Lithium niobate (LN) microring resonators, characterized by an exceptionally high second-order nonlinear coefficient and superior electro-optic tunability, serve as an outstanding platform for the precise control of integrated quantum frequency combs (QFCs). In this study, we introduce a bipartite entanglement criterion to investigate the pairwise entanglement characteristics of QFCs generated via the spontaneous parametric down-conversion (SPDC) process in lithium niobate microring resonators operating below threshold. Furthermore, we propose a universal framework for analyzing multimode squeezing in quadratic frequency combs, enabling the realization of ultrabroadband and high-degree multimode squeezing. We further reveal the underlying physical mechanism: modulation instability (MI), regulated by temporal walk-off control, not only enables the formation of frequency combs but also induces multimode squeezing in the corresponding resonant modes. This study uncovers the previously unexplored role of on-chip multimode squeezing in quadratic frequency combs while facilitating collective noise suppression across multiple modes, thus holding substantial potential for advancing quantum precision measurement and quantum information processing.

Periodic lattice structures offer a universal platform for investigating transport dynamics and topological properties across a broad range of physical systems. Although topological effects have been explored extensively in quantum and classical wave platforms, investigations specifically into thermal lattices are just beginning, where conventional discrete models face intrinsic limitations. Here, we find that long-range coupling naturally arises in thermal diffusion lattices due to the nonlocality of thermal fields, even in the absence of macroscopic long-range pathways. By incorporating linear temperature profiles within each site and coupling rod, we construct an extended tight-binding model that accurately captures both nearest and effective next-nearest-neighbor couplings. Furthermore, controlled tuning of the structural parameters enables the emergence of topological edge states driven by next-nearest-neighbor coupling. This work provides a general framework for accurately modeling thermal diffusion systems and offers a mechanism for designing heat transfer topological effects based on long-range interactions, opening avenues for exploring topological physics in diffusive media.

Demonstrating quantum speedup for approximate optimization of classical spin glasses is of current interest. Such a demonstration must be done with respect to the best-known scaling of classical heuristics at a given optimality gap of a given problem. For cubic-lattice classical Ising spin glasses, recent theoretical and experimental developments open up the possibility of showing quantum speedup for approximate optimization with quantum annealing. It is therefore desirable to understand the optimality-gap range over which such a speedup should be searched for. Here we show that on cubic-lattice tile-planting models, classical metaheuristics that are linear-time by construction can reach optimality gaps at which simulated annealing and parallel tempering exhibit superlinear scaling. This implies that the optimality gaps achieved by linear-time classical metaheuristics can serve as useful upper bounds for the optimality-gap range over which quantum speedups in approximate optimization should be searched for. We also explain how classical heuristics with fixed scaling that is beyond cubic can provide upper bounds to optimality-gap ranges for beyond-quadratic quantum speedups in approximate optimization. These results encourage the development of classical heuristics with fixed scaling that achieve optimality gaps as small as possible.

Hybrid quantum architectures that integrate matter and photonic degrees of freedom present a promising pathway toward scalable fault-tolerant quantum computing. This approach needs to combine well-established entangling operations between distant registers using photonic degrees of freedom with direct interactions between matter qubits within a solid-state register. The high-fidelity control of such a register, however, poses significant challenges. In this work, we address these challenges with pulsed control sequences that modulate all interspin interactions to preserve the nearest-neighbor couplings while eliminating unwanted long-range interactions. We derive pulse sequences, including broadband and selective gates, using composite-pulse and shaped-pulse techniques as well as optimal-control methods. This ensures a general pulse sequence in the presence of spin-position bias, robustness against static offset detunings, and Rabi-frequency fluctuations of the control fields. The control techniques developed here apply well beyond the present setting to a broad range of physical platforms. We demonstrate the efficacy of our methods for the resource-state generation for fusion-based quantum computing in four- and six-spin systems encoded in the electronic ground states of nitrogen-vacancy centers or other molecular solid-state qubits. We also outline other elements of the proposed architecture, highlighting its potential for advancing quantum computing technology.

Vortex wave tunneling through constricted spaces is fundamentally attractive and holds substantial potential for orbital angular momentum applications. However, methods to realize such tunneling remain largely scarce. Here, we introduce a novel approach for achieving acoustic vortex tunneling through subwavelength channels using topological-pair metasurfaces (TPMs). TPMs are engineered to exhibit opposite topological charges, harnessing non-Hermitian coupling to enable complete vortex absorption and subsequent lasing within a subwavelength channel, thereby facilitating perfect vortex tunneling. Crucially, such non-Hermitian TPMs incorporating intrinsic Fabry-Pérot resonances allow this tunneling effect to occur under lossless and remote conditions, which enables vortex tunneling transmission across arbitrary propagation routes. As a proof of concept, we experimentally demonstrate acoustic vortex tunneling transmission along straight, curved, and bifurcating propagation pathways. This work establishes a paradigm for extraordinary tunneling behaviors of complex structured fields and offers a promising platform for precise control of vortex field propagation, with significant implications for high-capacity communications and particle manipulation in practical applications.

Space-time-varying media with moving interfaces unlock new ways to manipulate electromagnetic waves: however, analytical solutions have been limited mostly to interfaces moving at constant velocity or constant proper acceleration. Here we present exact scattering solutions for an arbitrarily accelerating interface, derived directly in the laboratory frame through a suitable change of variables. We show that acceleration introduces rich effects that do not occur with uniform motion, including transitions between multiple velocity regimes, multiple scattering events, and generalized frequency chirping. We also solve the inverse problem of designing an interface trajectory that produces a desired chirping profile, demonstrating how tailored acceleration can synthesize complex frequency modulations. These results provide a fundamental framework to understand and control wave interactions with accelerated boundaries, opening pathways for advanced applications in space-time signal processing and dynamic pulse shaping.

Modern superconducting and semiconducting quantum hardware uses external charge and microwave flux drives to both tune and operate devices. However, each external drive is susceptible to low-frequency (e.g., $1/f$) noise that can drastically reduce the coherence time of the device unless the drive is placed at specific operating points that minimize the sensitivity to fluctuations. We show that operating a qubit in a driven frame using two periodic drives of distinct commensurate frequencies can have advantages over both monochromatically driven frames and static frames with constant offset drives. Employing Floquet theory, we analyze the spectral and lifetime characteristics of a two-level system under weak and strong bichromatic drives, identifying drive-parameter regions with high coherence (“sweet spots”) and highlighting regions where coherence is limited by additional sensitivity to noise at the drive frequencies (“sour spots”). We present analytical expressions for quasienergy gaps and dephasing rates, demonstrating that bichromatic driving can alleviate the trade-off between dc and ac noise robustness observed in monochromatic drives. This approach reveals continuous manifolds of doubly dynamical sweet spots, along which drive parameters can be varied without compromising coherence. Our results motivate further study of bichromatic Floquet engineering as a powerful strategy for maintaining tunability in high-coherence quantum systems.

Superconducting traveling-wave parametric amplifiers (TWPAs) have emerged as highly versatile devices, offering broadband amplification with quantum-limited noise performance. They hold significant potential for addressing the readout bottleneck in prototype quantum computers, enabling scalability. Key challenges with this technology include achieving sufficient gain with minimal gain ripple while maintaining low noise performance. Efficient phase matching between a weak signal and a strong pump over the entire length of the TWPA is critical to overcoming these challenges. We present an experimental demonstration of the inverse Kerr phase-matching technique in a TWPA, first proposed by Bell and Samolov [Phys. Rev. Appl. 4, 024014]. This method addresses several limitations of conventional dispersion engineering approaches of phase matching in the four-wave mixing parametric process in TWPAs, most notably the existence of an unusable region of gain near the pump frequency which typically corresponds to the region of most optimal phase matching and maximum gain. The inverse Kerr phase-matching approach allows for greater frequency separation between the region of optimal gain and pump, in situ tunability of the pump, minimal gain ripple, and a compact footprint which reduces losses. A TWPA employing the inverse Kerr phase-matching technique experimentally demonstrated 20 dB of gain over a 3-GHz instantaneous bandwidth, with a tunable bandwidth of 8 GHz, minimal gain ripple, and near quantum-limited noise performance, with 1.5 photons of added noise.

Strengthening magnetoacoustic coupling is crucial to the improvement of surface acoustic wave (SAW)-driven spintronics devices. A key challenge in enhancing magnetoacoustic coupling is minimizing the phonon dissipation of the SAW device, which usually requires complicated SAW engineering. This paper presents the observation of an order-of-magnitude enhancement of the magnetoacoustic coupling within a $\mathrm{Co}$/$\mathrm{Cu}$/$\mathrm{Ni}$-$\mathrm{Fe}$ multilayer structure deposited on a ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$ piezoelectric substrate. This enhancement is driven by spin current transmission, facilitated by the nonparallel alignment of magnetizations between the $\mathrm{Co}$ layer and the $\mathrm{Ni}$-$\mathrm{Fe}$ layer. This work provides a versatile platform for advancing magnetoacoustic coupling devices based on the principle of spin current, which exhibits potential for next-generation on-chip SAW spintronics devices.

The rising computational demand of modern workloads has renewed interest in energy-efficient paradigms, such as neuromorphic and analog computing. A fundamental operation in these systems is matrix-vector multiplication (MVM), ubiquitous in signal processing and machine learning. Here, we demonstrate MVM using inverse-designed metastructures that exploit heat conduction as the signal carrier. The proposed approach is based on a generalization of effective thermal conductivity to systems with multiple input and output ports: The input signal is encoded as a set of applied temperatures, while the output is represented by the power collected at designated terminals. The metastructures are obtained via density-based topology optimization, enabled by a differentiable thermal transport solver and automatic differentiation, achieving an accuracy greater than $99\mathrm{\%}$ in most cases across a pool of matrices with dimensions $2\times 2$ and $3\times 3$. We apply this methodology—termed thermal analog computing—to realize matrices relevant to practical tasks, including the discrete Fourier transform and convolutional filters. These findings open avenues for analog information processing in thermally active environments, including temperature-gradient sensing in microelectronics and thermal control systems.

We determine the macroscopic features of thermal transport in heterogeneous conductors by generalizing an exact, source-driven homogenization method originally developed for waves. The formulation accommodates random or periodic media of finite or infinite extent, with or without pores. Our homogenization shows that the effective heat flux and entropy are spatiotemporally nonlocal functions of both the effective temperature and its gradient, and that the emergent bianisotropic cross-couplings form an adjoint pair when the microscopic relations are self-adjoint. A spatially local approximation highlights how the homogenized diffusion equation can become hyperbolic due to temporal nonlocality, and that the medium’s thermal impedance can become direction dependent, as captured by the bianisotropic terms. In addition, we develop a retrieval method for one-dimensional deterministic composites, whose results reinforce our conclusions.

Despite the success of n-type transparent conducting oxides (TCOs), there is a notable scarcity of new p-type TCOs and transparent conducting materials (TCMs) in optoelectronics. We utilized 10 333 Heyd-Scuseria-Ernzerh (HSE) band gap data points for transfer learning to enhance the Perdew-Burke-Ernzerhof (PBE) band gap model, resulting in a reliable HSE model that aligns closely with 640 calculated values. We screened 518 materials with band gaps of 3.0 eV to 4.3 eV from 5276 compounds in the Materials Project, identifying two potential p-type (nine potential n-type) transparent conductors via high-throughput density functional theory. For n-type TCMs, cations of ${\mathrm{Al}\mathrm{Sb}\mathrm{O}}_4$, ${\mathrm{Ca}\mathrm{In}}_2{\mathrm{O}}_4$, ${\mathrm{Mg}}_2{\mathrm{Sn}\mathrm{O}}_4$, ${\mathrm{In}}_2{\mathrm{Ge}}_2{\mathrm{O}}_7$, and ${\mathrm{Mg}\mathrm{Ge}\mathrm{N}}_2$ possess a closed-shell electronic ${\mathit{\text{ns}}}^0$ configuration, with a forbidden dipole transition between the valence band maximum (VBM) and the conduction band minimum (CBM). Furthermore, p-type TCMs ${\mathrm{KGe}\mathrm{Cl}}_3$ and ${\mathrm{Rb}\mathrm{Sn}\mathrm{Cl}}_3$ feature anions with delocalized p orbitals that hybridize with cations’ $(n-1)d^{10}n{s}^2$ configurations, leading to a low hole effective mass. Moreover, ${\mathrm{Rb}\mathrm{Sn}\mathrm{Cl}}_3$ was identified as a potential p-type material based on intrinsic point defect properties analyzed using the HSE06 hybrid functional. This work expands the database of inorganic transparent conductors, necessitating further validation.

We show that the Purcell effect can lead to a substantial enhancement in the maximum cooling power for solid-state laser cooling. We numerically demonstrate such enhancement in a patterned slot-waveguide structure using ytterbium-doped silica as the active material. The enhancement arises primarily from the increase of saturation power density and the escape efficiency, and can persist in spite of the presence of parasitic absorption in the structure surrounding the active material. Our results point to an opportunity in photonic structure design for optical refrigeration.

Superconducting resonators with high kinetic inductance play a central role in hybrid quantum circuits, enabling strong coupling to systems with small electric dipole moment and providing the nonlinear response required for parametric amplification. However, simultaneously achieving these resonators with high internal quality factors ($Q_i$) and resilience to strong magnetic fields remains challenging. In this work, we present a systematic and quantitative comparison between niobium nitride ($\mathrm{Nb}\mathrm{N}$) and granular aluminum (grAl) nanowire resonators, two widely used high-kinetic-inductance superconductors that offer complementary properties in terms of magnetic robustness and intrinsic nonlinearity. The devices are fabricated to exhibit comparable sheet kinetic inductance ($L_k\sim 100$ pH/sq), to allow a direct assessment of material-dependent behavior under identical experimental conditions. At zero magnetic field, grAl resonators display higher $Q_i$ compared with their $\mathrm{Nb}\mathrm{N}$ counterparts, whereas under applied magnetic fields, $\mathrm{Nb}\mathrm{N}$ resonators demonstrate significantly better resilience, maintaining $Q_i>{10}^4$ up to several tesla. A nonmonotonic enhancement of $Q_i$ in $\mathrm{Nb}\mathrm{N}$ near 1 T is observed, providing new insight into dissipation mechanisms in disordered superconductors. In contrast, grAl resonators show monotonic $Q_i$ evolution and a distinct critical field above which $Q_i$ rapidly decreases. Characterization of nonlinear properties at zero magnetic field reveals that the self-Kerr coefficient in grAl is more than an order of magnitude higher than in $\mathrm{Nb}\mathrm{N}$, making grAl particularly attractive for applications requiring pronounced nonlinear interactions. This comparative study clarifies how microscopic disorder and superconducting energy scales influence field resilience and nonlinearity in high-$L_k$ materials providing practical guidelines for designing magnetic-field compatible, high-impedance resonators for hybrid quantum circuits.

This study investigates the enhancement of near-infrared (NIR) absorption in MXenes using a multiscale modeling approach that integrates density functional theory calculations and finite-difference time domain (FDTD) simulations for obtaining full-wave electromagnetic solutions. We performed a comprehensive investigation of the MXene material architectures, leading to the design of patterned structures with a significantly enhanced absorptivity across the 1–3 µm range, particularly for ${\mathrm{O}}_2$-terminated MXenes. The findings reveal that pyramidal and stacked cubic patterns significantly improve electric field confinement by creating localized resonant modes and side modes along the edges and base of the structures. The detailed understanding of these geometric resonances provides a pathway for designing MXene-based devices optimized for applications such as thermal emitters, infrared sensors, and wavelength-selective absorbers.

Acoustic metamaterials and active noise control (ANC) are two advanced noise-control treatments that can typically offer performance that exceeds that of conventional passive noise-control treatments. Acoustic metamaterials utilize subwavelength structures to realize sound-field control, while active noise-control treatments achieve control via the introduction of additional acoustic sources driven to generate a secondary sound field that interferes in a controlled way with the original primary sound field. This paper presents an investigation into combining these two noise-control techniques to achieve enhanced noise control over a spatial region using a “hybrid” device. In particular, conventional feedforward ANC is combined with a labyrinthine metasurface and the increase in performance offered by the hybrid solution is demonstrated.

Colloidal microrobots actuated by external stimuli often exhibit complex locomotion that is reminiscent of biological microswimmers. We investigate the electrophoretic transport of metallodielectric Janus microspheres functionalized with a UV-responsive photoactive dendrimer suspended in a nematic liquid crystal. By synergistically combining ultraviolet (UV) illumination and electric-field actuation, we achieve dynamic control of particle motion. The UV-induced conformational changes in the dendrimer trigger particle rotation and reversible transformations of associated topological defects, alternating between boojum and Saturn-ring configurations during cyclic UV exposure. This defect switching mediates transitions between pusher and puller swimming modes, resulting in abrupt changes in particle’s trajectories. These photoactive Janus microrobots demonstrate enhanced motional versatility and stochastic dynamics, including run-and-tumble-like behaviors that mimic adaptive navigation strategies found in living microorganisms. Our findings highlight the promise of multi-stimuli-responsive colloidal microrobots for microscale transport and studies of active matter in anisotropic soft environments.