Towards satellite-assisted quantum communication with reconfigurable networks and frequency-bin qubits

Abstract

The development of quantum networks will enable advanced applications in quantum cryptography, quantum-enhanced metrology, and quantum computing. Central to this vision is the ability to reliably distribute quantum entanglement between distant nodes. To date, quantum networks have been largely confined to metropolitan scales and a small number of nodes with predominantly static implementations, constraining their scalability and adaptability for broader deployment. Satellites provide a promising platform for distributing entanglement over global distances. However, the integration of satellites into terrestrial quantum networks poses significant challenges, including intermittent connectivity and high link attenuation during orbital passes. In this thesis, we first propose a reconfigurable quantum network architecture that dynamically adapts its topology according to satellite availability. This reconfiguration ensures efficient and continuous operation while accommodating satellite links within a metropolitan quantum network. We demonstrate this network architecture, using a correlated photon source specifically designed for Canada’s Quantum Encryption and Science Satellite (QEYSSat) mission. Using both frequency and time multiplexing, we demonstrate a linear performance improvement with minimal resource overhead. Moreover, we propose an integrated source design to facilitate deployment in realistic scenarios. Second, we investigate frequency-encoded quantum communication over free-space channels. We propose a novel approach that leverages linear interferometry and time-resolved detectors to decode frequency-bins without any adaptive optics or modal filtering. Furthermore, we investigate the phase stability requirements so that frequency-bin encoding could be feasible for satellite to ground quantum links. A proof-of-concept experiment is conducted over a turbulent free-space channel. Third, we distribute frequency-bin entangled photons over multi-mode channels and test their non-local correlations. We report, to the best of our knowledge, the first measurement of the joint temporal intensity between frequency-bin entangled photons revealing a rich temporal structure. By combining time-resolved detection with energy-correlation measurements, we perform full quantum state tomography and further certify our source's non-classicality via a violation of the time-energy entropic uncertainty relations. We extend this scheme to higher-dimensional frequency-bin states, opening new possibilities for high-capacity robust quantum communication and quantum information processing. The concepts, protocols, and experimental demonstrations presented in this thesis establish new approaches to utilize frequency-bin entanglement and contribute to the development of satellite-assisted quantum networks thus paving the way towards the realization of a global quantum network.