Quantum Repeaters to Extend the Communication Range: Present and Future Perspectives

Long-distance quantum communication faces significant challenges due to photon loss and operational errors in fiber optic channels. Quantum repeaters (QRs) offer a promising solution by extending the communication range and enabling secure exchange of quantum information over continental distances. This article provides an overview of the three generations of QRs, comparing their technological requirements and challenges. We introduce the basic techniques, such as entanglement swapping, distillation, and error correction, and discuss their relevance to each generation of QRs. In addition, we present a future direction that integrates superconducting qubits with optical fibers, enabled by recent advances in microwave-optical transduction. This new hybrid architecture offers promising prospects for scalable and efficient quantum networks. It is also applicable in quantum key distribution protocols, such as E91.