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

## TL;DR

This paper demonstrates a novel Rydberg atom-based detector for precise, sensitive, and room-temperature calibration of terahertz frequency combs, advancing terahertz spectroscopy into the quantum regime.

## Contribution

It introduces a new single-photon detection method using Rydberg atoms for calibrating and detecting terahertz frequency combs with high sensitivity and selectivity.

## Key findings

- Achieved electric field sensitivity down to 45.2 fW/cm²/Hz^0.5
- Calibrated comb intensity against atomic properties
- Enabled high-precision terahertz spectroscopy in a room-temperature setup

## 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 $\mathrm{fW\ cm^{-2}\ Hz^{-0.5}}$ (1.84 $\mathrm{fW\ Hz^{-0.5}}$) 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.