Electric-field metrology of a terahertz frequency comb using Rydberg atoms

Terahertz radiation finds an increasing number of applications, yet efficient generation and detection remain a challenge and an active area of research. In particular, the precise detection of weak and narrowband terahertz signals is notoriously difficult. Here, we employ a type of single-photon detector based on Rydberg atoms to both detect and calibrate a terahertz frequency comb over an octave-spanning range, yet with MHz-level selectivity. We calibrate the intensity of the electric field of the comb against the fundamental atomic properties while achieving the intensity (power) sensitivity down to 45.2f Wcm −2 Hz −0.5 (1.84f WHz −0.5 ) within a single mode of the frequency comb, all in a room-temperature-operated setup. Our results elucidate the transition of terahertz frequency combs into the quantum regime, enabling high-precision and high-sensitivity spectroscopy. This breakthrough allows terahertz science to better leverage revolutionary techniques developed for optical frequency combs.