Probing nonlinear photon scattering with artificial atoms coupled to a slow-light waveguide

Engineering the electromagnetic environment of a quantum emitter makes it possible to observe a plethora of exotic physical phenomena involving atom-light interactions. In particular, coupling quantum emitters to a finite-band waveguide, leads to the formation of long-lived atom-photon bound states with energy outside the photonic band, recently observed in experiments. Here, going beyond linear optics response, we experimentally probe these bound states through a nonlinear scattering process.
Our slow light waveguide consists of an array of compact, high-impedance superconducting resonators forming in a 1GHz-wide pass band. We couple two frequency-tunable transmon qubits to the array and study their interaction with this engineered environment. By sending multiphoton coherent packets into the waveguide, we demonstrate the excitation of atom-photon bound states through a nonlinear process, which allows on-demand trapping and releasing of the excitation.
This experiment opens novel perspectives for routing and controlling photon transport at the quantum level.