Optical and Quantum Sensing and Precision Metrology II
Vapor cell characterization and optimization for applications in Rydberg atom-based radio frequency sensing
Mohammad Noaman, Hadi Amarloo, Rajesh Pandiyan, Sanyasi Rao Bobbara, Somayeh M. A. Mirzaee, Kent A. Nickerson, Chang Liu, Donald W. Booth, James P. Shaffer
We measure radio frequency electromagnetic wave total scattering cross-sections and internal radio frequency electromagnetic field distributions for several novel types of MEMs atomic vapor cells, optimized for Rydberg atom-based radio frequency electric field sensing. Vapor cells that use metamaterial structures are described. The vapor cells are designed for high radio frequency transmission, uniform internal radio frequency field amplitudes, and low radar scattering cross-section. Experimental scattering data and radio frequency field amplitude maps from functioning vapor cells are presented. The total scattering cross-sections are calibrated to the total scattering cross-sections for a series of steel balls, whose scattering is quantified using Mie scattering theory. We measure across a span of radio frequencies ranging from ~1 GHz – 20 GHz. The work is important for engineering Rydberg atom-based radio frequency electric field sensors for deployment in applications such as test and measurement.
We measure radio frequency electromagnetic wave total scattering cross-sections and internal radio frequency electromagnetic field distributions for several novel types of MEMs atomic vapor cells, optimized for Rydberg atom-based radio frequency electric field sensing. Vapor cells that use metamaterial structures are described. The vapor cells are designed for high radio frequency transmission, uniform internal radio frequency field amplitudes, and low radar scattering cross-section. Experimental scattering data and radio frequency field amplitude maps from functioning vapor cells are presented. The total scattering cross-sections are calibrated to the total scattering cross-sections for a series of steel balls, whose scattering is quantified using Mie scattering theory. We measure across a span of radio frequencies ranging from ~1 GHz – 20 GHz. The work is important for engineering Rydberg atom-based radio frequency electric field sensors for deployment in applications such as test and measurement.
Rydberg atom-based sensors represent a cutting-edge technology for highly sensitive radio-frequency (RF) electric field detection. Their performance is strongly influenced by the atomic vapor cell's characteristics, which significantly affect the internal field distribution and consequently the sensor's sensitivity. This research examines how relative permittivity, wall thickness, and cell dimensions impact the electric field distribution. Motivated by the growing demand for broadband communication and high-frequency technologies in next-generation systems, the 1-30 GHz frequency range is selected as the operational bandwidth. Results reveal that the resonance frequency of the dielectric cell—determined by its dimensions, relative permittivity, and wall thickness—plays a crucial role in the internal field distribution, making the conventional cell-dimension-to-wavelength ratio alone insufficient for predicting field behavior. Beyond the resonance frequency, field distortion and non-uniformity decrease even as the cell-dimension- to-wavelength ratio increases. Contrary to expectations, reducing cell size does not uniformly diminish field distortion and can significantly enhance the internal field within specific frequency bands. While variations in relative permittivity and wall thickness have a limited effect on the internal field at lower frequencies, these parameters exert a substantial influence near resonance and can even lead to field enhancement, particularly at the cell center. These findings demonstrate that through optimized cell design, the internal field can be engineered to achieve either uniform distributions for high-accuracy metrology or enhanced fields for weak-signal detection. This study provides practical guidelines for developing next-generation quantum RF sensors, communication systems, and radar technologies.
We present a comprehensive numerical investigation into the radio frequency (RF) field behavior within miniaturized all-glass and hybrid vapor cell geometries designed for Rydberg atom-based electrometry. Using full-vector finite element modeling (FEM), we analyze electromagnetic field enhancement across a wide frequency range (0.05 GHz to 150 GHz) as a function of polarization, incidence angle, and structural configuration. Two primary vapor cell designs are evaluated: translationally invariant "open" cells and periodically structured "supported" cells composed entirely of low-loss glass, as well as hybrid structures incorporating highly doped silicon. Our simulations reveal that the structured all-glass vapor cells exhibit sharp, angle- and polarization-dependent resonant peaks due to guided-mode coupling, resulting in localized RF power enhancements exceeding 8x. In contrast, silicon-based structures demonstrate significant electric field attenuation and suppression of resonant features due to their high dielectric losses. Through k-vector and angle-resolved analyses, we show how cell geometry and material properties critically influence the RF field distribution and coupling efficiency. Our findings open new possibilities for optimizing vapor cell architectures to enhance field sensitivity, directional and polarization selectivity, and integration potential in chip-scale quantum sensing platforms based on Rydberg atoms.
Highly excited Rydberg atoms in a room-temperature vapor cell are promising for developing a radio-frequency (RF) electric field (E-field) sensor and relevant measurement standards with high accuracy and sensitivity. The all-optical sensing approach is based on electromagnetically-induced transparency and Autler-Townes splitting induced by the RF E-field. Systematic investigation of measurement uncertainty is of great importance for developing a national measurement standard. The presence of a dielectric vapor cell containing alkali atoms changes the magnitude, polarization, and spatial distribution of the incident RF field. In this paper, the field distortion of rubidium vapor cells is investigated, in terms of both field strength distortion and depolarization. Full-wave numerical simulation and analysis are employed to determine general optimization solutions for minimizing such distortion and validated by measuring the E-field vector distribution inside different vapor cells. This work can improve the accuracy of atom-based RF E-field measurements and contributes to the development of related RF quantum sensors.
We discuss a fundamentally new method for electric (E) field strength (V/m) metrology applicable to the near-field. This new approach is significantly different from currently used field measurement techniques in that it is based on the interaction of radio-frequency (RF) E-fields with Rydberg atoms (alkali atoms placed in a glass vapor cell that are excited optically to Rydberg states). The applied RF E-field alters the state of the atoms. The Rydberg atoms act like an RF-to-optical transducer, converting an RF E-field strength to an optical-frequency response. In this new approach, we employ the phenomena of electromagnetically induced transparency (EIT) and Autler-Townes splitting. The RF transition in the four-level atomic system causes a split of the EIT transmission spectrum of a probe laser into two peaks. This splitting is easily measured and is directly proportional to the applied RF E-field amplitude. The significant dipole response of Rydberg atoms enables this technique to make self-calibrating measurements over a large frequency band including 500 MHz to 500 GHz (and possibly up to 1 THz and down to 10s of megahertz). In this paper, we report on our results in the development of this metrology approach, including the first fiber-coupled vapor-cell for E-field measurements. We also discuss key applications, including self-calibrated measurements, millimeter-wave and sub-THz measurements, field mapping, and sub-wavelength and near-field imaging. We show results for mapping the fields inside vapor cells, for measuring the E-field distribution along the surface of a circuit board, and for measuring the near-field at the aperture in a cavity. We also discuss the uncertainties of this measurement technique.
Engineered, metamaterial vapor cells are useful for high-sensitivity Rydberg atom-based radio frequency (RF) sensors. We present recent advancements on a photonic crystal receiver (PCR) fabricated using MEMS technology for sensitive RF field detection. Beyond the established operational principles leveraging electromagnetically induced transparency (EIT) within alkali atom ensembles, we describe critical factors impacting the performance of the PCR, namely the generation of electric fields arising from Cesium atom interactions with the vapor cell materials. Through X-ray Photoelectron Spectroscopy (XPS) analysis of the glass and silicon components, we determine the amount of Cesium that is adsorbed to the glass and silicon surfaces. The insights into surface adsorption and its control are crucial for improving the stability and practical applicability of PCR-based RF sensors, as well as other types of MEMS vapor cells.
Significant progress has been made in atom-based measurements of length, time, gravity and electromagnetic fields in recently years. Rydberg atom-based microwave electric field measurement, using electromagnetically induced transparency (EIT) in room temperature alkali-metal vapors, has been extensively investigated and aroused the broad interest. This approach may establish a new standard for the measurements of microwave (MW) and radio frequency (RF) electric fields.In this review, we describe the work on a new method of measuring electric fields based on quantum interference by using either cesium or rubidium atoms contained in a dielectric vapor cell. Rydberg atoms with principal quantum number n >>1 have large direct current (DC) polarizabilities and microwave transition dipole moments, thereby making them extremely sensitive to external electric fields. Using the Rydberg three-level EIT to detect the level splitting and shift that is induced by the external field, we can realize a rapid and robust self-calibration method of measuring the electric field in a frequency range from 0.01 GHz to 1000 GHz. For the MW electric field (frequency range > 1 GHz), the MW field causes the Rydberg states to split, known as an Autler-Townes splitting (A-T) effect when the applied microwave can resonate with adjacent Rydberg states. The MW coupled A-T splitting is proportional to the applied electric field strength, from which the field strength is measured. Using the EIT window, a high sensitivity of 3 μV·cm-1·Hz-1/2 and small electric field of 1 μV/cm are expected to be achieved with a modest setup, and the limitations of the sensitivity are also addressed in the review. For the RF field at frequency mj EIT lines, and avoided crossings formed with the fine-structure levels of equal mj and different J's, which is used to calibrate and measure the RF field amplitude. On the other hand, the dependence of the EIT-line strength on the RF field polarization provides a fast and robust polarization measurement of RF fields based on matching experimental data with a theoretical simulation. The measurements of minimum strengths and sensitivity of RF fields based on Rydberg atoms are one order magnitude below the values obtained by traditional antenna methods. The atom-based field measurement paves the way for determining fields through calibration-free, invariable atomic properties and miniaturization. We also propose its various potential applications in the future.