Entanglement Swapping with Photons Generated on Demand by a Quantum Dot

Abstract

Photonic entanglement swapping, the procedure of entangling photons without any direct interaction, is a fundamental test of quantum mechanics 1 and an essential resource to the realization of quantum networks 2 . Probabilistic sources of non-classical light can be used for entanglement swapping, but quantum communication technologies with device-independent functionalities demand for push-button operation 3 that, in principle, can be implemented using single quantum emitters 4 . This, however, turned out to be an extraordinary challenge due to the stringent requirements on the efficiency and purity of generation of entangled states. Here we tackle this challenge and show that pairs of polarization-entangled photons generated on-demand by a GaAs quantum dot can be used to successfully demonstrate allphotonic entanglement swapping. Moreover, we develop a theoretical model that provides quantitative insight on the critical figures of merit for the performance of the swapping

Polarization Anisotropies in Strain-Free, Asymmetric, and Symmetric Quantum Dots Grown by Droplet Epitaxy

“…Although for the present work we selected three typical samples for extensive characterization, similar ones were implemented on the three surfaces while maintaining a comparably high quality (e.g., sharp line-width). More importantly, at least for some relevant cases, other groups have independently obtained very similar samples showcasing, for instance, quantum emission and entanglement from the (001) and (111)A surfaces with both droplet epitaxy and droplet etching [4,27,30,32].…”

“…A similar consideration holds for the negative-charged exciton counterpart X − . Beyond fundamental physics, this feature is extremely relevant for the implementation of entangled photon emission springing from XX-X-cascaded photon pairs [30][31][32]103], provided that the fine structure splitting (FSS) is negligible and the which-path-information is erased.…”

“…Droplet epitaxy [1][2][3][4] and droplet etching [5][6][7][8][9][10][11][12][13] (DE) are alternative growth protocols to Stranski-Krastanov for the fabrication of strain-free III-V-based semiconductor quantum dots (QDs). This emerging class of nanostructures has been efficiently exploited for the fabrication of classical optoelectronic devices such as photodetectors [14], lasers [15][16][17][18][19], and quantum emitters [13,[20][21][22][23][24][25][26][27][28][29][30][31][32], demonstrating the relevance of this approach for realistic applications.…”

Advanced Technologies for Quantum Photonic Devices Based on Epitaxial Quantum Dots

“…As a consequence of epitaxial growth methods, QD ensembles within a single wafer typically have significant spectral inhomogeneous broadening, with a typical value of full width at half maximum (FWHM) several tens of nanometers. The scalability of QD sources is a big challenge for photonic applications, as linking QDs through photonic quantum interference requires all photons emitted from individual QDs to be identical . Photons impinging on the beam splitter from two input arms need to be indistinguishable so that they could bunch together and leave the beam splitter through only one output arm by quantum interference effect .…”

A tuneable telecom wavelength entangled light emitting diode deployed in an installed fibre network

“…The latter has recently become very popular, achieving good photon indistinguishabilities with high purity and most importantly, the potential for fully deterministic operation 14 . Recent progress in the field culminated in first demonstrations of entanglement swapping 15,16 from this kind of source, an important step towards scalable quantum networks. However, these experiments require a sophisticated pulsed laser system combined with careful suppression of exciting laser light, making them at the moment not the first choice when it comes to field deployment of QD photon-pair sources in non-laboratory environments.…”