ИСТИНА

The spontaneous parametric down-conversion (SPDC) in the strongly non-degenerate regime can provide the idler wave frequency hitting the terahertz frequency (THz) range. In this case, the nonlinear crystal should act as a source of correlated photon pairs consisting of optical and terahertz frequency photons – optical-terahertz biphotons. These states might be of interest due to the different quantum information and quantum communication tasks, including the development of a single-photon terahertz frequency source, optical-terahertz twin beams, etc. The main complicating factor for generating the non-classical field states in the THz range is the high noise level due to the thermal radiation at room temperatures. Nevertheless, it might be suggested that in the nearest future the interest will arise to the quantum optics in the terahertz range. This might happen with the development of high-radiance (i.e. with high number of terahertz photons per mode) sources and single-photon THz detectors. In this paper, we discuss both theoretically and experimentally the measurement of correlation functions of the fields generated by means of SPDC in the terahertz idler frequency range, for different crystal temperatures and different schemes of the THz photon emission.