Driving Forbidden Transitions in the Fluxonium Artificial Atom

Superconducting artificial atoms are an emerging platform for the study of coherent quantum physics, and for quantum computation. However, their level-transition properties are currently much simpler than those of true atoms, which limits the quantum systems that can be implemented with this hardware. Here researchers use a nonlinear coupling element to engineer the selection rules of a fluxonium circuit, and thus gain access to previously forbidden transitions. Such a technique allows us to expand the set of quantum operations possible using superconducting circuitry, and is necessary for controlling and measuring physically protected quantum systems.