ИСТИНА

So far, only the classical properties of terahertz radiation have been widely studied for various applications. Nevertheless, the extension of quantum optical technologies to the terahertz range can be very useful for its further development. We show that quantum-correlated pairs of photons of optical and terahertz ranges, generated under spontaneous parametric down-conversion (SPDC) in a strongly frequency non-degenerate regime, could be first examples of non-classical radiation matching the terahertz gap. The problems and prospects of application of optical-terahertz biphotons are analyzed considering quantum sensing, ghost imaging, and quantum calibration of efficiencies of the terahertz detectors.