Resource-Efficient All-Photonic Quantum Repeaters with 9 km Spacing

Quantum communication between two distant parties will serve as a cornerstone of the future quantum internet. However, many existing quantum communication schemes face a critical bottleneck: the need to generate a sufficient number of entangled Bell pairs over long distances. The all-photonic quantum repeater scheme has recently emerged as a promising approach that relies solely on photonic qubits, without the need for matter-based quantum memories. However, several challenges remain. While previously proposed all-photonic schemes have been constrained by small repeater spacing and high qubit resource requirements, we propose an all-photonic quantum repeater scheme that enables quantum communication over a distance up to 1,500 km, with equidistant repeater spacing extended to 9 km—approximately two to six times larger than in previously proposed all-photonic schemes. The realization of this scheme requires fewer than 3,800 GKP qubits per repeater station per protocol run under realistic parameters, which is significantly fewer than in prior all-photonic proposals. These advancements arise from elementary entangled Bell pairs protected by both the bosonic Gottesman–Kitaev–Preskill (GKP) code and the [[7,1,3]] Steane code, together with an all-photonic free-space quantum memory for GKP qubits, whose storage efficiency significantly surpasses that of local fiber spools considered in previous all-photonic quantum networks.