Optical and acoustic communications based on orbital angular momentum (OAM) offer an additional degree of freedom for enhancing information capacity, yet practical implementations of broadband space-time-frequency division multiplexing (STFDM) remain challenging due to system complexity and limited tunability, particularly at low frequencies. Here, we demonstrate a compact and efficient method for broadband STFDM using acoustic rotating point sources (ARPS). We show that a single ARPS can generate multiple high-purity OAM modes with tunable topological charges, whose frequencies are intrinsically linked to the rotational Doppler effect. This mechanism enables simultaneous space, time, and frequency multiplexing within a single transmission path, while significantly reducing the number of required transmitters compared with conventional active array-based approaches. Of note, the proposed method operates continuously from low to high frequencies, extending broadband STFDM to low-frequency acoustic regimes that are particularly relevant for underwater communication. Moreover, we experimentally reveal, for the first time, the coherence properties of multiple acoustic OAM modes with identical topological charges and exploit this property to enhance the stability of high-order modes and mitigate mode crosstalk in OAM-based communication. This work provides a compact and versatile approach for OAM-based acoustic communication, paving the way for future high-capacity multiplexing systems.

Accurate characterization of nonlinear photonic integrated circuits is fundamentally limited by the inability of linear transmission measurements to distinguish input and output on/off-coupling efficiencies, which enter only through their product. We show that this degeneracy arises from an inherent input-output symmetry of linear optics and can be broken by exploiting the directional asymmetry of nonlinear processes. We introduce bidirectional nonlinear optical tomography (BNOT), which combines forward and backward pumping of complementary nonlinear interactions to uniquely infer individual on/off-coupling efficiencies from off-chip measurements. By jointly modeling the nonlinear response and detection statistics, BNOT enables unbiased reconstruction of on-chip nonlinear figures of merit with significantly reduced uncertainty, whereas conventional calibration yields systematically biased estimates. Monte Carlo simulations demonstrate reliable convergence of the inferred efficiencies across realistic noise and fluctuation regimes. Our results establish nonlinear directionality as a general symmetry-breaking resource for coupling-resolved characterization in integrated photonics, with immediate implications for scalable quantum light sources, frequency conversion, and precision optical metrology.

Thermoelectric efficiency benefits from suppressing lattice thermal conductivity (${\kappa }_l$), yet the microscopic origin of the glasslike ultralow ${\kappa }_l$ in ${\text{AgSbTe}}_2$ remains debated. Here we combine first-principles simulation of anharmonic lattice dynamics with the unified theory of thermal transport to quantify how Ag-Sb cation disorder controls heat conduction. We find that compared with cation-ordered $\mathrm{L}{1}_1$ and D4 phases, disordered structures exhibit a strongly reduced ${\kappa }_l$ across a wide temperature range [approximately equal to $0.48\text{W}/(\mathrm{m}\mathrm{K})$ at 300 K] and a much weaker temperature dependence ($\propto T^{-0.40}$). Our detailed analysis of the phonon spectrum and mode-resolved transport properties reveals that cation disorder disrupts the Te-centered octahedral network, softens phonons, lowers group velocities, and enhances low-frequency scattering, thus dramatically suppressing the diagonal (particlelike) contribution [approximately equal to $0.07\mathrm{W}/(\mathrm{m}\mathrm{K})$] while making the off-diagonal (wavelike) term dominant. Moreover, we performed a statistical analysis of ${\kappa }_l$ of 434 dynamically stable cation-disordered configurations, which reveals a robust positive correlation between ${\kappa }_l$ and the average frequency of acoustic modes. In addition, acoustic softening further correlates with increased Ag and Te participation and reduced participation ratios, indicating disorder-induced localization of heat-carrying modes. These results identify cation-disorder-driven localization and low-frequency scattering as key to the phonon-glass behavior of ${\text{AgSbTe}}_2$, and suggest disorder engineering as a route to tune ${\kappa }_l$ in multication thermoelectrics.

We present a variational quantum algorithm that solves the one-dimensional diffusion problem with a space-dependent diffusion constant $D(x)$. This problem is relevant for the exchange of hydroxide ion across a two-layer membrane in an alkaline electrolyzer, where the concentration of ${\text{OH}}^{-}$ ion determines the chemical stability for longer time periods. We use 16 to 64 grid points across the membrane, resulting from $n=4$ to 6 data qubits for the ideal statevector and shot-based quantum simulations implemented using Qiskit. For these qubit numbers, the depth of the parametric quantum circuit has been chosen to ensure sufficient expressibility. The state preparation requires particular attention since the diffusivity $D$ is piecewise constant in the different layers with discontinuities at the interface. Furthermore, we compare different classical optimization schemes with respect to their convergence in the variational quantum algorithms (VQA) method. We demonstrate the applicability of the quantum algorithm to a problem with nontrivial boundary conditions and jump conditions of the diffusion constant and outline possible extensions of the proof-of-concept application case of quantum computing. Our simulations show that pronounced hydroxide-ion concentration gradients, and thus chemical instabilities, can occur only when the ratio of diffusivity in both layers of the membrane exceeds approximately 50.

We present an approach to the molecular beam epitaxy of high-$Q$ planar GaAs-based microcavities in which the AlGaAs high-index layers of the distributed Bragg reflectors are replaced by short-period GaAs/AlAs superlattices (digital alloys) engineered to provide the same effective Al content. This design enables a significant reduction of interface roughness, precise control of both the $\lambda /4$ optical thickness and the effective Al content, suppression of the propagation of certain structural defects, and efficient tuning of the intrinsic absorption at the polariton emission wavelength through optimization of the superlattice parameters. Using this approach, we have grown a microcavity with a low polariton lasing threshold of $P_{\mathrm{th}}\approx 570\pm 90\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$ and a high experimental quality factor of $Q_{\mathrm{expt}}\approx (5.4\pm 0.1)\times {10}^4$. This value exceeds by a factor of 2 the theoretical estimate obtained within a model in which the digital alloy is replaced by a ternary AlGaAs alloy with the same effective Al content. We demonstrate that accurate modeling of the stop-band characteristics and the $Q$ factor requires incorporation of the modified electronic density of states in the superlattice, including quantum-confinement and excitonic effects.

We present a gradient-based method to construct memory-efficient, high-fidelity, single-qubit gates for fluxonium qubits. These gates are constructed using a sequence of single-flux quantum (SFQ) pulses that are sent to the qubit through either capacitive or inductive coupling. The schedule of SFQ pulses is constructed with an on-ramp and an off-ramp applied prior to and after a pulse train, where the pulses are spaced at intervals equal to the qubit period. We reduce the optimization problem to the scheduling of a fixed number of SFQ pulses in the on-ramp and solve it by relaxing the discretization constraint of the SFQ clock as an intermediate step, allowing the use of the Broyden-Fletcher-Goldfarb-Shanno optimizer. Using this approach, gate fidelities of 99.99% can be achieved for inductive coupling and 99.9% for capacitive coupling, with leakage being the main source of coherent errors for both approaches.

The microscopic coexistence of ferroelectricity and ferromagnetism in solids remains a fundamental challenge in condensed matter physics, with far-reaching implications for multifunctional materials and next-generation electronic devices. Using first-principles calculations, we predict emergent sliding ferroelectricity and doping-mediated ferromagnetism in bilayer (BL) InSe. The energetically favored AB-stacked BL-InSe spontaneously breaks the out-of-plane mirror symmetry, resulting in a switchable polarization with a saturated component of 0.089 pC/m and a low transition barrier of 28.8 meV per unit cell. Strikingly, low-concentration electrostatic doping enhances rather than suppresses the ferroelectric polarization due to the abnormal layer-dependent electronic occupation in BL-InSe, in contrast to the conventional screening paradigm. In addition, the characteristic Mexican-hat-shaped valence band enables doping-induced itinerant half-metallic ferromagnetism, where the interlayer spin density difference scales linearly with doping concentration and can be reversed by switching the polarization direction, revealing a direct coupling between polarization and spin degrees of freedom. These results demonstrate the coexistence of ferroelectric and ferromagnetic orders in BL-InSe and establish a viable platform for realizing voltage-tunable multiferroicity through stacking and carrier doping in otherwise nonpolar and nonmagnetic semiconductors.

Decoders, which function as the “precision translators” in digital systems, have traditionally required external memory to integrate storage and computation, leading to high circuit complexity and component counts. This work presents a novel nonvolatile decoding mechanism that exploits the ferroelectric polarization reversal and electron transport anisotropy of two-dimensional materials. Based on a $\text{GaTe}/{\text{In}}_2{\text{Se}}_3$ two-dimensional van der Waals heterostructure, we designed a four-terminal, dual-channel ferroelectric tunnel junction. First-principles calculations demonstrate that the device can be stabilized into four distinct resistance states through the synergistic control of polarization direction and charge transport path, thereby fully enabling the binary decoding of “00”, “01”, “10”, and “11”. This design integrates combinational logic and memory within a single ferroelectric device, which not only minimizes data movement but also enhances storage density, offering a promising pathway for designing low-power, high-density integrated circuits in the post-Moore era.

We investigate the effects of alloying and growth orientation on the electronic properties of the ultrawide bandgap semiconductor $\beta {\text{-Ga}}_2{\mathrm{O}}_3$ and pseudomorphic $({\text{Al}}_x{\text{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$ alloy heterojunctions. Band offsets are computed from first principles using density functional theory with the Heyd-Scuseria-Ernzerhof hybrid functional for different aluminum concentrations and four growth orientations, namely, (100)B, (010), (001)B, and ($\overline{2}01$). Significant variations are found and ascribed to the strained pseudomorphic alloys. The values of the band offsets are fed into technology computer-aided design (TCAD) models of Schottky barrier diodes (SBD). $I$-$V$ and $C$-$V$ characteristics from the TCAD models show reasonable agreement with recent experimental measurements in the forward bias region. Discrepancies in the negative bias region are expected due to the ideality of the Schottky junctions considered in this study. Our findings underscore the critical role of growth orientation and strain in the accurate modeling of $\beta {\text{-Ga}}_2{\mathrm{O}}_3$-based SBD.

Phononic nanodevices offer a promising route toward quantum technologies, as phonons combine strong confinement within matter with broad coupling capabilities to various quantum systems. In particular, the piezoelectric response of materials, such as lithium niobate, enables coupling between superconducting qubits and gigahertz-frequency phonons. However, bulk lithium niobate phononic devices typically rely on surface acoustic waves and are therefore inherently subject to leakage from the surface into the bulk substrate. Here, we explore the acoustic behavior of resonator cavities supporting GHz-frequency Lamb waves in a 200-nm-thick suspended lithium niobate layer. We characterize the acoustic response at both room and millikelvin temperatures. We find that our resonator cavities with strong confinement reach intrinsic quality factors of approximately 6000 at the single phonon level. We use the measured parameters of the resonators to model their coupling to a superconducting transmon qubit, allowing us to evaluate their potential as quantum acoustic devices.

Privacy is a fundamental requirement in distributed quantum sensor networks, where multiple clients estimate spatially distributed parameters using shared quantum resources while interacting with potentially untrusted servers. Despite its importance, existing privacy conditions rely on idealized quantum bounds and do not fully capture the operational constraints imposed by realistic measurements. Here, we introduce a universal operational privacy framework for distributed quantum sensing, formulated in terms of the experimentally accessible Fisher information matrix and applicable to arbitrary protocols characterized by singular information structures. The proposed condition provides a protocol-independent criterion, ensuring that no information about individual parameters is accessible to untrusted parties. We further experimentally demonstrate that a distributed quantum sensing protocol employing fewer photons than the number of estimated parameters simultaneously satisfies the universal privacy condition and achieves Heisenberg-limited precision. Our results establish universal operational constraints governing privacy in distributed quantum sensor networks and provide a foundation for practical, privacy-preserving quantum sensing beyond full-rank regimes.

Aluminum remains the central material for superconducting qubits, and considerable effort has been devoted to optimizing its deposition and patterning for quantum devices. However, postprocessing strategies focused on oxide removal of Nb- and Ta-based resonators using buffered oxide etch (BOE), which cannot be used for aluminum (Al). This challenge becomes particularly relevant for industry-scale fabrication with multichip bonding, where delays between sample preparation and cooldown require surface treatments that preserve low dielectric loss during extended exposure to ambient conditions. In this work, we investigate surface modification approaches for Al resonators subjected to a 24-h delay prior to cryogenic measurement. Passivation using self-limiting oxygen and fluorine chemistries was evaluated utilizing different plasma processes. Remote oxygen plasma treatment reduced dielectric losses, in contrast to direct oxygen plasma. A fluorine-based plasma process was developed that passivated the Al surface for subsequent BOE treatment. However, the fluorine content on the surface resulted in higher loss, identifying fluorine as an unsuitable passivation material for Al resonators. Above all, selective oxide removal using HF vapor and phosphoric acid yielded median dielectric losses as low as ${\tilde{\delta }}_{\mathrm{LP}}=5.7\times {10}^{-7}$ ($Q_{\mathrm{LP}}\approx 1.7\mathrm{M}$) with ${\tilde{\delta }}_{\mathrm{TLS}}=3.6\times {10}^{-7}$ ($Q_{\mathrm{TLS}}\approx 2.8\mathrm{M}$) in the single-photon regime. Selective oxide removal provides a promising pathway for robust Al-based qubit fabrication, as it preserves low dielectric losses for a 24-h delay before cooldown.

This work investigates the behavior of a spin-exchange relaxation-free magnetometer integrated into the feedback branch of a closed-loop control circuit, designed to realize a noise-suppressed current source. In this configuration, the magnetometer bandwidth is enhanced by almost 2 orders of magnitude as compared to the open-loop setup. Incorporating an injection transformer, the proposed system effectively reduces current noise to below $3\mathrm{n}\mathrm{A}/\sqrt{\text{Hz}}$ over a broad frequency bandwidth, independent of dc-current offsets. Analysis of the system sensitivity reveals the performance to be currently limited by technical noise. If this were to be eliminated, the system would achieve a current-sensing sensitivity on the order of a few $\mathrm{p}\mathrm{A}/\sqrt{\text{Hz}}$ while maintaining perfect galvanic isolation from the target circuit.

High-temperature superconductors (HTS) are considered for broad applications from medical devices and electric motors to future particle colliders and fusion reactors. The superconductors are subject to quenching, which leads to a loss of superconductivity and interruption of magnet operation. Yet, the timely detection of quench development is still on the list of “challenges to be resolved.” Microwave time and frequency domain reflectometry has recently been suggested as a possible solution enabling “noninvasive,” “operation performance time resilience,” and in-time quench monitoring. The technique considers using HTS cables’ cooling channels to measure the flowing gas temperature evolution via monitoring its electromagnetic properties. The channel surface critical temperature ($T_{\text{sc}}$), linked to HTS critical temperature and limiting the time interval for quench detection, is introduced. The two stages of the hot-spot evolution inside the gas channel during the heat release are identified and studied. The variations of the electromagnetic properties of the gas inside the channel are discussed, and experimental confirmations of the theoretical predictions are presented. We show that, depending on the heat power released and cooling gas parameters, the heating process follows different scenarios. It has been noted that the technique suggested can be used for other applications where channel-confined fluids may be affected by external changes that should be monitored.

Reducing materials- and processing-induced decoherence is critical to the development of utility-scale quantum processors based on superconducting qubits. Here, we report on the impact of two fluorine-based wet etches, which we use to treat the silicon surface underneath the Josephson junctions (JJs) of fixed-frequency transmon qubits made with aluminum base metallization. Using several materials analysis techniques, we demonstrate that these surface treatments can remove germanium residue introduced by our JJ fabrication, with no other changes to the overall process flow. When combined with argon ion milling before JJ fabrication, these surface treatments result in significantly improved energy relaxation times for the highest-performing process, with median $T_1=334\mathrm{\mu }\mathrm{s}$, corresponding to quality factor $Q=6.6\times {10}^6$. This result suggests that the metal-substrate interface directly underneath the JJs was a major contributor to microwave loss in these transmon qubits prior to the integration of these surface treatments. Furthermore, this work illustrates how quantum device performance metrics, in conjunction with materials analysis targeted at identifying the impacts of specific processing steps, can be used to improve the performance of superconducting qubits.

Electrogenerated gas nanobubbles strongly influence the performance of electrochemical energy-conversion systems, yet their nucleation and early evolution remain poorly understood due to fundamental limitations of existing experimental and computational approaches. Operando imaging lacks the temporal resolution required to capture nucleation events, while molecular dynamics simulations are restricted to nanometer-scale domains containing at most a few bubbles. Here, we develop a thermodynamically consistent phase-field framework that unifies dissolved-gas transport, curvature-dependent interfacial thermodynamics, and implicit bubble nucleation within a single continuum description. Using hydrogen nanobubble formation during electrocatalysis as a canonical test case, the model captures nucleation without prescribing nuclei, resolves diffusion-controlled growth under strong curvature effects, and remains computationally tractable at the micrometer scale despite hydrogen’s extremely low solubility in water. Simulations reveal how nanobubble nucleation occurs once a local supersaturation threshold is exceeded, triggering a reorganization of the chemical-potential field that focuses dissolved gas toward the nascent bubble. In multicatalyst systems, overlapping diffusion fields lead to strong bubble-bubble interactions, including competitive growth, Ostwald ripening, and source occlusion. Extending the framework to dispersed catalyst populations shows that nanobubble survival is governed not only by catalyst size but also by spatial arrangement and diffusive competition, such that only a subset of bubbles persist while others dissolve and act as transient feeders. These results reframe electrogenerated nanobubbles as emergent, spatially organized features rather than unavoidable parasitic byproducts, and point toward electrode designs that deliberately control where bubbles nucleate and grow to preserve active area and mitigate transport losses.

Two-photon states generated from spontaneous parametric down-conversion (SPDC) can display entanglement in all degrees of freedom (DoFs) of light, including spatial, temporal, and polarization. The coupling between different DoFs of a two-photon state has been shown to display rich structures that enable novel and robust information processing schemes. While the existing literature has studied these couplings by postselecting the SPDC field, a comprehensive understanding of the inherent spatial-polarization coupling produced in the SPDC process is still lacking. This work produces a full spatial map of the polarization entanglement generated across the entire SPDC field, which contains an entire class of near-maximally polarization-entangled states with an average concurrence of $0.8303\pm 0.0004$. The spatial-polarization coupling manifests as radially or linearly varying polarization-entangled states, whose wavefunctions are dependent on the transverse momenta of the down-converted photons and the pump beam, respectively. Our study lays important groundwork for further exploiting the coupling between entanglement in different DoFs for future quantum technologies.

Forced excitations at frequencies in the range of the first-order azimuthal spin waves of a magnetic disk in the vortex state are known to scatter into the vortex gyration mode, thereby allowing the growth of Floquet spin waves forming a frequency comb. We study the temporal emergence of this dynamical state using time-resolved microwave electrical measurements. The most intense Floquet mode emerges synchronously with the gyration mode after a common incubation delay, which diverges at the scattering threshold. This delay is minimal when the drive is resonant with one of the first-order azimuthal spin waves. It can be as short as 3 ns for the maximum investigated power. We conclude that the first-to-occur scattering mechanism is the three-wave splitting of a regular azimuthal eigenmode into a coherent pair formed by a gyration magnon and a Floquet spin wave.