arXiv subjects

Liron Stern

Publications and source records attributed to Liron Stern.

At least 19 recordsLinked to original sources

arXiv2026

Photogalvanic second harmonic generation in Si3N4 for 1 Hz level on-chip metrology and spectroscopy

The coherent photogalvanic (PG) effect induces an effective $\chi^{(2)}$ nonlinearity in natively $\chi^{(3)}$ silicon nitride integrated photonics, unlocking pathways toward chip-scale precision spectroscopy and optical clockworks via second harmonic generation (SHG). While quasi-phase-matched PG-SHG using spatially varying internal electric fields offers tuning flexibility, it is often accompanied by pump-power- and detuning-dependent frequency offsets. Here, we investigate whether direct phase-matching---utilizing an intermodal scheme that generates a spatially uniform electric field---can support metrologically compatible SHG. By comparing the fundamental and doubled optical frequencies in a silicon nitride microresonator, we test the preservation of the (2:1) frequency ratio in directly phase-matched PG-SHG. We observe a frequency offset of $< 1\mathrm{~Hz}$, contrasting with previous limitations in quasi-phase-matched configurations. Furthermore, we measure a residual fractional frequency instability of $2\times 10^{-15}$ at $1\mathrm{~s}$, averaging down to the $10^{-16}$ level at $1000\mathrm{~s}$, with multi-hour deviations remaining below $1\mathrm{~Hz}$. These results establish directly phase-matched PG-SHG as a robust, metrologically compatible route to effective $\chi^{(2)}$ functionality, combining sub-Hz frequency-ratio fidelity and high coherence on a mature integrated platform for optical clockworks, self-referencing, and precision spectroscopy.

physics.optics↗

arXiv2026

Sub-Hz Stability and Correlation in Pair-Generated Primary Kerr Comb Tones

Kerr microcombs provide a compact route to broadband optical frequency grids, yet the primary comb states formed at the onset of Kerr-comb generation have received little attention as metrological objects. Here we characterize the coherence and frequency stability of pair-generated primary-comb tones in a silicon nitride microresonator using synchronized multi-channel frequency counting referenced to a hydrogen-maser-stabilized difference-frequency comb, enabling direct measurement of temporal fluctuations and correlations among the pump, signal, and idler tones. We show that the generated tones are strongly constrained by parametric energy conservation: under weakly locked conditions with MHz-level frequency excursions, the residual deviation from $2f_p=f_s+f_i$ remains sub-hertz in the mean, and the signal-idler regression deviates from the ideal $-1$ response by only $2.4\times10^{-9}$. When two of the three tones are tightly phase-locked, the energy-conservation residual of the full pump-signal-idler triad, equivalently the deviation of the measured idler from the value inferred from the locked pump and signal, reaches a fractional-instability floor near $6 \times 10^{-16}$ at $\tau\approx100~\mathrm{s}$. This demonstrates metrological-level preservation of the parametric constraint while revealing subtle mode-dependent noise transfer. Together, these results establish primary Kerr tones as a strongly correlated chip-scale parametric frequency triad suitable for demanding precision-frequency applications.

physics.optics↗

arXiv2026

Nonlinear Frequency Translation in Micromachined Rb Vapor Cells

The exceptional nonlinearity of alkali-metal vapors enables highly efficient nonlinear optical processes even at relatively low optical intensities. However, such processes have traditionally relied on centimeter-scale vapor cells. Here, we utilize a versatile chip-scale Rb vapor platform to generate coherent blue and mid-IR light in continuous-wave mode by means of resonant four-wave mixing. Optimized optical overlap with the atomic medium enables blue light generation of $\sim$20 $\mu$W over a very short interaction length, while maintaining a directly measured linewidth of $\sim$1 MHz, which is presently limited by the measurement apparatus. Comparison with a conventional glassblown vapor cell further shows that the micromachined platform can achieve higher coherent blue-light generation efficiency despite its substantially shorter interaction length. Moreover, an anodically bonded Si window enables to detect coherent mid-IR emission with collected powers of $\sim$50 nW. We further characterize the temperature dependence and input-power scaling of the blue emission, confirming efficient nonlinear conversion within these compact vapor cells. This chip-scale platform provides a versatile foundation for a range of nonlinear optical functions, from precise wavelength references and quantum light sources to next-generation quantum sensors.

physics.optics↗

arXiv2025

Quantum Co-Magnetometer Using Diamond Nitrogen-Vacancy Centers and Rubidium Cells

Recent advances in chip scale magnetic quantum sensing have produced platforms that pair unprecedented sensitivity with extreme miniaturization. Here, we demonstrate a hybrid quantum sensor by combining Nitrogen-Vacancy (NV) centers in diamond with a rubidium (Rb) vapor cell, designed for precise magnetic field measurements and quantum exploration. The hybrid comagnetometer leverages the high resolution vector magnetic sensing of NV centers along with the high scalar field sensitivity of the Rb vapor, enhancing the estimation of the magnetic field in terms of magnitude, direction and spatial distribution. A micromachined mm scale vapor cell containing Rb atoms is paired with a bulk diamond, enabling optical and microwave control of both quantum systems for integrated field estimation. Simulations and experimental results confirm the improved accuracy of the system in magnetic field measurements, demonstrating a beyond 10 dB improvement. This NV and Rb platform offers a versatile route toward portable, sensitive magnetometry and opens new possibilities for integrated, multi-modal quantum sensing.

quant-ph↗

arXiv2025

Hybrid-Locked Kerr Microcombs for Flexible On-Chip Optical Clock Division

Optical atomic clocks deliver unrivaled precision, yet their size and complexity still confine them to specialized laboratories. Frequency combs provide the crucial optical-to-microwave division needed for clock readout, but conventional fiber- or bulk-laser combs are far too large for portable use. The advent of chip-integrated microcombs, frequency combs generated in micron-scale resonators, has revolutionized this landscape, enabling fully miniaturized, low-power clocks that bridge optical and radio-frequency domains on a single chip. Nevertheless, stabilizing a microcomb solely through pump laser control entangles otherwise independent feedback parameters, injects extra technical noise, and prevents flexible partial division of the optical frequency. Here, we propose and demonstrate a universal on-chip optical-clock architecture that supports both partial and full optical division. A hybrid passive-active scheme enables locking any two microcomb teeth independently, eliminating cross-coupling of control loops. Using the pump laser as a nonlinear actuator to stabilize an arbitrary tooth, we achieve a residual relative frequency instability of 1e-16. This advance brings integrated optical clocks closer to real-world deployment and opens new avenues for precision timing and navigation.

physics.optics↗

arXiv2025

Subwavelength micromachined vapor-cell based Rydberg sensing

In recent years, micromachined vapor cells have been revolutionizing the field of chip-scale quantum sensors such as magnetometers and atomic clocks. In parallel, Rydberg atomic quantum sensing has emerged as a powerful technique for broadband, non-invasive and ultra-sensitive electrometry. Yet, to date, Rydberg sensing has largely been limited to glass-blown, centimeter-scale vapor cells. Here, we perform Rydberg spectroscopy using a wafer-scale fabricated Pyrex-Si-Pyrex cell with millimeter-scale dimensions. The Rydberg spectroscopic line is characterized with respect to critical parameters such as temperature, the frequency and amplitude of the applied radiofrequency field, light intensity, and the spatial position of the interrogating beam. Our study reveals lineshapes directly influenced by a complex landscape of electrostatic fields with values up to approximately 0.6 V/cm. By controlling key parameters, we were able to reduce the effect of these internal electric fields and demonstrate the detection of RF fields with a sensitivity as low as $10\,\mu\mathrm{V/cm}$ These results highlight the potential of micromachined vapor cells for sub-wavelength electromagnetic field measurements, with applications in communications, near-field RF imaging, and chip-scale quantum technologies.

physics.atom-ph↗

arXiv2025

Chip-Scale Atomic Birefringent Diffractive-Optical-Elements

The interaction between light and vapors in the presence of magnetic fields is fundamental to many quantum technologies and applications. Recently, the ability to geometrically confine atoms into periodic structures has enabled the creation of chip-scale, micromachined hybrid atomic-diffractive optical elements. However, applying magnetic fields to such structures remains largely unexplored, offering potential for both fundamental and applied insights. Here, we present measurements of an atomic-diffractive optical element subject to magnetic fields. In contrast to the well-known polarization rotation in a Faraday medium, these diffractive atomic elements exhibit additional, rapidly oscillating rotation terms, which we validate both theoretically and experimentally. Moreover, we find that the introduction of spatially varying magnetic fields leads to a reduction in fringe visibility, which can be leveraged for gradiometric applications. Together, these effects establish a chip-scale platform where diffraction and quantum sensing are inseparably co-engineered, unveiling previously inaccessible regimes of atom-photon-magnetic interaction. By probing the magneto-optic response of periodically confined vapors, our results lay the groundwork for integrated smart-cell magnetometers and open new avenues for flat-optics-enabled quantum photonic devices.

physics.app-ph↗

arXiv2024

Laser Offset Stabilization with Chip-Scale Atomic Diffractive Elements

Achieving precise and adjustable control over laser frequency is an essential requirement in numerous applications such as precision spectroscopy, quantum control, and sensing. In many such applications it is desired to stabilize a laser with a variable detuning from an atomic line. In this study, we employ an offset-stabilization scheme by utilizing phase contrast spectroscopy in microfabricated atomic diffractive elements vapor-cells. The spectroscopic response of such a device generates oscillating optical fringes, providing multiple optical frequency stabilization points across a bandwidth of tens of gigahertz, centered around the absorption resonances of Rb. Using this device, we demonstrate laser stabilization at various offset frequencies with instabilities reaching sub-megahertz levels. We further explore the fundamental limitations of our hybrid atomic-photonic device, drawing parallels to birefringent and dichroic spectroscopy apparatuses, which are commonly employed for offset stabilization. Our system showcases a broad offset lock bandwidth, a highly compact footprint, scalability to chip-scale production, and the ability to operate without reliance on magnetic fields. These attributes pave the way for a multitude of applications in quantum technologies.

physics.app-ph↗

arXiv2024

Broadband Cavity-Enhanced Kerr Comb Spectroscopy on Chip

The broad and equidistant spectrum of frequency combs has had a profound impact on spectroscopic studies. Particularly, experiments involving the coupling of frequency combs to cavities have already enabled unprecedented broadband and sensitive spectroscopy on a single-molecule level. The emergence of integrated, compact and broadband Kerr-microcombs holds promise to bring many metrological and spectroscopic studies outside of the lab. However, performing cavity-enhanced direct frequency comb spectroscopy on-chip has remained a challenge. Here, we couple a microcomb source with a microcavity to extend the advantages of cavity-enhanced spectroscopy to photonically integrated circuits. By harnessing the coherent nature of the Kerr-comb and high-Q microcavity enhancement, we obtain a detailed dispersion landscape of the guided-wave mode and comprehensive frequency-dependent cavity lineshapes. Our microcomb-cavity coupling can facilitate photonically integrated cavity-enhanced biochemical spectroscopy by evanescently coupling analytes to the cavity's guided mode, a mode of operation we analyze and provide guidelines for. Demonstrated detailed dispersion measurements, overperforming state-of-the-art table-top tunable lasers in available bandwidth, show potential for integrated nonlinear optics applications, as precise dispersion management is crucial for such processes. Our chip-scale comb-cavity coupled platform suggests an integrated, broadband, cost-effective and accurate tool for the nonlinear optics studies as well as for ultra-compact bio- and chemical- sensing platform.

physics.optics↗

arXiv2023

Remote Chip-Scale Quantum Sensing of Magnetic Fields

Quantum sensing is an ever-evolving research field describing the use of a quantum phenomenon to perform measurement of a physical quantity. Amongst different types of quantum sensors, atomic vapor-based quantum effects are extensively used to measure quantities such as time, velocity, acceleration, and electric and magnetic fields. Here, we propose and demonstrate remote quantum sensing using a chip-scale atomic vapor cell. Specifically, we remotely interrogate mm-scale micromachined vapor cells, and measure the ambient Earth's magnetic field at a standoff distance of ~10 meters and a sensitivity of ~1 pT/Hz^0.5 . Simultaneously we are able measure the distance between micro-cell and the interrogating system by means of time-of-flight measurements, thus correlating between position and magnetic field. Consequently, we provide a novel toolset to measure and map arbitrary, remote, and hard to access magnetic field in unshielded environments with high sensitivity and spatial resolution, paving the way to a variety of novel applications in diverse fields such as medicine, communication, defense, space-exploration, and quantum technologies.

physics.atom-ph↗

arXiv2021

Optically synchronized fiber links with spectrally pure integrated lasers

Precision frequency and phase synchronization between distinct fiber interconnected nodes is critical for a wide range of applications, including atomic timekeeping, quantum networking, database synchronization, ultra-high-capacity coherent optical communications and hyper-scale data centers. Today, many of these applications utilize precision, tabletop laser systems, and would benefit from integration in terms of reduced size, power, cost, and reliability. In this paper we report a record low 3x10^-4 rad^2 residual phase error variance for synchronization based on independent, spectrally pure, ultra-high mutual coherence, photonic integrated lasers. This performance is achieved with stimulated Brillouin scattering lasers that are stabilized to independent microcavity references, realizing sources with 30 Hz integral linewidth and a fractional frequency instability less than or equal to 2x10^-13 at 50 ms. This level of low phase noise and carrier stability enables a new type of optical-frequency-stabilized phase-locked loop (OFS-PLL) that operates with a less than 800 kHz loop bandwidth, eliminating traditional power consuming high bandwidth electronics and digital signal processors used to phase lock optical carriers. Additionally, we measure the residual phase error down to a received carrier power of -34 dBm, removing the need to transmit in-band or out-of-band synchronized carriers. These results highlight the promise for a path to spectrally pure, ultra-stable, integrated lasers for network synchronization, precision time distribution protocols, quantum-clock networks, and multiple-Terabit per second coherent DSP-free fiber-optic interconnects.

physics.optics↗

arXiv2020

Ultraprecise optical-frequency stabilization with heterogeneous III-V/Si lasers

Demand for low-noise, continuous-wave, frequency-tunable lasers based on semiconductor integrated photonics has been advancing in support of numerous applications. In particular, an important goal is to achieve narrow spectral linewidth, commensurate with bulk-optic or fiber-optic laser platforms. Here, we report on laser-frequency-stabilization experiments with a heterogeneously integrated III/V-Si widely tunable laser and a high-finesse, thermal-noise-limited photonic resonator. This hybrid architecture offers a chip-scale optical-frequency reference with an integrated linewidth of 60 Hz and a fractional frequency stability of 2.5e-13 at 1-second integration time. We explore the potential for stabilization with respect to a resonator with lower thermal noise by characterizing laser-noise contributions such as residual amplitude modulation and photodetection noise. Widely tunable, compact and integrated, cost effective, stable and narrow linewidth lasers are envisioned for use in various fields, including communication, spectroscopy, and metrology.

physics.optics↗

arXiv2019

Ultranarrow linewidth photonic-atomic laser

Lasers with high spectral purity can enable a diverse application space, including precision spectroscopy, coherent high-speed communications, physical sensing, and manipulation of quantum systems. Already, meticulous design and construction of bench Fabry-Perot cavities has made possible dramatic achievements in active laser-linewidth reduction, predominantly for optical-atomic clocks. Yet there is increasing demand for miniaturized laser systems operating with high performance in ambient environments. Here, we report a compact and robust photonic-atomic laser comprising a 2.5 cm long, 20,000 finesse, monolithic Fabry-Perot cavity integrated with a micromachined rubidium vapor cell. By leveraging the short-time frequency stability of the cavity and the long-time frequency stability of atoms, we realize an ultranarrow-linewidth laser that enables integration for extended measurements. Specifically, our laser supports a fractional-frequency stability of $1\times 10^{-13}$ at an averaging time of 20 ms, $7 \times 10^{-13}$ at 300 s, an integrated linewidth of 25 Hz that results from thermal noise, a Lorentzian linewidth as low as 0.06 Hz$^2$/Hz, and a passive vibration immunity as low as $10^{-10}$/g. Our work explores hybrid laser systems with monolithic photonic and atomic packages based on physical design.

physics.optics↗

arXiv2018

Direct Kerr-frequency-comb atomic spectroscopy

Microresonator-based soliton frequency combs - microcombs - have recently emerged to offer low-noise, photonic-chip sources for optical measurements. Owing to nonlinear-optical physics, microcombs can be built with various materials and tuned or stabilized with a consistent framework. Some applications require phase stabilization, including optical-frequency synthesis and measurements, optical-frequency division, and optical clocks. Partially stabilized microcombs can also benefit applications, such as oscillators, ranging, dual-comb spectroscopy, wavelength calibration, and optical communications. Broad optical bandwidth, brightness, coherence, and frequency stability have made frequency-comb sources important for studying comb-matter interactions with atoms and molecules. Here, we explore direct microcomb atomic spectroscopy, utilizing a cascaded, two-photon 1529-nm atomic transition of rubidium. Both the microcomb and the atomic vapor are implemented with planar fabrication techniques to support integration. By fine and simultaneous control of the repetition rate and carrier-envelope-offset frequency of the soliton microcomb, we obtain direct sub-Doppler and hyperfine spectroscopy of the $4^2D_{5/2}$ manifold. Moreover, the entire set of microcomb modes are stabilized to this atomic transition, yielding absolute optical-frequency fluctuations of the microcomb at the kilohertz-level over a few seconds and < 1 MHz day-to-day accuracy. Our work demonstrates atomic spectroscopy with microcombs and provides a rubidium-stabilized microcomb laser source, operating across the 1550 nm band for sensing, dimensional metrology, and communication.

physics.optics↗

arXiv2018

Chip-scale atomic diffractive optical elements

Atomic systems have long provided a useful material platform with unique quantum properties. The efficient light-matter interaction in atomic vapors has led to numerous seminal scientific achievements including accurate and precise metrology and quantum devices. In the last few decades, the field of thin optical elements with miniscule features has been extensively studied demonstrating an unprecedented ability to control photonic degrees of freedom, both linearly and non-linearly, with applications spanning from photography and spatial light modulators to cataract surgery implants. Hybridization of atoms with such thin devices may offer a new material system allowing traditional vapor cells with enhanced functionality. Here, we fabricate and demonstrate chip-scale, quantum diffractive optical elements which map atomic states to the spatial distribution of diffracted light. Two foundational diffractive elements, lamellar gratings and Fresnel lenses, are hybridized with atomic channels containing hot atomic vapors which demonstrate exceptionally strong frequency dependent behaviors. Providing the design tools for chip-scale atomic diffractive optical elements develops a path for a variety of compact thin quantum-optical elements.

physics.optics↗

arXiv2016

Enhanced light-vapor interactions and all optical switching in a chip scale micro-ring resonator coupled with atomic vapor

The coupling of atomic and photonic resonances serves as an important tool for enhancing light-matter interactions and enables the observation of multitude of fascinating and fundamental phenomena. Here, by exploiting the platform of atomic-cladding wave guides, we experimentally demonstrate the resonant coupling of rubidium vapor and an atomic cladding micro ring resonator. Specifically, we observed cavity-atom coupling in the form of Fano resonances having a distinct dependency on the relative frequency detuning between the photonic and the atomic resonances. Moreover, we were able to significantly enhance the efficiency of all optical switching in the V-type pump-probe scheme. The coupled system of micro-ring resonator and atomic vapor is a promising building block for a variety of light vapor experiments, as it offers a very small footprint, high degree of integration and extremely strong confinement of light and vapor. As such it may be used for important applications, such as all optical switching, dispersion engineering (e.g. slow and fast light) and metrology, as well as for the observation of important effects such as strong coupling, Purcell enhancement and bistability.

physics.optics↗

arXiv2016

Strong coupling and high contrast all optical modulation in atomic cladding waveguides

In recent years we are witnessing a flourish in research aimed to facilitate alkali vapors in guided wave configurations. Owing to the significant reduction in device dimensions, the increase in density of states, the interaction with surfaces and primarily the high intensities carried along the structure, a rich world of light vapor interactions can be studied, and new functionalities, e.g. low power nonlinear light-matter interactions can be achieved. One immense remaining challenge is to study the effects of quantum coherence and shifts in such nano-scale waveguides, characterized by ultra-small mode areas and fast dynamics. Here, we construct a serpentine silicon-nitride wave guide, having atomic vapor as its cladding. The unprecedented mode volume of 5e-13 m^3 supported over a length of 17 mm is used to demonstrate efficient linear and non-linear spectroscopy. Fascinating and important phenomena such as van der Waals shifts, dynamical stark shifts, and coherent effects such as strong coupling (in the form of Autler Townes splitting) are all observed. The serpentine atomic cladding is a promising building block for a variety of light vapor experiments, as it offers a very small footprint, enables operation with relatively low density of atoms and extremely strong confinement of light and vapor. As such it may be used for important applications, such as all optical switching, frequency referencing, and magnetometry to name a few.

physics.optics↗

arXiv2015

Interactions of space-variant polarization beams with Zeeman-shifted rubidium vapor

Space variant beams are of great importance as a variety of applications have emerged in recent years. As such, manipulation of their degrees of freedom is highly desired. Here, by exploiting the circular dichroism and circular birefringence in a Zeeman-shifted Rb medium, we study the general interaction of space variant beams with such a medium. We present two particular cases of radial polarization and hybrid polarization beams where the control of the polarization states is demonstrated experimentally. Moreover, we show that a Zeeman-shifted atomic system can be used as an analyzer for such space variant beams

physics.optics↗