Advanced Experimental Methods for Quantum Communication

The thesis presents advancements in quantum communication, focusing on enhancing quantum key distribution (QKD) through novel device designs and experimental setups. A time-bin optical encoder, integrating state and decoy preparation within a single topology, is introduced for fiber-based QKD, achieving record-low error rates. To extend communication distances, the thesis explores the feasibility of satellite-based QKD by laying the groundwork for Hong-Ou-Mandel (HOM) interference between a backreflected photon from a satellite and one propagated from the ground, proposing solutions for Doppler compensation and timing synchronization. In addition, the development of a heralded single-photon source, using non-degenerate spontaneous parametric down-conversion in nonlinear waveguides, is investigated for use as the ground-based source in HOM interference, while also serving as a standalone single-photon source for QKD. Finally, a scalable optical phased array system for long-range communication is analyzed, offering potential for deep-space transmission with lightweight components and low power consumption. Together, these innovations address current limitations in QKD, advancing secure communication on a global scale, as well as providing efficient solutions for low-photon classical communication scenarios.