  Engineering a Terahertz (THz) frequency comb spectroscopy at atomic level
advances the precisely measurement in spectroscopy and sensing. Current
progresses on THz frequency comb rely on difference-frequency generation,
optical parametric oscillation, and other methods. Generating a THz frequency
comb poses challenges in source stability and achieving a narrow bandwidth,
which traditional THz devices are difficult to achieve. Furthermore, accurately
measuring the generated THz frequency comb necessitates a high-performance THz
detector. Rydberg atoms are well-suited for electric field sensing due to their
ultra-wide radio frequency transition energy levels, making them especially
sensitive to external electric fields in the DC to THz bandwidth. However,
there have been no reports about generating THz frequency comb spectroscopy at
the atomic level until now. This work presents a THz frequency comb
spectroscopy with Rydberg atoms, in which a Floquet comb-like transition is
engineered through a time-periodic drive field. Our approach simplifies the
setup required for THz frequency comb spectroscopy while extending the working
bandwidth for Rydberg atomic sensors. The THz frequency comb spectroscopy at
the atomic level reported in this article shows great potential for various
applications in astronomy, remote sensing, spectral detection of biological
samples, and other related fields.
