Rydberg-assisted atomic electrometry using alkali-metal atoms contained inside a vacuum environment for detecting external electric fields at frequencies below a few kilohertz has been quite challenging due to the low-frequency electric-field-screening effect that is caused by the alkali-metal atoms adsorbed on the inner surface of the container. We report a very slow electric-field-screening phenomenon with a time scale up to the order of seconds on a rubidium-vapor cell that is made of monocrystalline sapphire. Using this sapphire rubidium-vapor cell with an optically induced, internal bias electric field, we demonstrate vapor-cell-based, low-frequency atomic electrometry that responds to the electric field strength linearly. Limited by the given experimental conditions, this demonstrated atomic electrometer uses an active volume of $11\phantom{\rule{0.2em}{0ex}}{\mathrm{mm}}^{3}$ and delivers a spectral noise floor of around $0.34\phantom{\rule{0.2em}{0ex}}\mathrm{mV}/\mathrm{m}\phantom{\rule{0.1em}{0ex}}\sqrt{\mathrm{Hz}}$ and a 3-dB low cutoff frequency of around 770 Hz inside the vapor cell. This work investigates a regime of vapor-cell-based atomic electrometry that was seldom studied before, which may enable more applications that use atomic electric-field-sensing technology.
Rydberg-assisted atomic electrometry using alkali-metal atoms contained inside a vacuum environment for detecting external electric fields at frequencies below a few kilohertz has been quite challenging due to the low-frequency electric-field-screening effect that is caused by the alkali-metal atoms adsorbed on the inner surface of the container. We report a very slow electric-field-screening phenomenon with a time scale up to the order of seconds on a rubidium-vapor cell that is made of monocrystalline sapphire. Using this sapphire rubidium-vapor cell with an optically induced, internal bias electric field, we demonstrate vapor-cell-based, low-frequency atomic electrometry that responds to the electric field strength linearly. Limited by the given experimental conditions, this demonstrated atomic electrometer uses an active volume of 11mm3 and delivers a spectral noise floor of around 0.34mV/mHz and a 3-dB low cutoff frequency of around 770 Hz inside the vapor cell. This work investigates a regime of vapor-cell-based atomic electrometry that was seldom studied before, which may enable more applications that use atomic electric-field-sensing technology.
We report several technical approaches that significantly improve the performance of a vapor-cell atomic electrometer operating in the quasi-DC frequency domain (≪ 1 kHz). With a very small active volume of approximately 11 mm3 inside the vapor cell, we demonstrated a noise floor for electric field (E-field) sensitivity ranging from 0.2 to 7.7 mV/mHz for a frequency band of 1--100 Hz. Our work utilizes only a bare vapor cell for electrometry, without any metal parts or electrodes, to ensure minimal distortion of the measured E-field and to minimize the effective sensing volume for high spatial resolution. The E-field-sensitive atomic state (Rydberg state) is excited and read out optically, maximizing the simplicity of the system design and enabling the miniaturization of quasi-DC E-field sensors for potential applications, such as diagnostics of electronics without physical contact, communications in and below the super-low frequency (SLF) band, proximity detection, remote activity surveillance, tracing charge signatures, and research in bioscience and geoscience.
Fields with frequencies below megahertz are challenging for Rydberg-atom-based measurements, due to the low-frequency electric field screening effect caused by the alkali-metal atoms adsorbed on the inner surface of the container. In this paper, we investigate electric field measurements in the ultralow frequency (ULF), very low frequency (VLF), and low frequency (LF) bands in a Cs vapor cell with built-in parallel electrodes. With optimization of the applied DC field, we achieve high-sensitive detection of the electric field at frequencies of 1 kHz, 10 kHz, and 100 kHz based on the Rydberg-atom sensor, with the minimum electric field strength down to 18.0 μV/cm, 6.9 μV/cm, and 3.0 μV/cm, respectively. The corresponding sensitivity is 5.7 μV/cm/Hz 1/2 , 2.2 μV/cm/Hz 1/2 , and 0.95 μV/cm/Hz 1/2 for the ULF, VLF, and LF fields, which is better than a 1-cm dipole antenna. Besides, the linear dynamic range of the Rydberg-atom sensor is over 50 dB. This work presents the potential to enable more applications that utilize atomic sensing technology in the ULF, VLF, and LF fields.
Low-frequency (LF) electric-field measurements with Rydberg atoms are limited by alkali-induced cell-surface screening and excess laser-intensity noise. Here, we address these limitations using a Cs vapor cell with built-in parallel electrodes, active laser-power stabilization, and a home-built balanced detector to suppress 10 Hz-kHz intensity noise. A 15 kHz local-oscillator field is introduced to up-convert Hz-scale signals to the lower-noise kHz band through Rydberg atom-mediated sum-frequency mixing (SFM), improving the optical readout signal-to-noise ratio. The system achieves a minimum detectable electric field of 190 nV/cm within 0.5 Hz-1.006 kHz, a linear dynamic range exceeding 67 dB, and a spectral resolution of 18 mHz.
Fields with frequencies below megahertz are challenging for Rydberg-atom-based measurements, due to the low-frequency electric field screening effect that is caused by the alkali-metal atoms adsorbed on the inner surface of the container. In this paper, we investigate on electric fields measurements in the ULF, VLF and LF bands in a Cs vapor cell with built-in parallel electrodes. With optimization of the applied DC field, we achieve high-sensitive detection of the electric field at frequencies of 1kHz, 10kHz and 100kHz based on Rydberg-atom sensor, with the minimum electric field strength down to 18.0μV/cm, 6.9μV/cm and 3.0μV/cm, respectively. The corresponding sensitivity is 5.7 μV/cm/{\sqrt{Hz}}, 2.2μV/cm/{\sqrt{Hz}} and 0.95μV/cm/{\sqrt{Hz}} for ULF, VLF and LF fields, which is better than 1-cm dipole antenna. Besides, the linear dynamic range of Rydberg-atom sensor is over 50 dB. This work presents the potential to enable more applications that utilize atomic sensing technology in ULF, VLF and LF fields.
We present a model-independent experimental method for calibrating the amplitude of a low-frequency electric field in an alkali vapor cell. Three-photon excitation to a Rydberg state in atomic rubidium produces an electromagnetically induced transparency (EIT) signal that is sensitive to low-frequency fields originating outside the cell. We superpose the measured shape of the EIT resonance in the presence of an electric field with the expected line shape, obtained by numerically time-averaging the effect of the DC-Stark shift. The value of the fractional field amplitude transmission, caused by Faraday screening by the metallic rubidium layer on the cell interior, is a direct result of this comparison. A transmission spectrum is obtained by making measurements between 0 and 100 kHz, which demonstrates high-pass filtering behavior described by two cutoff frequencies. Independently, finite-element simulation provides supporting evidence of the accuracy of the measurement, which is responsive to the nonuniform alkali distribution on the vapor cell wall. In combination with recent advances in the sensitivity of low-frequency electrometry, this may improve absolute, free-space measurements of weak, low-frequency electric fields that are of interest in basic and applied research.
Rydberg-atom electric field sensing has shown great potential from near-DC to THz with state-of-the-art measurement metrics realized in sensitivity, phase extraction, multi-band receptivity, etc. While Rydberg-atom sensors have shown exceptional performance in the GHz regime, low-frequency operation has remained challenging because of electric-field-screening in conventional vapor cells, which suppresses externally applied fields. We overcome this limitation by combining auxiliary modulation and lock-in detection with a paraffin-coated vapor cell, and demonstrate an electrode-free, wideband method for sensing frequencies, ranging from 0.5 Hz to 10 kHz. Our work extends Rydberg-atom sensor range to VLF, ULF, SLF, ELF and sub-ELF frequency bands. In our method, high state-of-the-art sensitivities have been achieved - 819 μV/cm/Hz for 1 Hz, 33 μV/cm/Hz for 10 Hz, 10 μV/cm/Hz for 100 Hz and 2 μV/cm/Hz for 1 kHz.