FisMat2017 - Submission - View

Abstract's title: Droplet epitaxy GaAs nanostructures as ideal entangled photon sources for hybrid quantum networking
Submitting author: Francesco Basso Basset
Affiliation: University of Milano-Bicocca
Affiliation Address: Via Roberto Cozzi, 55, 20125 Milano
Country: Italy
Oral presentation/Poster (Author's request): Oral presentation
Other authors and affiliations: Sergio Bietti (L-NESS and Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, Milano, Italy), Luca Esposito (L-NESS and Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, Milano, Italy), Alexey Fedorov (L-NESS and CNR‐IFN, Como, Italy), Marcus Reindl (Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Linz, Austria), Daniel Huber (Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Linz, Austria), Emanuele Grilli (L-NESS and Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, Milano, Italy), Armando Rastelli (Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Linz, Austria), Emiliano Bonera (L-NESS and Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, Milano, Italy), Rinaldo Trotta (Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Linz, Austria), Stefano Sanguinetti (L-NESS and Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, Milano, Italy and CNR‐IFN, Como, Italy)
Abstract
Great attention is being devoted to epitaxial semiconductor quantum dots (QDs) as polarization-entangled photon sources [1]. In order for the biexciton-exciton radiative cascade to exhibit high fidelity values, a high QD structural symmetry and a proper choice of materials are crucial to tackle the main sources of entanglement degradation, namely the presence of a fine structure energy splitting (FSS) between the two bright exciton states [2] and fluctuating nuclear magnetic fields [3] due to the hyperfine interaction.
In this work we present GaAs/AlGaAs QDs grown on a (111)A substrate by a novel approach based on droplet epitaxy, where the fundamental crystallization step is performed at a temperature which is significantly higher than in previous reports [4,5]. Thanks to the specific substrate orientation, we overcome a long-standing limitation hampering standard droplet epitaxy, which must rely upon a high As flux and a low substrate temperature because of the elevated Ga diffusivity on the AlGaAs (100) surface. The increase in growth temperature improves the crystalline quality of the QDs and strongly reduces the impact of interdiffusion, as determined by morphological characterization combined with ensemble optical spectroscopy. We demonstrate as well that the (111)A orientation results in nanostructures with high in-plane symmetry, which is an essential requirement to achieve vanishing FSS. The control over the growth dynamics leads to the fabrication of QDs with different aspect ratios and to the reproducible design of the emission wavelength. We demonstrate also the possibility of operation in the 780 nm range, which allows frequency-matching with Rb-based quantum memories, an important target for the realization of quantum repeaters and long distance qubit teleportation [6].
Polarization-resolved single dot photoluminescence reveals a remarkable improvement in optical quality, evaluated in terms of neutral exciton linewidth, and a very low average FSS of (4 ± 2) μeV in the spectral region of interest. Time-resolved measurements under resonant excitation unveil a short exciton lifetime of about 230 ps, so that a high fraction of emitters meets the basic requirements for generating an entangled photon pair. Fidelity measurements were successfully performed under two-photon resonant excitation and yielded a value of 0.8, which already reaches the state-of-the-art for the more studied In(Ga)As/GaAs QDs in absence of postselection or external FSS tuning, thus confirming the intriguing potentiality of this materials system.
[1] C. Y. Lu et al., Nat. Photon. 8, 174–176 (2014).
[2] R. Singh et al., Phys. Rev. Lett. 103, 063601 (2009).
[3] E. A. Chekhovich et al., Nat. Mater. 12, 694–504 (2013).
[4] T. Mano et al., Appl. Phys. Express 3, 065203 (2010).
[5] T. Kuroda et al., Phys. Rev. B 88, 041306 (2013).
[6] N. Akopian et al., Nat. Photon. 5, 230-233 (2011).