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.

Optical image differentiation is a key operation for edge extraction in imaging and machine vision, yet most existing implementations rely on momentum-domain filtering elements and are typically developed within a scalar-wave framework. Here we demonstrate a nonlinear vectorial mechanism for optical image differentiation based on parametric wave mixing. By solving the full vector wave equation with a nonlinear polarization source term, we show analytically that frequency conversion intrinsically generates cross-polarized field components that correspond to spatial derivatives of the incident field. Exploiting the polarization-selective phase-matching conditions of second-order nonlinear crystals, particularly uniaxial crystals, we propose filter-free imaging schemes that simultaneously perform spatial differentiation and wavelength conversion. This nonlinear vector differentiation platform enables compact, wavelength-agile, and edge-enhanced imaging, offering alternative opportunities for midinfrared imaging and all-optical signal processing.

We theoretically investigate a high-efficiency and broadband microwave storage and retrieval scheme employing a superconducting artificial chiral molecule embedded in a one-dimensional transmission line. By optimizing the parametric coupling, the chiral $\mathrm{\Lambda }$-type molecule enables near 100% storage efficiency and fidelity across a bandwidth of 100 MHz. Our results provide a feasible pathway toward implementing microwave quantum memories compatible with broadband quantum networks.

Measurement-induced quantum computation with continuous-variable cluster states utilizes teleportation to transmit and alter quantum states via measurement-and-feedforward control. One of the key challenges of this approach is the deterioration of quantum states caused by the noise added due to imperfect entanglement of the cluster. We analyze the propagation of a quantum non-Gaussian state with nonlinear squeezing through a small cluster state. We show that a nonlinear feedforward in the deterministic teleportation protocol reduces the added noise and improves the nonlinear squeezing transferred. In a probabilistic regime, the improvement can be manifested even with current experimental resources. Better processing of non-Gaussian states can bring us closer to the necessary interplay between cluster states and non-Gaussianity required by quantum computing.

Identity authentication between communicating parties is a fundamental prerequisite for secure communication. Classical authentication systems face serious threats from the advent of quantum computing. In contrast, quantum identity authentication (QIA) can provide security based on the fundamental principle of quantum mechanics and has consequently attracted significant research interest. However, currently most QIA schemes either belong to one-way identity authentication or suffer from information leakage during the identity authentication process. Here, we for the first time propose a bidirectional QIA scheme with zero-knowledge proof. This scheme will not disclose any information other than the authenticity of the statement itself, and it possesses the merits of simple structure and easy execution. Theoretical analysis has been conducted on the completeness, robustness, and zero-knowledge nature of the proposed scheme. Furthermore, corresponding experimental demonstrations have been carried out by utilizing entanglement sources. This work has effectively improved the practical security and practicability of QIA, paving the way for the construction of a large-scale quantum internet in the future.

Arrays of Josephson junctions can be tuned through anomalous metallic, quantum-critical, and insulating regimes. We introduce an alternative experimental probe, capturing microwave radiation across all three regimes, using a two-dimensional array of superconductor-semiconductor hybrid Josephson junctions as a model system. Our approach allows in situ calibration of the sample’s circuit parameters and provides isolation from measurement back-action effects. We measure the radiation temperature of the anomalous metal and find that it is hotter than both the quantum-critical and insulating regimes. We further show that the anomalous metallic regime is more susceptible to additional heating than other regimes, explaining its emergence in otherwise thermalized systems. Turning to the quantum-critical regime, we discover nonlinear scaling of radiative noise with applied bias, consistent with theoretical predictions of universal nonequilibrium behavior at quantum-critical points.

The search for material systems exhibiting a large spin Hall effect is central to the development of ultrafast, energy-efficient spintronic technologies. We systematically investigate the spin Hall angle (SHA) in Ru-Pt binary alloys using three complementary techniques: spin-torque magneto-optic Kerr effect, spin-torque ferromagnetic resonance, and time-domain terahertz emission spectroscopy. Within the measured composition range, a maximum SHA of 0.158 is observed in ${\mathrm{Ru}}_{38}{\mathrm{Pt}}_{62}$, representing a 56% enhancement over Pt while maintaining a resistivity below $70\mathrm{\mu \Omega }\mathrm{cm}$. Notably, these high SHA values are achieved in as-grown sputtered films across the full composition range without the need for complex fabrication procedures or high-temperature annealing. These results establish Ru-Pt as a scalable model alloy system in which composition-driven disorder, together with gradual structural evolution, governs spin-charge conversion, providing a practical pathway for optimizing materials for spin-orbit torque devices.

Terahertz radiation pulses can be generated efficiently through femtosecond laser excitation of a ferromagnetic/nonmagnetic heterostructure, wherein an ultrafast laser-induced spin current results in an electromagnetic THz pulse due to spin-charge conversion. It is, however, still poorly understood how the THz emission amplitude and its bandwidth in the frequency regime can be optimized. Here, we perform a systematic analysis of the THz emission from various magnetic heterostructures. The dynamics of the spin current is described by the semiclassical, superdiffusive spin-transport model, and the energy dependence of the spin Hall effect of hot electrons is taken into account, leading to emission profiles for $\text{Co}(2\mathrm{nm})/\text{Pt}(4\mathrm{nm})$ bilayer in good agreement with experiment. To identify the optimal conditions for THz emission, we study the properties of the emitted THz wave profile by systematically varying the layer thicknesses of metallic bilayers, their interfacial spin-current transmission properties, their materials’ dependence, and the influence of the pump laser-pulse width, allowing us to give optimization guidelines. We find that thin nonmagnetic layer thicknesses of 5–6 nm provide the largest bandwidth in the case of $\text{Co}/\text{Pt}$ and that the peak frequency of the THz emission depends only on the geometry of the emitter and not on the laser pulse width. The THz bandwidth is conversely found to depend on several factors such as exciting laser pulse width, layers’ thicknesses, and interface transmission-reflection properties, with the limitation that an increase in the bandwidth by tuning the interface properties comes with a trade-off in the energy efficiency of the emitter. Finally, we propose a double pulse excitation protocol of a trilayer system that could provide broadband THz emission with a large bandwidth. Our results contribute to establishing guidelines for optimizing spintronic THz generation.

Resonator-photon-induced dephasing presents a critical challenge for superconducting qubit coherence. This study examines the influence of the frequency and number of coherent photons on quantum coherence degradation. Our measurements show that the dephasing profile across photon frequencies closely follows the resonator’s spectral characteristics, establishing a direct link between dephasing dynamics and resonator-qubit interaction parameters. Of note, dynamical decoupling demonstrated robust performance in mitigating coherence decay under a wide range of photon conditions. This underscores its potential for addressing various forms of coherent photon noise, including ac Stark shifts and additional photon-mediated dephasing.