Fig. 3: Demonstration of pure and indistinguishable single photons by pulsed deterministic resonant excitation.

a QD resonance-fluorescence intensity under cw laser excitation at a power of P = 0.01 ⋅ P_sat, where P_sat is the saturation power. b Power dependence of the resonance-fluorescence intensity and the photon impurity ξ. The Rabi oscillations (red curve) of the two-level system are modeled including a pure dephasing rate of γ_d = 0.2 ns⁻¹. c The intensity-correlation histogram in a Hanbury Brown and Twiss experiment for π − pulse excitation. The second-order correlation function g⁽²⁾(0) = 0.02 ± 0.005 is extracted from the fitted amplitude of the central peak relative to the fitted amplitude for peaks at a time delay of 50 μs (dashed line). The inset shows g⁽²⁾(τ) measured by integrating the coincidences under the peak over the 50 μs time span. d Schematic of the Hong–Ou–Mandel interferometer used for measuring the indistinguishability of two subsequent photons delayed by the laser pulse separation of 13.7 ns. e Coincidence counts after the Hong–Ou–Mandel interferometer when the input photons are co-polarized (blue) and cross-polarized (red).