Autonomous stabilization of remote entanglement in a cascaded quantum network

Remote entanglement between independent and widely separated qubits is an essential quantum phenomenon and a critical resource for quantum information applications. Generating entanglement between qubits at arbitrary distances requires the distribution of propagating quantum states. This necessity raises the intriguing question whether the entanglement can be stabilized indefinitely, instead of only periodically reestablished after decay. Here, we report autonomous stabilization of entanglement between two separate superconducting-qubit devices. Combining nonreciprocal waveguide coupling and local driving, we experimentally realize distance-independent steady-state remote entanglement in a coherent quantum-absorber scheme. Enhancing this scheme with a new approach for overcoming inevitable disorder, we achieve a concurrence approaching 0.5. Our results set the stage for on-demand entanglement delivery in quantum processors and networks, and for protecting multipartite entanglement in open systems.