Multihop entanglement distribution in a software-defined quantum network

The development of quantum networking requires architectures capable of dynamically reconfigurable entanglement distribution to meet diverse user needs and ensure tolerance against transmission disruptions. Current quantum networks often face limitations in scalability and robustness due to their reliance on direct links for entanglement distribution. To address these limitations, we introduce multihop quantum networks to improve network reach and resilience. By enabling quantum communications across intermediate nodes, our approach broadens network connectivity beyond direct links, allowing for more extensive and flexible network topologies and increasing overall scalability. We implemented multihop two-qubit polarization-entanglement distribution within a quantum network at the Oak Ridge National Laboratory campus. Our system employs wavelength-selective switches for adaptive bandwidth management, with a software-defined quantum network integrating quantum and classical channels and control planes, enabling a flexible, reconfigurable mesh network. Our network distributes entanglement across six nodes within three subnetworks, each located in a separate building.