Semiconductor-based single-photon sources for quantum radiometry and their metrolgical characterization

This work is dedicated to the realization of efficient single-photon sources, which are necessary
for reaching high accuracy and metrological traceability in the field of quantum radiometry.
Semiconductor quantum dots have promising properties for metrological applications: a spectral
emission bandwidth below 50 pm and a decay time of about 1 ns, allowing fast pulsed operation.
The InGaAs quantum dots were metrologically characterized regarding their spectral
characteristics, single-photon purity, absolute photon flux and absolute optical power. High
efficiency of the self-made confocal setup is obtained by combining high transmission objectives
with ultra-narrow bandpass filters for low-loss spectral filtering. The light extraction efficiency
of the sample is enhanced by integrating a single quantum dot into a monolithic microlens
or micromesa. The highest measured photon flux at the detector was (2.55 ± 0.02) ⋅ 106 s−1,
which corresponds to a radiant flux of (545 ± 4) fW. The 𝑔(2)(0) value increased with the count
rate, but it remained below 0.25 even for photon fluxes close to saturation. An Allan deviation
analysis of the count rate stability yielded an optimal averaging time of 92 s.
The feasibility of the direct implementation of this single-photon source in quantum
radiometry is demonstrated by a calibration of the detection efficiency of a single-photon
avalanche detector (SPAD). A relative calibration using the fiber exchange technique reached a
relative standard uncertainty of 0.7 % for the ratio of detection efficiencies of two Si-SPADs.
Moreover, an absolute calibration was performed by a direct comparison of a SPAD with
a calibrated low-noise analog detector via the substitution method. The relative standard
uncertainties at different count rates varied between 0.9 % and 3.2 %. At low photon fluxes, the
results were consistent with the standard calibration technique with attenuated laser light. At
high photon fluxes, the diminished nonlinearity of the apparent detection efficiency proved the
superior properties of semiconductor quantum dots over laser light for applications in the field
of quantum radiometry.
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