Single- and entangled-photon emission from strain tunable quantum dots devices

• Main Author: Zhang, Jiaxiang
• Other Authors: TU Chemnitz, Fakultät für Naturwissenschaften
• Format: Doctoral Thesis
• Language: English
• Published: Universitätsbibliothek Chemnitz 2015
• Subjects: Quantenpunkte; Feinstrukturaufspaltung; verschraenkte Phtonenpaare; Ferroelektrischer Kristall; single-photon source; quantum dots; light-emitting diode; PMN-PT; excitation repetition rate; fidelity; nanomembrane; quantum tomography; entangled-light-emitting diode; Bell inequality; Peres criteria; light-hole; coherence time; ddc:530; Quantenpunkt; Halbleiter
• Online Access: http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-177579; http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-177579; http://www.qucosa.de/fileadmin/data/qucosa/documents/17757/Thesis_for%20pulication_jiaxiang.pdf; http://www.qucosa.de/fileadmin/data/qucosa/documents/17757/signatur.txt.asc

On demand single-photon and entangled-photon sources are key building-blocks for many proposed photonic quantum technologies. For practical device applications, epitaxially grown quantum dots (QDs) are of increasing importance due to their bright photon emission with sharp line width. Particularly, they are solid-state systems and can be easily embedded within a light-emitting diode (LED) to achieve electrically driven sources. Therefore, one would expect a full-fledged optoelectronic quantum network that is running on macroscopically separated, QD-based single- and entangled-photon devices. An all-electrically operated wavelength-tunable on demand single-photon source (SPS) is demonstrated first. The device consists of a LED in the form of self-assembled InGaAs QDs containing nanomembrane integrated onto a piezoelectric crystal. Triggered single photons are generated via injection of ultra-short electrical pulses into the diode, while their energy can be precisely tuned over a broad range of about 4.8 meV by varying the voltage applied to the piezoelectric crystal. High speed operation of this single-photon emitting diode up to 0.8 GHz is demonstrated. In the second part of this thesis, a fast strain-tunable entangled-light-emitting diode (ELED) is demonstrated. It has been shown that the fine structure splitting of the exciton can be effectively overcome by employing a specific anisotropic strain field. By injecting ultra-fast electrical pulses to the diode, electrically triggered entangled-photon emission with high degree of entanglement is successfully realized. A statistical investigation reveals that more than 30% of the QDs in the strain-tunable quantum LED emit polarization-entangled photon-pairs with entanglement-fidelities up to f+ = 0.83(5). Driven at the highest operation speed ever reported so far (400 MHz), the strain-tunable quantum LED emerges as unique devices for high-data rate entangled-photon applications. In the end of this thesis, on demand and wavelength-tunable LH single-photon emission from strain engineered GaAs QDs is demonstrated. Fourier-transform spectroscopy is performed, from which the coherence time of the LH single-photon emission is studied. It is envisioned that this new type of LH exciton-based SPS can be applied to realize an all-semiconductor based quantum interface in the foreseeable distributed quantum networks.