While most experimental developments have focused on room-temperature vapors so far, using cold atoms has the advantage of strongly reducing the frequency broadening associated with Doppler effect, while increasing the interaction time between the atoms and the probing beams, offering prospects to make the most of the intrinsic narrow linewidth of Rydberg atoms and perform long-term, stable measurements. Scientists researchers at ONERA have previously used cold atoms to perform absolute measurements of the gravity field onboard moving carriers, showing that this technology is now compatible with practical applications out of the lab. We have recently developed at ONERA a novel approach to sense electromagnetic fields with cold
While most experimental developments have focused on room-temperature vapors so far, using cold atoms has the advantage of strongly reducing the frequency broadening associated with Doppler effect, while increasing the interaction time between the atoms and the probing beams, offering prospects to make the most of the intrinsic narrow linewidth of Rydberg atoms and perform long-term, stable measurements. Scientists researchers at ONERA have previously used cold atoms to perform absolute measurements of the gravity field onboard moving carriers, showing that this technology is now compatible with practical applications out of the lab. We have recently developed at ONERA a novel approach to sense electromagnetic fields with cold
Rydberg atoms are highly promising for microwave electric field sensing owing to their large dipole matrix elements. While most experimental developments have focused on room-temperature vapors so far, utilizing cold atoms in this context could open new possibilities for applications where accuracy, long term stability and highresolution at large integration times are required, such as calibrating blackbody shifts in state-of-the-art optical clocks or measuring the cosmic MW background. Here, we report a novel approach [1] for the metrology of microwave fields with cold 87 Rubidium Rydberg atoms based on trap-loss-spectroscopy in a magneto-optical trap (MOT).
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.
Rydberg atoms, where one valence electron is promoted to an orbit far away from the nucleus, have very large dipole moments, making them good candidates to be used as very sensitive probes of electromagnetic fields (Fancher et al., IEEE Transactions on Quantum Engineering, 2, 1–13, 2021). Compared to classical antennae, they can be made dielectric, their size is independent of the wavelength to be measured, and they offer the potential to perform self-calibrated measurements, referenced on the properties of the atoms themselves. So far, most of the research in this field has focused on sensing electromagnetic fields with room-temperature (or hotter) Rydberg atoms, where the absorption of a probe laser beam can be made dependent of the microwave field to be measured via the phenomenon of electromagnetically - induced transparency.
Due to their high sensitivity, wide frequency range, SI-traceability and reduced size at low frequency, Rydberg atoms based- sensors of RF/THz fields hold great prospects for many applications including telecommunications, radar, and THz imaging. So far, almost all of these sensors have consisted in probing by means of EIT spectroscopy the Autler-Townes effect resulting from the interaction between the field and a warm vapor of alkaline Rydberg atoms. Despite significant improvement using heterodyning, this approach suffers several limitations caused by broadening mechanisms inherent to warm vapors, and by using EIT as a probe. We report here on a new approach based on trap-loss spectroscopy of the Autler-Townes effect in cold 87Rb atoms confined in a MOT. The doublet of dressed Rydberg states measured this way obeys well the theoretical model of Autler-Townes effect provided lightshifts from neighboring Rydberg states are considered, suggesting the possibility to infer the characteristics of the field from those of the doublet. Study of the resulting sensor revealed a very good linearity, with residual errors of 1%, and a resolution of 5 µV/cm after an integration time of 2600s.
Trap loss spectroscopy, based on fluorescence detection, provides a real-time measurement technique that is advantageous for ultra-cold atomic systems, to monitor the interaction between microwave fields and Rydberg atoms. By employing the polarization combinations of excitation lasers and microwave fields, we achieve trap loss spectroscopy of multi-path transitions in magnetic Rydberg hyperfine states and observe Zeeman broadening. The contributions of laser power, Zeeman effect, and collision effects to the broadening of the trap loss spectrum were comprehensively analyzed. Additionally, we have observed the broadening and splitting of the trap loss spectrum in response to variations in microwave field power and frequency. The transition from broadening to splitting of the spectral profile is observed with an increase in microwave field power. The full width at half maximum (FWHM) of trap loss spectroscopy exhibited a proportional relationship with the square root of microwave power, while the peak separation demonstrated a direct proportionality with higher microwave power. Our detailed exploration of trap loss spectroscopy under microwave fields may provide what we believe to be a novel approach for microwave field sensing.
We demonstrate the quantum sensing of radiofrequency fields based on cold Rydberg atoms in a super-molasses trap, without the need for magnetic coils. Our approach combines the metrological advantages of cold atoms with a metal-free dielectric sensor head minimizing perturbations to the electromagnetic environment, a feature that was previously restricted to vapor-cell-based devices. Moreover, the absence of inductive loads allows to rapidly alternate between the cooling phase and the Rydberg excitation, leading to trap-loss spectroscopy signals one order of magnitude narrower than for conventional magneto-optical traps. This enables self-calibrated microwave power measurements with an unprecedented dynamic range of 43dB, opening the door to new perspectives of applications in calibration measurements. We also report a scale factor linearity better than 1%, the absence of drifts over several tens of minutes leading to a 3μV/cm resolution, and the possibility to retrieve the ellipticity of the applied microwave field. By demonstrating a cold-atom metrological platform in a compact dielectric sensor head, this work paves the way for new applications in the field of radiofrequency measurements with Rydberg atoms, and in other fields of quantum sensing based on cold atoms such as magnetometry, gravimetry or inertial navigation.