Simulating Kondo quantum impurity with fluxonium qubits

The Kondo model is central to our understanding of many strongly correlated systems. Here we present our approach to its analog quantum simulation using superconducting fluxonium qubits. Due to its strong anharmonicity, fluxonium is particularly well-suited for recreating the Kondo impurity. Our simulator consists of a high-impedance transmission line – the bath – comprising 20,000 Josephson junctions and a fluxonium qubit – the spin – inductively coupled to one of the line's ends. By measuring elastic and inelastic scattering rates of single microwave photons interacting with the fluxonium impurity, we extract key model parameters, including the dynamical spin susceptibility and the Kondo temperature, that are hard to access in electronic reincarnations of the model.