Metrology of microwave fields based on trap-loss spectroscopy with cold Rydberg atoms

We demonstrate a new approach for the metrology of microwave fields based on the trap-loss spectroscopy of cold Rydberg atoms in a magneto-optical trap. Compared to state-of-the-art sensors using room-temperature vapors, cold atoms allow longer interaction times, better isolation from the environment, and a reduced Doppler effect. Our approach is particularly simple, as the detection relies on fluorescence measurements only. Moreover, our signal is well described by a two-level model across a broad measurement range, allowing one, in principle, to reconstruct the amplitude and the frequency of the microwave field simultaneously without the need for an external reference field. We report on a scale-factor linearity at the percent level and no noticeable drifts over two hours, paving the way for new applications of cold Rydberg atoms in metrology, such as calibrating black-body shifts in state-of-the-art optical clocks, monitoring the Earth's cryosphere from space, measuring the cosmic microwave background, or searching for dark matter.