Single photons as a standard: PTB and NIST measured the same quantum-dot source with nearly matching results
On 31 August 2026 PTB described a comparison in which the German and US national metrology institutes measured the same single-photon source with different methods and obtained very close results. According to PTB this is an important step towards a common standard for comparing sources and calibrating single-photon detectors.
- The source is based on an InGaAs quantum dot in a micro-mesa. According to the paper in Applied Physics Letters (December 2024) it delivers a maximum flux of (2.74 ± 0.03) × 10⁶ photons per second at a wavelength of (929.7 ± 0.1) nm, with a multiphoton suppression of g⁽²⁾(0) = 0.22 ± 0.02.
- The key quantity was how often the source “accidentally” emits two photons at once. Despite different methods, the two institutes’ results were very close, and the source stayed stable after its trip to the USA and many cooling cycles; the chip can be installed in any cryogenic system, which makes interlaboratory comparisons easier.
- PTB notes that the purity of this source was not yet fully satisfactory — two or more photons sometimes came out at once — and that it already has better sources; it also works with universities, measuring the photon emitters they send in.
- Single photons carry information in quantum communication and cryptography, and detecting the smallest amounts of light is needed in fluorescence microscopy, precise distance measurement for autonomous vehicles and sensitive cameras, among other things. A standard source would make it possible to assess other sources and calibrate detectors more accurately.
Source: PTB — Einzelne Lichtteilchen für die Quantentechnologie-Industrie (31.08.2026)