Conference on Precision Electromagnetic Measurements
Real-time Detection of Modulated Radiofrequency Signals in Rydberg Atoms enabled by Optical Frequency Comb Spectroscopy
Sean M. Bresler, David A. Long, Alexandra B. Artusio‐Glimpse, Nikunjkumar Prajapati, Dangka Shylla, Andrew P. Rotunno, Matthew T. Simons, Samuel Berweger, Noah Schlossberger, Thomas W. LeBrun, Christopher L. Holloway
We present a method for measuring radiofrequency (RF) fields using Rydberg atoms. Instead of using a locked probe laser, we use a carrier-locked optical frequency comb to detect the time-dependent RF field. Using high-speed digitizers, we capture interferograms as a modulated signal dynamically shifts the energy levels of the system. This method enables us to simultaneously calibrate the RF field strength and read out modulated signals encoded within multiple EIT features in real-time.
We present a method for measuring radiofrequency (RF) fields using Rydberg atoms. Instead of using a locked probe laser, we use a carrier-locked optical frequency comb to detect the time-dependent RF field. Using high-speed digitizers, we capture interferograms as a modulated signal dynamically shifts the energy levels of the system. This method enables us to simultaneously calibrate the RF field strength and read out modulated signals encoded within multiple EIT features in real-time.
Atom-based radio-frequency (rf) electromagnetic field sensing using atomic Rydberg states is a promising technique that has recently attracted significant interest. Its unique advantages, such as extraordinary bandwidth, self-calibration, and all-dielectric sensors, are a tangible improvement over antenna-based methods in applications such as test and measurement and development of broad-bandwidth receivers. Here, we demonstrate how an optical-frequency comb can be used to acquire data in the Autler-Townes regime of Rydberg-atom-based electrometry in a massively parallel fashion, eliminating the need for laser scanning. Two-photon electromagnetically induced transparency readout and preparation of cesium is used for the demonstration. A flat quasicontinuous optical comb is generated with the probe laser at 852 nm using an electro-optic modulator and arbitrary waveform generator. A single-frequency coupling laser at 509 nm is tuned to the Rydberg launch state. An enhanced transmission signal is obtained using self-heterodyne spectroscopy, where the comb signal is beat against a local oscillator derived from the single-frequency probe laser on a fast photodiode. The transmission of each probe-laser comb tooth is observed. We resolve electromagnetically induced transparency peaks with line widths below 5 MHz, with and without laser locking. Radio-frequency electromagnetic fields as low as $66\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}{\mathrm{Vcm}}^{\ensuremath{-}1}$ are detected, with sensitivities of $2.3\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}{\mathrm{Vcm}}^{\ensuremath{-}1}{\mathrm{Hz}}^{\ensuremath{-}1/2}$. The method offers a significant advantage for reading out electromagnetically induced transparency and Autler-Townes splitting, as neither laser needs to be scanned and slow frequency drifts can be tolerated in some applications. The method enables the detection of the amplitude of a pulsed rf electromagnetic field when the incoming pulse Autler-Townes splits the electromagnetically induced transparency peak.
Rydberg atom radio-frequency sensors are a unique platform for precision electromagnetic field measurement; e.g., they have extraordinary carrier bandwidth spanning MHz to THz and can be self-calibrated. These photonic sensors use lasers to prepare and read out the atomic response to a radio-frequency electromagnetic field. Most work on Rydberg atom sensors centers on radio-frequency electric field strength because the sensor functions as a square law detector, unless an external radio-frequency heterodyning field is used. A heterodyning field acts as a local oscillator and enables phase readout at the expense of the radio-frequency equipment necessary to generate it. In order to overcome the disadvantages of a radio-frequency local oscillator, we investigate all-optical phase-sensitive detection using a five-level closed-loop excitation scheme. We show that under finite detuning of the loop fields, the atomic response oscillates at the frequency of the detuning. The oscillation is transferred to a probe laser absorption signal. The phase, frequency, and amplitude of the radio-frequency signal are imprinted on the oscillatory dynamics and can be determined using demodulation and matched filter techniques applied to the probe laser transmission signal.
Up to now, the measurement of radio-frequency (RF) electric field achieved using the electromagnetically-induced transparency (EIT) of Rydberg atoms has proved to be of high-sensitivity and shows a potential to produce a promising atomic RF receiver at resonance between two chosen Rydberg states. In this paper, we study the extension of the feasibility of digital communication via this quantum-based antenna over a continuously tunable RF-carrier at off-resonance. Our experiment shows that the digital communication at a rate of 500 kbps can be performed reliably within a tunable bandwidth of 200 MHz near a 10.22 GHz carrier. Outside of this range, the bit error rate (BER) increases, rising to, for example, 15% at an RF-detuning of ±150 MHz. In the measurement, the time-varying RF field is retrieved by detecting the optical power of the probe laser at the center frequency of RF-induced symmetric or asymmetric Autler-Townes splitting in EIT. Prior to the digital test, we studied the RF-reception quality as a function of various parameters including the RF detuning and found that a choice of linear gain response to the RF-amplitude can suppress the signal distortion. The modulating signal can be decoded at speeds up to 500 kHz in the tunable bandwidth. Our test consolidates the physical basis for reliable communication and spectral sensing over a wider broadband RF-carrier, which paves a way for the concurrent multi-channel communications founded on the same pair of Rydberg states.
Rydberg atoms have emerged as a versatile and efficient platform for high-sensitivity quantum sensing of free-space electric fields, with remarkable progress in detecting low-frequency signals. To date, low-frequency Rydberg receivers have relied on a constant bias field, typically realized via intra-cell electrodes or Rydberg plasmas generated by photoelectric effects or inter-atomic interactions. While these approaches improve sensitivity, they suffer from inherent challenges in calibration, long-term stability, and robustness, hindering practical deployment. Here, we propose, design, and experimentally demonstrate a quantum sensing scheme for low-frequency electric signals using modulated auxiliary fields in Rydberg atoms. Unlike conventional methods that employ external DC electric fields that are often fully shielded by adsorbed atom layers on the cell walls, we introduce an AC-field modulation strategy. The incoming low-frequency signal mixes with the auxiliary field, and together they induce Stark shifts of the Rydberg level. These shifts are mapped onto the probe laser via electromagnetically induced transparency (EIT), in a manner analogous to heterodyne detection. We demonstrate a sensitivity of 7.5±2.6μV/(cm⋅Hz1/2) at 5 kHz and a minimal detectable field of 0.26±0.04μV/cm with an integration time of 1000 s. Furthermore, we extend this approach to systematically analyze the performance of generalized auxiliary fields containing multiple frequency components. By virtue of modulated auxiliary field and quantum frequency mixing, our results establish a robust and systematic framework for quantum sensing of low-frequency electric fields with Rydberg atoms, offering improved sensitivity, stability, and immunity to environmental drifts.
We report on the development of detection methods for amplitude and phase of pulsed radio-frequency (RF) electromagnetic fields with Rydberg atoms. We begin with an overview of the basic principles of Rydberg-atom-based sensing and measurement of RF electromagnetic fields. An overview of the underlying atomic physics and the method for amplitude as well as phase sensing of electromagnetic radiation with Rydberg atoms is provided. Atomic RF receivers using Rydberg atoms for analog and digital communications and sensing of modulated RF fields are discussed. Detection of pulse-modulated RF and time-domain RF pulse waveform imaging with a Rydberg-atom receiver are demonstrated. The transient response of the Rydberg-atom vapor to a modulated RF field is observed at the 10-nanosecond level, from which a new lower limit to the achievable instantaneous signal bandwidth of atomic RF receivers is established. Finally, we present and describe a new method to measure the phase of an RF field implemented to not require an RF reference wave. The method employs phase-coherent excitation pathways involving the optical fields in the atomic sensing medium with the signal RF field. The optical RF phase-sensing approach lends itself to the realization of atomic RF sensors, measurement and imaging devices that are relevant to applications in RF communications and sensing.
Rydberg atom based sensors allow for SI traceable measurements and show promise for applications in the field of communication and radar technologies. In this article, we investigate the bandwidth and sensitivity of a Rydberg atom-based sensor in a rubidium vapor cell using Rydberg electromagnetically induced transparency (EIT) spectroscopy. We employ a radio-frequency (RF) heterodyne measurement technique in combination with an optical homodyne setup to extend the achievable range between sensitivity and bandwidth in a Rydberg sensor. While the bandwidth of Rydberg sensors are limited by the transit time of atoms and the Rabi frequency of the coupling field, achieving higher bandwidth through smaller beam sizes is thought to compromise sensitivity due to reduced EIT signal strength. Using optical homodyne detection, we demonstrate that sensitivity is preserved while achieving a response bandwidth of 8 MHz. In addition, using the Rydberg sensor, we receive digital communication signals and present error vector magnitude (EVM) measurements as a function of varying symbol rates and bandwidth of the Rydberg sensor. Furthermore, the sensor's performance is compared with a conventional RF mixer. We establish that the bandwidth of a Rydberg sensor when receiving a pure tone is not the same as the bandwidth of the sensor when receiving a modulated signal. This difference results from the spreading of symbols in the frequency domain, leading to a reduction of the signal to noise ratio (SNR) and an accumulation of noise over the total span of the modulated signal.