Fig. 1: Simplified schematic of the experimental setup.
The four-junction CSFQ (purple) is controlled via two bias lines that thread x (green) and z (orange) fluxes into their corresponding loops. The flux waveforms have a 1-ns time resolution. The qubit is coupled to a dispersive readout resonator (gray) and to a persistent-current readout circuit (dark blue). The latter measures the direction of the circulating current in the qubit z loop. Note that the CSFQ floats in the physical device; the displayed ground defines the zero point for the circuit node parameters in the Hamiltonian derivation. Details of the persistent-current readout can be found in ref. 37. Relevant device parameters are discussed in “Methods”.
