arXiv subjects

Mohamed ElKabbash

Publications and source records attributed to Mohamed ElKabbash.

14 recordsLinked to original sources

arXiv2026

Angular displacement readout of a mechanical oscillator with a guided mode resonance

Measuring the angular displacement of a mechanical oscillator is a ubiquitous task; however, the multimode nature of angular optomechanical coupling makes coherent signal enhancement challenging. Here we demonstrate coherently enhanced angular displacement readout with an integrated guided mode resonance (GMR) structure, applying it to precision readout of a nanomechanical oscillator. Specifically, we fabricate subwavelength gratings into 100-nm-thick Si$_3$N$_4$ membranes and record their vibration by direct transmission measurements. The narrow linewidth $\approx 2.5\;\text{mrad}$ of the GMR enables a shot-noise-limited displacement imprecision of $ 10^{-9}\;\text{rad}/\sqrt{\text{Hz}}$ with nanowatts of optical power, sufficient to resolve the thermal motion of a $Q\approx 10^6$ torsion mode with a signal-to-noise ratio of 47 dB. Control experiments based on polarization and wavelength detuning confirm that the measured signal arises from GMR-mediated transduction. These results establish guided-mode resonance as an on-chip approach to angular displacement readout in quantum optomechanical sensors.

physics.optics↗

arXiv2026

Metasurface-Based Dual-Basis Polarization Beam Splitter for efficient entanglement witnessing

Entanglement witnessing is essential for quantum technologies such as computing, key distribution, and networking. Conventional bulk-optics methods require sequential reconfiguration across multiple polarization bases, limiting efficiency and scalability. We propose a metasurface-based analyzer that performs dual-basis (σ_z and σ_y) projections simultaneously by mapping them to orthogonal spatial modes. This allows direct access to the commuting two-photon correlators \langle σ_z \otimes σ_z \rangle and \langle σ_y \otimes σ_y \rangle required for entanglement witnessing. The metasurface design employs meta-atoms engineered to impart independent linear and circular phase delays through anisotropy and geometric control, resulting in polarization-dependent beam deflection that separates H/V and R/L components. This approach halves the measurement overhead compared to sequential analysis while offering a compact, integrable platform for chip-scale quantum photonics. The proposed scheme provides a path toward efficient entanglement verification with applications in quantum key distribution, quantum repeaters, and scalable quantum networks.

quant-ph↗

arXiv2026

Observation of Light-Driven Levitation Near Epsilon-Near-Zero Surfaces

Optical manipulation of micro- and nanoparticles near surfaces is fundamental for applications in sensing and microfluidics, yet controlling particle-surface interactions remains challenging. Here we experimentally investigate light-induced forces on dielectric particles near epsilon-near-zero (ENZ) metamaterial surfaces using photonic force microscopy. By illuminating trapped particles with tunable visible light, we observe a wavelength-dependent repulsive force unique to ENZ surfaces, contrasting with the attractive forces near dielectric or metallic substrates. This repulsion peaks near the ENZ frequency and may be attributed to combined optical ENZ effects and thermophoretic forces. Our findings demonstrate that ENZ metamaterials can induce stable levitation of particles via light-driven forces, offering a novel mechanism for contactless manipulation in microfluidic environments. This work advances understanding of light-matter interactions at ENZ interfaces and suggests potential for ENZ-based optical control of micro- and nanoscale objects, with potential applications in micro- and nanofluidic environments.

physics.optics↗

arXiv2025

Probing General Relativity-Induced Decoherence Using an on-chip Sagnac Interferometer

The intersection of quantum mechanics and general relativity remains an open frontier in fundamental physics, with few experimentally accessible phenomena connecting the two. Recent theoretical proposals suggest that relativistic proper time can act as a source of decoherence in quantum systems, providing a testable overlap between the two theories. Here, we propose a chip-integrated Sagnac interferometer where rotation induces a proper time difference between clockwise and counterclockwise single-photon paths. When this time delay exceeds the photon's coherence time, interference visibility is predicted to decrease, offering a direct signature of relativistic time dilation-induced decoherence. We theoretically derive the proper time difference arising from the Sagnac effect and estimate that for a loop radius of 18.9 cm and a rotation speed of 1000 rad/s, decoherence should occur for single-photon wavepackets with a coherence time of 10 femtoseconds. We also present a practical chip design that accommodates the required high-speed mechanical rotation and includes an all-optical readout scheme to eliminate wiring constraints. This approach enables a stable, on-chip implementation using realistic parameters, with rotation speed serving as a continuously tunable knob to control decoherence. Our platform opens a new route for experimentally probing the interplay between quantum coherence and relativistic proper time in a scalable and compact form.

physics.optics↗

arXiv2025

Inverse Drexhage effect in Epsilon-Near-Zero Substrates

The Drexhage effect, caused by interference between a dipole and its image formed in a substrate, modifies the local density of optical states of quantum emitters which can either enhance or suppress their spontaneous emission rate depending on the dipole orientation and distance from the substrate. Here, we show that for an epsilon-near-zero (ENZ) substrate, the observed orientation and distance dependence of the spontaneous emission rate is reversed compared to metals. This inverse Drexhage effect is studied for ideal ENZ and real ENZ substrates compared with ideal and real metallic substrates. ENZ metamaterials consisting of a subwavelength metal-dielectric stack are shown to exhibit the conventional Drexhage effects due to the large optical losses associated with these materials. Our results could find applications in quantum sensing, quantum information, and energy-efficient optoelectronic devices.

physics.optics↗

arXiv2025

Ultrafast quantum light uncertainty dynamics in real time

Advancements in quantum optics and squeezed light generation have transformed various domains of quantum science and technology. However, real-time quantum dynamics remain an underexplored frontier. Here, we extend quantum optics into the ultrafast regime, providing direct experimental evidence that quantum uncertainty is not a static constraint but evolves dynamically with the system state and interactions. Using ultrafast squeezed light generated via a four-wave mixing nonlinear process, we observe the temporal dynamics of amplitude uncertainty, demonstrating that quantum uncertainty is a controllable and tunable physical quantity. This offers new insights into fundamental quantum mechanics in real-time. Additionally, we demonstrate control over the quantum state of light by switching between amplitude and phase squeezing. Our ability to generate and manipulate ultrafast squeezed light waveforms with attosecond resolution unlocks exciting possibilities for quantum technologies, including petahertz scale secure quantum communication, quantum computing, and ultrafast spectroscopy. We also introduce an ultrafast quantum encryption protocol leveraging squeezed light for secure digital communication at unprecedented speeds. This work paves the way for exploring quantum uncertainty dynamics and establishes the foundation for the emerging field of ultrafast quantum science.

physics.optics↗

arXiv2024

LNoS: Lithium Niobate on Silicon Spatial Light Modulator

Programmable spatiotemporal control of light is crucial for advancements in optical communications, imaging, and quantum technologies. Commercial spatial light modulators (SLMs) typically have megapixel-scale apertures but are limited to ~kHz operational speeds. Developing a device that controls a similar number of spatial modes at high speeds could potentially transform fields such as imaging through scattering media, quantum computing with cold atoms and ions, and high-speed machine vision, but to date remains an open challenge. In this work we introduce and demonstrate a free-form, resonant electro-optic (EO) modulator with megapixel apertures using CMOS integration. The optical layer features a Lithium Niobate (LN) thin-film integrated with a photonic crystal (PhC), yielding a guided mode resonance (GMR) with a Q-factor>1000, a field overlap coefficient ~90% and a 1.6 GHz 3-dB modulation bandwidth (detector limited). To realize a free-form and scalable SLM, we fabricate the PhC via interference lithography and develop a procedure to bond the device to a megapixel CMOS backplane. We identify limitations in existing EO materials and CMOS backplanes that must be overcome to simultaneously achieve megapixel-scale, GHz-rate operation. The `LN on Silicon' (LNoS) architecture we present is a blueprint towards realizing such devices.

physics.optics↗

arXiv2023

Metal-Optic Nanophotonic Modulators in Standard CMOS Technology

Integrating nanophotonics with electronics promises revolutionary applications, from LiDAR to holographic displays. Although silicon photonics is maturing, realizing active nanophotonics in the ubiquitous bulk CMOS processes remains challenging. We introduce a fabless approach to embed active nanophotonics in bulk CMOS by co-designing the back-end-of-line metal layers for optical functionality. Using a 65nm CMOS process, we create plasmonic liquid crystal modulators with switching speeds 100x faster than commercial technologies. This zero-change nanophotonics method could equip mass-produced chips with optical communications, sensing and imaging. Embedding nanophotonics in the dominant electronics platform democratizes nanofabrication, spawning technologies from chip-scale LiDAR to holographic light-field displays.

physics.optics↗

arXiv2023

Measuring gravitational force from Femto-gram source masses

Gravity is the weakest of all known forces. Measuring the force of gravity from micro and nano-scale source masses is an essential first step toward low-energy quantum gravity tests. In addition, measuring gravitational forces where the center-of-mass inter-distance is at the sub-mm scale extends the experimentally achievable parameter space for tests of Yukawa-like corrections to Newtonian gravity and tests for higher dimensions proposed to resolve the hierarchy problem of fundamental forces. Here, we propose an experiment using two optically trapped particles in ultrahigh vacuum conditions where the center of mass inter-distance is on the order of $10^2 nm$. In the proposed experiment, the source mass is a rotating Janus nano-particle such that the test mass (sensor) experiences a periodic gravitational potential. Using realistic experimental parameters, a signal-to-noise ratio $\geq 1$ is obtained for a Janus particle with radius $\geq 10^2 nm$ and a mass $\geq \text{10 } fg$. The proposed experiment extends the search of Yukawa corrections to gravity at $\approx 10^{-5}$ times gravity regime at $10^{2}nm $ interaction range, opens the door to low energy tests for quantum gravity, and enables direct experimental tests of extra-dimensional solutions to the hierarchy problem.

gr-qc↗

arXiv2022

Radiative Cooling with Angular Shields: Mitigating Atmospheric Radiation and Parasitic Heating

Radiative cooling emerged as a possible sustainable solution to the energy hungry vapor compression-based cooling. However, realizing subfreezing temperatures through radiative cooling remains challenging in environments with high humidity and often requires extreme heat management, e.g., by placing the thermal emitter in ultrahigh vacuum conditions. This work theoretically investigates the introduction of angular selective thermal emission through surrounding the emitter with an angular shield. The effect of the spectral selectivity of the emitter, the humidity of the environment, and the introduction of parasitic heating on the cooling performance is studied. The optimal angle for the shield under ideal conditions is shown to be 45°. In addition, spectral selectivity of thermal emission is necessary to obtain noticeable improvement in the minimum equilibrium temperature. In humid environments, angular selectivity through engineering the thermal emissivity function of the emitter provides a better cooling performance compared to angular shields. Conversely, angular shields performance is superior when introducing parasitic heating. Using angular shields enables cooling emitters to subfreezing temperatures without vacuum and under humid levels higher than the global average.

physics.optics↗

arXiv2022

Integrated Metasurface-based Wavelengths Division Demultiplexers

We present a design approach for realizing on-chip wavelength division demultiplexing (WDD) schemes by integrating all-dielectric metasurfaces of TiO2 nanorod arrays into a SiN waveguide. The designed metasurface locally modifies the effective refractive index of the SiN waveguide, creating an effective WDD that selectively passes a certain band of wavelengths into a specific output port. A set of representative 2-channel and 3-channel WDDs schemes were demonstrated for input TE00/TM00 modes and operating in different bands, showing the flexibility of our design approach. The proposed WDD schemes are compatible with visible to infrared wavelengths, photolithography-based fabrication, high efficiency with maximum transmission of 91%, and a small footprint at a few microns. Our design method paves the way for realizing several on-chip integrated devices for applications in optical data processing and biological sensing.

physics.optics↗

arXiv2022

Fano Resonant Optical coatings platform for Full Gamut and High Purity Structural Colors

Structural coloring is a photostable and environmentally friendly coloring approach that harnesses optical interference and nanophotonic resonances to obtain colors with a range of applications including steganography, décor, data storage, and anticounterfeiting measures. We show that optical coatings exhibiting the photonic Fano Resonance is an ideal platform for structural coloring -- it provides full color access, high color purity, high brightness, controlled iridescence, and scalable manufacturability. We show that an additional oxide film deposited on Fano resonant optical coatings (FROCs) increases the color purity (up to 97%) and color gamut coverage range (> 99% coverage of the sRGB and Adobe color spaces). For coloring applications that do not require high spatial resolution, FROCs provide a significant advantage over existing structural coloring schemes.

physics.optics↗

arXiv2019

Generalized Brewster-angle effect in thin-film optical absorbers and its application for graphene hydrogen sensing

Generalized Brewster angle (GBA) is the incidence angle at which polarization by reflection for p- and s-polarized light takes place. Realizing s-polarization Brewster effect requires a material with magnetic response which is challenging at optical frequencies since the magnetic response of materials at these frequencies is extremely weak. Here, we experimentally realize GBA effect in the visible using a thin-film absorber system consisting of a dielectric film on an absorbing substrate. Polarization by reflection is realized for both p- and s- polarized light at different angles of incidence and multiple wavelengths. We provide a theoretical framework for the generalized Brewster effect in thin-film light absorbers. We demonstrate hydrogen gas sensing using a single layer graphene film transferred on a thin-film absorber at the GBA with ~1 fg/mm2 aerial mass sensitivity. The ultrahigh sensitivity stems from the strong phase sensitivity near point of darkness, particularly at the GBA, and the strong light-matter interaction in planar nanocavities. These findings depart from the traditional domain of thin-films as mere interference optical coatings and highlight its many potential applications including gas sensing and biosensing.

physics.optics↗

arXiv2019

Cooperative energy transfer controls the spontaneous emission rate beyond field enhancement limits

Quantum emitters located in proximity to a metal nanostructure individually transfer their energy via near-field excitation of surface plasmons. The energy transfer process increases the spontaneous emission (SE) rate due to plasmon-enhanced local field. Here, we demonstrate significant acceleration of quantum emitter SE rate in a plasmonic nano-cavity due to cooperative energy transfer (CET) from plasmon-correlated emitters. Using an integrated plasmonic nano-cavity, we realize up to six-fold enhancement in the emission rate of emitters coupled to the same nano-cavity on top of the plasmonic enhancement of the local density of states. The radiated power spectrum retains the plasmon resonance central frequency and lineshape, with the peak amplitude proportional to the number of excited emitters indicating that the observed cooperative SE is distinct from super-radiance. Plasmon-assisted CET offers unprecedented control over the SE rate and allows to dynamically control the spontaneous emission rate at room temperature enabling an SE rate based optical modulator.

cond-mat.mes-hall↗