Terahertz quantum sensing with visible light

In quantum sensing experiments, photons in the spectral region of interest interact with a sample and their properties are transferred via biphoton-correlation to another spectral region, where widely available and highly developed detectors can be used. Especially spectral regions where the photon detection is quite difficult can benefit from this novel technique. We report on the first demonstration of quantum sensing in the terahertz frequency range, in which the terahertz photons interact with a sample in free space determining the thickness of polytetrafluoroethylene plates by only detecting visible photons.