Universal recovery of the bright-exciton level-degeneracy in quantum dots without structural symmetry

TL;DR

This paper demonstrates that applying combined strain and electric fields can universally restore bright-exciton degeneracy in quantum dots, overcoming structural asymmetry and enabling high-fidelity entangled photon sources.

Contribution

It shows experimentally and theoretically that degeneracy can be recovered in any quantum dot by using two external perturbations simultaneously.

Findings

Degeneracy restored in various quantum dot structures.

External fields align exciton polarization and erase energy splitting.

Potential for scalable quantum-technology applications.

Abstract

The lack of structural symmetry which usually characterizes semiconductor quantum dots lifts the energetic degeneracy of the bright excitonic states and hampers severely their use as high fidelity sources of entangled photons. We demonstrate experimentally and theoretically that it is always possible to restore the excitonic degeneracy by the simultaneous application of large strain and electric fields, despite the fact that this possibility has fundamentally been doubted. This is achieved by using one external perturbation to align the polarization of the exciton emission along the axis of the second perturbation, which then erases completely the energy splitting of the states. This result, which holds for any QD structure, highlights the potential of combining complementary external fields to create artificial atoms meeting the stringent requirements posed by scalable semiconductor-based quantum-technology.