Abstract Rydberg atom-based sensors use atoms dressed by lasers to detect and measure radio frequency electromagnetic fields. The absorptive properties of the atomic gas, configured as a Rydberg atom-based sensor, change in the presence of a radio frequency electromagnetic field. While these sensors are reasonably sensitive, the best conventional radio frequency sensors still outperform Rydberg atom-based sensors with respect to sensitivity. One approach to increase the sensitivity of Rydberg atom-based sensors is to engineer the vapor cell that contains the atomic gas. In this work, we introduce a passive, all-dielectric amplifier integrated into a Rydberg atom-based sensor vapor cell. The vapor cell is a combination of a slot waveguide and a photonic crystal. The structural features of the vapor cell yield a power amplification of ~ 24 dB. The radio frequency electromagnetic field is coupled adiabatically into the slot waveguide and slowed to increase the interaction between the radio frequency field and the atoms to effectively amplify the incoming signal, i.e., increase the Rabi frequency on the radio frequency transition. The work shows the utility of vapor cell engineering for atom-based quantum technologies and paves the way for other such devices.
Abstract Rydberg atom-based sensors use atoms dressed by lasers to detect and measure radio frequency electromagnetic fields. The absorptive properties of the atomic gas, configured as a Rydberg atom-based sensor, change in the presence of a radio frequency electromagnetic field. While these sensors are reasonably sensitive, the best conventional radio frequency sensors still outperform Rydberg atom-based sensors with respect to sensitivity. One approach to increase the sensitivity of Rydberg atom-based sensors is to engineer the vapor cell that contains the atomic gas. In this work, we introduce a passive, all-dielectric amplifier integrated into a Rydberg atom-based sensor vapor cell. The vapor cell is a combination of a slot waveguide and a photonic crystal. The structural features of the vapor cell yield a power amplification of ~ 24 dB. The radio frequency electromagnetic field is coupled adiabatically into the slot waveguide and slowed to increase the interaction between the radio frequency field and the atoms to effectively amplify the incoming signal, i.e., increase the Rabi frequency on the radio frequency transition. The work shows the utility of vapor cell engineering for atom-based quantum technologies and paves the way for other such devices.
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.
In this work, theoretical and experimental works on Rydberg-atom based radio-frequency (RF) sensors are presented. The results were obtained in close collaboration with the Quantum Valley Ideas Lab, whose goal is the miniaturization and prototyping of these sensors. The Rydberg-atom based RF sensors utilize lasers to coherently excite an atomic vapor in a vapor cell at room temperature to a highly excited Rydberg state, which is extremely sensitive to external environmental influences. In this work, Rydberg-atom based RF sensing is described as coherent multi-photon interference in the atom-light coupled system by introducing atom-light coherences. The presence of the RF wave influences the absorption of a probe laser propagating through the atomic medium. The atomic response of the Rydberg-atoms can be engineered by changing the atom-light coherences through laser power and frequency. Analytic expressions for the atomic response to the incident RF wave are derived in the weak probe limit and provide a deeper understanding of the underlying coherent multi-photon interference processes, which help to further tailor the Rydberg-atom for the purpose of the application. Good agreement with full numerical simulations of the Lindblad-master equation is found. An analysis of the various Doppler limits strongly motivates an excitation scheme where the effective wave vector mismatch on the Rydberg transition vanishes, as a promising candidate to achieve narrower spectral linewidths and, consequently, a higher sensitivity. The level structure of cesium presents a unique three-photon excitation scheme where residual Doppler shifts become comparable to the spectral linewidth of the coupling lasers. The experimental realization of this excitation scheme is demonstrated. A spectral linewidth of the Rydberg transition of 190 kHz is achieved. The measurements present the world record sensitivity, 45 nV/cm/Hz^1/2, for all-optical RF sensing with room temperature operation. These results make the three-photon excitation scheme a prime candidate for the next generation of Rydberg-atom based RF sensor prototypes. Finally, all-optical phase-sensitive RF detection is theoretically investigated in a closed-loop excitation scheme. An analytic expression is derived that intuitively describes the atomic response. Furthermore, it provides insights into the probe intensity dynamics that occur when the system is operated under finite detuning. These oscillatory dynamics allow for the extraction of the in- (I) and out- (Q) of-phase response to the RF wave, thereby enabling the simultaneous detection of the RF E-field amplitude and phase. A blueprint for the experimental realization is presented, and angle-of-arrival tolerances for the RF wave are estimated. A quadrature amplitude modulation (QAM) sequence was modelled and the simultaneous extraction of the phase and amplitude of the RF wave of interest was successfully demonstrated.
Research of hot atomic vapor systems has a long history. Recently, much-improved technologies, such as lasers, microwaves and digital/analog control systems, have led to exciting progress in this reviving field. Due to its cryogenic-free and vacuum-free deployment potential, room-temperature and quantum-enabled sensing devices using gaseous atoms have become a popular research topic, and engineering such devices has received considerable attention. Proof-of-principle experiments have been performed demonstrating new ideas such as quantum-enhanced motion sensors, next-generation magnetometers, Rydberg enabled microwave sensors, etc. This thesis focuses on my work related to electromagnetic-field sensing using Rydberg atoms in vapor cells, where Rydberg atoms are excited and detected by electromagnetically induced transparency (EIT) spectroscopy. I first investigate the detection of strong magnetic fields (sim 1~T) in the Paschen-Back regime. The diamagnetic (quadratic) response of the Rydberg levels makes the atoms sensitive to small fluctuations in field strength on a large background. By implementing an isotope-mixed cell, we demonstrate that accurate measurement, within a relative uncertainty of pm0.12%. Many Rydberg-enabled radio frequency and microwave sensing applications require a capability of zeroing or intentional tuning of small DC electric fields inside the vapor cell. For this purpose, I explore an in-situ DC electric-field sensing and tuning method without using any bulk or thin film electrodes. I find that the photoelectric effect on the vapor cell walls (with invisible, atomic Rb aggregate layers covering the surfaces) can generate tuning fields up to 0.8~V/cm, with an inhomogeneity of about 2%. The spatial distribution of these fields can be directly monitored by quadratic Stark shifts of the Rydberg atoms. This work may inspire new approaches for DC-field control in miniaturized, metal-free atomic vapor-cell devices. Like many other quantum measurements on hot gaseous samples, short interaction time and other technical decoherence processes are the major factors which limit the precision and, in certain cases, the accuracy of the metrological results. In order to study these effects in the context of EIT, I performed an EIT experiment using a Lambda-type quantum system consisting of the hyperfine ground states and the first excited electronic state of the Rb atoms contained in a buffer-gas-free thermal vapor cell without anti-relaxation coating. Technical line-broadening effects due to inhomogeneity of stray magnetic fields, laser frequency jitter, transverse beam intensity distribution, interaction time distribution, and atom-wall/impurity gas collisions are studied. Experimental results and numerical simulations are compared. These results provide crucial information and quantitative insights for vapor cell sensor design. The development of compact and multi-functional spectroscopy vapor cells is widely considered to be a critical engineering step towards manufacturing field-deployable sensors for real life applications. My R&D efforts towards fabrication of glass spectroscopy cells with integrated, highly-conductive silicon components are presented in the last part of my thesis. I explored various technical challenges and successfully developed a proof-of-principle prototype from scratch. The device allows the application of electric fields inside the cell for particle trapping and for tuning Rydberg transitions. Further, the highly-conductive silicon components enable microwave polarization filtering for microwave sensing applications, plasma-physics studies, etc. Preliminary experimental/technical data and simulations are presented. In summary, in my thesis I report on a comprehensive study of several spectroscopic and field sensing applications of Rydberg and ground-state atoms in vapor cells, as well as forays into novel methods to engineer vapor cells with embedded electrodes.
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.
Rydberg atom-based radio frequency electromagnetic field sensors are drawing wide-spread interest because of their unique properties, such as small size, dielectric construction, and self-calibration. These photonic sensors use lasers to prepare atoms and read out the atomic response to a radio frequency electromagnetic field based on electromagnetically induced transparency, or related phenomena. Much of the theoretical work has focused on the Autler-Townes splitting induced by the radio frequency wave. The amplitude regime, where the change in transmission observed on resonance is measured to determine electric field strength, has received less attention. In this paper, we deliver analytic expressions that are useful for calculating the absorption coefficient in the amplitude regime. Our main goal is to describe the analytic expressions for the absorption coefficient and demonstrate their validity over a large range of the interesting parameter space. The effect of the thermal motion of the atoms is explicitly addressed. The analytic formulas for the absorption coefficient for different types of Doppler broadening are compared to estimate the sensitivity under conditions where it is limited by the laser shot noise. Residual Doppler shifts are shown to limit sensitivity. The expressions, approximations and descriptions presented in the paper are important for understanding the absorption of Rydberg atom-based sensors in the amplitude regime. This provides insight into the physics of multi-level interference phenomena.
Rydberg-atom-based electrometry provides a quantum, SI-traceable approach to radio-frequency (RF) and microwave electric-field sensing by linking optical spectra to absolute field strength through electromagnetically induced trans parency. Over the past decade, rapid advances in excitation schemes, field-tuning methods, interferometric readout, and cavity-assisted coupling have significantly improved sensitivity, bandwidth, and tunability of Rydberg-based sensors. In parallel, progress in fiber-coupled modules, microfabricated vapor cells, and photonic integration is enabling compact and deployable receiver architectures. This review presents a comprehensive and metrology-oriented synthesis of the physical principles, system architectures, standardized performance metrics, and uncertainty considerations relevant to Rydberg-atom RF sensing. By con solidating diverse developments into a unified performance and evaluation framework, this work provides a critical reference for the design, comparison, and advancement of next-generation quantum RF sensors and standards.