We demonstrate niobium nitride based superconducting single-photon detectors sensitive in the spectral range 452 nm -2300 nm. The system performance was tested in a real-life experiment with correlated photons generated by means of spontaneous parametric down conversion, where one of photon was in the visible range and the other was in the infrared range. We measured a signal to noise ratio as high as 4 × 10 4 in our detection setting. A photon detection efficiency as high as 64% at 1550 nm and 15 % at 2300 nm was observed. arXiv:1807.04273v2 [physics.ins-det]

Proper characterization of nonlinear crystals is essential for designing single photon sources. We show a technique for dispersion characterization of a nonlinear material by making use of phase matching in the process of parametric down conversion. We use our procedure to improve the Sellmeier coefficients measured by another methods. Our method is demonstrated on an exemplary periodically poled potassium titanyl phosphate KTiOPO 4 crystal phase-matched for 396 nm to 532 nm and 1550 nm. We show a procedure to characterize the dispersion in the range of 390 to 1800 nm by means of only one spectrometer for the UV-visible range.

A simple, room-temperature, cavity-and vacuum-free interface for an efficient photon-matter interaction is implemented. In the experiment a heralded single photon generated by the process of spontaneous parametric down-conversion is absorbed by a single atom-like system, specifically a nitrogen-vacancy color center in diamond. Here phonon-assisted absorption solves the mismatch problem of a narrow absorption bandwidth in a typical atomic medium and broadband spectrum of quantum light. The source is tunable in the spectral range 452 − 575 nm, which overlaps well with the absorption spectrum of nitrogen-vacancy centers. This can also be considered as a useful technique paving the way for development of novel quantum information processing and sensing applications.arXiv:1909.05843v1 [quant-ph]

A simple, room-temperature, cavity- and vacuum-free interface for a photon-matter interaction is implemented. In the experiment, a heralded single photon generated by the process of spontaneous parametric down-conversion is absorbed by an ensemble of nitrogen-vacancy color centers. The broad absorption spectrum associated with the phonon sideband solves the mismatch problem of a narrow absorption bandwidth in a typical atomic medium and broadband spectrum of quantum light. The heralded single photon source is tunable in the spectral range 452 − 575 nm, which overlaps well with the absorption spectrum of nitrogen-vacancy centers.