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

Abstract

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 novel 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 a 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 45.2 $\mathrm{fW}\mathrm{c}{\mathrm{m}}^{-2}\mathrm{H}{\mathrm{z}}^{-0.5}$ (1.84 $\mathrm{fW}\mathrm{H}{\mathrm{z}}^{-0.5}$) 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.

13 pages, 9 figures, 2 tables

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