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Abstract
In many traditional quantum-information protocols, quantum entanglement is carried by either discrete variables (DV) or continuous variables (CV). In DV mode, the quantum information is usually encoded into the polarization or the number of photons. In CV mode, the quantum information is encoded into the quadrature of the optical field. Compared to DV protocols, CV protocols use homodyne (or heterodyne) detectors which are faster and more efficient. In the context of satellite communication, it is of great interest to interconnect terrestrial devices running on mixed technologies by exploring the use of hybrid teleportation protocols. As a proof of concept, the Micius experiment has demonstrated an experiment for QKD between a satellite in Low-Earth-Orbit (LEO), which is about 500km above the ground, and a ground station. However, the engineering and deployment of quantum satellite payloads are very challenging. Once the satellite is deployed, it is very difficult to modify the payload for different functionalities. Hybrid technologies, in contrast, can interoperate with both the DV and CV protocols. In this thesis, I investigate hybrid protocols where the teleportation channel is a CV entangled state (which will henceforth be called the CV channel) and apply them to different quantum communication protocols over long distances. In these protocols, instead of directly distributing quantum entanglement from the satellite (direct distribution scheme), where the transmission loss directly affects the DV modes, the CV channel is pre-distributed from the satellite to teleport different quantum states. As a result, the satellite loss enters indirectly through the teleportation channel. My first contribution shows that using a CV channel to transfer one mode of a DV entangled state yields higher entanglement quality than directly distributing the DV entanglement from the satellite. In my second contribution, by using the CV channel to teleport a Schrodinger's cat state, I also show that the teleportation protocol can preserve higher fidelity than a fixed-attenuation channel. In my last contribution, I investigate the teleportation of a hybrid entangled state over the CV channel. My results show that for the typical loss of the Satellite-Earth channel, teleportation is always better than direct distribution.
