Quantum impurity physics simulation with superconducting circuits II: many-body regime

We report our progress in the field of quantum impurity simulations with superconducting circuits. Our simulator consists of a split Josephson junction terminating a high-impedance transmission line, which is made of a linear chain of up to 40,000 junctions [1,2]. In part I, we start with a relatively large area split-junction, such that its quartic anharmonicity can be treated as a perturbation. In this regime, the system is well-described by a Caldeira-Leggett model of a quantum degree of freedom interacting with an Ohmic bath. The interaction effects are revealed through the measurement of the frequency shifts of over 100 discrete modes of the bath. In part II, we explore small-area impurity junction where the non-linearity is non-perturbative. Now the system can be described by a boundary sine-Gordon quantum impurity model. It is expected that inelastic scattering of single photons becomes the dominant photon loss mechanism, with the loss frequency dependence containing information on the many-body correlation functions. We will present the measurements at various line impedances and impurity parameters.
[1] R. Kuzmin, R. Mencia, N. Grabon, N. Mehta, Y.-H. Lin, V. E. Manucharyan, arXiv 1805.07379
[2] R. Kuzmin, N. Mehta, N. Grabon, R. Mencia, V. E. Manucharyan, arXiv 1809.10739