In quantum communication systems, the precise estimation of the detector´s response to the incoming light is necessary to avoid security breaches. The typical working regime uses a free-running single-photon avalanche diode in combination with attenuated laser pulses at telecom wavelength for encoding information. We demonstrate the validity of an analytical model for this regime which considers the effects of dark counts and dead time on the measured count rate. For the purpose of gaining a better understanding of these effects, the photon detections were separated from the dark counts via a software-induced gating mechanism. The model was verified by experimental data for mean photon numbers covering three orders of magnitude as well as for laser repetition frequencies below and above the inverse dead time. Consequently, our model would be of interest for predicting the detector response not only in the field of quantum...

The Max-Planck-RIKEN-PTB Center for Time, Constants, and Fundamental Symmetries holds a workshop on recent advances on Tuesday March 9th, 2021, with the following speakers:

Ichiro Ushijima (RIKEN): Transportable optical lattice clocks with 18 digit precision
Richard Lange (PTB): Improved Limits for Violations of Local Position Invariance and Local Lorentz Invariance from Atomic Clocks
Peter Micke (PTB): Coherent laser spectroscopy of highly charged ions using quantum logic
Matthew Anders Bohman (MPIK/RIKEN): Sympathetic Cooling of Trapped Protons
Antonia Schneider (MPIK): High-precision measurement of the hyperfine structure of 3He+ in a Penningtrap
Kathrin Kromer (MPIK): Latest results of the high-precision mass measurements with PENTATRAP
Jack Devlin (CERN/RIKEN): Constraining the coupling between axion-like dark matter and photons using an antiproton superconducting detection circuit in a cryogenic Penning trap

In the finalized project BiRD JRP 16NRM08 (https://www.birdproject.eu), funded by the EU program EURAMET EMPIR Call 2016 – „Metrology Research for Pre‐ and Co‐normative projects“, basic research was carried out on such measurands which determine the appearance of products. These are, amongst color and its angle-dependent distribution also gloss, sparkle, and graininess. The term sparkle describes the specific appearance of surfaces which can be observed under directed illumination by reflection of point-like scattering centers and is similar to the appearance of sparkling stars in the night-sky. This effect is generated e.g. by high-reflective microparticles, which are embedded in the lacquer coat of a surface. Well-known examples are metallic automobile coatings. Graininess describes the appearance of such surfaces when illuminated diffusely [1]. Although the sparkle-effect is widely applied in industrial production, there is no...