We demonstrate a continuously tunable electric field measurement based on the far off-resonant AC stark effect in a Rydberg atomic vapor cell. In this configuration, a strong far off-resonant field, denoted as a local oscillator (LO) field, acts as a gain to shift the Rydberg level to a high sensitivity region. An incident weak signal field with a few hundreds of kHz difference from the LO field is mixed with the LO field in the Rydberg system to generate an intermediate frequency signal, which is read out by Rydberg electromagnetically induced transparency (Rydberg-EIT) spectroscopy. Not like resonant EIT-Autler–Townes spectra, we realize the electric field measurement of the signal frequency from 2 to 5 GHz using a single Rydberg state. The detectable field strength is down to 2.25 μV/cm with sensitivity of the electrometry 712 nV cm⁻¹Hz^−1/2, and a linear dynamic range is over 65 dB. The detectable field strength is comparable with a resonant microwave-dressed Rydberg heterodyne receiver using the same system, which is 0.96 μV/cm with sensitivity of 304 nV cm^–1Hz^−1/2. We also show the system has an inherent polarization selectivity feature. Our method can provide high sensitivity of electric field measurement and be extended to arbitrary frequency measurements.

We investigate atom-based electric-field calibration and polarization measurement of a 100-MHz linearly polarized radio-frequency (rf) field using cesium Rydberg-atom electromagnetically induced transparency in a room-temperature vapor cell. The calibration method is based on matching experimental data with the results of a theoretical Floquet model. The utilized $60D_J$ fine-structure Floquet levels exhibit $J$- and $m_j$-dependent ac Stark shifts and splittings, and they develop even-order rf-modulation sidebands. The Floquet map of cesium $60D_J$ fine-structure states exhibits a series of exact crossings between states of different $m_j$’s which are not rf coupled. These exact level crossings are employed to perform a rapid and precise ($\pm 0.5\%$) calibration of the rf electric field. We also map out three series of narrow avoided crossings between fine-structure Floquet levels of equal $m_j$’s and different $J$’s, which are weakly coupled by the rf field via a Raman process. The coupling leads to narrow avoided crossings that can also be applied as spectroscopic markers for rf-field calibration. We further find that the line-strength ratio of intersecting Floquet levels with different $m_j$’s provides a fast and robust measurement of the rf field’s polarization.

We study Rydberg atoms modulated by strong radio-frequency (rf) fields with a frequency of 70 MHz. The Rydberg atoms are prepared in a room-temperature cesium cell, and their level structure is probed using electromagnetically induced transparency (EIT). As the rf field increases from the weak- into the strong-field regime, the range of observed rf-induced phenomena progresses from ac level shifts through increasingly pronounced and numerous rf modulation sidebands to complex state mixing and level crossings with $\mathrm{high}-l$ hydrogenlike states. Weak anharmonic admixtures in the rf field generate clearly visible modifications in the Rydberg EIT spectra. A Floquet analysis is employed to model the Rydberg spectra, and good agreement with the experimental observations is found. Our results show that all-optical spectroscopy of Rydberg atoms in vapor cells can serve as an antenna-free, atom-based, and calibration-free technique to measure rf electric fields and to analyze their higher-harmonic contents.

We propose a novel type of Rydberg dimer, consisting of a Rydberg-state atom bound to a distant positive ion. The molecule is formed through long-range electric-multipole interaction between the Rydberg atom and the pointlike ion. We present potential energy curves (PECs) that are asymptotically connected with Rydberg $nP$ or $nD$ states of rubidium or cesium. The PECs exhibit deep, long-range wells which support many vibrational states of Rydberg-atom-ion molecules (RAIMs). We consider photoassociation of RAIMs in both the weak and the strong optical-coupling regimes between initial and Rydberg states of the neutral atom. Experimental considerations for the realization of RAIMs are discussed.

We demonstrate the measurement of super low-frequency electric field using Rydberg atoms in an atomic vapor cell with inside parallel electrodes, thus overcoming the low-frequency electric-field-screening effect at frequencies below a few kHz. Rydberg electromagnetically induced transparency (EIT) spectra involving 52D_5/2 state is employed to measure the signal electric field. An auxiliary DC field is applied to improve the sensitivity. A DC Stark map is demonstrated, where the utilized 52D_5/2 exhibits m _j = 1/2, 3/2, 5/2 Stark shifts and splittings. The m _j = 1/2 state is employed to detect the signal field because of its larger polarizability than that of m _j = 3/2, 5/2. Also, we show that the strength of the spectrum is dependent on the angle between the laser polarizations and the electric field. With optimization of the applied DC field to shift the m _j = 1/2 Rydberg energy level to a high sensitivity region and the laser polarizations to obtain the maximum m _j = 1/2 signal, we achieve the detection of the signal electric field with a frequency of 100 Hz down to 214.8 µV/cm with a sensitivity of 67.9 µV cm⁻¹Hz^−1/2, and the linear dynamic range is over 37 dB. Our work extends the measurement frequency of Rydberg sensors to super low frequency with high sensitivity, which has the advantages of high sensitivity and miniaturization for receiving super low frequency.