Condensed Matter Seminar: Scattering microwave photons off small Josephson junctions

Although universal digital quantum computers are still far from being realized, the advances in circuit quantum electrodynamics (cQED) provide new ways of tackling old condensed matter problems. In this talk, I will present our cQED approach to two such problems: a generalization of the boundary sine-Gordon quantum impurity problem and a dissipative phase transition related to it. Physically, both models can be realized as a long section of a high-impedance transmission line connected to a single small-capacitance Josephson junction. The setup allows us to study how a small junction scatters microwave photons as we tune the photons’ frequency and system’s parameters. Remarkably, because of the junction’s nonlinearity, a single photon scatters not only elastically, but also inelastically due to the spontaneous decay to many lower-frequency photons. Both elastic and inelastic scattering rates and their scaling with the photon’s frequency provide a new tool for learning about the physics of Josephson junctions and corresponding condensed matter problems.