A minimal and integrable device for routing arbitrary microwave quantum states in waveguide quantum electrodynamics

Routing traveling photons in a controlled directional manner is essential for operating a quantum network. Communicating information between arbitrary quantum nodes using itinerant photons requires controllable directionality, high-fidelity signal processing, and loss resilience. Implementing such a network in the microwave domain is currently limited by losses due to commercially available directional devices such as circulators and isolators [1-3]. Recent efforts have addressed this challenge and have demonstrated controlled directional emissions of flying qubit states in the 0/1 Fock state basis [4, 5]. Here we present the design and realization of a device that extends this functionality to arbitrary quantum states, such as error-correctable bosonic states. Our device features an integrable on-chip design with three SNAIL (Superconducting Nonlinear Asymmetric Inductive eLements) modes. By controlling the interference between these modes with external microwave drives, we can realize in-situ tunable directionality with low loss. We present experimental data from an experiment in which we have realized a parametrically controllable isolator and gyrator, along with analytical and numerical modeling. From our analysis, we infer that emission and absorption of arbitrary quantum states with high fidelity is achievable. This result will enable routing arbitrary quantum states with in-situ control, which will be an enabling component for remote entanglement distribution and state transfer in error-corrected modular quantum networks.



[1] Campagne-Ibarcq, P., et al. Phys. Rev. Letter (2018)

[2] Axline, Christopher J., et al. Nat Phys. (2018)

[3] Kurpiers, Philipp, et al. Nature (2018)

[4] Kannan, Bharath, et al. Nature Phys. (2023)

[5] Chaitali Joshi, et al. Phys. Rev. X (2023)