Room-temperature ultrasensitive photon-level detection in the subterahertz frequency regime

In recent years, subterahertz (sub-THz) electromagnetic waves have been increasingly applied in next-generation wireless communications, imaging, spectroscopy, and nondestructive sensing. However, high-sensitivity detection of sub-THz waves is a difficult task for conventional electronic and photonic techniques. Here, we report the first successful demonstration of ultrasensitive room-temperature detection of sub-THz waves using a frequency up-conversion technique based on a backward optical parametric process in periodically poled lithium niobate (PPLN) crystals. The detection sensitivity reached 50 attojoules (aJ), outperforming those of cryogenically cooled bolometers and commercial pyroelectric detectors by several orders of magnitude. Furthermore, the frequency can be flexibly tuned by simply rotating the PPLN crystals. This simple, stable, and highly sensitive photonic scheme can potentially realize sub-THz wave detection for future wireless communications (6G/7G), sensing, imaging, and spectroscopic applications.