Quantum networks with satellites
hardware, protocol and architectures
V. Dominguez Tubio (TU Delft - QID/Wehner Group)
S.D.C. Wehner – Promotor (TU Delft - QID/Wehner Group, TU Delft - Electrical Engineering, Mathematics and Computer Science)
C. Errando Herranz – Copromotor (TU Delft - Electrical Engineering, Mathematics and Computer Science, TU Delft - QID/Herranz Lab)
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Abstract
The implementation of a quantum network opens up a range of new opportunities for secure communication and distributed quantum computing. To achieve this, entanglement must be distributed between remote users, using photons as carriers of quantum information. However, the probability of photon absorption in optical fibers increases exponentially with distance. To address this, quantum repeaters have been proposed, dividing the total distance into shorter segments where direct transmission is more feasible. Nevertheless, for long-distance links, satellite-assisted free-space channels offer a promising near-term alternative that avoids the complexity of quantum repeaters needed to compensate for transmission losses. The distribution of quantum keys between distant users has already been demonstrated via a single satellite link over distances of up to 7000 km. In this thesis, we focus on the development and analysis of satellite-based quantum networks.
To this end, we begin by exploring how current satellite links can be made more efficient, specifically, how to increase the amount of quantum information reaching the ground stations, avoiding the requirement of long coherent time in the quantum memories and without altering the satellite hardware. We propose the use of high-dimensional encoding, showing an improvement in the rate of entanglement compared with conventional qubit encoding.
From there, the discussion expands to a full quantum network architecture using several quantum repeaters place in space, with the aim of achieving secure liks across intercontinental distances. We propose a setup based on individually trapped atoms acting as both single-photon sources and quantum memories. Incorporating hardware imperfections and modeling transmission losses through free space and the atmosphere, we estimate the hardware performance required to achieve high-fidelity entanglement at a chosen transmission rate.
Finally, we go to a more specific example of distributing quantum key (QKD) to different cities of the Iberian Peninsula. Taking into account real-time weather conditions, atmospheric effects, and propagating losses, we analyze the feasibility of deploying current use cases of satellite-based QKD.