Fig. 4

Subgap resistance from microwave cavity measurements. a Extracted sub-gap resistance at as a function of gate voltage. The values are calculated by calibrating the cavity properties and using the junction model shown connected to the transmission line cavity to fit the observed cavity response. Inset shows the cavity response at V_g = 30 V. The horizontal and vertical axis divisions are 10 MHz and 10 dB respectively. b Predicted linewidth for a graphene transmon qubit, obtained by taking the RCSJ parameters as a function of gate and adding a capacitance C_q such that the final operating frequency remains \(\omega {\mathrm{/}}2\pi\) = \(\left( {2\pi \sqrt {(L_{\mathrm{j}}(C_{\mathrm{j}} + C_{\mathrm{q}}))} } \right)^{ - 1}\) = \(6\,{\mathrm{GHz}}\). We assume the internal junction losses dominate the total linewidth. The horizontal line represents the anharmonicity of a typical SIS transmon E_c/h = 100 MHz. In regions where the blue line falls under the dashed line, a gJJ transmon would be capable of operating as a qubit. The error bands for both panels can be found in Supplementary Fig. 5