Quantum Sensing with Extreme Light

Optical nonlinear conversion processes are ubiquitously applied to scientific as well industrial tasks. In particular, employed generate radiation in many frequency ranges. plenty of these processes, the generation paired photons occurs — so-called signal and idler photons. Although this type has undergone a tremendous development over last decades, either generated or been used experimentally. contrast, novel quantum-based measurement principles enable usage both partners photon pairs based on their correlation. These approaches have an enormous potential for future applications, they allow transfer information from one spectral range another. ranges where detection is particularly challenging can benefit principle. Above all, include extreme ranges, such low-frequency side mid far infrared even terahertz range, but also high-frequency ultraviolet X-ray range. review article, theoretical experimental developments correlated biphotons described specifically regions.