Absorbing a Directional Microwave Photon with Waveguide Quantum Electrodynamics

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 resonantly coupling nearby nodes. The utility is determined by the type of emitter, propagation channel, and receiver. Conventional 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 composed of an emitter, receiver, and propagation channel that circumvent issues of prior work. We have demonstrated high-fidelity directional microwave photon emission using an artificial molecule comprising two superconducting qubits strongly coupled to a bidirectional waveguide. Quantum interference between the photon emission pathways from the molecule generates single photons that selectively propagate in a chosen direction. By emitting time-symmetric photons from one module, we operate another identical module tiled along the same waveguide as an absorber of directional microwave photons, developing an interconnect capable of hosting remote entanglement for extensible quantum networks.