Figure 1

(a) PL spectrum of a single QD. (b) Schematic description of the biexciton-radiative cascade in natural QDs with its two colinearly polarized photons (either $H$ or $V$) and energetically distinguishable paths. (c), (d) High resolution polarization sensitive PL spectra of the biexciton $X{X}^0$ and exciton $X^0$ lines, respectively. Because of spectral diffusion (see text), the measured line widths are larger than the radiative widths, shown schematically in (b).Reuse & Permissions

Figure 2

(a) [(b)] The temporal intensity cross-correlation measurements between the exciton $X^0$ and the biexciton $X{X}^0$ spectral lines for collinear [cross-linear] polarizations. (c) The same-cascade correlation measurements obtained by the difference between the collinearly polarized curves in (a) and the average curve of the cross-linearly polarized measurements in (b). (d) Tomographical measurements of the same-cascade intensity cross-correlation functions with spectral resolution of $25\mu \mathrm{eV}$. $D$ stands for linear polarizer at 45° relative to the $H$ direction and $R$ ($L$) stands for right (left) hand circular polarizer. The integrated numbers of coincidences in each measurement are indicated.Reuse & Permissions

Figure 3

The measured two photons’ density matrix for photon pairs from a biexciton cascade: (a) [(b)] obtained with spectral window of 200 [25] $\mu \mathrm{eV}$.Reuse & Permissions

Figure 4

Measured (symbols) and calculated (lines) normalized number of coincidences $|P|\psi ⟩{|}^2$ (dash-lines) and off diagonal density matrix element $|{\gamma }^{\prime }|$ (solid-lines) vs the spectral window width $w$. For the calculations we used $\Gamma =1.6\mu \mathrm{eV}$ and $\Delta =27\mu \mathrm{eV}$, as experimentally determined. Thick (thin) line represents calculation which includes (ignores) spectral diffusion averaged over normally distributed photon energy shifts, with width of $50\mu \mathrm{eV}$ at half-maximum.Reuse & Permissions