arXiv subjects

James P. Shaffer

Publications and source records attributed to James P. Shaffer.

At least 19 recordsLinked to original sources

arXiv2026

Coherent All-Optical Radio Frequency Phase Sensing Using Multiphoton Dressing and Interference

Multi-photon dressing and interference in atomic systems is a key to several cutting edge technologies like Rydberg atom radio frequency sensors, clocks and magnetometers because it enables the engineering of atomic properties. Rydberg atom sensors are attracting significant interest because they can be used for applications where it is difficult or impossible to use conventional antennas, opening a number of new opportunities in fields like communications, test and measurement and radar. To date, radio frequency field amplitude detection is well-established in Rydberg electrometry. Phase detection, which is crucial for encoding radio frequency signals, typically requires an external heterodyning field or an atomic closed-loop interferometer. The heterodyne method compromises the intrinsic transparency of the sensor to the radio frequency wave and its inherently broad carrier bandwidth, in addition to increasing its complexity by introducing a local oscillator. In prior theoretical work, aimed at overcoming the disadvantages of the heterodyne method, we theoretically investigated the possibility of using the oscillatory dynamics of an all-optical five-level closed loop to sense the phase and amplitude of the target radio frequency fields. In this work, we experimentally demonstrate the scheme. We determine the coherence time of the loop to be on the order of ms and show that in-phase and quadrature signals can be extracted from a radio frequency signal.

physics.atom-ph↗

arXiv2025

Micro-Electro-Mechanical System Vapor Cells With Passivated Internal Cavities

Micro-Electro-Mechanical, so called 'MEMs,' vapor cells are a key component in atom-based quantum sensors, such as clocks, gyroscopes, electric field sensors and magnetometers. MEMs vapor cell fabrication for Rydberg atom radio frequency sensors is particularly demanding. The Rydberg states used for the sensor can shift in a constant electric field which can be generated by the internal surfaces of the vapor cell cavity. The ratio of the detection wavelength to vapor cell size can span a large range, meaning that the radio frequency field-vapor cell interaction is a critical design consideration. In many radio frequency sensing cases, there is a desire to minimize the interaction between the vapor cell and the target radio frequency field, as well as assure that every vapor cell behaves uniformly. These criterion favor MEMs vapor cells with low background electric fields. Known inert, organic coatings cannot survive the bonding temperatures required for conventional anodic bonding of a MEMs vapor cell. Applying inert, organic coatings to the internal cavities of MEMs vapor cells is a longstanding challenge. In this paper, we present a low temperature bonding scheme that is compatible with coating the internal cavity of a MEMs vapor cell with Octadecyltrichlorosilane (CH$_3\,$(CH$_2$)$_{17}\,$SiCl$_3$, OTS). The coating prevents the Cs used in the vapor cell from sticking to the walls. Spectral linewidths of $\sim300\,$kHz are obtained using Rydberg spectroscopy, with energy shifts corresponding to electric fields $<$10$\,$mV$\,$cm$^{-1}$.

physics.atom-ph↗

arXiv2025

The Impact of Thermal Fields on Rydberg Atom Radio Frequency Sensors

Rydberg atom radio frequency sensors are unique in a number of ways, including possessing extraordinary carrier bandwidth, self-calibration and accuracy. In this paper, we examine the impact of thermal radiation on Rydberg atom sensors. Antennas are limited by their thermal background, while Rydberg atom sensors are coherent sensors. Incoherent thermal radiation does not limit Rydberg atom sensors in the same way as an antenna. The primary consequence of a thermal radiation field on Rydberg atom sensors is to decrease their coherence, as the decay rates of the Rydberg states used for sensing the radio frequency field are increased due to the thermal field, i.e. blackbody, modification of the atomic decay rates. Thermal and coherent field excitation are fundamentally different in that thermal fields produce statistically independent excitations with well-defined frequency, polarization, and propagation direction, while coherent states are coherent superpositions of photon number states. Consequently, thermal fields do not contribute to the coherences of the density matrix that are used for Rydberg atom sensing, except for damping them.

physics.atom-ph↗

arXiv2025

Transient Phase Sensing in a Three-Photon Rydberg Ladder Scheme

Although Rydberg atoms have shown promise for use in novel types of radio frequency receivers, they have generally not been considered phase sensitive without the use of closed-loop interferometry or auxiliary radio frequency fields. Here, we show that the high coherency of a narrow-linewidth three-photon ladder excitation scheme unique to Cesium atoms enables all-optical sensing of transient changes in RF phase within a room temperature vapor cell. The transient response on the probe laser's transmission originates from phase-to-amplitude conversion via a disturbance of the coherency of the system in response to the phase shift of the radio frequency field. We show that the amplitude and frequency of the oscillatory response provides information on the magnitude and direction of any radio frequency field detuning. We demonstrate that the detuning sensitivity can be used to identify Doppler shifts in radar applications, by applying phase shifts embedded in radio frequency pulses. The phase modulation within the radar pulse acts as a form of compression that facilitates the simultaneous detection of both target position and velocity.

physics.atom-ph↗

arXiv2025

Precision measurement of Cs($nF_J$) quantum defects and calculations of scalar and tensor polarizabilities of the $nS_{1/2}$, $nP_J$ ,$nD_J$ , and $nF_J$ series

In this paper, we extend our recent work on cesium S and D states [Phys. Rev. Lett. 133, 233005 (2024)] to the F states. We present absolute frequency measurements of the $|6S_{1/2}, F = 3\rangle \rightarrow nF_{5/2,7/2}(n = 28-68)$ Rydberg series to measure the spectrum of $^{133}$Cs. Atomic spectra are obtained using a three-photon excitation scheme referenced to an optical frequency comb in a sample of ultracold $^{133}$Cs. By globally fitting the absolute-frequency measurements to the modified Ritz formula, we determine the quantum defects of the $nF_{5/2}$ and $nF_{7/2}$ series. The ionization potential extracted for both series from the modified Ritz formula agrees with our measurements based on the S and D series. Fine-structure intervals are calculated and parameterized. The wave functions computed for the energies from the quantum defects are used to calculate transition dipole moments. We compare the reduced electric-dipole matrix elements with available benchmarks and find agreement within the precision of those works. The scalar and tensor polarizabilities of the $nS_{1/2}$, $nP_J$ , $nD_J$ and $nF_J$ series are calculated based on the now more accurate set of wave functions. Moreover, we report the polarizability as a series in powers of the effective principal quantum number and find the main coefficients of the expansion. The results will be useful for calculating properties of $^{133}$Cs such as collision and decay rates, polarizabilities, and magic wavelengths.

physics.atom-ph↗

arXiv2025

All-optical radio-frequency phase detection for Rydberg atom sensors using oscillatory dynamics

Rydberg atom radio frequency sensors are a unique platform for precision electromagnetic field measurement, e.g. they have extraordinary carrier bandwidth spanning MHz-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 read out 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.

physics.atom-ph↗

arXiv2024

A Photonic Crystal Receiver for Rydberg Atom-Based Sensing

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.

physics.atom-ph↗

arXiv2024

Ultra precise determination of Cs($nS_{1/2}$) and Cs($nD_J$) quantum defects for sensing and computing: Evaluation of core contributions

We make absolute frequency measurements of Cs Rydberg transitions, $\vert 6S_{1/2}, F=3 \rangle \rightarrow \vert nS_{1/2}~(n=23\rm{-}90)\rangle$ and $\vert nD_{3/2,5/2}~(n=21\rm{-}90)\rangle$, with an accuracy of less than $ 72\,\rm kHz$. The quantum defect parameters for the measured Rydberg series are the most precise obtained to date. The quantum defect series is terminated at $\delta_4$, showing that prior fits requiring higher order quantum defects reflect uncertainties in the observations. The precision of the measured quantum defects allow for the calculation of Rydberg electric-dipole transitions and fine-structure intervals extrapolated from high principal quantum numbers, to rival that of sophisticated many-body relativistic calculations carried out at low Rydberg principal quantum numbers. We quantitatively predict the contributions to the quantum defect parameters from core polarization and core penetration of Cs inner shell electrons. A new value for the ionization energy, consistent across the $ nS_{1/2}$ and $ nD_{3/2,5/2}$ Rydberg series, is reported at $31406.467 751 48 (14)~\rm{cm}^{-1}$.

physics.atom-ph↗

arXiv2023

Rydberg atom-based radio frequency sensors: amplitude regime sensing

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 and sensitivity in the amplitude regime. We describe the approximations that we applied to obtain the analytic expressions 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. Residual Doppler shifts are shown to limit sensitivity. An analytic expression for the amplitude regime of Rydberg atom-based sensing has not, to our knowledge, been obtained previously. The expressions, approximations and descriptions presented in the paper are important for maximizing the sensitivity of Rydberg atom-based sensors and for providing insight into the physics of multi-level interference phenomena.

physics.atom-ph↗

arXiv2023

Rydberg Atom Sensors in Multichromatic Radio Frequency Fields

Rydberg atom-based sensors are a new type of radio frequency sensor that is inherently quantum mechanical. Several configurations of the sensor use a local oscillator to determine the properties of the target radio frequency field. We explain how the physics of Rydberg atom-based sensors in two or more radio frequency fields can be precisely described by a multiply dressed Jaynes-Cummings model. Studying Rydberg atom-based sensors in two or more near resonant radio frequency fields is important for understanding how interfering signals as well as the local oscillator can affect measurements. Studies, so far, focus on a simplified approximation for the local oscillator-target field interaction that uses an analogy to radio frequency heterodyning. The atom acts as a medium for exchanging electromagnetic field excitations of the field modes whose spectrum is a ladder. The Jaynes-Cummings states and their avoided crossings can be used to determine the properties of the radio frequency fields. Radio frequency field sensitivity enhancement for non-resonant radio frequencies is achieved and self-calibrated measurements are recovered under specific conditions described by the theory.

physics.atom-ph↗

arXiv2023

A Three-Photon Rydberg Atom-Based Radio Frequency Sensing Scheme with Narrow Linewidth

We demonstrate Rydberg atom-based radio frequency sensing with a colinear three-photon scheme in a room temperature cesium vapor cell that minimizes residual Doppler broadening of the probe laser absorption feature. A sub-200 kHz spectral linewidth is observed and extends the self-calibrated Autler-Townes sensing regime to weaker fields by a factor of ~18 compared to the theoretical limit of the most commonly used two-photon scheme. The sensitivity of the method to microsecond pulses is shown to be sufficient to detect radio frequency Rabi frequencies of 2$\pi$ x 0.44 MHz using a 480 kHz bandwidth at 108.9 GHz, demonstrating the ability to sense time-dependent signals suitable for radar and communications.

physics.atom-ph↗

arXiv2022

Rydberg atom-based Electrometry Using a Self-Heterodyne Frequency Comb Readout and Preparation Scheme

Atom-based radio frequency 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 read-out and preparation of cesium is used for the demonstration. A flat, quasi-continuous 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. 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 linewidths below 5 MHz, with and without laser locking. Radio frequency electromagnetic fields as low as 66 $μ$Vcm$^{-1}$ are detected with sensitivities of 2.3 $μ$Vcm$^{-1}$Hz$^{-1/2}$. 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 radio frequency electromagnetic field when the incoming pulse Autler-Townes splits the electromagnetically induced transparency peak.

physics.atom-ph↗

arXiv2022

The Origins of Rydberg Atom Electrometer Transient Response and its Impact on Radio Frequency Pulse Sensing

Rydberg atoms have shown significant promise as the basis for highly sensitive detectors of continuous radio-frequency (RF) E-fields. Here, we study their time-dependent response to pulse-modulated RF E-fields at 19.4 GHz using a cesium vapour cell at room temperature. We use density matrix simulations to explain the time scales that shape the transient atomic response under different laser conditions, finding them to be limited by dephasing mechanisms including transit time broadening, Rydberg-Rydberg collisions, and ionization. Using a matched filter, we demonstrate the detection of individual pulses with durations from 10 $μ$s down to 50 ns and amplitudes from 15000 $μ$V cm$^{-1}$ down to ~170 $μ$V cm$^{-1}$, corresponding to a sensitivity of ~240 nV cm$^{-1}$ Hz$^{-1/2}$. Finally, we highlight the potential of a Rydberg vapour cell as a receiver by detecting pulse trains from a rotating emitter on a simulated passing aircraft.

physics.atom-ph↗

arXiv2019

Anisotropic Interactions in Electric Field Polarized Ultracold Rydberg Gases

We calculate pair potential curves for interacting Rydberg atoms in a constant electric field and use them to determine the effective $C_3$ dipole-dipole and $C_6$ van der Waals coefficients. We compare the $C_3$ and $C_6$ with experiments where the angle of a polarizing electric field is varied with respect to the axis of a quasi-1-dimensional trap at ultracold temperatures. The dipoles produced via polarization of the atoms have an angular dependent dipole-dipole interaction. We focus on the interaction potential of two rubidium Rydberg atoms in $50S_{1/2}$ states in the blockade regime. For internuclear distances close to the blockade radius, $R_{bl} \approx 4 - 6\,μ$m, molecular calculations are in much better agreement with experimental results than those based on the properties of single atoms and independent calculations of $C_3$ and $C_6$ which were used to analyze the original experiment. We find that the calculated $C_6$ coefficient is within $8\%$ of the experimental value while the $C_3$ coefficient is within $20\%$ of the experimental value.

physics.atom-ph↗

arXiv2019

Effective three-body interactions in Cs($6s$)-Cs($nd$) Rydberg trimers

Ultralong-range Rydberg trimer molecules are spectroscopically observed in an ultracold gas of Cs($nd_{3/2}$) atoms. The atomic Rydberg state anisotropy allows for the formation of angular trimer states, whose energies may not be obtained from integer multiples of dimer energies. These nonadditive trimers are predicted to coexist with Rydberg dimer lines. The existence of such effective three-body interactions is confirmed with observation of asymmetric line profiles and interpreted by a theoretical approach which includes relativistic spin interactions. Simulations of the observed spectra with and without angular trimer lines lends convincing support to the existence of effective three-body interactions.

physics.atom-ph↗

arXiv2019

The interplay between thermal Rydberg gases and plasmas

We investigate the phenomenon of bistability in a thermal gas of cesium atoms excited to Rydberg states. We present both measurements and a numerical model of the phenomena based on collisions. By directly measuring the plasma frequency, we show that the origin of the bistable behavior lies in the creation of a plasma formed by ionized Rydberg atoms. Recombination of ions and electrons manifests as fluorescence which allows us to characterize the plasma properties and study the transient dynamics of the hysteresis that occurs. We determine scaling parameters for the point of plasma formation, and verify our numerical model by comparing measured and simulated spectra. These measurements yield a detailed microscopic picture of ionization and avalanche processes occurring in thermal Rydberg gases. From this set of measurements, we conclude that plasma formation is a fundamental ingredient in the optical bistability taking place in thermal Rydberg gases and imposes a limit on usable Rydberg densities for many applications.

physics.atom-ph↗

arXiv2017

Intracavity Rydberg atom electromagnetically induced transparency using a high finesse optical cavity

We present an experimental study of cavity assisted Rydberg atom electromagnetically induced transparency (EIT) using a high-finesse optical cavity ($F \sim 28000$). Rydberg atoms are excited via a two-photon transition in a ladder-type EIT configuration. A three-peak structure of the cavity transmission spectrum is observed when Rydberg EIT is generated inside the cavity. The two symmetrically spaced side peaks are caused by bright-state polaritons, while the central peak corresponds to a dark-state polariton. Anti-crossing phenomenon and the effects of mirror adsorbate electric fields are studied under different experimental conditions. We determine a lower bound on the coherence time for the system of $7.26 \pm 0.06 \,μ$s, most likely limited by laser dephasing. The cavity-Rydberg EIT system can be useful for single photon generation using the Rydberg blockade effect, studying many-body physics, and generating novel quantum states amongst many other applications.

physics.atom-ph↗

arXiv2017

Rydberg-atom based radio-frequency electrometry using frequency modulation spectroscopy in room temperature vapor cells

Rydberg atom-based electrometry enables traceable electric field measurements with high sensitivity over a large frequency range, from gigahertz to terahertz. Such measurements are particularly useful for the calibration of radio frequency and terahertz devices, as well as other applications like near field imaging of electric fields. We utilize frequency modulated spectroscopy with active control of residual amplitude modulation to improve the signal to noise ratio of the optical readout of Rydberg atom-based radio frequency electrometry. Matched filtering of the signal is also implemented. Although we have reached similarly, high sensitivity with other read-out methods, frequency modulated spectroscopy is advantageous because it is well-suited for building a compact, portable sensor. In the current experiment, $\sim 3 μV cm^{-1}Hz^{-1/2}$ sensitivity is achieved and is found to be photon shot noise limited.

quant-ph↗