Fig. 1
From: Non-Gaussian noise spectroscopy with a superconducting qubit sensor
Experimental setup and non-Gaussian dephasing noise in a superconducting qubit. a Schematic of the circuit QED system. An engineered flux qubit comprises a superconducting loop (blue) interrupted by one small-area and eight large-area Josephson junctions (crosses) and is inductively coupled to a local antenna (red). The qubit junctions have internal capacitance, C and αC, and are externally shunted by capacitance Csh. See Supplementary Note 1. b SEM image of the device. The flux threading the qubit loop Φ is modulated by applying a current through the local antenna. c Frequency spectroscopy of the qubit’s |0〉 → |1〉 transition. At (away from) the degeneracy point Φ = Φ0/2, the qubit frequency ωq has a quadratic (linear) dependence on the external flux, as indicated by the indigo (yellow) arrow. d Probability distribution of the qubit frequency under Gaussian flux noise in the linear regime (yellow) vs. the quadratic regime (indigo). In the quadratic regime, the right-skewness of the distribution illustrates the non-Gaussianity of the resulting noise process
