complementarity is imitated with classical resources. The Kochen-Specker (KS) theorem provides protection against these attacks, without requiring entanglement or spatially separated composite systems. We analyze the maximum tolerated noise to guarantee the security of a KS-protected cryptographic scheme against these attacks, and describe a photonic realization of this scheme using hybrid ququarts defined by the polarization and orbital angular momentum of single photons. 
Adan Cabello, Vincenzo D'Ambrosio, Eleonora Nagali, Fabio Sciarrino
quant-ph