The aim of this paper is coupling of temperature oscillations and melt-pool dynamics experimentally observed in laser melting. The literature survey has shown that the developed explanations are mainly focused on the capillary and hydrodynamic aspects of the problem. As shown, complete analysis is only possible if the temperature oscillations are properly accounted for. Specifically, this effect is a governing mechanism that controls the melt-pool dynamics via feedback coupling of heating, evaporation, capillarity, and free-surface contraction. The present study suggests a physically consistent model validated on the detailed data of the time-resolved absorptance measured in Simonds et al. [Phys. Rev. Appl. 10, 044061 (2018)]. An analytical equation is derived for oscillation spectra within this approach. It has been proved that the surface oscillations can be initiated without the keyhole effect. However, keyhole formation can cause additional modes to appear in the oscillation spectrum. The practical results include the formulas that are convenient for real-time monitoring of the surface temperature and characteristic flow velocity in the molten pool using the measured absorptance spectra. The impact of the temperature coefficient of surface tension on the maximal temperature, pool length, natural frequency of the free-surface oscillations, and attenuation coefficient is thoroughly studied. All results are presented as closed-form formulas suitable for design of industrial laser systems.

The development of test mass with ultralow magnetic susceptibility (χ < ${10}^{-6}{\mathrm{cm}}^3/\mathrm{mol}$) is critical for gravitational-wave detection. Binary $\mathrm{Au}\mathrm{Pt}$ alloys have been identified as promising candidates, though their mechanical, thermal, and electrical properties require further improvement. Introducing a third metal element represents a promising strategy for enhancing their overall performance. In this work, we employ the virtual crystal approximation (VCA) to model ternary $\mathrm{Au}\text{−}\mathrm{Pt}\text{−}\mathrm{Pd}$ alloys and optimize their structures. Using first-principles calculations within the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) framework, we systematically investigate the magnetic susceptibility and its composition dependence in $\mathrm{Au}\text{−}\mathrm{Pt}\text{−}\mathrm{Pd}$ alloys. Our results show that (i) the alloy retains ultralow magnetic susceptibility (χ < ${10}^{-6}{\mathrm{cm}}^3/\mathrm{mol}$) across a wide composition range, notably around 82.0–85.0 at. % $\mathrm{Au}$ and 3.0–5.0 at. % $\mathrm{Pd}$; (ii) the three-dimensional magnetic phase diagram reveals nonlinear hybridization behavior of magnetic susceptibility, with a stable contour of nearly zero susceptibility (χ ≈ 0) near ${\mathrm{Au}}_{82.8}{\mathrm{Pt}}_{14.2}{\mathrm{Pd}}_3$, indicating that $\mathrm{Pd}$ doping can synergistically improve magnetic properties; (iii) this theoretical study elucidates the microscopic mechanisms, electron transfer, and orbital decoupling, underlying the ultralow magnetic susceptibility in multicomponent alloys, and provides quantitative guidance for the design of test masses in next-generation gravitational-wave detectors and related applications, such as medical implant materials.

Tunable coupling architectures consisting of frequency-tunable qubits and couplers are widely employed in superconducting quantum processors. Magnetic flux crosstalk between these components poses a significant challenge to platform scalability, while quantum crosstalk induced by strong qubit-coupler interactions further complicates the compensation of flux crosstalk. To address these issues, we propose and experimentally validate a spin-echo-based method that effectively separates quantum and flux crosstalk, enabling accurate characterization of flux crosstalk. Furthermore, we integrate learning-based algorithm with a high-parallelism measurement scheme to improve efficiency. This approach achieves the stabilization of frequency-shift fluctuations at a noise baseline of approximately 20 kHz, with the accuracy of the crosstalk coefficient reaching an order of ${10}^{-5}$ after compensation. The method provides a robust and efficient framework for mitigating crosstalk, paving the way for high-fidelity control of large-scale quantum processors.

Nitrogen-vacancy (NV) centers in diamond are utilized extensively as quantum sensors for imaging fields at the nanoscale. The ultrahigh sensitivity of NV magnetometers has enabled the detection and spectroscopy of individual electron spins, with potentially far-reaching applications in condensed matter physics, spintronics, and molecular biology. However, the surfaces of these diamond sensors naturally contain electron spins, which create a background signal that can be hard to differentiate from the signal of the target spins. In this study, we develop a surface modification approach that eliminates the unwanted signal of these so-called dark electron spins. Our surface passivation technique, based on coating diamond surfaces with a thin titanium oxide (${\mathrm{Ti}\mathrm{O}}_2$) layer, reduces the dark spin density. The observed reduction in dark spin density aligns with our findings on the electronic structure of the diamond-${\mathrm{Ti}\mathrm{O}}_2$ interface. The reduction, from a typical value of $2000\text{μ}{\mathrm{m}}^{-2}$ to a value below that set by the detection limit of our NV sensors ($200\text{μ}{\mathrm{m}}^{-2}$), results in a twofold increase in Hahn-echo coherence time of near surface NV centers. Furthermore, we derive a comprehensive spin model that connects dark spin relaxation with NV coherence, providing additional insights into the mechanisms behind the observed spin dynamics. Our findings are directly transferable to other quantum platforms, including nanoscale solid-state qubits and superconducting qubits.

In this study, a soft robot driven by optical-magnetic coupling and equipped with real-time self-sensing capability was developed. By integrally combining the carbon-black-grease flexible sensing system with the polydimethylsiloxane magnetically driven body, the robot achieved self-monitoring and feedback of resistance signals during its deformation process under magnetic-field drive for the first time. With the combination of programmed magnetic control via Helmholtz coils and local optical control using photothermally responsive shape memory alloys, the robot is capable of multimodal movement, controllable steering, and object grasping and release. It also demonstrated excellent operational performance in tasks such as obstacle clearance and cargo transportation. This research provides an alternative approach for the “driving-sensing” integrated design of intelligent soft robots.

Three-dimensional (3D) crystals offer a route to scaling up trapped-ion systems for quantum sensing and quantum simulation applications; however, engineering coherent spin-motion couplings and effective spin-spin interactions in large crystals poses technical challenges associated with decoherence and prolonged timescales to generate appreciable entanglement. Here, we explore the possibility of speeding up these interactions in 3D crystals via parametric amplification. For this purpose, we derive a general Hamiltonian for the parametric amplification of spin-motion coupling that is broadly applicable to normal modes with motion transverse to or along the spatial extent of the crystal. Unlike in lower-dimensional crystals, we find that the ability to faithfully (uniformly) amplify the spin-spin interactions in 3D crystals depends on the physical implementation of the spin-motion coupling. We consider the light-shift gate, and the so-called phase-insensitive and phase-sensitive Mølmer-Sørensen (MS) gates, and we find that only the phase-sensitive MS gate can be faithfully amplified in general 3D crystals. We discuss a situation where nonuniform amplification can be advantageous. We also reconsider the effect of counter-rotating terms on parametric amplification and find that they are not as detrimental as previous studies suggest.

Ultrabright, well-collimated MeV bremsstrahlung radiation was generated through the interaction of high-current electron beams produced via direct laser acceleration (DLA) with a high-$Z$ converter. The DLA mechanism was initiated by a 200 TW, subpicosecond PHELIX laser pulse at a moderately relativistic intensity of (1–2) $\times {10}^{19}\mathrm{W}{\mathrm{cm}}^{-2}$, delivering approximately 60 J of energy into preionized, overcritical-density foam targets. The electron spectrum measured along the laser axis exhibited an effective temperature of approximately $30\mathrm{MeV}$ and energies exceeding 100 MeV, with a total charge of about 300 nC for electrons with energies $>1.5\mathrm{MeV}$ (ponderomotive potential), while 100 nC of them is directed along the laser axis within a half-angle cone of ${12}^{\circ }$. The directed fraction of DLA electrons with energies exceeding 7.5 MeV carries a charge of 20 to 30 nC, corresponding to a flux up to $2\times {10}^{24}{\mathrm{sr}}^{-1}{\mathrm{s}}^{-1}$. These high-current relativistic electron beams efficiently generate MeV x-rays, enabling the subsequent production of isotopes, positrons, and neutrons with exceptional yield and application potential. In laser shots employing overcritical-density foam targets placed in front of a high-$Z$ converter, bremsstrahlung photons with energies up to 70 MeV were generated and analyzed via nuclear activation of tantalum and gold. The formation of the isotopes ${}^{174}\mathrm{Ta}$ and ${}^{190}\mathrm{Au}$, whose photonuclear cross-section peaks at approximately 65 MeV, confirmed the presence of high-energy photons. In contrast, no activation was observed in control shots where the laser was directed onto the converter without foam, indicating that high-energy photon generation is intrinsically linked to the DLA process in the preionized foam targets. Autoradiographic measurements revealed a divergence of the bremsstrahlung beam of approximately ${22}^{\circ }$ (half-angle) in the 14–21-MeV range. These diagnostics indicate an unprecedented photon flux of approximately $2\times {10}^{22}{\mathrm{sr}}^{-1}{\mathrm{s}}^{-1}$, corresponding to about ${10}^{11}$ photons per shot with energies exceeding 7.5 MeV. The conversion efficiency of focused laser energy to bremsstrahlung photons is greater than 1% (within the FWHM of x-ray beam and laser beam). More than $2\times {10}^9$ photoneutrons per shot were emitted isotropically, corresponding to a peak flux of $2\times {10}^{20}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ ($4\times {10}^{18}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{J}}^{-1}$ of laser energy on target). This approach demonstrates a robust and scalable method for generating ultraintense MeV photon beams at kilojoule, petawatt-class laser facilities operating at moderate relativistic intensities, with strong implications for high-energy-density physics and nuclear astrophysics research.

With a view to measuring the thermal properties of exfoliated atomically thin materials, we demonstrate simultaneous measurements of the thermal conductivity and specific heat in suspended membranes. We use the $3\omega$ technique applied to quasi-two-dimensional silicon nitride membranes having a metal line heater patterned on the surface to both deliver heat and directly measure the thermal impedance of the membrane at the heating frequency, $Z(2\omega )$. We derive an expression for the complex thermal impedance as a function of frequency, approximating the actual rectangular membranes with a one-dimensional model. The derivation accounts for potential parasitic heat-loss mechanisms, including conduction along the heater line and by the gas load in an imperfect vacuum. Qualitatively, the thermal impedance response resembles a low-pass filter due to the combination of the total thermal resistance and total specific heat. Fitting $Z(2\omega )$ to measurements across a few decades in frequency, we extract values of the thermal conductivity and specific heat of silicon nitride in agreement with literature values. We also study the dependence on the heating current and compare it to measurements of the thermal conductivity at zero frequency.

Noise is a significant challenge in imaging. Conventional intensity-based techniques mitigate noise through various filtering methods, but they often require prior knowledge of noise characteristics and struggle, especially under low-light conditions and with spatially structured noise. Quantum distillation provides enhanced noise rejection; however, its applicability is limited as it requires specialized illumination and substantial modifications to existing imaging setups. In this paper, we introduce a coherence-based image-distillation approach that separates object from noise by leveraging the difference in their temporal coherence properties. We implement this through our interferometric protocol, which enables imaging based on spatial coherence while simultaneously filtering out noise via temporal coherence. This overcomes the limitations of both intensity-based and quantum distillation methods. We experimentally demonstrate noise resilience by successfully recovering feature-rich objects, such as QR codes and grayscale wheels, obscured by spatially uniform and structured noise 20 times as intense as the object. We further show that our method remains effective for fields with substantial spectral overlap, outperforming spectral filtering in regimes where the latter provides little noise suppression. This approach provides a robust framework for noise-resilient imaging with applications in optical communication, fluorescence microscopy, and biological imaging at both high and low light levels.

At cryogenic temperatures and microwave frequencies, the perovskite crystals strontium titanate (STO) and potassium tantalate (KTO) have large, tunable permittivity arising from a quantum paraelectric phase. As such, these materials hold promise as a platform to realize compact, variable capacitance elements for use as three-wave-mixing elements in quantum devices. From modulating this capacitance within a resonant circuit, we propose the development of a quantum “paraelectric nonlinear dielectric amplifier” (PANDA). We calculate that a PANDA made from a nanofabricated parallel plate capacitor and realistic design constraints can demonstrate a three-wave-mixing strength of order MHz, in comparison to an effective Kerr strength of sub-Hz. This suggests excellent performance as a degenerate parametric amplifier, with high compression power in analogy to superconducting parametric amplifiers based on kinetic inductance. Beyond parametric amplifiers, we predict that compact, tunable capacitors based on STO, KTO, and related materials can enable a wide class of cryogenic quantum circuits including alternative filters, switches, circulators, and qubits.

Levitated mechanical oscillators are emerging ultrasensitive sensors with tremendous potential in both applied and fundamental physics. Levitated ferromagnets, with internal spin noises rapidly averaged, promise ultrahigh magnetic sensitivity. Here, we demonstrate a milligram-scale diamagnetically levitated ferromagnet system operating at room temperature. Through optimized geometry and multichannel dissipation control, we achieve a magnetic sensitivity of $23\mathrm{fT}/\sqrt{\mathrm{Hz}}$ at the 100-Hz frequency level. We anticipate that a ferromagnetic magnetometer with subfemtotesla sensitivity is within reach, after modest technical improvements. This platform establishes a high-performance magnetometer for biomagnetic field detection and beyond-standard-model force searches.

Topological defects in two-dimensional (2D) and three-dimensional topological materials can induce exotic phenomena, such as protected localized modes. The introduction of synthetic dimensions further enables the exploration of such effects in higher-dimensional systems. Recent studies reveal that a 2D photonic crystal with 2D synthetic translation space ($\mathrm{\Delta }x,\mathrm{\Delta }y$) supports gapless dislocation modes, protected by the second Chern number of the four-dimensional pseudomomentum space $(k_x,\mathrm{\Delta }x,k_y,\mathrm{\Delta }y)$. However, the complexity of the dislocation lattice and the unclear mode-formation mechanism hinder applications in wave devices. To simplify the structure and clarify the physics, we discretize the lattice into four sectors. So that the sectored dislocation lattice can be viewed as the interface between two one-dimensional (1D) edge systems with edge states. The $(k_y,\mathrm{\Delta }y)$ subspace topology staggers the edge bands of two 1D edge systems, yielding a common edge gap with differing band counts below it, while the $(k_x,\mathrm{\Delta }x)$ subspace topology ensures a first Chern number of $-1$ to each band. Their joint contribution guarantees a gapless dislocation band spanning the common edge gap, protected by the second Chern number. Based on this mechanism, we propose an easy-to-integrate topological wavelength-selective component using sectored translation scheme. This work elucidates the formation mechanism of gapless dislocation modes and expands the design paradigm for topological functional systems in synthetic translation dimensions.

We propose and demonstrate a direct volumetric imaging method based on spatial coherence of light and sequential illumination from pointlike sources distributed along a ring. We prove that when the source geometry restricts illumination to high-angle modes matching the system numerical aperture, linear annular illumination achieves the same lateral resolution and similar axial sectioning as planar full-disk illumination, while offering the advantage of a threefold faster acquisition and an even lighter computational demand. The proposed approach offers a simplified and efficient alternative to conventional light-field and computational imaging, opening new paths for fast, cost-effective, real-time volumetric imaging and three-dimensional microscopy.

Controlling the amplitude, phase, and polarization of electromagnetic waves is essential for multifunctional metasurfaces; however, conventional designs become exponentially more complex as additional functionalities are added. Here, we present a modular approach to a universal, multifunctional polarization controller that combines wavefront, phase, and polarization manipulation. First, we propose a set of chiral enantiomer metasurfaces for polarization conversion, and these are then combined with phase-gradient metasurfaces to construct dual-functional modules. These modules enable simultaneous wavefront shaping and polarization conversion with over 95% efficiency across a 27.6% relative bandwidth from 9.7 to 12.8 GHz. Our experimental results demonstrate that cascading the modules at optimized distances with mechanical rotations achieves broadband control over the wavefront, polarization, and amplitude. This includes linear and circular polarization beam splitters with a conversion efficiency greater than 90% and an axis ratio below 3 dB, neutral-density-filter-like devices with tunable transmittance ranging from 0% to 90%, and arbitrary polarization rotators spanning from $0^{\circ }$ to ${180}^{\circ }$. The architecture enables reconfigurable functionality without active components, relying on Fabry-Pérot interference and spatial arrangement. This work establishes a paradigm for compact electromagnetic systems with applications in beam steering and adaptive optics and paves the way for industrial adoption through simplified fabrication.

This study investigates the optoelectronic properties of n-n isotype ${\mathrm{Ga}}_2{\mathrm{O}}_3/\mathrm{Ga}\mathrm{N}$ heterojunctions, demonstrating their potential as light-activated diodes under ultraviolet (UV) spectra. The heterojunction exhibits type II staggered band alignment with a valence-band offset of 1.56 eV and conduction-band offset of −0.16 eV. Under dark conditions, the heterojunction device acts as a double Schottky diode connected back-to-back with asymmetric I-V characteristics. Under UV illumination (254–365 nm), the device transitions from OFF state to a rectifying state, achieving a rectification ratio exceeding ${10}^3$ with a photo-to-dark-current ratio of ≈1.3 × ${10}^3$. This rectification arises from band offset and interface trap states, enabling unidirectional photocurrent flow dominated by thermionic field emission under forward bias. The device also demonstrates high responsivity and functions effectively as a half-wave rectifier for sinusoidal signals, with minimal power consumption (1.76 nW) in the dark. This isotype ${\mathrm{Ga}}_2{\mathrm{O}}_3/\mathrm{Ga}\mathrm{N}$ heterojunction can offer a promising platform for applications in optical logic, secure communication, crosstalk-free UV imaging, and light-triggered switches, advancing the development of high-performance, optically controlled rectifiers.

Miniaturized, unique, stable, and information-rich tags are crucial for anticounterfeiting efforts in the handling and distribution of consumable goods. Despite ongoing research into various tag technologies, a systematic approach to engineering their physical properties for optimal security is often missing. Through a numerical approach focused on in-depth modeling of the interacting magnetic nanoparticle properties, we demonstrate how their collective magnetic behavior, after suitable field conditioning, boosts the security of magnetic tags. Our miniaturized tag leverages the nonlinear response of assemblies of interacting ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles to store custom information into binary keys. The magnetic properties of the nanoparticles and their spatial correlations result to be crucial to effectively decorrelate all keys from a large batch of tags produced under identical conditions. This ensures each tag encodes unique, virtually unclonable information, guaranteeing secure product identification, traceability, and quality control, enhancing consumer safety and fighting counterfeiting. The tag stability against transient disturbances of thermal and magnetic nature has been assessed. Our numerical analysis establishes magnetic nanoparticle tags as highly promising primitives characterized by high entropic information and security resilience to cloning, paving the way to better-engineered devices that harness the collective magnetic properties of nanoparticles.