Abstract
Moving at the speed of light, the photon is the ideal physical support to transmit information. Polarization of a photon is the predominant quantum property used to encode information, but other encoding domains, such as the spatial-mode degree of freedom, have been considered. In this paper, we put forward the entanglement degree of freedom of a photon as an exploitable resource for encoding information in quantum cryptographic protocols. We show how classical information can be extracted from the quantum state of a photon by distinguishing between a singular, independent state and an entangled state through interferometry. We also give a direct application of our technique to quantum key distribution as a proof of concept for future quantum protocols that may use coding in the entanglement domain in combination with other degrees of freedom that are currently exploited for cryptographic purposes.