arXiv subjects

Samuel Berweger

Publications and source records attributed to Samuel Berweger.

36 records · Page 2Linked to original sources

arXiv2023

High angular momentum coupling for enhanced Rydberg-atom sensing in the VHF band

Recent advances in Rydberg atom electrometry detail promising applications in radio frequency (RF) communications. Presently, most applications use carrier frequencies greater than 1~GHz where resonant Autler-Townes splitting provides the highest sensitivity. This letter documents a series of experiments with Rydberg atomic sensors to collect and process waveforms from the automated identification system (AIS) used in maritime navigation in the Very High Frequency (VHF) band. Detection in this band is difficult with conventional resonant Autler-Townes based Rydberg sensing and requires a new approach. We show the results from a new method called High Angular Momentum Matching Excited Raman (HAMMER), which enhances low frequency detection and exhibits superior sensitivity compared to the traditional AC Stark effect. From measurements of electromagnetically induced transparency (EIT) in rubidium and cesium vapor cells, we show the relationship between incident electric field strength and observed signal-to-noise ratio and find that the sensitivity of the HAMMER scheme in rubidium achieved an equivalent single VHF tone sensitivity of $\mathrm{100~μV/m/\sqrt{Hz}}$. With these results, we estimate the usable range of the atomic vapor cell antenna for AIS waveforms given current technology and detection techniques.

physics.atom-ph↗

arXiv2023

Phase-Resolved Rydberg Atom Field Sensing using Quantum Interferometry

Although Rydberg atom-based electric field sensing provides key advantages over traditional antenna-based detection, it remains limited by the need for a local oscillator (LO) for low-field and phase resolved detection. In this work, we demonstrate that closed-loop quantum interferometric schemes can be used to generate a system-internal reference that can directly replace an external LO for Rydberg field sensing. We reveal that this quantum-interferometrically defined internal reference phase and frequency can be used analogously to a traditional LO for atom-based down-mixing to an intermediate frequency for lock-in phase detection. We demonstrate that this LO-equivalent functionality provides analogous benefits to an LO, including full 360$^\circ$ phase resolution as well as improved sensitivity. The general applicability of this approach is confirmed by demodulating a four phase-state signal broadcast on the atoms. Our approach opens up new sensing schemes and provides a clear path towards all-optical Rydberg atom sensing implementations.

physics.atom-ph↗

arXiv2023

EIT spectra of Rydberg atoms dressed with dual-tone radio-frequency fields

We examine spectral signatures of Rydberg atoms driven with near-resonant dual-tone radio-frequency (RF) fields in the regime of strong driving. We experimentally demonstrate and theoretically model a variety of nonlinear and multiphoton phenomena in the atomic Rydberg response that manifest in the EIT spectra. Our results echo previous studies of two-level atoms driven with bichromatic optical fields. In comparison to the optical studies, the RF-driven Rydberg system utilizes a more complex excitation pathway, and electromagnetic fields from two different spectral regimes: a two-photon optical excitation continuously creates highly excited Rydberg atoms, while RF fields drive resonant coupling between the Rydberg levels and generate strong mixing. Yet, our spectra reflect nearly identical effects of the dual-tone RF fields on the atomic Rydberg observables, showing detuning-dependent splittings and Rabi frequency dependent peak numbers and relative strengths, and avoided crossings at subharmonic resonances. We thus validate previous two-state models in this more complex physical system. In the context of Rydberg electrometry, we use these investigations to explore a technique where we tune a known RF field to observe spectra which give frequency and power of an unknown RF field using the complex dual-tone spectra.

physics.atom-ph↗

arXiv2023

Inverse Transform Sampling for Efficient Doppler-Averaged Spectroscopy Simulations

We present a thermal velocity sampling method for calculating Doppler-broadened atomic spectra, which more efficiently reaches a smooth limit than regular velocity weighted sampling. The method uses equal-population sampling of the 1-D thermal distribution, sampling the 'inverse transform' of the cumulative distribution function, and is broadly applicable to normal distributions. We also discuss efficiencies from eliminating velocity classes which don't significantly contribute to observed atomic lines, and comment on the application of this method in 2- and 3-dimensions.

physics.atom-ph↗

arXiv2023

Detection of HF and VHF Fields through Floquet Sideband Gaps by `Rabi Matching' Dressed Rydberg Atoms

Radio frequencies in the HF and VHF (3 MHz to 300 MHz) bands are challenging for Rydberg atom-based detection schemes, as resonant detection requires exciting the atoms to extremely high energy states. We demonstrate a method for detecting and measuring radio frequency (RF) carriers in the HF and VHF bands via a controlled Autler-Townes line splitting. Using a resonant, high-frequency (GHz) RF field, the absorption signal from Townes-Merrit sidebands created by a low frequency, non-resonant RF field can be enhanced. Notably, this technique uses a measurement of the optical frequency separation of an avoided crossing to determine the amplitude of a non-resonant, low frequency RF field. This technique also provides frequency-selective measurements of low frequency RF electric fields. To show this, we demonstrate amplitude modulated signal transduction on a low frequency VHF carrier. We further demonstrate reception of multiple tones simultaneously, creating a Rydberg `spectrum analyzer' over the VHF range.

physics.atom-ph↗

arXiv2022

Sensitivity Comparison of Two-photon vs Three-photon Rydberg Electrometry

We investigate the sensitivity of three-photon EIT in Rydberg atoms to radio frequency detection and compare it against conventional two-photon systems. Specifically, we model the 4-level and 5-level atomic system and compare how the transmission of the probe changes with different powers of the lasers used and strengths of the RF field. In this model, we also define a sensitivity metric to best relate to the operation of the current best experimental implementation based on shot noise limited detection. We find that the three-photon system boasts much narrower line widths compared to the conventional two-photon EIT. However, these narrow line features do not align with the regions of the best sensitivity. In addition to this, we calculate the expected sensitivity for the two-photon Rydberg sensor and find that the best achievable sensitivity is over an order of magnitude better than the current measured values of 5 uV/m/Hz. However, by accounting for the additional noise sources in the experiment and the quantum efficiency of the photo-detectors, the values are in good agreement.

physics.atom-ph↗

arXiv2022

Rydberg state engineering: A comparison of tuning schemes for continuous frequency sensing

On-resonance Rydberg atom-based radio-frequency (RF) electric field sensing methods remain limited by the narrow frequency signal detection bands available by resonant transitions. The use of an additional RF tuner field to dress or shift a target Rydberg state can be used to return a detuned signal field to resonance and thus dramatically extend the frequency range available for resonant sensing. Here we investigate three distinct tuning level schemes based on adjacent Rydberg transitions, which are shown to have distinct characteristics and can be controlled with mechanisms based on the tuning field frequency or field strength. We further show that a two-photon Raman feature can be used as an effective tuning mechanism separate from conventional Autler-Townes splitting. We compare our tuning schemes to AC Stark effect-based broadband RF field sensing and show that although the sensitivity is diminished as we tune away from a resonant state, it nevertheless can be used in configurations where there is a low density of Rydberg states, which would result in a weak AC Stark effect.

physics.atom-ph↗

arXiv2022

Modeling Line Broadening and Distortion Due to Spatially Non-Uniform Fields in Rydberg Electrometry

We present a model for calculating broadened Autler-Townes spectra when probing ac electric field magnitudes by use of Rydberg atom electromagnetically-induced transparency. This model approximates the atom vapor as a multi-layered media and uses Beer's law to combine probe beam absorption through many discrete thin segments, replicating the broadening seen in experimental measurements. The methodology can be easily applied to other non-uniform optical parameters when monitoring total spectral transmission or phase delay. Field non-uniformity is present in standing waves of unmatched waveguides and glass vapor cells, which are generally due to source characteristics and environmental reflections. We present broadening and distortion effects caused by various types of electric-field distributions, and compare this model to results obtained from measured atomic spectra.

physics.atom-ph↗

arXiv2022

TV and Video Game Streaming with a Quantum Receiver: A Study on a Rydberg atom-based receivers bandwidth and reception clarity

We demonstrate the ability to receive live color analog television and video game signals with the use of the Rydberg atom receiver. The typical signal expected for traditional 480i NSTC format video signals requires a bandwidth of over 3 MHz. We determine the beam sizes, powers, and detection method required for the Rydberg atoms to receive this type of signal. The beam size affects the average time the atoms remain in the interaction volume, which is inversely proportional to the bandwidth of the receiver. We find that small beam diameters (less than 100 μm) lead to much faster responses and allow for color reception. We demonstrate the effect of beam size on bandwidth by receiving a live 480i video stream with the Rydberg atom receiver. The best fidelity was achieved with a beam width of 85 μm full-width at half-max.

quant-ph↗

arXiv2022

Rydberg atom-based field sensing enhancement using a split-ring resonator

We investigate the use of a split-ring resonator (SRR) incorporated with an atomic-vapor cell to improve the sensitivity and the minimal detectable electric (E) field of Rydberg atom-based sensors. In this approach, a sub-wavelength SRR is placed around an atomic vapor-cell filled with cesium atoms for E-field measurements at 1.3~GHz. The SRR provides a factor of 100 in the enhancement of the E-field measurement sensitivity. Using electromagnetically induced transparency (EIT) with Aulter-Townes splitting, E-field measurements down to 5~mV/m are demonstrated with the SRR, while in the absence of the SRR, the minimal detectable field is 500~mV/m. We demonstrate that by combining EIT with a heterodyne Rydberg atom-based mixer approach, the SRR allows for the a sensitivity of 5.5~$μ$V/m$\sqrt{\rm Hz}$, which is two-orders of magnitude improvement in sensitivity than when the SRR is not used.

physics.atom-ph↗

arXiv2021

Quantum phase modulation with acoustic cavities and quantum dots

Fast, efficient, and low power modulation of light at microwave frequencies is crucial for chip-scale classical and quantum processing as well as for long-range networks of superconducting quantum processors. A successful approach to bridge the gap between microwave and optical photons has been to use intermediate platforms such as acoustic waves, which can couple efficiently to a variety of quantum systems. Here, we use gigahertz-frequency focusing surface acoustic wave cavities on GaAs that are piezo-electrically coupled to superconducting circuits and parametrically coupled, via strain, to photons scattered from InAs quantum dots . We demonstrate strong modulation of single photons with a half-wave voltage as low as 44 mV, and subnatural modulation sideband linewidths. These demonstrations pave the way for efficient and low-noise transduction of quantum information between microwave and optical domains.

quant-ph↗

arXiv2021

Enhancement of electromagnetically induced transparency based Rydberg-atom electrometry through population repumping

We demonstrate improved sensitivity of Rydberg electrometry based on electromagnetically induced transparency (EIT) with a ground state repumping laser. Though there are many factors that limit the sensitivity of radio frequency field measurements, we show that repumping can enhance the interaction strength while avoiding additional Doppler or power broadening. Through this method, we nearly double the EIT amplitude without an increase in the width of the peak. A similar increase in amplitude without the repumping field is not possible through simple optimization.We also establish that one of the key limits to detection is the photon shot noise of the probe laser. We show an improvement on the sensitivity of the device by a factor of nearly 2 in the presence of the repump field.

physics.atom-ph↗

arXiv2020

Spatially Resolved Persistent Photoconductivity in MoS$_2$-WS$_2$ Lateral Heterostructures

The optical and electronic properties of 2D semiconductors are intrinsically linked via the strong interactions between optically excited bound species and free carriers. Here we use near-field scanning microwave microscopy (SMM) to image spatial variations in photoconductivity in MoS$_2$--WS$_2$ lateral multijunction heterostructures using photon energy-resolved narrowband illumination. We find that the onset of photoconductivity in individual domains corresponds to the optical absorption onset, confirming that the tightly bound excitons in transition metal dichalcogenides can nonetheless dissociate into free carriers. These photogenerated carriers are most likely n-type and are seen to persist for up to days, and informed by finite element modeling we reveal that they can increase the carrier density by up to 200 times. This persistent photoconductivity appears to be dominated by contributions from the multilayer MoS$_2$ domains, and we attribute the flake-wide response in part to charge transfer across the heterointerface. Spatial correlation of our SMM imaging with photoluminescence (PL) mapping confirms the strong link between PL peak emission photon energy, PL intensity, and the local accumulated charge. This work reveals the spatially and temporally complex optoelectronic response of these systems and cautions that properties measured during or after illumination may not reflect the true dark state of these materials but rather a metastable charged state.

cond-mat.mes-hall↗

arXiv2018

Imaging Carrier Inhomogeneities in Ambipolar Tellurene Field Effect Transistors

Developing van der Waals (vdW) homojunction devices requires materials with narrow bandgaps and simultaneously high hole and electron mobilities for bipolar transport, as well as methods to image and study spatial variations in carrier type and associated conductivity with nanometer spatial resolution. Here we demonstrate the general capability of near-field scanning microwave microscopy (SMM) to image and study the local carrier type and associated conductivity in operando by studying ambiploar field effect transistors (FETs) of the 1D vdW material tellurium in 2D form. To quantitatively understand electronic variations across the device, we produce nanometer resolved maps of the local carrier equivalence backgate voltage. We show that the global device conductivity minimum determined from transport measurements does not arise from uniform carrier neutrality, but rather from the continued coexistence of p-type regions at the device edge and n-type regions in the interior of our micron-scale devices. This work both underscores and addresses the need to image and understand spatial variations in the electronic properties of nanoscale devices.

cond-mat.mes-hall↗

arXiv2015

Amplitude- and phase-resolved nano-spectral imaging of phonon polaritons in hexagonal boron nitride

Phonon polaritons are quasiparticles resulting from strong coupling of photons with optical phonons. Excitation and control of these quasiparticles in 2D materials offer the opportunity to confine and transport light at the nanoscale. Here, we image the phonon polariton (PhP) spectral response in thin hexagonal boron nitride (hBN) crystals as a representative 2D material using amplitude- and phase-resolved near-field interferometry with broadband mid-IR synchrotron radiation. The large spectral bandwidth enables the simultaneous measurement of both out-of-plane (780 cm-1) and in-plane (1370 cm-1) hBN phonon modes. In contrast to the strong and dispersive in-plane mode, the out-of-plane mode PhP response is weak. Measurements of the PhP wavelength reveal a proportional dependence on sample thickness for thin hBN flakes, which can be understood by a general model describing two-dimensional polariton excitation in ultrathin materials.

cond-mat.mes-hall↗

arXiv2014

Phase Resolved Surface Plasmon Interferometry of Graphene

The surface plasmon polaritons (SPP) of graphene reflect the microscopic spatial variations of underlying electronic structure and dynamics. Access to this information requires probing the full SPP response function. We image the graphene SPP phase and amplitude by combining scanning probe tip coupled surface plasmon interferometry with phase resolved near-field signal detection. We show that a simple analytical cavity model can self-consistently describe the phase and amplitude response both for edge, grain boundary, and defect SPP reflection and scattering. The derived complex SPP wavevector, damping, and carrier mobility agree with the results from more complex models. This phase information opens a new degree of freedom for spatial and spectral graphene SPP tuning and modulation for opto-electronics applications.

cond-mat.mes-hall↗

arXiv2011

Ultrafast nano-focusing with full optical waveform control

The spatial confinement and temporal control of an optical excitation on nanometer length scales and femtosecond time scales has been a long-standing challenge in optics. It would provide spectroscopic access to the elementary optical excitations in matter on their natural length and time scales and enable applications from ultrafast nano-opto-electronics to single molecule quantum coherent control. Previous approaches have largely focused on using surface plasmon polariton (SPP) resonant nanostructures or SPP waveguides to generate nanometer localized excitations. However, these implementations generally suffer from mode mismatch between the far-field propagating light and the near-field confinement. In addition, the spatial localization in itself may depend on the spectral phase and amplitude of the driving laser pulse thus limiting the degrees of freedom available to independently control the nano-optical waveform. Here we utilize femtosecond broadband SPP coupling, by laterally chirped fan gratings, onto the shaft of a monolithic noble metal tip, leading to adiabatic SPP compression and localization at the tip apex. In combination with spectral pulse shaping with feedback on the intrinsic nonlinear response of the tip apex, we demonstrate the continuous micro- to nano-scale self-similar mode matched transformation of the propagating femtosecond SPP field into a 20 nm spatially and 16 fs temporally confined light pulse at the tip apex. Furthermore, with the essentially wavelength and phase independent 3D focusing mechanism we show the generation of arbitrary optical waveforms nanofocused at the tip. This unique femtosecond nano-torch with high nano-scale power delivery in free space and full spectral and temporal control opens the door for the extension of the powerful nonlinear and ultrafast vibrational and electronic spectroscopies to the nanoscale.

cond-mat.mes-hall↗

arXiv2008

Tip-enhanced Raman imaging and spectroscopy: sensitivity, symmetry and selection rules

This article reviews the new developments in Tip-enhanced Raman scattering (TERS). The fundamental mechanisms underlying the Raman enhancement are discussed, including the role of the plasmonic character of the metallic tips, the nature of the optical tip-sample coupling and the resulting local-field confinement responsible for ultrahigh spatial resolution down to just several nanometers. Criteria for the distinction of near-field signature from far-field imaging artifacts are addressed and TERS results of molecules and nanostructures are presented. With enhancement factors as high as 10$^9$, single molecule spectroscopy is demonstrated. Spatially resolved vibrational mapping of crystalline nanostructures and determination of crystallographic orientation and domains is shown making use of the unique symmetry properties of the tip in conjunction with the intrinsic Raman selection rules.

physics.chem-ph↗