Figure 3.

(a) EL spectra of a second QD, acquired with a double spectrometer equipped with two 1200 l/mm gratings (spectral resolution ∼30 μeV). The two spectra correspond to two orthogonal polarization directions. Only the bright line marked by arrows (with a line width of 58 μeV) is used in the following measurement. (b) HBT setup used to extract the second-order correlation function, g⁽²⁾(τ), of the EL emitted by a single QD embedded in the Q-LED. A 75 mm long ⁸⁷Rb vapor cell is inserted in one of the arms of the setup. (c) Black: g⁽²⁾(τ) measurement of the EL emission when the photon energy is tuned off resonance with respect to the ⁸⁷Rb D₂ transitions. Red and blue: g⁽²⁾(τ) values when the photon energy is tuned on resonance with the ⁸⁷Rb D₂ lines and the Rb cell temperature is 96 (red), and 100 °C (blue). The corresponding minimum values of g⁽²⁾(τ), reached at a T_Rb-dependent delay time τ_c(T_Rb) are 0.15, 0.44, and 0.53 for the data displayed in of the black, red, and blue, respectively. The gradual increase of τ_c and of g⁽²⁾(τ_c) with increasing T_Rb comes from the dispersion of the atomic optical medium. This leads to slow light and, due to the finite line width of our photon source, to time-jitter and consequent broadening of the g⁽²⁾(τ) curve.