arXiv subjects

Rajavardhan Talashila

Publications and source records attributed to Rajavardhan Talashila.

12 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

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↗

arXiv2025

Uniqueness Theorem: With Normal Components Specified on External Spherical Surface

A uniqueness theorem for time-harmonic electromagnetic fields which requires the normal components of electromagnetic fields specified on a spherical surface is proposed and proved. The statement of the theorem is : "For a spherical volume $V$ that contains only perfect conductors and homogeneous lossless materials and for which the impressed currents $\mathbf{J}$ are specified, a time-harmonic solution to the Maxwell's equations within the volume, having outgoing waves alone, is uniquely specified by the values of the radial components of both $\mathbf{E}$ and $\mathbf{B}$ over the exterior spherical surface $V$ and the tangential components of either $\mathbf{E}$ or $\mathbf{B}$ on the interior surfaces." The proof of this theorem relies on the uniqueness of multipole expansion of electromagnetic fields outside the enclosing sphere. The conventional uniqueness theorem for the volume $V$ having loss-less materials is considered to be the case of lossy materials in the limit the dissipation approaching zero.

math-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

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

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↗

arXiv2025

Imaging of induced surface charge distribution effects in glass vapor cells used for Rydberg atom-based sensors

We demonstrate the imaging of localized surface electric (E) field effects on the atomic spectrum in a vapor cell used in Rydberg atom-based sensors. These surface E-fields can result from an induced electric charge distribution on the surface. Induced surface charge distributions can dramatically perturb the atomic spectrum, hence degrading the ability to perform electrometry. These effects become pronounced near the walls of the vapor cell, posing challenges for vapor cell miniaturization. Using a fluorescence imaging technique, we investigate the effects of surface charge on the atomic spectrum generated with electromagnetically induced transparency (EIT). Our results reveal that visible light (480 nm and 511 nm), i.e., the coupling laser used in two-photon Rydberg EIT schemes, generates localized patches of charge or dipoles where this light interacts with the glass walls of the vapor cell, while a three-photon Rydberg EIT scheme using only near-infrared wavelength lasers shows no measurable field induction. Additionally, imaging in a vacuum chamber where a glass plate is placed between large electrodes confirms that the induced charge is positive. We further validate these findings by studying the photoelectric effect with broadband light during EIT and impedance measurements. These results demonstrate the power of the fluorescence imaging technique to study localized E-field distributions in vapor cells and to target the photoelectric effect of the alkali-exposed glass of vapor cells as a major disruptor in Rydberg atom-based sensors.

physics.atom-ph↗

arXiv2024

Two-dimensional imaging of electromagnetic fields via light sheet fluorescence imaging with Rydberg atoms

The ability to image electromagnetic fields holds key scientific and industrial applications, including electromagnetic compatibility, diagnostics of high-frequency devices, and experimental scientific work involving field interactions. Generally electric and magnetic field measurements require conductive elements which significantly distort the field. However, electromagnetic fields can be measured without altering the field via the shift they induce on Rydberg states of alkali atoms in atomic vapor, which are highly sensitive to electric fields. Previous field measurements using Rydberg atoms utilized electromagnetically induced transparency to read out the shift on the states induced by the fields, but did not provide spatial resolution. In this work, we demonstrate that electromagnetically induced transparency can be spatially resolved by imaging the fluorescence of the atoms. We demonstrate that this can be used to image $\sim$ V/cm scale electric fields in the DC-GHz range and $\sim$ mT scale static magnetic fields, with minimal distortion to the fields. We also demonstrate the ability to image $\sim$ 5 mV/cm scale fields for resonant microwave radiation and measure standing waves generated by the partial reflection of the vapor cell walls in this regime. With additional processing techniques like lock-in detection, we predict that our sensitivities could reach down to nV/cm levels. We perform this field imaging with a spatial resolution of 160 $μ$m, limited by our imaging system, and estimate the fundamental resolution limitation to be 5 $μ$m.

physics.atom-ph↗

arXiv2024

Primary quantum thermometry of mm-wave blackbody radiation via induced state transfer in Rydberg states of cold atoms

Rydberg states of alkali atoms are highly sensitive to electromagnetic radiation in the GHz-to-THz regime because their transitions have large electric dipole moments. Consequently, environmental blackbody radiation (BBR) can couple Rydberg states together at $μ$s timescales. Here, we track the BBR-induced transfer of a prepared Rydberg state to its neighbors and use the evolution of these state populations to characterize the BBR field at the relevant wavelengths, primarily at 130 GHz. We use selective field ionization readout of Rydberg states with principal quantum number $n\sim30$ in $^{85}$Rb and substantiate our ionization signal with a theoretical model. With this detection method, we measure the associated blackbody-radiation-induced time dynamics of these states, reproduce the results with a simple semi-classical population transfer model, and demonstrate that this measurement is temperature sensitive with a statistical sensitivity to the fractional temperature uncertainty of 0.09 Hz$^{-1/2}$, corresponding to 26 K$\cdot$Hz$^{-1/2}$ at room temperature. This represents a calibration-free SI-traceable temperature measurement, for which we calculate a systematic fractional temperature uncertainty of 0.006, corresponding to 2 K at room temperature when used as a primary temperature standard.

physics.atom-ph↗