Hy-Q Seminar: Ana Predojević and Carsten Schuck

Both the implementation of quantum technologies and the fundamental tests of quantum mechanics strongly benefit from having access to sources of on-demand photon pairs. Quantum dots are among the most promising systems that could potentially provide such a source, with demonstrated potential in quantum communication and quantum computation. While the on-demand generation of single photons and photon pairs in quantum dots is ensured by a coherent and resonant excitation, the collection efficiency is limited by the high refractive index contrast between the air and the semiconductor host material. To solve this problem one needs to recur to engineering of photonic structures that enhance the photon extraction efficiency.To date, successful quantum dots integration into photonics environments such as optical microcavities has been probed, bringing up significantly the single photon collection efficiency. In particular, quantum dots integration into micropillar devices has stood up as a promising solution. The key of this approach is the use of micropillars with moderate to high quality factors (Q-factors), which results in a strong enhancement of the emission into the cavity mode (Purcell effect). In return, high photon extraction efficiencies are attained. However, these high Q-factor cavities are narrowband cavities and cannot accommodate the cavity-mediated emission of photon pairs. As a reduction in the Q factor was believed to ultimately deteriorate the device performance, most of the proposed solutions capable of extracting photon pairs that are found in the literature, imply the design and nanofabrication of costly and complex photonic structures.We demonstrate a significantly simpler solution based on a deterministic low-Q factor micropillar cavity device. The broadband cavity design is suitable for the extraction of photon pairs, and we experimentally demonstrate unprecedented extraction efficiency of 69.4 (10)%. Such a high extraction efficiency is explained due to the suppression of the emission into unwanted background modes, which is present for certain discrete values of micropillar lateral
size.

Quantum Technology promises tremendous advances in information processing, communication, and sensing, but current approaches do not readily scale to large system size. We try to overcome such limitations by leveraging modern nanotechnology as efficient means for replicating optical and electronic circuit components in large numbers on nanophotonic chips to make a new range of applications and physics questions in quantum optics accessible. I will present progress on integrating quantum light sources with nanophotonic networks as well as a novel design approach for improving the performance and footprint of photonic integrated circuit components. Efficient single photon detection presents another crucial building block for future quantum technology implementations. We address this with waveguide-integrated superconducting nanowire single-photon detectors (SNSPDs), which we realize in large numbers and with leading performance parameters for quantum key distribution, remote sensing, a variety of quantum optics experiments as well as fundamental studies of superconducting fluctuation phenomena. To address systems aspects of quantum emitters embedded in a nanophotonic network we progress towards integrating sources, circuits, and superconducting single-photon detectors on silicon chips, thus catering to a wide range of use cases in quantum computing, simulation, communication, and sensing.