Fig. 2: Time-resolved lifetime and photon-correlation measurements.

a Resonance fluorescence linewidth measured on the singly-charged exciton, X¹⁻ (QD1). The measurement is performed by sweeping a narrow-bandwidth laser over the X¹⁻ resonance. The overall time for the shown scan is  ~8 min. A Lorentzian function (red line) fits perfectly to the data (blue dots), showing an optical linewidth of 0.64 ± 0.01 GHz. b Lifetime measurement on X¹⁻ under pulsed resonant excitation. The gate voltage is the same as in a. The measured decay rate (Γ_r= 3.71 ± 0.04 GHz, corresponding to a lifetime of 1/Γ_r = 270 ± 3 ps) implies a lifetime-limited linewidth of Γ_r/2π = 0.59 ± 0.01 GHz (Exponential fit). c Resonance fluorescence of X¹⁻ (QD2) as a function of the gate voltage. d Resonance fluorescence linewidth along with the lifetime-limit (obtained from separate lifetime measurements at the corresponding gate voltages). Similar to QD1, the linewidth of QD2 stays very close to the lifetime limit in the plateau centre. e Auto-correlation (g⁽²⁾) measured under resonant π-pulse excitation. f Auto-correlation of the resonance fluorescence measured under weak continuous-wave excitation shown on a short time-scale. The g⁽²⁾-measurement is normalised⁴⁴ by dividing the number of coincidences by its expectation value T ⋅ t_bin ⋅ x₁ ⋅ x₂, where T is the overall integration time, t_bin is the binning time, and x₁, x₂ are the count-rates on the two single-photon detectors. g The same auto-correlation measurement as in f but evaluated on a much longer time-scale (milliseconds). The perfectly flat g⁽²⁾ reveals the absence of blinking.