Hybrid satellite-fiber quantum network

TL;DR

This work addresses the bottleneck of long-distance entanglement distribution for quantum networks by proposing a hybrid architecture that combines optical-fiber links with medium-Earth-orbit satellites. A detailed network model for the continental United States shows how a hybrid protocol—routing via satellite-ground stations and performing entanglement swapping across repeater nodes—outperforms both fiber-only and satellite-only designs at large scales. The study analyzes rate–fidelity trade-offs, optimizes repeater placement, and demonstrates the potential for distillation to maintain high fidelity, with scalability demonstrated via increased ion-photon and satellite emission rates. The results highlight the practical value of co-designing network architecture and quantum hardware to enable nationwide or global quantum communication and sensing networks.

Abstract

Quantum networks hold promise for key distribution, private and distributed computing, and quantum sensing, among other applications. The scale of such networks for ground users is currently limited by one's ability to distribute entanglement between distant locations. This can in principle be carried out by transmitting entangled photons through optical fibers or satellites. The former is limited by fiber-optic attenuation while the latter is limited by atmospheric extinction and diffraction. Here, we propose a hybrid network and protocol that outperform both ground- and satellite-based designs and lead to high-fidelity entanglement at a continental or even global scale.

Figures (13)

• Figure 1: Idealized diagram of ground-based and satellite-based entanglement distribution. (a) Optical-fiber path between Alice and Bob equipped with evenly distributed trapped-ion repeaters and intermediate photon repeaters. Top to bottom: end-point entanglement is achieved by ion-entangled photon transmission followed by entanglement swapping at the photon repeaters and then at the trapped-ion repeaters. (b) Satellite-mediated entanglement generation, where entanglement between ground stations is established by detecting entangled photon pairs emitted by the satellite.
• Figure 2: Entanglement distribution rate and fidelity through optical fibers. (a) Distribution rate without repeaters (black) and for an optimal number of evenly placed photon (and thus intermediate trapped-ion) repeaters (blue) as a function of the optical fiber length $L$. The optimal number of photon repeaters is marked on the top axis. Inset: magnification of both curves for small $L$. (b) Resulting end-to-end fidelity as the number of evenly placed repeaters is varied. (c) Corresponding entanglement distribution rate for two fixed values of $L$ as the number of repeaters is varied.
• Figure 3: Model optical-fiber network of the contiguous U.S. (a) Network structure, where each node represents a census tract and each link represents an optical fiber. Links that require intermediate repeaters, namely those longer than 61.7 km, are marked green. The orange path illustrates an entanglement distribution route between end nodes Alice and Bob. (b-d) Histograms of node degrees (b), link lengths (c), and optical-fiber path lengths between $10\,000$ randomly sampled end-node pairs (d) in the network.
• Figure 4: Entanglement distribution efficiency through the exclusive use of optical fibers or MEO satellites for 10 000 randomly sampled Alice-and-Bob pairs in the network shown in Fig. \ref{['fig:fiber_map']}(a). (a) Distribution rate through optical fibers (blue) and a satellite (orange). For a fair comparison, the fidelity for the satellite and target fidelity for the ground network are both assumed to be $0.87$. (b) Fidelity of the end-to-end entanglement for the time needed to establish one entanglement via satellite, color-coded as in (a). The points $D^\star_\text{R}$ and $D^\star_\text{F}$ mark the distances where the relative efficiency inverts. Repeaters are placed to achieve optimal distribution rate in (a) and optimal fidelity in (b). (c) Scattered plot (purple) and histogram (grey) of the distribution rate in (a) and fidelity in (b).
• Figure 5: Hybrid network protocol for sparse placement of satellite ground stations. The orange dots indicate ground stations placed on nodes in the network closest to the intersection points of a given grid. In the hybrid protocol, entanglement requests between distant Alice and Bob nodes are first routed (through shortest paths) to their nearest ground stations; entanglement is then established using a combination of satellite links and optical-fiber links.