Abstract: Superconducting circuits are ubiquitous in quantum simulations, computing, and metrology. In this talk, I will show a superconducting circuit platform extended to the extreme, in which the circuits actually become insulating. Remarkably, such nominally insulating circuits are a valuable resource. They create a tunable high-impedance environment and facilitate exceptionally strong interactions between photons and superconducting qubits. This opens up new directions for analog quantum simulations of interacting many-body problems, with examples ranging from quantum phase transitions to many-body localization.
In particular, I will start with the demonstration of a dissipative quantum phase transition in a Josephson junction facing an Ohmic environment. Despite many experimental attempts, the existence of such a transition remains controversial. Using the high-impedance circuit environment, I will present evidence of the transition with a conceptually new approach, which relies on monitoring environmental degrees of freedom. A similar approach applies to analog quantum simulations of other strongly interacting models, which I will illustrate on two quantum impurity models relevant to the physics of Luttinger liquids and the Kondo effect. In the latter case, interactions induced by a quantum impurity in a finite size system allow us to observe the phenomenon of many-body localization. Finally, I will argue that the high-impedance circuit platform can contribute to the development of various areas of quantum science and technology.