Hyper-entanglement preservation in quantum optical circuits

Secure optical data links can be implemented using quantum communication (QC) protocols that offer physical-layer encryption without the mathematical complexity of traditional cryptography. Data encoding can be achieved using polarization entanglement and it is further proposed to obtain additional degrees of freedom for each single particle quantum state by using hyper-entanglement. For example, multiple carrier signals arriving at the same time can be assigned specific frequencies in the 100 GHz International Telecommunication Union (ITU) grid and be processed simultaneously by a receiver that uses a hyperspectral quantum optical circuit. In this paper, we address preservation of hyper-entanglement as the signals propagate through optical components of the quantum circuits and encounter their realistic properties.