Extended Data Fig. 5: Single-qubit temperature dependence, stability, and noise characteristics.

a, Ratio of T₁ to T₂ as a function of temperature in different regimes. This ratio indicates the amount of bias in the proportion of depolarisation errors to that of dephasing errors. A large variation in the bias and its temperature dependence is seen at temperatures below 1 K, whereas these metrics become similar above T = 1 K. At this point, \({T}_{{\rm{1}}}/{T}_{{\rm{2}}}^{{\rm{* }}}\) shows a high-order roll-off. However, the temperature dependence is weaker when echoing is incorporated, as seen in \({T}_{{\rm{1}}}/{T}_{{\rm{2}}}^{{\rm{Hahn}}}\). The overall T₁/T₂ biases remain above 100 within T = 1.5 K. b, Sequences for tracking slow changes in f_ESR over a long time with respect to T₂⁴⁹. c, Sequences for tracking the amount of adjustment in microwave power to maintain a constant f_Rabi over time⁴⁸. P₁, P₂ correspond to the different projection outcomes and β is a conversion factor. d, Results of a and b at B₀ = 0.5 T and T = 1 K. P₁, P₂ correspond to the different projection outcomes and β is a conversion factor. e, Sequence for the noise spectroscopy based on the Carr-Purcell-Meiboom-Gill (CPMG) protocol^44,45 and the full set of noise spectra of Q1 at temperatures from 0.14 K to 1.2 K. f, We examine the microwave effect on the qubit coherence time by applying the Hahn echo sequence on Q1. During the wait time, we apply a microwave signal far from the resonance of either qubit to capture the incoherent noise induced. We measure \({T}_{2}^{{\rm{Hahn}}}\) varying the microwave power at T = 0.14 K and T = 1 K. We observe a notably less evident effect from the microwave at T = 1 K compared to at T = 0.14 K. Error bars represent the 95 % confidence level.