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Single photons as light source for radiometry

Annual Report 2020
03.03.2021

Schematic representation of the molecule-based single-photon source for applications in quantum radiometry, for example to calibrate a single-photon detector (1, SPAD) via a reference detector (2, analog). The value of g(2)(0) = 0.08 means there is a very small probability that two photons may be emitted at the same time. With an emission linewidth of 0.2 nm, the bandwidth of the source is very narrow and emits up to 1.5 million photons per second. DBT: dibenzoterrylene

PTB has been working intensively on developing and metrologically characterizing single-photon sources for quantum radiometry. This has been done in collaboration with research partners in European metrology research programs (e.g. EMPIR). Within the scope of the ongoing EMPIR project titled “Single Photon Sources as New Quantum Standards” (SIQUST), a newly developed single-photon source based on the organic dye molecule dibenzoterrylene represents an important step towards establishing a standard single-photon source.

Single-photon sources are so-called nonclassical light sources. In contrast to lasers or incandescent lamps, these sources emit light only as single quanta (photons).

Single-photon sources are interesting in particular for the field of quantum radiometry, where very low optical powers in the femtowatt range (approx. a billionth of the power of a laser pointer) have to be measured with very small uncertainty. The single photons are generated by exciting one single atom, molecule or ion which can emit exactly one photon per excitation process. In principle, such a single-photon source offers the possibility of realizing a new primary standard for optical power as a complement to the blackbody radiator and the synchrotron radiation source.