Nanowire Quantum Dots as an Ideal Source of Entangled Photon Pairs

We predict that heterostructure quantum wires and [111] grown quantum dots have a vanishing fine-structure splitting on the grounds of their symmetry, and are therefore ideal candidates to generate entangled photon pairs. We underpin this proposal by atomistic million-atom many-body pseudopotential calculations of realistic structures and find that the vanishing fine-structure splitting is robust against possible variations in morphology.

Figure 1

Symmetry analysis of different nanostructures. The left column of each panel gives the symmetry of the valence band maximum and the conduction band minimum. The right column gives the resulting excitons with their corresponding point group symmetries. A thick red (black dashed) line indicates optically bright (dark) states.

Figure 2

Square of the wave functions for the first three electron ($e_0$, $e_1$, $e_2$) and hole ($h_0$, $h_1$, $h_2$) states of the structures $S1$, $S5$, $S7$, $S8$, and $S9$, described in Table . The isosurfaces enclose 75% of the probability densities. Corresponding absorption spectra in arbitrary units. The inset for structure $S9$ and $S10$ is a blowup of the excitonic line separated by the FSS (lower part).

Figure 3

(a) Schematic of the biexciton cascade with FSS and transitions $X1$ and $X2$. (b) FSS as a function of elongation for the shape $S9$ of Table . (c) Polar plots of the oscillator strength of the transitions $X1$, $X2$ and the sum of both. The polar axis represents the $E$-field direction of light.