CyberSec Research

We demonstrate a novel concept for measuring time-varying electric field transients of petahertz-scale photons down to a single-photon regime. We observe a clear transition from classical to quantum nature of light that agrees with our Monte Carlo model. We reach unprecedented yoctojoule-level sensitivity and a dynamic range exceeding 90 decibels. We utilize this capability to measure time-dependent intrapulse light coherence - a regime inaccessible to conventional, time-averaged spectroscopy. This opens new avenues for quantum information, cryptography, and quantum light-matter interactions on sub-cycle time scales with attosecond precision.

Interpretation of time-resolved spectroscopies such as transient absorption (TA) or two-dimensional (2D) spectroscopy often relies on the perturbative description of light-matter interaction. In many cases the third order of nonlinear response is the leading and desired term. When pulse amplitudes are high, higher orders of light-matter interaction can both distort lineshapes and dynamics and provide valuable information. Here, we present a general procedure to separately measure the nonlinear response orders in both TA and 2D spectroscopies, using linear combinations of intensity-dependent spectra. We analyze the residual contamination and random errors and show how to choose optimal intensities to minimize the total error in the extracted orders. For an experimental demonstration, we separate the nonlinear orders in the 2D electronic spectroscopy of squaraine polymers up to 11$^{th}$ order.

Localized surface plasmons can confine light within a deep-subwavelength volume comparable to the scale of atoms and molecules, enabling ultrasensitive responses to near-field variations. On the other hand, this extreme localization also inevitably amplifies the unwanted noise from the response of local morphological imperfections, leading to complex spectral variations and reduced consistency across the plasmonic nanostructures. Seeking uniform optical responses has therefore long been a sought-after goal in nanoplasmonics. However, conventional probing techniques by dark-field (DF) confocal microscopy, such as image analysis or spectral measurements, can be inaccurate and time-consuming, respectively. Here, we introduce SPARX, a deep-learning-powered paradigm that surpasses conventional imaging and spectroscopic capabilities. In particular, SPARX can batch-predict broadband DF spectra (e.g., 500-1000 nm) of numerous nanoparticles simultaneously from an information-limited RGB image (i.e., below 700 nm). It achieves this extrapolative inference beyond the camera's capture capabilities by learning the underlying physical relationships among multiple orders of optical resonances. The spectral predictions only take milliseconds, achieving a speedup of three to four orders of magnitude compared to traditional spectral acquisition, which may take from hours to days. As a proof-of-principle demonstration for screening identical resonances, the selection accuracy achieved by SPARX is comparable to that of conventional spectroscopy techniques. This breakthrough paves the way for consistent plasmonic applications and next-generation microscopies.

Exceptional points at which eigenvalues and eigenvectors of non-Hermitian matrices coalesce are ubiquitous in the description of a wide range of platforms from photonic or mechanical metamaterials to open quantum systems. Here, we introduce a class of Hopf exceptional points (HEPs) that are protected by the Hopf invariants (including the higher-dimensional generalizations) and which exhibit phenomenology sharply distinct from conventional exceptional points. Saliently, owing to their $\mathbb{Z}_2$ topological invariant related to the Witten anomaly, three-fold HEPs and symmetry-protected five-fold HEPs act as their own ``antiparticles". Furthermore, based on higher homotopy groups of spheres, we predict the existence of multifold HEPs and symmetry-protected HEPs with non-Hermitian topology captured by a range of finite groups (such as $\mathbb{Z}_3$, $\mathbb{Z}_{12}$, or $\mathbb{Z}_{24}$) beyond the periodic table of Bernard-LeClair symmetry classes.

Shallow water waves are a striking example of nonlinear hydrodynamics, giving rise to phenomena such as tsunamis and undular waves. These dynamics are typically studied in hundreds-of-meter-long wave flumes. Here, we demonstrate a chip-scale, quantum-enabled wave flume. The wave flume exploits nanometer-thick superfluid helium films and optomechanical interactions to achieve nonlinearities surpassing those of extreme terrestrial flows. Measurements reveal wave steepening, shock fronts, and soliton fission -- nonlinear behaviors long predicted in superfluid helium but never previously directly observed. Our approach enables lithography-defined wave flume geometries, optomechanical control of hydrodynamic properties, and orders of magnitude faster measurements than terrestrial flumes. Together, this opens a new frontier in hydrodynamics, combining quantum fluids and nanophotonics to explore complex wave dynamics at microscale.

Arrayed Waveguide Gratings (AWGs) are widely used photonic components for splitting and combining different wavelengths of light. They play a key role in wavelength division multiplexing (WDM) systems by enabling efficient routing of multiple data channels over a single optical fiber and as a building block for various optical signal processing, computing, imaging, and spectroscopic applications. Recently, there has been growing interest in integrating AWGs in ferroelectric material platforms, as the platform simultaneously provide efficient electro-optic modulation capability and thus hold the promise for fully integrated WDM transmitters. To date, several demonstrations have been made in the X-cut thin-film lithium niobate ($\mathrm{LiNbO}_3$) platform, yet, the large anisotropy of $\mathrm{LiNbO}_3$ complicates the design and degrades the performance of the AWGs. To address this limitation, we use the recently developed photonic integrated circuits (PICs) based on thin-film lithium tantalate ($\mathrm{LiTaO}_3$), a material with a similar Pockels coefficient as $\mathrm{LiNbO}_3$ but significantly reduced optical anisotropy, as an alternative viable platform. In this work, we manufacture $\mathrm{LiTaO}_3$ AWGs using deep ultraviolet lithography on a wafer-scale. The fabricated AWGs feature a channel spacing of 100 GHz, an insertion loss of < 4 dB and crosstalk of < -14 dB. In addition, we demonstrate a cyclic AWG, as well as a multiplexing and demultiplexing AWG pair for the first time on $\mathrm{LiTaO}_3$ platform. The wafer-scale fabrication of these AWGs not only ensures uniformity and reproducibility, but also paves the way for realizing volume-manufactured integrated WDM transmitters in ferroelectric photonic integrated platforms.

Much experimental evidence reveals that Coulomb explosion governs non-thermal material removal under femtosecond or even shorter laser pulses, and non-thermal laser damage has been a topic widely discussed. Nevertheless, there is still no continuum mechanical model capable of describing the evolution of such damage. In this study, we develop a model that characterizes solid damage through a phase field variable governed by Allen-Cahn dynamics. The parameter of the model is defined by a conceptual mechanism: during Coulomb explosion, electron pressure surpasses the interatomic barrier potential, dissociates material from the solid surface as small equivalent particles and resulting in localized damage. The numerical simulation validates the model's availability and demonstrate its ability to predict damage morphology under varying laser conditions. This work advances the understanding of non-thermal ablation and provides a tool for optimizing ultrafast laser processing.

We propose a straightforward mechanism for achieving unique $k$-space resonance modes in one-dimensional time-varying cavities where periodic temporal modulation creates momentum band gaps through Floquet dynamics. By engineering the synergy between cavity resonance conditions and Floquet mode formation in photonic time crystals, we demonstrate the emergence of a single dominant momentum state that exhibits remarkable robustness against temporal disorder. Through analytical modeling and numerical verification, we show that the interplay between time-varying medium and cavity boundary conditions leads to amplification of specific waves followed by spatial mode selection. This engineered resonance mechanism enables insensitivity to initial wave source configuration and strong temporal disorder immunity. Our findings give a simple mechanism for exploiting narrow momentum bandgaps, and establish a foundation for developing high-quality temporal cavity lasers and advancing extreme temporal predictability in time-modulated systems.

The ultimate feature size is key in ultrafast laser material processing. A capacity to signiicantly exceed optical limits and to structure below 100nm is essential to advance ultrafast processing into the field of metamaterials. Such achievement requires to combine the control of optical near-fields and of material reactions, while preserving the exibility of long working distances, compatible with a mature laser process. Using sub-ps and ps non-diffractive Bessel beams, we demonstrate unprecedented feature sizes below a hundredth of the incident 1$\mu$m wavelength over an extended focus depth of tens of $\mu$m. Record features sizes, down to 7nm, result from self-generated near-field light components initiated by cavities induced by far-field radiation in a back-surface illumination geometry. This sustains the generation of more confined near-field evanescent components along the laser scan with nm pitch, perpendicular to the incident field direction, driving by local thermal ablation a super-resolved laser structuring process. The near-field pattern is replicated with high robustness, advancing towards a 10nm nanoscribing tool with a $\mu$m-sized laser pen. The process is controllable by the field orientation. The non-diffractive irradiation develops evanescent fields over the focusing length, resulting in a high aspect ratio trenching with nm section and $\mu$m depth. Higher energy doses trigger the self-organization of quasi-periodic patterns seeded by spatially modulated scattering, similarly to optical modelocking. A predictive multipulse simulation method validates the far-field-induced near-field electromagnetic scenario of void nanochannel growth and replication, indicating the processing range and resolution on the surface and in the depth.

A remarkable phenomenon of superoscillations implies that electromagnetic waves can locally oscillate in space or time faster than the fastest spatial and temporal Fourier component of the entire function. This phenomenon allows to focus light into an arbitrary small hotspot enabling superresolution imaging and optical metrology with accuracy far beyond the Abbey-Reileigh diffraction limit. Here we show that, in band-limited supertoroidal light pulses, the temporal and spatial superoscillations can be observed simultaneously at a specific region in space and at a specific interval in time.

Anderson transition in quasiperiodic potentials and the associated mobility edges have been a central focus in quantum simulation across multidisciplinary physical platforms. While these transitions have been experimentally observed in ultracold atoms, acoustic systems, optical waveguides, and superconducting junctions, their interplay between quasiperiodic potential and long-range hopping remains unexplored experimentally. In this work, we report the observation of localization-delocalization transition induced by the hopping between the next-nearest neighboring sites using quasiperiodic photonic waveguides. Our findings demonstrate that increasing the next-nearest hopping strength induces a reentrant phase transition, where the system transitions from an initially extended phase into a localized phase before eventually returning to an extended phase. This remarkable interplay between hopping and quasiperiodic potential in the lattice models provides crucial insights into the mechanism of Anderson transition. Furthermore, our numerical simulation reveals that this phase transition exhibits a critical exponent of $\nu \simeq 1/3$, which is experimentally observable for system sizes $L\sim10^3$ - $10^4$. These results establish a framework for direct observation of the Anderson transition and precise determination of its critical exponents, which can significantly advance our understanding of localization physics in quasiperiodic systems.

The single-band high-efficiency light absorption of nanostructures finds extensive applications in var ious fields such as photothermal conversion, optical sensing, and biomedicine. In this paper, a vertically stacked nanohybrid structure is designed with aluminum arsenide (AlAs), indium tin ox ide (ITO) and gallium arsenide (GaAs) stacked, and the photon absorption characteristics of this structure under near-infrared light at a single wavelength of 1240 nm are exploredbased on the finite difference time domain (FDTD) method. When AlAs, ITO, and GaAs are stacked and incident light enters from the GaAs side, a local light enhancement phenomenon occurs. The absorption rate can reach 91.67%, and the temperature change rate reaches 55. 53%, allowing for a wide-range regulation the absorption rate by temperature. In addition, the AlAs/ITO/GaAs sandwich-type hybrid structure also exhibits obvious nonreciprocity. With the change in temperature, the absorption rate of different structural sizes varies differently. The structure can be optimized and designed according to the requirements, providing new ideas for the design of multifunctional optoelectronic devices.

A crucial component of photonic quantum information processing platforms is the ability to modulate, route, convert, and switch quantum states of light noiselessly with low insertion loss. For instance, a high-speed, low-loss optical switch is crucial for scaling quantum photonic systems that rely on measurement-based feed-forward approaches. Here, we demonstrate ultrafast all-optical switching of heralded photon-number states using the optical Kerr effect in a single-mode fiber. A local birefringence is created by a high-intensity pump pulse at a center wavelength of 1030nm that temporally overlaps with the 1550nm photon-number states in the fiber. By taking advantage of the dispersion profile of commercially available single-mode fibers, we achieve all-optical switching of photon-number states, with up to 6 photons, with a switching resolution of 2.3ps. A switching efficiency of >99% is reached with a signal-to-noise ratio of 32,000.

We investigate the long-time dynamics of the Sine-Gordon (SG) model under a class of perturbations whose quantum field theoretic analog - via bosonization - corresponds to the massive Schwinger model describing 1+1D relativistic QED of Dirac fermions. Classical SG solutions offer critical insight into non-perturbative effects in this quantum theory, but capturing their long-time behavior poses significant numerical challenges. To address this, we extend a coarse-graining method to spacetime using a dual-mesh construction based on the Minkowski-metric. We first validate the approach against the well-studied variant of the SG model describing magnetic fluxon dynamics in Josephson transmission lines (JTLs), where analytical and numerical benchmarks exist. We then apply the method to the Schwinger-inspired SG model and uncover long-lived bound states - "Schwinger atoms" - in which a soliton is trapped by a fixed central charge. In certain regimes, the system exhibits limit cycles that give rise to positronium-like states of oppositely charged solitons, while in others such formation is suppressed. Accessing such long-time solutions requires a rigorous implementation of outgoing boundary conditions on a finite computational domain that provide radiative dissipation to allow relaxation toward states that exist only in an infinite domain. Here we provide such a construction. Our results also suggest the possibility of analog quantum simulation of relativistic quantum field theories with JTLs. These results demonstrate the utility of spatio-temporal coarse-graining methodology for probing non-perturbative structure formation in non-linear field theories.

Extreme ultraviolet (EUV) scatterometry is an increasingly important metrology that can measure critical parameters of periodic nanostructured materials in a fast, accurate, and repeatable manner and with high sensitivity to nanoscale structure and material composition. Because of this, EUV scatterometry could support manufacturing of semiconductor devices or polymer metamaterials, addressing the limitations of traditional imaging methods such as resolution and field of view, sample damage, throughput, or low sensitivity. Here we use EUV scatterometry to measure the profile of an industrially relevant 2D periodic interconnect structure, using $\lambda = 29$ nm light from a table-top high harmonic generation source. We show that EUV scatterometry is sensitive to out-of-plane features with single-nanometer sensitivity. Furthermore, we also apply a methodology based on the Fisher information matrix to optimize experimental design parameters, such as incidence angles and wavelength, to show how measurement sensitivity can be maximized. This methodology reveals the strong dependence of measurement sensitivity on both incidence angle and wavelength $-$ even in a simple two-parameter case. Through a simultaneous optimization of incidence angles and wavelength, we determine that the most sensitive measurement of the quantities of interest can be made at a wavelength of $\sim$14 nm. In the future, by reducing sample contamination due to sample preparation, deep sub-nanometer sensitivity to axial profiles and 2D structures will be possible. Our results are an important step in guiding EUV scatterometry towards increased accuracy and throughput with a priori computations and by leveraging new experimental capabilities.

We demonstrate structured illumination super-resolution imaging in the Terahertz (THz) frequency band using the Virtually Structured Detection (VSD) method. Leveraging our previously reported high-speed, high-sensitivity atomic-based THz imager, we achieve a resolution enhancement of 74(3)% at 0.55 THz, without the aid of deconvolution methods. We show a high-speed THz imaging system is compatible with the use of advanced optical techniques, with potential disruptive effects on applications requiring both high speed and high spatial resolution imaging in the THz range.

The generation of intense, waveform-controlled, single-cycle pulses based on Yb:KGW amplifiers is central to integrating these lasers with attosecond metrology and spectroscopy. Here, we demonstrate single-stage, multi-octave (~ 2.4 octaves) spectral broadening of Yb:KGW amplified pulses in a neon-pressurized hollow-core fiber (HCF) capillary and their compression to the single-cycle regime (1.1 cycles at 880 nm) using chirped mirrors. Utilizing Homochromatic Attosecond Streaking (HAS), we characterize the field waveforms of the generated pulses and demonstrate precise control of their carrier-envelope phase. Our results provide a simplified route to single-cycle pulse generation using Yb:KGW technology, previously possible only with Ti:Sapphire-based front ends. This work paves the way for advanced applications in attosecond science, strong-field physics, and spectroscopy.

Non-orientable manifolds, such as the M\"obius strip and the Klein bottle, defy conventional geometric intuition through their twisted boundary conditions. As a result, topological defects on non-orientable manifolds give rise to novel physical phenomena. We study the adiabatic transport of exceptional points (EPs) along non-orientable closed loops and uncover distinct topological responses arising from the lack of global orientation. Notably, we demonstrate that the cyclic permutation of eigenstates across an EP depends sensitively on the loop orientation, yielding inequivalent braid representations for clockwise and counterclockwise encirclement; this is a feature unique to non-orientable geometries. Orientation-dependent geometric quantities, such as the winding number, cannot be consistently defined due to the absence of a global orientation. However, when a boundary is introduced, such quantities become well defined within the local interior, even though the global manifold remains non-orientable. We further demonstrate the adiabatic evolution of EPs and the emergence of orientation-sensitive observables in a Klein Brillouin zone, described by an effective non-Hermitian Hamiltonian that preserves momentum-space glide symmetry. Finally, we numerically implement these ideas in a microdisk cavity with embedded scatterers using synthetic momenta.