A research team from the Faculty of Physics and the Centre for Quantum Optical Technologies at the Centre of New Technologies, University of Warsaw has introduced a new way to measure hard-to-detect terahertz signals using a "quantum antenna." In their work, the scientists applied an innovative radio wave detection setup based on Rydberg atoms that not only senses terahertz radiation, but also accurately calibrates a so-called frequency comb in this part of the spectrum. Until recently, the terahertz range was considered a blank area in the electromagnetic spectrum, and the method reported in the journal Optica opens the door to extremely sensitive spectroscopy and a new class of room-temperature quantum sensors.

Terahertz (THz) radiation, being part of the electromagnetic spectrum, lies at the boundary of electronics and optics, positioned between microwaves (used, for example, in Wi-Fi) and infrared. Although it holds immense potential for applications that include inspecting packages without harmful X-rays, superspeed 6G communication, and spectroscopy and imaging of organic compounds, turning this potential into precise and sensitive measurements has been technically very difficult. In the past few years, scientists have made major strides in both generating and detecting terahertz radiation, yet until now they had not been able to measure a frequency comb in this region with the required precision.