Analysis of entanglement in multi-access quantum optical circuits

Free-space optical communication channels offer unsurpassed advantages over traditional radio frequency systems. They can be implemented in a point-to-point topology and, if necessary, augmented with additional security features for privacy-critical applications. The adoption of quantum mechanical principles in optical communication networks became a foundation for quantum communication protocols that offer added security without the mathematical complexity of traditional cryptography. Encryption can be achieved at the physical layer by using quantized values of photons, which makes exploitation of such communication links extremely difficult. Additional challenges are encountered when the focus is shifted from point-to-point links to multi-access communication systems arranged in a hub-and-spokes topology. To facilitate connectivity, the "hub" can use a single aperture to establish connection to a target platform within its fieldof- view. Polarization entanglement is proposed for data encoding, and additional degrees of freedom can be achieved for each quantum state by using hyper-entanglement. For example, if carrier waves arriving at the same time from multiple transmitters (spokes) are assigned specific frequencies in the 200 GHz ITU grid, their messages can be processed simultaneously by a receiver (hub) that uses a hyperspectral quantum optical circuit. In this paper, we present analysis of the components in the optical trains and propagation of hyper-entangled states in the quantum circuits. The results obtained in this project can be used as the first step before physical implementation of the quantum communication systems.