Photon-instanton collider implemented by a superconducting circuit

Instantons, spacetime-localized quantum field tunneling events, are ubiquitous in correlated condensed matter and high energy systems. However, their direct observation through collisions with conventional particles has not been considered possible. We show how recent advances in circuit quantum electrodynamics, namely embedding a single quantum phase-slip defect into a high-impedance superconducting waveguide, allow the observation of inelastic collisions of single microwave photons with instantons (phase slips). We show both experimentally and theoretically that a single photon-instanton collision can cause a splitting of the incident photon into a possibly large (odd) number of lower-energy photons, with a nearly unit probability. This effect has no analogues in non-linear optics and is rather tied to the dynamics of quantum impurity models near quantum critical points.