Figure 1

Sample and measurement setup. (a) Sketch of the sample chip. Dark blue: Resonator groundplanes. Green: Resonator center conductors. Light blue: Feed line center conductors. The insets are (false color) optical micrographs of the coupling capacitors (orange), the rf SQUID (red), and the rf SQUID junction (yellow). (b) Operating principle of the device: Both resonators share an inductance \(L_{0}\) (purple) with the SQUID and the SQUID itself can be treated as an effective inductance \(L_{\mathrm{rf}}(\Phi)\) (red, see Equation (4)), resulting in an effective mutual inductance of \(M_{\mathrm{AB}}=L_{ 0}^{2}/L_{\mathrm{rf}}(\Phi)\) between both resonators (see Equation (7)). The sketched measurement setup contains attenuated input lines (indicated by wiggly arrows), output lines including cryogenic and room temperature microwave amplifiers (triangular symbols), and possible measurement paths (blue dashed arrows).