The magnitude response of the measured signal is proportional to the magnitude of the emission operator 〈σ−〉 of the qubit while the phase response increases linearly with time as δω01τ. a A single trace of the magnitude response of Γ2 measurements after a π/2-pulse, showing the decoherence processes of the qubit within time τ. The data is fitted to an exponential decay. b The corresponding phase response from (a), showing that the phase of the emitted photon from the qubit evolves with a slope corresponding to the detuning δω01/2π = 125 kHz where δω01 = ω01 − ωpulse. c Histogram of Γ2 from the magnitude response of the measurements from 975 traces, spanning 4.27 × 105 s (approximately 119 h). d Histogram of Γ2 from the corresponding phase response of the measurements taken in (c). Both (c) and (d) have been fitted (solid line) to a Gaussian distribution with parameters shown. e The decay of the qubit state by averaging all the measured traces in (c) to extract the decoherence rate. f A π-pulse is applied to flip the qubit to the excited state with 1.92 × 109 averages, where P(τ) is the power emitted by the qubit at time τ after the pulse. By fitting the emitted power (blue circles) to an exponential decay, we extract Γ1/2π = 273 ± 11 kHz. Except for the histograms, the error bars are for 95% confidence.