CyberSec Research

We characterize sets of fractional orbital angular momentum (OAM) modes of a light beam using unitary-invariant properties encoded by two-mode overlaps. Using basis-independent coherence and dimension witnesses, we experimentally certify, on a triple of fractional modes, both the presence of coherence and that the states necessarily span a space of dimension 3. We propose and implement a practical, fast experimental method to extract two-mode overlaps requiring only a single intensity image per interference pair. These results lay the groundwork for using fractional OAM states in high-dimensional quantum information protocols.

Photons, unlike electrons, do not couple directly to magnetic fields, yet synthetic gauge fields can impart magnetic-like responses and enable topological transport. Discretized Floquet evolution provides a controlled route, where the time-ordered sequencing of non-commuting Hamiltonians imprints complex hopping phases and breaks time-reversal symmetry. However, stabilizing such driven dynamics and observing unambiguous topological signatures on a reconfigurable platform has remained challenging. Here we demonstrate synthetic gauge fields for light on a programmable photonic processor by implementing discretized Floquet drives that combine static and dynamic phases. This approach reveals hallmark features of topological transport: chiral circulation that reverses under drive inversion, flux-controlled interference with high visibility, and robust directional flow stabilized by maximizing the minimal Floquet quasi-energy gap. The dynamics are further characterized by a first-harmonic phase order parameter, whose per-period winding number quantifies angular drift and reverses sign with the drive order. These results establish discretized, gap-optimized Floquet evolution as a versatile and fully programmable framework for topological photonics, providing a compact route to engineer gauge fields, stabilize driven phases, and probe winding-number signatures of chiral transport.

We report optical evidence of cesium (Cs) evaporation from a bialkali (SbKCs) photo- cathode during controlled heating of a photomultiplier tube (PMT). A DFB laser scanned across the 852.113 nm Cs D2 line reveals absorption features only above 60 degrees Celsius, indicating thermal desorption. The absorption correlates with temperature and offers a non-invasive method to monitor photocathode degradation in sealed detectors.

Modern high-definition display and augmented reality technologies require the development of ultracompact micro- and nano-pixels with colors covering the full gamut and high brightness. In this regard, lasing nano-pixels emitting light in the spectral range 400-700 nm are highly demanded. Despite progress in red, green, and ultraviolet nanolasers, the demonstrated blue-range (400-500 nm) single-particle-based lasers are still not subwavelength yet. Here we fabricate CsPbCl$_3$ cubic-shaped single-crystal nanolasers on a silver substrate by wet chemistry synthesis, producing their size range around 100-500 nm, where the nanoparticle with sizes 0.145$\mu$m$\times$0.195$\mu$m$\times$0.19$\mu$m and volume 0.005 $\mu$m$^3$ (i.e. $\sim\lambda^3$/13) is the smallest nanolaser among the lasers operating in the blue range reported so far, with emission wavelength around $\lambda\approx 415$ nm. Experimental results at a temperature of 80 K and theoretical modeling show that the CsPbCl$_3$ nanolaser is a polaritonic laser where exciton-polaritons are strongly coupled with Mie resonances enhanced by the metallic substrate. As a result, the combination of the strong excitonic response of CsPbCl$_3$ materials, its high crystalline quality, and optimized optical resonant properties resulting in a population-inversion-free lasing regime are the key factors making the proposed nanolaser design superior among previously reported ones in the blue spectral range.

We demonstrate that narrowband multi-cycle terahertz (MC-THz) sources based on periodically-poled lithium niobate (PPLN) wafer stacks can be driven by high repetition-rate, high energy femtosecond ytterbium-doped lasers. Operating at 10-kHz repetition rate with up to 104 W of pump power on a 10-wafer stack, we measure 26.4 mW of THz average power for a narrowband multi-cycle source. We identify and quantify strong lensing effects causing dramatic beam focusing in 47 wafer stacks which act as a primary limitation in the current configuration, and present mitigation strategies for future scaling. This first study of high average power narrowband multi-cycle THz sources offers a path forward to Watt-level high repetition rate sources using thin lithium niobate plates.

Unlocking the full potential of integrated photonics requires versatile, multi-functional devices that can adapt to diverse application demands. However, confronting this challenge with conventional single-function resonators often results in tedious and complex systems. We present an elegant solution: a versatile and reconfigurable dual-polarization Si3N4 microresonator that represents a paradigm shift in on-chip photonic designs. Our device, based on a binary-star orbital architecture, can be dynamically reconfigured into three distinct topologies: a M\"obius-like microcavity, a Fabry-P\'erot resonator, and a microring resonator. This unprecedented functionality is enabled by a tunable balanced Mach-Zehnder interferometer that facilitates controllable mutual mode coupling of counterpropagating lights using a single control knob. We experimentally demonstrate that the device not only supports polarization-diverse operation on a compact footprint but also gives rise to a rich variety of physical phenomena, including a standing wave cavity, a traveling wave cavity, free spectral range multiplication, and the photonic pinning effect. These behaviors are accurately modeled using the Transfer Matrix Method and intuitively explained by Temporal Coupled Mode Theory. Our results underscore the profound potential for a chip-scale platform to realize reconfigurable reconstructive spectrometers and on-chip synthetic dimensions for topological physics.

Two-wavelength adaptive optics (AO) systems sense wavefront errors using a beacon at one wavelength, while correcting for subsequent imaging or beam projection at another. Although most AO systems operate in this manner, the relevant AO literature is generally concerned with quantifying system performance at a single wavelength, effectively ignoring the two-wavelength nature of the problem. In this paper, we study the effects of anisoplanatism, or the physical separation of the beacon and transmit light, on two-wavelength AO systems for imaging and beam projection applications. We derive the piston-removed (PR) and piston-and-tilt-removed (PTR) optical-path-difference (OPD) variances including anisoplanatism, which are key metrics of AO system performance. We compare our closed-form PR and PTR OPD variances to numerical results and discuss their physical significance. In addition, we introduce the two-wavelength isoplanatic angle and show how it can be used to quickly assess two-wavelength AO system performance. At large, the analysis contained in this paper will inform the design and implementation of two-wavelength AO systems for multiple imaging and beam projection applications.

Optical analog computing enables powerful functionalities, including spatial differentiation, image processing, and ultrafast linear operations. Yet, most existing approaches rely on resonant or periodic structures, whose performance is strongly wavelength-dependent, imposing bandwidth limitations and demanding stringent fabrication tolerances. Here, to address some of these challenges, we introduce a highly tunable platform for optical processing, composed of two cascaded uniform slabs exhibiting both circular and linear birefringence, whose response exhibits features relevant to optical processing without relying on resonances. Specifically, using a coupled-wave theory framework we show that sharp reflection minima, referred to as spectral holes, emerge from destructive interference between counter-propagating circularly polarized waves in uniform birefringent slabs, and can be engineered solely through parameter tuning without requiring any spatial periodicity. Unlike traditional Bragg scattering, this mechanism operates without a resonance condition and enables a comparatively broader spectral response through material parameter tuning in spatially uniform media. When operated in the negative refraction regime enabled by giant chirality, the proposed system acts as a polarization-selective Laplacian-like operator, whose functionality is evidenced by an edge-detection proof of concept. The required material parameters align closely with recent experimental demonstrations of giant, tunable chirality via meta-optics, presenting a promising pathway towards compact and reconfigurable platforms for all-optical pattern recognition and image restoration.

As electronic computing approaches its performance limits, photonic accelerators have emerged as promising alternatives. Photonic accelerators exploiting semiconductor-laser synchronization have been studied for decision-making. While conventional cross-correlation methods are computationally intensive and memory demanding, we propose a frequency-based approach using optical frequency differences. Simulations and experiments confirm that this method achieves decision making with reduced cost and memory requirements.

We present a method for determining the azimuthal phase (angle) of a magnetic field by exploiting phase matching of laser beams in a ground-state Hanle effect (GHSE) configuration. This approach is based on the symmetry of the system's Hamiltonian and the existence of a phase-independent frame, allowing for direct determination of the field orientation. As a proof of concept, we performed preliminary experiments using the Fg=1 to Fe=0 transition of the D2 line in 87Rb, with three laser beams to demonstrate the phase (azimuthal) dependence of the observed Hanle resonance signals. While our current setup does not include active phase control, the key features predicted by our method were observed, validating its conceptual foundation. Additionally, we measured two components of the stray magnetic field in our laboratory as an illustration. This method leverages the Hanle effect's inherent sensitivity to both the magnitude and orientation of magnetic fields, as well as the underlying symmetry properties of the atomic system, and offers a pathway for precise, calibration-free determination of magnetic field orientation.

High-harmonic spectroscopy (HHS) in liquids promises real-time access to ultrafast electronic dynamics in the native environment of chemical and biological processes. While electron recollision has been established as the dominant mechanism of high-harmonic generation (HHG) in liquids, resolving the underlying electron dynamics has remained elusive. Here we demonstrate attosecond-resolved measurements of recolliding electron wave packets, extending HHS from neat liquids to aqueous solutions. Using phase-controlled two-colour fields, we observe a linear scaling of the two-colour delay that maximizes even-harmonic emission with photon energy, yielding slopes of 208+/-55 as/eV in ethanol and 124+/-42 as/eV in water, the latter matching ab initio simulations (125+/-48 as/eV). In aqueous salt solutions, we uncover interference minima whose appearance depends on solute type and concentration, arising from destructive interference between solute and solvent emission. By measuring the relative phase of solvent and solute HHG, we retrieve a variation of electron transit time by 113+/-32 as/eV, consistent with our neat-liquid results. These findings establish HHS as a powerful attosecond-resolved probe of electron dynamics in disordered media, opening transformative opportunities for studying ultrafast processes such as energy transfer, charge migration, and proton dynamics in liquids and solutions.

Flat bands, characterized by zero group velocity and strong energy localization, enable interaction-enhanced phenomena across both quantum and classical systems. Existing photonic flat-band implementations were limited to evanescent-wave systems, specific lattice symmetries, or complex supercell modulations. A simple, universal, and efficient approach to realizing flat bands without dedicated source excitation is to be explored. Here, inspired by geometrically frustrated configurations, we theoretically proposed and experimentally demonstrated threefold-degenerate flat bands by integrating orbital and rotational degrees of freedom in a photonic dipolar kagome lattice. By rotating the dipole orientation, the system exhibits a band flip transition at which point all bands achieve complete flatness and degeneracy across the entire Brillouin zone. In contrast to conventional s-orbital kagome lattices with only a single flat band, our approach flattens the entire band structure, eliminating dispersive modes and enabling compatibility with arbitrary excitations. These results establish a new mechanism for flat-band engineering, offering a tunable strategy for enhancing light-matter interactions and may have applications in compact photonic devices and energy-efficient information processing.

Advances in fluorescence microscopy have reached a plateau in improving depth-to-resolution ratios for imaging scattering tissues, highlighting an urgent need for innovative techniques. We introduce Wavelens, a groundbreaking opaque lens that combines dynamic wavefront shaping with a passive, angularly anisotropic photonic scattering plate-designed to scatter light predominantly in one direction. This compact, robust optoelectronic device, comparable in size to a conventional microscope lens, delivers superior light sheet formation capabilities. Using Wavelens, we achieved high-resolution LSFM imaging of diverse biological specimens, including 3D tumor spheroids and the intricate neural architecture of Caenorhabditis elegans in vivo. Notably, Wavelens maintains consistent light sheet properties even in dense, scattering-prone samples, overcoming a long-standing limitation of traditional microscopy. This innovative approach has the potential to revolutionize optical imaging, offering unprecedented clarity and resilience, even within dense, scattering-prone biological samples.

Nonlinear chiral light sources are crucial for emerging applications in chiroptics, including ultrafast spin dynamics and quantum state manipulation. However, achieving precise and dynamic control over nonlinear optical chirality with natural materials and metasurfaces, particularly those based on non-centrosymmetric materials such as lithium niobate (LN), is hindered by the complex tensorial nature of the second-order nonlinear susceptibility. Here, we demonstrate a nonlinear nonlocal metasurface, comprising plasmonic nanoantennas atop an x-cut LN thin film, that enables dynamic and continuous control of second-harmonic (SH) chirality. By leveraging two spectrally detuned resonances arising from the excitation of orthogonally propagating guided modes, enabled by lattice anisotropy and LN birefringence, we achieve full-range tuning of SH chirality, from right- to left-handed circular polarization, simply by rotating the polarization of a linearly polarized pump. The SH chirality, quantified by the Stokes parameter S3, is thereby continuously tuned from 0.991 to -0.993 in simulations and from 0.920 to -0.815 in experiments, while maintaining consistently enhanced SH intensity across the entire tuning range. Our approach opens new avenues for developing compact and tunable chiral sources, with potential applications in integrated nonlinear photonics and adaptable quantum technologies.

Phase retrieval in inline holography is a fundamental yet ill-posed inverse problem due to the nonlinear coupling between amplitude and phase in coherent imaging. We present a novel off-the-shelf solution that leverages a diffusion model trained solely on object amplitude to recover both amplitude and phase from diffraction intensities. Using a predictor-corrector sampling framework with separate likelihood gradients for amplitude and phase, our method enables complex field reconstruction without requiring ground-truth phase data for training. We validate the proposed approach through extensive simulations and experiments, demonstrating robust generalization across diverse object shapes, imaging system configurations, and modalities, including lensless setups. Notably, a diffusion prior trained on simple amplitude data (e.g., polystyrene beads) successfully reconstructs complex biological tissue structures, highlighting the method's adaptability. This framework provides a cost-effective, generalizable solution for nonlinear inverse problems in computational imaging, and establishes a foundation for broader coherent imaging applications beyond holography.

Silicon's indirect bandgap has long been seen as a limitation, fundamentally restricting its ability to emit light and hindering the development of silicon-based light sources. Here, we present a conceptually new solution to this persistent challenge. We demonstrate ultrabroadband photo- and electroluminescence from silicon, enabled by a novel radiative pathway mediated by momentum-expanded Heisenberg photonic states that bypass phonon-assisted transitions. This mechanism, previously demonstrated using metallic nanoparticles as photon confiners, is now realized in an all-silicon material using embedded sub-1.5 nm silicon nanoparticles to create confined photonic states. The results show excellent agreement with prior studies, confirming that the confinement size, rather than the specific confining material, is the main factor for activating radiative transitions in a momentum-forbidden system. Consistent with the photonic momentum expansion concept, both photo- and electro-driven emissions span the visible and near-infrared spectral ranges, with electroluminescence visible to the naked eye even under ambient daylight conditions. The simplicity and material-agnostic nature of this approach promise compatibility with standard fabrication processes, offering a practical and transformative route toward high-performance, all-silicon light-emitting diodes and laser sources. More generally, these findings reveal the emergence of a new hybrid light-matter regime, photonic Heisenberg matter, where extreme photon confinement directly reshapes the electronic transition landscape.

The propagation path of topologically protected states is bound to the interface between regions with different topology, and as such, the functionality of linear photonic devices leveraging these states is fixed during fabrication. Here, we propose a mechanism for dynamic control over a driven dissipative system's local topology, yielding reconfigurable topological interfaces and thus tunable paths for protected routing. We illustrate our approach in non-resonantly pumped polariton lattices, where the nonlinear interaction between the polaritons and the exciton reservoir due to non-resonant pumping can yield a dynamical change of the topology. Moreover, using a continuous model of the polariton system based on a driven-dissipative Gross-Pitaevskii equation alongside the spectral localizer framework, we show that the local changes in the nonlinear non-Hermitian system's topology are captured by a local Chern marker. Looking forward, we anticipate such reconfigurable topological routing will enable the realization of novel classes of topological photonic devices.

Unidirectional emission holds significant potential for advancing integrated photonics and quantum information technologies. However, the inherent randomness of spontaneous emission fundamentally makes its efficient realization rather challenging. To address this, here we develop a quantitative metric -- iso-frequency contour straightness and implement Fourier-transform analysis of radiation patterns to systematically evaluate directional quality of emission in photonic crystal (PhC) slabs. Through structural optimization, we demonstrate single-emitter radiation efficiency enhancement while maintaining low-loss unidirectional propagation. Furthermore, by strategically positioning multi-emitter arrays within PhC platforms, we simultaneously achieve scalable intensity amplification and superradiant emission via cooperative effects. This synergy of photonic band engineering and collective emitter coupling is able to realize unprecedented spatiotemporal coherence control in quantum emitter arrays.