Deterministic Bidirectional Remote Entanglement with Waveguide Quantum Electrodynamics (Part 2)

Routing quantum information between non-local computational nodes is a foundation for extensible networks of quantum processors. Quantum information transfer between arbitrary nodes is generally mediated either by photons that propagate between them or by resonant couplers. The utility is determined by the type of emitter, propagation channel, and receiver. Existing approaches involving propagating microwave photons have limited fidelity due to photon loss and are often unidirectional, whereas architectures that use direct resonant coupling are bidirectional in principle, but can generally accommodate only a few local nodes. In this work, we develop a quantum interconnect comprising an emitter, receiver, and propagation channel that circumvent these issues [1]. We have demonstrated high-fidelity directional microwave photon emission using an artificial molecule comprising two superconducting qubits strongly coupled to a bidirectional waveguide [2]. Quantum interference between the photon emission pathways from the molecule generates single photons that selectively propagate in a chosen direction. After emitting time-symmetric, directional photons from one module, we absorb those itinerant microwave photons with another identical module tiled along the same waveguide. We extend the absorption protocol to demonstrate remote entanglement, a key resource for an extensible quantum network. Part 2 describes the latest experimental results and the absorption optimization scheme via reinforcement learning.



[1] Gheeraert, N. et al. Phys. Rev. A 102, 053720 (2020)



[2] Kannan, B., Almanakly, et al. Nat. Phys. 19, 394–400 (2023).