Three-photon Rydberg-atom-based radio-frequency sensing scheme with narrow linewidth

The self-calibration of rf sensors using Rydberg-atom vapor cells is a major advantage over conventional rf antennas, but has been limited by Doppler broadening. In this study, ultranarrow linewidths comparable to those in ultracold gases are obtained in a room-temperature vapor cell, by overcoming Doppler shifts via a three-photon scheme to reduce the spectral linewidth to less than 200 kHz. This narrow linewidth extends the self-calibrated regime of such sensors by over an order of magnitude, compared to what has been achieved in standard two-photon schemes.