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    Wavelength-tunable entangled photons from silicon-integrated III–V quantum dots
    (London : Nature Publishing Group, 2016) Chen, Yan; Zhang, Jiaxiang; Zopf, Michael; Jung, Kyubong; Zhang, Yang; Keil, Robert; Ding, Fei; Schmidt, Oliver G.
    Many of the quantum information applications rely on indistinguishable sources of polarization-entangled photons. Semiconductor quantum dots are among the leading candidates for a deterministic entangled photon source; however, due to their random growth nature, it is impossible to find different quantum dots emitting entangled photons with identical wavelengths. The wavelength tunability has therefore become a fundamental requirement for a number of envisioned applications, for example, nesting different dots via the entanglement swapping and interfacing dots with cavities/atoms. Here we report the generation of wavelength-tunable entangled photons from on-chip integrated InAs/GaAs quantum dots. With a novel anisotropic strain engineering technique based on PMN-PT/silicon micro-electromechanical system, we can recover the quantum dot electronic symmetry at different exciton emission wavelengths. Together with a footprint of several hundred microns, our device facilitates the scalable integration of indistinguishable entangled photon sources on-chip, and therefore removes a major stumbling block to the quantum-dot-based solid-state quantum information platforms.
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    Quantum dot-based broadband optical antenna for efficient extraction of single photons in the telecom O-band
    (Washington, DC : The Optical Society, 2020) Yang, Jingzhong; Nawrath, Cornelius; Keil, Robert; Joos, Raphael; Zhang, Xi; Höfer, Bianca; Chen, Yan; Zopf, Michael; Jetter, Michael; Portalupi, Simone Luca; Ding, Fei; Michler, Peter; Schmidt, Oliver G.
    Long-distance fiber-based quantum communication relies on efficient non-classical light sources operating at telecommunication wavelengths. Semiconductor quantum dots are promising candidates for on-demand generation of single photons and entangled photon pairs for such applications. However, their brightness is strongly limited due to total internal reflection at the semiconductor/vacuum interface. Here we overcome this limitation using a dielectric antenna structure. The non-classical light source consists of a gallium phosphide solid immersion lens in combination with a quantum dot nanomembrane emitting single photons in the telecom O-band. With this device, the photon extraction is strongly increased in a broad spectral range. A brightness of 17% (numerical aperture of 0.6) is obtained experimentally, with a single photon purity of 𝑔(2)(0)=0.049±0.02 at saturation power. This brings the practical implementation of quantum communication networks one step closer.