Researchers demonstrate first terahertz quantum sensor

Scheme and nomenclature for the theoretical analysis. In addition to a laser pump (for simplification, not drawn here), the signal (s1) and idler (i1) input modes enter the nonlinear crystal (NL). The interaction in the crystal leads to the generation of signal and idler photons in the output modes s'1 and i'1, respectively. They are separated by an indium tin oxide (ITO)–coated glass. Afterward, the signal radiation and the pump beam are reflected back into the crystal by the mirror Ms. The input modes for the second passage are denoted by i2 and s2, which is, because of the alignment, equal to s'1. The idler mode i'1 passes through the object (O), is reflected by the mirror Mi, and propagates through the object again. This acts as a beam splitter (BS) with second input mode 3 and output modes i''1 and 3′. Aligning the idler beams, the mode i''1 corresponds to i2. The output modes after the second passage are s'2 and i''2. Last, the signal radiation (in mode s'2) is detected by the detector. The inset shows the simulated interference signal in the Stokes (red) and anti-Stokes (blue) regions based on the detailed model. Credit: Science Advances, doi: 10.1126/sciadv.aaz8065

A research team in Germany described the first demonstration of quantum sensing in the terahertz frequency range.

During the experiments, terahertz frequencies interacted with a sample in free space and provided information about the sample thickness by detecting the visible photons. The team obtained layer thickness measurements with terahertz photons based on biphoton interference. 

The report has been published in Science Advances. (

Read more.