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The gravitational wave (GW) observatories calibrate interferometer displacement using photon momentum, with laser power serving as the measurand. These observatories are traceable to the International System of Units through a primary standard maintained by the US’s National Metrology Institute (NMI), the National Institute of Standards and Technology (NIST). The bilateral degree of equivalence of laser power measurements for various NMIs indicated in the 2010 EUROMET.PR-S2 supplementary comparison reveals scale realization uncertainty unacceptably large for GW event parameterization. We offer here an analysis to identify the source of the discrepancy between the Physikalisch-Technische Bundesanstalt (PTB) and NIST results. Using an improved transfer standard in a bilateral comparison, with representatives of the Laser Interferometer Gravitational-Wave Observatory (LIGO) receiving results prior to their comparison, NIST and PTB demonstrated a degree of equivalence of −0.15% with an uncertainty of 0.95% (k = 2) for combined 100 mW and 300 mW comparison results.

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We apply an InGaAs quantum dot based single-photon source for the absolute detection efficiency calibration of a silicon single-photon avalanche diode operating in Geiger mode. The single-photon source delivers up to (2.55 ± 0.02) × 106 photons per second inside a multimode fiber at the wavelength of 929.8 nm for above-band pulsed excitation with a repetition rate of 80 MHz. The purity of the single photon emission, expressed by the value of the 2nd order correlation function g(2)(τ = 0), is between 0.14 and 0.24 depending on the excitation power applied to the quantum dot. The single-photon flux is sufficient to be measured with an analog low-noise reference detector, which is traceable to the national standard for optical radiant flux. The measured detection efficiency using the single-photon source remains constant within the measurement uncertainty for different photon fluxes. The corresponding weighted mean thus amounts to 0.3263 with a standard uncertainty of 0.0022.

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Im Rahmen des BMBF-Projektes SiM4diM entwickelt die PTB zusammen mit den Firmen JCMwave und Carl Zeiss IMT sowie der Hochschule Aalen neue Verfahren zur vollständigen Modellierung mikroskopisch-bildgebender Messsysteme auf der Grundlage rigoroser Beugungsrechnungen. Ziel ist es, mit diesem „virtuellen Mikroskop“ die bildbasierte industrielle Messtechnik signifikant zu verbessern und die Unsicherheit dimensionaler Metrologie auch im industriellen Umfeld um mehr als eine Größenordnung zu verringern.

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This contribution presents experimental and simulation results of a tiltable line scanning low coherence interferometer applied for form measurement of spherical and aspherical objects with a diameter of up to 300 mm.
The region of interest is sampled by multiple annular subapertures that are realigned employing stitching algorithms based on Cartesian- and Zernike polynomial fittings.
The paper addresses common challenges in the reduction and modeling of displacement errors associated with the motion of the interferometric sensor between subaperture measurements and compares the topography deviations of the experimental results with those simulated by a Monte Carlo based model.

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Uncertainty quantification by ensemble learning is explored in terms of an application known from the field of computational optical form measurements. The application requires solving a large-scale, nonlinear inverse problem. Ensemble learning is used to extend the scope of a recently developed deep learning approach for this problem in order to provide an uncertainty quantification of the solution to the inverse problem predicted by the deep learning method. By systematically inserting out-of-distribution errors as well as noisy data, the reliability of the developed uncertainty quantification is explored. Results are encouraging and the proposed application exemplifies the ability of ensemble methods to make trustworthy predictions on the basis of high-dimensional data in a real-world context.

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The EMPIR Project “Single and entangled photon sources for quantum metrology (SEQUME)” is set to start on June 1st, 2021, for a three-year funding period. The aim of SEQUME project is to develop bright entangled photon sources based on different application-oriented platforms and to exploit high-purity single-photon sources to demonstrate the quantum advantage achieved by using these sources for specific measurements. Making single-photon and entangled-photon sources, with the required performance parameters, more readily available, would be significant for the development of quantum technologies and the advancement of quantum-enhanced measurements. At PTB, Stefan Kück, Hristina Georgieva, Franziska Hirt, Marco Lopez, Sebastian Raupach, Andreas Schell, and Pablo Tieben are involved in the project. The project is coordinated by Stefan Kück at PTB and involves 8 NMIs and 10 Universities as partners.

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The EMPIR Project “Quantum sensors for metrology based on single-atom-like device technology (QADeT)” is set to start on June 1st 2021 for a three-year funding period. The aim of the QADeT project is to realize single-atom-like systems (SALSs) in suitable materials, e.g. diamond, capable to perform nanoscale, high-sensitivity (electro-magnetic (EM) fields, temperature, stress, etc.) measurements.  Moreover, optimal methods to assess reproducibility in production and characterization of these systems and the host materials will be defined, paving the way for a standardization of the processes.

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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 communications, but also in any other quantum physics experiment where high detection rates are needed.

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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

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