Browsing by Author "Joos, Raphael"

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    Bright source of Purcell‐enhanced, triggered, single photons in the telecom C‐band
    (2023) Nawrath, Cornelius; Joos, Raphael; Kolatschek, Sascha; Bauer, Stephanie; Pruy, Pascal; Hornung, Florian; Fischer, Julius; Huang, Jiasheng; Vijayan, Ponraj; Sittig, Robert; Jetter, Michael; Portalupi, Simone Luca; Michler, Peter
    Several emission features mark semiconductor quantum dots as promising non-classical light sources for prospective quantum implementations. For long-distance transmission and Si-based on-chip processing, the possibility to match the telecom C-band is decisive, while source brightness and high single-photon purity are key features in virtually any quantum implementation. An InAs/InGaAs/GaAs quantum dot emitting in the telecom C-band coupled to a circular Bragg grating is presented here. This cavity structure stands out due to its high broadband collection efficiency and high attainable Purcell factors. Here, simultaneously high brightness with a fiber-coupled single-photon count rate of 13.9 MHz for an excitation repetition rate of 228 MHz (first-lens single-photon collection efficiency ≈17% for NA = 0.6), while maintaining a low multi-photon contribution of g(2)(0) = 0.0052 is demonstrated. Moreover, the compatibility with temperatures of up to 40 K attainable with compact cryo coolers, further underlines the suitability for out-of-the-lab implementations.
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    High-rate intercity quantum key distribution with a semiconductor single-photon source
    (2024) Yang, Jingzhong; Jiang, Zenghui; Benthin, Frederik; Hanel, Joscha; Fandrich, Tom; Joos, Raphael; Bauer, Stephanie; Kolatschek, Sascha; Hreibi, Ali; Rugeramigabo, Eddy Patrick; Jetter, Michael; Portalupi, Simone Luca; Zopf, Michael; Michler, Peter; Kück, Stefan; Ding, Fei
    Quantum key distribution (QKD) enables the transmission of information that is secure against general attacks by eavesdroppers. The use of on-demand quantum light sources in QKD protocols is expected to help improve security and maximum tolerable loss. Semiconductor quantum dots (QDs) are a promising building block for quantum communication applications because of the deterministic emission of single photons with high brightness and low multiphoton contribution. Here we report on the first intercity QKD experiment using a bright deterministic single photon source. A BB84 protocol based on polarisation encoding is realised using the high-rate single photons in the telecommunication C-band emitted from a semiconductor QD embedded in a circular Bragg grating structure. Utilising the 79 km long link with 25.49 dB loss (equivalent to 130 km for the direct-connected optical fibre) between the German cities of Hannover and Braunschweig, a record-high secret key bits per pulse of 4.8 × 10 -5 with an average quantum bit error ratio of ~ 0.65% are demonstrated. An asymptotic maximum tolerable loss of 28.11 dB is found, corresponding to a length of 144 km of standard telecommunication fibre. Deterministic semiconductor sources therefore challenge state-of-the-art QKD protocols and have the potential to excel in measurement device independent protocols and quantum repeater applications.