Highly Reduced Fine-Structure Splitting inInAs/InPQuantum Dots Offering an Efficient On-Demand Entangled 1.55-μmPhoton Emitter

To generate entangled photon pairs via quantum dots (QDs), the exciton fine-structure splitting (FSS) must be comparable to the exciton homogeneous linewidth. Yet in the $(\mathrm{In},\mathrm{Ga})\mathrm{As}/\mathrm{GaAs}$ QD, the intrinsic FSS is about a few tens $\mu \mathrm{eV}$. To achieve photon entanglement, it is necessary to cherry-pick a sample with extremely small FSS from a large number of samples or to apply a strong in-plane magnetic field. Using theoretical modeling of the fundamental causes of FSS in QDs, we predict that the intrinsic FSS of $\mathrm{InAs}/\mathrm{InP}$ QDs is an order of magnitude smaller than that of $\mathrm{InAs}/\mathrm{GaAs}$ dots, and, better yet, their excitonic gap matches the $1.55\mu \mathrm{m}$ fiber optic wavelength and, therefore, offers efficient on-demand entangled photon emitters for long distance quantum communication.