arXiv subjects

Christopher L. Holloway

Publications and source records attributed to Christopher L. Holloway.

At least 19 recordsLinked to original sources

arXiv2026

Angle-of-Arrival Determination of Radio-Frequency Fields Using Stark-Shifted Rydberg-EIT Spectra

We demonstrate a method for determining the magnitude of the angle of arrival (AoA) of a linearly polarized radio-frequency (RF) field using the angle-dependent spectral amplitudes of AC Stark-shifted electromagnetically induced transparency (EIT) resonances. An off-resonant RF field produces distinct Stark shifts of the $|m_J|$ sublevels, while their relative excitation strengths depend strongly on the relative orientation of the RF and optical polarizations. Under the controlled polarization geometry considered here, this dependence enables determination of the AoA magnitude without requiring RF phase measurements or spatially separated sensing locations. We experimentally demonstrate the method at RF frequencies of 1.27 GHz, 2 GHz, 3 GHz, and 4 GHz using a subwavelength cesium vapor cell. Within the $20^\circ-40^\circ$ region of highest angular sensitivity, the estimated repeatability-based $1σ$ AoA uncertainty ranges from approximately $0.6^\circ$ to $2^\circ$ across the investigated RF frequencies. A model combining Floquet-Shirley calculations of the RF-dressed Rydberg states with a coherent hyperfine-to-fine-structure optical excitation model qualitatively reproduces the experimental observations. These results establish a path toward compact, phase-independent AoA sensing using spatially localized Rydberg-atom spectroscopy.

physics.atom-ph↗

arXiv2026

Floquet Interpretation of Avoided Crossings in AC Stark-Shifted Rydberg-EIT Spectra

We present a combined experimental and Floquet-theoretical study of avoided crossings in the AC Stark-shifted electromagnetically induced transparency (EIT) spectra of Rydberg atoms. Observed avoided-crossing structures cannot be fully explained by conventional AC Stark maps alone, which provide the energy shifts but do not reveal the underlying state composition and coupling pathways. Using the Shirley method, we analyze the Floquet eigenstates to establish a direct connection between the measured spectra and the underlying dressed-state dynamics. By tracking the evolution of state mixing, bare-state composition, and dominant higher-order Floquet coupling pathways, we reveal the physical mechanisms responsible for the formation of avoided crossings across different principal quantum numbers and RF frequencies. Our results demonstrate that Floquet-eigenstate analysis provides a powerful framework for interpreting complex AC Stark-shifted Rydberg-EIT spectra and the underlying higher-order Floquet coupling interactions.

physics.atom-ph↗

arXiv2026

Vapor-Cell-Induced Uncertainty in Rydberg Atom Measurements via the Electric-Field Volume-Integral-Equation Method

Electromagnetic scattering effects of a vapor cell on electric-field measurements using Rydberg atom-based sensors are analyzed with the aid of the volume integral equation method. In a manner similar to measurement, this computational approach determines the electric field over grid points within the vapor cell. Its relatively high computational efficiency makes it suitable for use in optimization routines and statistical uncertainty studies. We apply this method to compare uncertainty contributions arising due to the presence of the vapor cell, such as uncertainty in the glass relative permittivity or standing wave formation inside the cell, to those arising from the atomic spectroscopic measurement, such as uncertainty in the atomic dipole moment. For vapor cell dimensions less than half a wavelength, the dominant uncertainty source arises from uncertainty in the glass relative permittivity, resulting in a total uncertainty of $\sim$3.5\% -- comparable to the best uncertainties obtained with traditional field generation methods at national metrology institutes. Precise permittivity measurements have the potential to further reduce measurement uncertainty to $<1$\%.

physics.atom-ph↗

arXiv2026

Resolving magnetic-sublevel structure in Rydberg Autler-Townes spectra with arbitrary RF polarization

We investigate the role of magnetic sublevels in Autler-Townes spectra of Rydberg atoms driven by radio-frequency (RF) fields with arbitrary polarization. While conventional treatments predict two symmetric sidebands from independent mJ transitions, experiments have reported additional unexplained spectral features. We show that these arise from elliptical RF polarization, which coherently couples multiple magnetic sublevels and requires a full multi-level treatment. We develop and diagonalize a Hamiltonian including all coupled mJ sublevels, predicting polarization-dependent degeneracies that produce two, three, or four resolved peaks. Using long-wavelength transitions and an anechoic environment we realize homogeneous RF fields that for the first time enable complete resolution of the mJ-dependent dressed states. We observe excellent agreement with theory as the RF ellipticity is varied. These results demonstrate that RF polarization fundamentally modifies Autler-Townes spectra and provide a consistent framework for interpreting magnetic-sublevel structure, with implications for Rydberg-based RF electrometry and polarimetry.

physics.atom-ph↗

arXiv2026

Frequency Comb Behavior of Time Crystals in an RF-Driven Dissipative Rydberg System

Driven nonlinear oscillators constitute a universal paradigm for understanding synchronization, frequency pulling, and frequency comb formation in nonequilibrium systems. Here, we realize such an emergent nonlinear oscillator in strongly interacting cesium Rydberg vapor, where coherent optical excitation, dissipation, and long-range interactions give rise to a driven-dissipative time crystal phase with intrinsic oscillation frequencies. Applying a radio-frequency (RF) field allows controlled tuning of the intrinsic oscillation frequency. Under RF heterodyne conditions, we observe intermodulation, frequency pulling, and, at strong drive, the emergence of a comb-like spectrum in the atomic coherence. We quantitatively capture these observations using a four-level mean-field model and demonstrate a classical analogue with a driven Van der Pol oscillator. Our results establish interacting Rydberg ensembles as a tunable platform for exploring nonequilibrium time-crystalline order, nonlinear synchronization, and frequency comb generation in many-body atomic systems.

physics.atom-ph↗

arXiv2026

Electromagnetically induced transparency and population repump readout of Rydberg states of Cs atoms in a J-scheme

Rydberg atom electrometry offers traceable electric field measurements over many decades of radio frequencies in a single device. Miniaturization of these sensors is primarily limited by requirements of the lasers used. Here we demonstrate a three-photon sensing scheme using a J-shaped energy level coupling that can be achieved using external cavity diode lasers, without the need for a doubling crystal or tapered amplifier. In the low laser power regime, we demonstrate a full-width at half-maximum linewidth of 1.3 MHz. We demonstrate that for RF field electrometry using conventional heterodyne techniques, we can detect 4.7 GHz at a sensitivity of 27 μV m-1 Hz-1/2, comparable to that of two-photon detection schemes which require the use of a tapered amplifier. We also investigate a modified scheme where the probe laser is locked to a different hyperfine state, thus measuring the two-photon electromagnetically induced transparency in the other two lasers via the change in population of this separate state due to repumping. In this scheme we find the sensitivity for a 4.7 GHz field to be 39 μV m-1 Hz-1/2, and demonstrate that the amplitude scaling with probe power offers a different saturation profile than the linked J-scheme counterpart.

physics.atom-ph↗

arXiv2026

MHz to sub-kHz field detection with an all-dielectric potassium Rydberg-atom sensor

Rydberg sensors have significant promise as an alternative to the antenna systems used for sub-MHz frequency communications, where the scale of high-efficiency antennas is often impractically large, forcing the use of low-efficiency, electrically small antennas. The exploration of Rydberg sensors at these frequencies has been hampered by the low field transmission of the silicate vapor cells. We dramatically improve the low-frequency field transmission of silicate vapor cells by using potassium as the active medium instead of rubidium or cesium. The potassium Rydberg sensor can measure fields with frequencies down to 500 Hz in an all-dielectric sensor, effectively extending the low-frequency cutoff of the sensor by nearly four orders of magnitude compared to an equivalent rubidium vapor cell. With this simple substitution, experimentation with low-frequency sensing becomes dramatically more accessible to the community.

physics.atom-ph↗

arXiv2026

Fundamental linewidth limit of electromagnetically induced transparency in a thermal Rydberg ladder

Spectroscopy of Rydberg states has become a popular platform for quantum sensing, with the most common readout scheme being two-photon electromagnetically induced transparency (EIT) using counter-propagating laser beams. In this scheme, the energy resolution of the Rydberg state is set by the spectral linewidth of the EIT feature. While selection criteria for the two-photon resonance can narrow the linewidth to the order of the Rydberg state decay rate for a single atom, the Doppler shift from thermal velocity of the atoms broadens the ensemble linewidth to the order of the decay rate of the intermediate state. Here, we derive an analytic expression for the Doppler residual lineshape in the low-power limit and corroborate the results with experiment. For Rb, we find the full-width at half-maximum linewidth limit to be 1.84 MHz when scanning the coupling laser and measure an experimental linewidth of 2.04 MHz. These linewidths are around a factor of two narrower than previous theoretical estimates as well as previously reported measured linewidths. With this, we demonstrate the most precise two-photon energy resolution of a Rydberg state in thermal vapor to date. We then map out broadening mechanisms near this limit.

physics.atom-ph↗

arXiv2026

Simultaneous Detection, Demodulation, and Angle-of-Arrival Determination of Communication Signals Using a Dual Ladder Rydberg Receiver

In a typical Rydberg mixer, modulated communication signals are detected using a radio frequency (RF) heterodyne technique. The mixer outputs an intermediate frequency (IF), which must be filtered and mixed down to baseband. In this work, we apply an RF-homodyne technique to demonstrate simultaneous detection and a direct, baseband readout of the in-phase (I) and quadrature (Q) components of standard communication signals using a dual ladder Rydberg receiver. We further show that the inherent polarization sensitivity of this receiver can be used to determine the signal's angle of arrival. We also compare the dual ladder system with a typical Rydberg mixer. The RF-heterodyne-based system's maximum detectable symbol rate is constrained by a signal amplitude which decays with the heterodyne field's detuning from the Rydberg-Rydberg atomic transition used to detect the signal, but the dual ladder design is not subject to this limitation. However, the dual ladder system is more sensitive to low-frequency noise. As a result, its performance is degraded relative to its conventional counterpart when subjected to pink noise. We show that once pink noise effects have been accounted for, both systems behave comparably.

physics.atom-ph↗

arXiv2026

Development of a Quantum Blackbody Thermometer toward Primary On-orbit Thermometry

We present a roadmap to a deployable, intrinsically calibrated thermometer with long-term accuracy of 30 mK, exceeding existing on-orbit resistance-based thermometers. Our quantum blackbody thermometer is based on measuring fluorescence ratios of optically excited rubidium atoms in microfabricated vapor cells. The key advantage of the quantum blackbody thermometer is that long-term stability of the fluorescence ratios is guaranteed by the immutable physical properties (transition strengths) of the rubidium atom. This should be compared against resistance-based thermometers, such as platinum resistance thermometers, which may be calibrated with exceptional accuracy but are susceptible to temporal drift and shifts due to improper handling.

physics.atom-ph↗

arXiv2025

Probing Bandwidth and Sensitivity in Rydberg Atom Sensing via Optical Homodyne and RF Heterodyne Detection

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.

quant-ph↗

arXiv2025

Sensitivity Comparison of Rydberg Atom-Based Radio-Frequency Electric Field Detection: Ionization Current Versus Optical Readout

We investigate a technique for detecting radio-frequency (RF) electric fields in a Cesium (Cs) vapor cell at room temperature by collecting charge from ionized Rydberg atoms and compare its performance with the established method of electromagnetically induced transparency (EIT). By applying a known RF field, we measure the response from both the electrical (ionization current-based) and optical (EIT-based) readouts. The ionization current-based method yields a sensitivity of 22~$μ$Vm$^{-1}$Hz$^{-1/2}$, while the EIT-based method achieves 3.7~$μ$Vm$^{-1}$Hz$^{-1/2}$. The sensitivity of the ionization current-based method is limited by thermal noise arising from a 2.2~k$Ω$ resistance between the collection electrodes, attributed to a thin Cs film on the inner surfaces of the vapor cell. Controlling or eliminating the Cs layer can significantly improve the sensitivity of this ionization approach.

physics.atom-ph↗

arXiv2025

Rydberg atom reception of a handheld UHF frequency-modulated two-way radio

Rydberg atoms, due to their large polarizabilities and strong transition dipole moments, have been utilized as sensitive electric field sensors. While their capability to detect modulated signals has been previously demonstrated, these studies have largely been limited to laboratory-generated signals tailored specifically for atomic detection. Here, we extend the practical applicability of Rydberg sensors by demonstrating the reception of real-world frequency-modulated (FM) audio transmissions using a consumer-grade handheld two-way radio operating in the UHF band. Detection is based on the AC Stark shift induced by the radio signal in a Rydberg atomic vapor, with demodulation performed using an offset local oscillator and lock-in amplification. We successfully demodulate speech signals and evaluate the audio spectral response and reception range. We show that all consumer-accessible radio channels can be simultaneously detected, and demonstrate simultaneous reception of two neighboring channels with at least 53 dB of isolation. This work underscores the potential of Rydberg atom-based receivers for practical, real-world FM signal detection.

physics.app-ph↗

arXiv2025

An Imaging Radar Using a Rydberg Atom Receiver

Rydberg atoms in a gas form are highly sensitive electric field probes capable of detecting and measuring the amplitude, phase, and polarization of broadband time-varying signals. Here, we present the performance of a frequency modulated continuous wave (FMCW) radar using a Rydberg atom-based subwavelength sensor as a receiver. This sensor down converts the radar echoes, eliminates key FMCW electrical components, and performs two-dimensional target localization. To demonstrate its capabilities, we present an RF image of a scene containing targets in an anechoic room with radar cross sections down to 0 dBsm at a distance up to 5 m and with a range resolution of 4.7 cm.

physics.atom-ph↗

arXiv2025

Population-resolved measurement of an avoided crossing of light-dressed states

A two-level system coupled by a coherent field is a ubiquitous system in atomic and molecular physics. In the rotating wave approximation, the light-dressed states are well described by a simple 2x2 Hamiltonian which can be easily solved analytically and is thus used in quantum mechanics education and as a basis for intuition for more complicated systems. The solution to the Hamiltonian is an avoided crossing between the light-dressed ground and excited states. In experiments, the avoided crossing is probed spectroscopically, meaning only the energies, or eigenvalues of the Hamiltonian, are measured. Here, we present a measurement of the avoided crossing which also resolves population, thus indicating the amplitude coefficients of the eigenvectors of the Hamiltonian. We perform the measurement in Rydberg states of cold rubidium atoms, resolving the energies spectroscopically with our pump lasers and the populations of each state using selective field ionization.

physics.atom-ph↗

arXiv2025

Angle-of-arrival detection of radio-frequency waves via Rydberg atom fluorescence imaging of standing waves in a glass vapor cell

We present a method for measuring the angle-of-arrival of 40 GHz radio-frequency (RF) radiation by mapping the standing waves generated in a rectangular glass vapor cell. These standing waves have regular and well-defined structure from which we can infer the angle and sign of the wavevector of the RF field. We map the field using spatially resolved light sheet spectroscopy of Rydberg states of rubidium atoms in the cell. Unlike traditional phased arrays, this detection scheme is compact and low-complexity, has an active area of nearly 4$π$ steradians, and is sensitive to all RF polarizations. For in-plane measurements ($ϕ= 0$), we demonstrate quantitative angle-of-arrival measurements with an uncertainty on the order of one degree in an 11~s measurement, and for out-of-plane measurements (arbitrary $θ$,$ϕ$), we demonstrate angle-of-arrival detection with uncertainty on the order of several degrees.

physics.atom-ph↗

arXiv2025

Wafer-level fabrication of all-dielectric vapor cells enabling optically addressed Rydberg atom electrometry

Rydberg-atom electrometry enables highly sensitive electric-field measurements by exploiting the extreme polarizability of Rydberg states in alkali atoms. Millimeter-scale atomic vapor cells can be accurately and economically batch-fabricated by anodically bonding silicon and glass wafers, enabling the large-volume manufacturing of miniature atomic clocks and quantum sensors. However, silicon is not always an ideal constitutive material for electric-field sensing because of its high dielectric constant and conductive losses at millimeter wave frequencies. A broader selection of low-loss all-dielectric alternatives may be beneficial for specific applications. Here, we present an all-glass wafer-level microfabrication process that eliminates silicon, creating hermetically sealed vapor cells that are stable over long timelines with embedded cesium dispensers. Femtosecond laser machining precisely defines the cell geometry, and laser-activated alkali loading ensures reliable filling. We demonstrate long-term vacuum stability and robust Rydberg excitation through electromagnetically induced transparency measurements of several Rydberg states. We then use these cells to measure a 34 GHz millimeter wave field resonant with the 58D$_{5/2}\rightarrow$60P$_{3/2}$ transition using Autler-Townes splitting showing expected linear dependence with field strength. This work demonstrates that the all-glass approach offers a highly durable low-loss cell alternative for miniaturized millimeter wave and microwave quantum sensing, with the potential to flexibly incorporate a range of other dielectric and semiconductor materials and integrated photonic and electronic technologies.

physics.atom-ph↗

arXiv2025

Determining angle of arrival of radio frequency fields using subwavelength, amplitude-only measurements of standing waves in a Rydberg atom sensor

Deep subwavelength RF imaging with atomic Rydberg sensors has overcome fundamental limitations of traditional antennas and enabled ultra-wideband detection of omni-directional time varying fields all in a compact form factor. However, in most applications, Rydberg sensors require the use of a secondary strong RF reference field to serve as a phase reference. Here, we demonstrate a new type of Rydberg sensor for angle-of-arrival (AoA) sensing which utilizes subwavelength imaging of standing wave fields. By placing a metallic plate within the Rydberg cell, we can determine the AoA independent of the strength of incoming RF field and without requiring a secondary strong RF phase reference field. We perform precision AoA measurements with a robotic antenna positioning system for 4.2, 5.0, and 5.7 GHz signals and demonstrate a 1.7 deg polar angular resolution from 0 deg to 60 deg AoA and 4.1 deg over all possible angles.

physics.atom-ph↗