High-Yield Fabrication of Entangled Photon Emitters for Hybrid Quantum Networking Using High-Temperature Droplet Epitaxy

The search for a suitable entangled photon source is an active research direction because such sources play an important role in key quantum communication protocols and different quantum computation approaches. We present the fabrication and the characterization of an entangled photon source based on GaAs/AlGaAs QDs grown on a ( l l l )A substrate by a novel approach based on droplet epitaxy. DE is still quite far from meeting the fundamental requirements for the practical realization of a hybrid semiconductor−atomic quantum network. The average fine structure splitting value is still too high and gives rise to a minor fraction of only approximately 5% of entanglement-ready emitters. Additionally, we want to match the QDs emission with Rb—based quantum memories (around 780 nm). Finally, a long-standing drawback is the low substrate temperature during the formation of the nanostructures and the surrounding barrier, which places a limit on the crystalline and optical quality of the material, issue that can be only partially overcome with an annealing process. Thanks to the specific choice of substrate orientation, the use of low Al concentration in the barrier and finely tuned growth conditions, we overcome this limitations. Our method drastically improves the yield of entanglement-ready photon sources near the emission wavelength of interest, which can be as high as 95% due to the low values of fine structure splitting and radiative lifetime, together with the reduced exciton dephasing offered by the choice of GaAs/AlGaAs materials. Fidelity measurements under two-photon resonant excitation yielded a value of 0.8. which already reaches the state-of the art for the more studied InGaAs/GaAs QDs in absence of postselection or external FSS tilting, thus confirming the intriguing potentiality of this technique.