Fine structure splitting cancellation in highly asymmetric InAs/InP droplet epitaxy quantum dots

TL;DR

This paper demonstrates that highly asymmetric InAs/InP droplet epitaxy quantum dots can exhibit nearly zero fine structure splitting due to cancellation effects, enabling high-quality entangled photon pair generation.

Contribution

It reveals that asymmetry in quantum dots can lead to FSS cancellation, challenging the assumption that symmetry is necessary for low FSS.

Findings

FSS nearly vanishes in highly asymmetric dots due to cancellation effects.

FSS can be minimized at specific etch pit displacements from the dot center.

Asymmetric quantum dots can produce indistinguishable, polarization-entangled photon pairs.

Abstract

We find the single exciton's fine structure splitting (FSS), which splits its degenerate ground state manifold into singlets, nearly vanishes in highly asymmetric quantum dots due to the cancellation of splitting effects with markedly different origin. The dots simulated are those that emerge on top of etch pits through the droplet epitaxy growth process; these etch pit dots break square ($C_{4v}$) spatial symmetry, which has been previously associated with small FSS. Configuration interaction calculations predict a vanishing FSS at a specific finite etch pit displacement from the center of the dot, for a structure far from square symmetry. We thus predict that highly asymmetric quantum dots may still display negligible fine structure splitting, providing new avenues for high-fidelity generation of indistinguishable, polarization entangled photon pairs on demand.