Quantum Steganography by Harnessing Entanglement as a Degree of Freedom

The ability of a Mach-Zehnder interferometer to distinguish between a photon with a well-defined, independent quantum state and one that is part of an entangled pair opens the door for entanglement to be harnessed as a degree of freedom of the photon and, consequently, to encode information into the entanglement domain of an elementary particle. In this article, we propose a new idea for a quantum steganographic technique that exploits the entanglement domain as a secondary way to represent information. Thus, if photons are used as the physical support for encoding information, the cover data can be encoded into the polarization domain, while the concealed data is embedded into the entanglement domain. The scheme has clear advantages compared to previous quantum steganographic attempts in terms of efficiency, versatility and practicability.