Fig. 6: Read-out power dependence of the relaxation time and variance.

a Relaxation time versus temperature for the membrane resonator at different on-chip read-out powers, indicated by the colors. The red data points and theory lines are the same as in Fig. 2. b Corresponding variances extracted from the same fits to σ₂-fluctuations. Error bars indicating the statistical fit errors are smaller than the data points, for both panels. A higher read-out power leads to a larger variance and smaller lifetime, which is consistent with microwave power-induced excess quasiparticles¹⁷. To limit these effects, we set the read-out power to the minimal value in this figure (red data set) and obtain the data in Fig. 2. See Supplementary Section 7 for an estimation of the read-out power effects at this lowest read-out power.