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Generation of complex multi-photon states in miniaturized semiconductor based quantum devices

Subject Area Experimental Condensed Matter Physics
Term from 2018 to 2025
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 403555215
 
Final Report Year 2023

Final Report Abstract

While single photons with high quality and emission rate can nowadays be generated using highly optimized quantum dot light sources, the generation of multiphoton states and the application of these quantum states are still in their infancy. During the project, it was investigated under which conditions two-photon states can be generated and detected using semiconductor quantum dots in suitable resonators. In the first approach, we investigated the two-photon emission by the decay of a quantum dot biexciton via a virtual state into the resonator mode of a micropillar. For this purpose, individual quantum dots were specifically embedded in micropillars using deterministic nanofabrication. This device integration strongly increased the light-matter interaction to maximize the two-photon emission efficiency, and the necessary fine-tuning of the two-photon resonance was achieved via temperature tuning. Unfortunately, no evidence of two-photon resonance could be observed in the samples prepared. For a future successful observation of two-photon emission, the light-matter coupling strength needs to be increased and piezo tuning should be used as fine-tuning mechanism. Additionally, the possibility of a simultaneous increase in the collection efficiency of the excitonic and biexcitonic transition in a quantum dot by means of a resonantly tuned open double resonator was investigated. In resonance, an accelerated decay of both the excitonic and the biexcitonic decay could be observed. This result demonstrated for the first time the great flexibility of an open tunable double resonator for the efficient emission of the two photons of the radiating biexciton-exciton cascade. Finally, a two-photon state was produced using the Hong-Ou-Mandel effect and could be successfully detected using a Hanbury-Brown and Twiss interferometer. In the second approach, we realized energy-time entangled photon pairs using Fransoninterferometry. Due to their robustness, such energy-time entangled photon pairs are particularly attractive in fiber-based networks for long-distance quantum communication. To generate energytime entangled photon pairs, we first developed and deterministically fabricated quantum dot microlenses and micromesas with broadband enhancement emission of the integrated quantum emitter. The single-QD devices were fabricated by means of in-situ electron beam lithography and feature excellent optical and quantum optical properties. Some of these quantum devices were equipped with piezo elements for spectral fine-tuning. Then, we set up an ultra-stable, laser-controlled Franson-interferometer with high light throughput optimized for experiments using the resonantly driven biexciton-exciton cascade of a quantum dot for entanglement generation. Using this quantum optical setup, we succeeded in the on-demand generation of energy-time entangled photon pairs with a Franson visibility of (73±2)%, which overcomes the Clauser, Horne, Shimony, and Holt (CHSH) inequality by more than one standard deviation. Further activities could focus on achieving even higher Franson visibility using quantum dots embedded into bullseye resonators with enhanced light-matter coupling efficiency.

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