ИСТИНА

We study optimal temperature, spectral and other experimental conditions for generation of optical–terahertz biphotons with the highest possible values of the correlation parameters, a second-order correlation function g(2) at low gain, and the photon noise reduction factor or covariance at high parametric gain. The current absence of single-photon terahertz detectors makes it impossible to use typical quantum optical circuits for direct detection of the photon coincidences. The new approaches are developed for detection of the biphoton correlations, based on analysis of joint statistical distributions of analog readings of an optical detector in the signal channel and a terahertz detector in the idler channel of the SPDC set-up. Measurement of exact values of correlation parameters is of key importance in applications of the optical-terahertz biphotons in terahertz quantum ghost imaging with a single-pixel terahertz receiver, construction of single-photon terahertz sources, reference-free calibration of the spectral sensitivity of terahertz detectors, and other perspective tasks. Our current work is devoted to the study and absolute measurement of quantum effi ciencies of the analog superconducting terahertz HEB bolometers. Experimental approaches based on the SPDC generation scheme with a nonlinear crystal placed in the He cryostat together with HEB and a single-photon detector in the optical detection channel are analyzed.