We show that by embedding a liquid-filled acoustofluidic cavity in a metamaterial, the quality factor of the cavity at selected acoustic resonance modes can be enhanced by 2–3 orders of magnitude relative to a comparable conventional cavity by matching the coarse-grained elastic moduli of the metamaterial to the acoustic properties of the liquid. The corresponding decrease in dissipation in the cavities is caused by the synchronized motion of the metamaterial and the liquid, which strongly suppresses the resulting acoustic streaming. The weak streaming combined with the enhanced quality factor enables fast acoustophoretic focusing of submicron particles in the cavity.

Precise mapping of the geomagnetic field is essential for understanding Earth’s geodynamics, space weather interactions, and navigation applications. Traditional magnetometers face limitations in sensitivity for a wide dynamic range, and compactness. To address these challenges, the OSCAR-QUBE quantum magnetometer based on nitrogen-vacancy centers in diamond was developed, providing a sensitive and compact solution for space-based magnetic-field measurements. Our system employs optically detected magnetic resonance to measure magnetic fields utilizing the quantum properties of nitrogen-vacancy centers in a miniaturized design. The form factor of the final device was 1U ($10\times 10\times 10{\mathrm{cm}}^3$), weighing 420 g, and had a power consumption of 5 W. Deployed aboard the International Space Station, our magnetometer measured high-resolution magnetic-field maps, achieving a sensitivity of $<300\mathrm{nT}/\sqrt{\mathrm{Hz}}$ and successfully demonstrating in situ vector magnetic-field mapping under low-Earth-orbit conditions. These results validate the flight-proven application of diamond quantum sensing in space, demonstrating the feasibility of solid-state quantum magnetometry for next-generation remote sensing and Earth observation missions. This work lays the foundation for future compact, multisensor quantum payloads for both scientific and commercial space applications.

Artificial transmission lines (ATLs) built with lumped-element inductors and capacitors form the backbone of broadband, nearly quantum-limited traveling-wave parametric amplifiers (TWPAs). When tailoring these transmission lines for parametric processes, nonlinear elements are added, typically nonlinear inductances in superconducting circuits, and energy and momentum conservation between interacting tones must be enforced through careful design of the ATL dispersion relation. However, a unified theoretical framework describing achievable dispersion relations is lacking. Here, I develop such a framework, borrowing from periodic structure theory and passive network synthesis. These complementary approaches divide the design space: periodic loading synthesis employs spatial modulation of frequency-independent components, while filter synthesis employs frequency-dependent responses in spatially uniform components. The framework reveals fundamental constraints and enables the discovery of novel TWPA architectures. In particular, I design a kinetic inductance TWPA with an alternative phase-matching architecture, and a backward-pumped Josephson TWPA exploiting an ambidextrous (i.e., right-left-handed) transmission line.

The spontaneous magnetostrictive effect induces anomalous negative thermal expansion in certain magnetic materials due to spin-spin correlations. Traditionally, this phenomenon is identified by lattice constant measurements, which do not directly reveal the dominant spin interactions. Using ultrafast, site-selective crystal-field excitations in polar antiferromagnetic ${\mathrm{Fe}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$, we uncover an excitation site–dependent strain pulse generation. This enables the realization of negative thermal expansion and the construction of spin-spin correlation functions. We find that strain pulses generated from $\mathrm{Fe}$ octahedral sites diminish near spin-ordering onset, while those from $\mathrm{Fe}$ tetrahedral sites decreases in intensity near the Néel temperature, independent of soft-mode behavior. This excitation site–dependent strain pulse emerges as a highly sensitive tool for measuring anomalous thermal expansion through phase shifts in probe interference and for identifying dominant spin-spin correlations via temperature-dependent strain intensity variations. Supported by magnetic field–dependent experiments and theoretical analysis, we confirm the absence of forced magnetostriction in the generation mechanism. This innovative approach bridges mechanical properties and spin-spin interactions, advancing the study of acoustic strain pulses and magnetic materials.

Integrated photonic quantum information processing (QIP) has advanced rapidly due to progress in various nanophotonic platforms. Single-photon detectors have been the subject of intense study due to their ubiquity in QIP systems, yet many detectors operate at cryogenic temperatures under vacuum and are limited in operating speed by their dead times. We propose and characterize an all-optical single-photon detection scheme based on optical parametric amplification in nanophotonic lithium niobate (LN) combined with a macroscopic photodetector. We use quantum detector tomography and experimentally determine the positive operator-valued measure of the detector. The detector operates at room temperature at a count rate of 250 MHz and is readily integrated in LN nanophotonics. While the demonstrated experimental performance falls short of existing photon detectors, we show that in the future, by improving the nonlinearity-to-loss ratio and using homodyne detection on a squeezed pump, the detector can achieve a performance sufficient to create non-Gaussian states, such as Schrödinger’s cat states. Our results highlight a path toward all-optical photon detection for scalable high-throughput nanophotonic quantum communication and information processing.

Electron-on-neon (eNe) charge states coupled to superconducting circuits are a promising platform for quantum computing. Control over the formation of these charge states requires techniques to track and control the growth of solid $\mathrm{Ne}$ films on the circuit surface. We demonstrate a real-time $\mathrm{Ne}$ film-growth monitor using high-transition-temperature (high-$T_c$) YBCO microwave resonators. The high $T_c$ enables tracking of the film thickness near $\mathrm{Ne}$’s triple temperature and below. Across more than 300 solidification experiments, we find that the final $\mathrm{Ne}$ thickness varies stochastically from a few nanometers to a few microns for films solidified from the liquid phase. By increasing the driving power in the resonator, we consistently reduce the final thickness to below 100 nm. These results represent an important step toward controlled formation of $\mathrm{Ne}$ films for eNe qubits and highlight the broader utility of high-$T_c$ resonators for hybrid quantum systems.

We report on the characteristics of a microwave photon-counter device based on a superconducting transmon qubit. Its design is similar to that described by Balembois et al. [Phys. Rev. Appl. 21, 014043 (2024)], which achieved a sensitivity of ${10}^{-22}\mathrm{W}/\sqrt{\mathrm{Hz}}$, but with an additional bandwidth-tuning circuit that permits tuning the detection bandwidth over an order of magnitude to optimize the efficiency and noise level of the device. As a result of this feature and improvements in device fabrication, a power sensitivity of $3\times {10}^{-23}\mathrm{W}/\sqrt{\mathrm{Hz}}$ is reached. We confirm the high performance of the device by measuring single-spin microwave fluorescence.

Forecasting complex, chaotic signals is a central challenge across science and technology, with implications ranging from secure communications to climate modeling. Here we demonstrate that magnons, the collective spin excitations in magnetically ordered materials, can serve as an efficient physical reservoir for predicting such dynamics. Using a magnetic vortex-state microdisk as a magnon-scattering reservoir, we show that intrinsic nonlinear interactions transform a simple microwave input into a high-dimensional spectral output suitable for time-series predictions. Trained on the Mackey-Glass benchmark, which generates a cyclic yet aperiodic time series, the system achieves accurate and reliable predictions that rival other state-of-the-art physical reservoirs. We further identify key design principles: spectral resolution governs the tradeoff between dimensionality and accuracy, while combining multiple device geometries systematically improves performance. These results establish magnonics as a promising platform for unconventional computing, offering a path toward scalable and CMOS-compatible hardware for real-time prediction tasks.

We experimentally demonstrate an interferometric architecture for next-generation gravity missions, featuring a laser ranging interferometer (LRI) that enables monoaxial transmission and reception of laser beams between two optical benches with a heterodyne frequency of 7.3 MHz. Active beam-steering loops, utilizing differential wavefront sensing signals, ensure coalignment between the receiving beam and the transmitting beam. With spacecraft attitude jitter simulated by hexapod-driven rotations, the interferometric link achieves a pointing stability below $10\text{μ}\mathrm{rad}/\sqrt{\mathrm{Hz}}$ in the frequency range between 0.2 mHz and 0.5 Hz, and the fluctuation of the transmitting beam’s polarization state results in a reduction of 0.14% in the carrier-to-noise-density ratio over a 15 h continuous measurement. Additionally, tilt-to-length coupling is experimentally investigated using the periodic scanning of the hexapod. Experimental results show that the on-axis LRI enables the interspacecraft ranging measurements with nanometer accuracy, making it a potential candidate for future GRACE-like missions.

We identify the topological nodal-line semimetal (NLSM) $\mathrm{Ca}\mathrm{Ag}\mathrm{As}$ as an efficient electrocatalyst for the nitric oxide reduction reaction, offering an alternative to the energy- and carbon-intensive Haber-Bosch process. First-principles calculations reveal that $\mathrm{Ca}\mathrm{Ag}\mathrm{As}$ hosts a nodal loop around the Fermi level, generating drumheadlike topological surface states (TSSs) protected by mirror symmetry. These TSSs provide a high surface density of states (SDOS) near the Fermi level, which underpins excellent catalytic activity of $\mathrm{Ca}\mathrm{Ag}\mathrm{As}$. The Gibbs free energy ($\mathrm{\Delta }G$) of the potential-determining step is 0.22 eV, lower than that of conventional $\mathrm{Cu}$ catalysts, while high ammonia selectivity is ensured by larger free-energy increases required for byproduct formation ($>1.48$ eV) and suppression of the hydrogen evolution reaction. External perturbations, such as strain and doping, are applied to $\mathrm{Ca}\mathrm{Ag}\mathrm{As}$, revealing a quantitative linear correlation between the SDOS and $\mathrm{\Delta }G$, thereby highlighting the role of TSSs. Strain engineering can further reduce $\mathrm{\Delta }G$ to 0.08 eV by tuning the nodal-loop size. Symmetry-breaking strategies confirm that the catalytic performance deteriorates when TSSs are destroyed, as $\mathrm{Ca}\mathrm{Ag}\mathrm{As}$ transitions to a Weyl semimetal or a trivial insulator. Overall, this work uncovers an application of NLSMs in electrocatalysis and provides a topological design strategy for eco-friendly ammonia synthesis.

The recent breakthroughs in laser-driving the ${}^{229}\mathrm{Th}$ nuclear transition have created an urgent demand for scalable vacuum-ultraviolet (VUV) sources capable of supporting high power spectral density at the critical 148.38 nm isomer energy. However, generating sufficient photon flux to overcome the low nuclear excitation probability remains a challenge for compact setups. While resonant dispersive-wave emission in gas-filled hollow-core fibers offers a promising route, standard capillaries face a fundamental trade-off: maximizing input coupling requires large core diameters, whereas efficient nonlinear VUV conversion demands high intensities and small cores. Here we resolve this conflict using a gas-filled tapered capillary fiber. This architecture uses a longitudinally decreasing core diameter to combine a large input aperture with adiabatic field concentration, thereby continuously enhancing the nonlinear interaction. Experimentally, we demonstrate a widely tunable source (135–240 nm) that achieves a twofold efficiency increase specifically at a wavelength of 148.38 nm compared with uniform geometries. By providing a scalable route to high-flux VUV generation, this work establishes a critical tabletop tool for advancing solid-state nuclear clocks and time-resolved spectroscopy.

Nonlocal connectivity is a critical resource for universal logical quantum gates and low-overhead quantum error correction codes, and is unavailable on current superconducting devices with nearest-neighbor connections. To rectify the deficiency in connectivity of superconducting circuit systems, we experimentally demonstrate a convenient on-chip coupler of centimeters length and with quality factor close to $1\times {10}^6$. The entangling gate is performed between two fluxonium qubits, reaching a fidelity of 99.37% within 120 ns, while the system static $ZZ$ interaction rate remains as low as 144 Hz without active cancellation or circuit parameter targeting. This high-fidelity low-crosstalk nonlocal coupler can be the building block of a binary-tree connectivity graph, reducing the average qubit entangling distance from $O(N)$ to $O({\log }_2N)$. With the high-fidelity nonlocal entanglement, novel quantum algorithms can be implemented on the superconducting qubit system, positioning it as a strong competitor to other physics systems regarding circuit connectivity.

We introduce a superconducting transconductance amplifier based on the thermal modulation of a superconductor-insulator-normal metal-insulator-superconductor (SINIS) configuration. The device consists of a normal metal island interfaced with two superconducting leads via tunnel barriers, forming a voltage-biased symmetric SINIS setup. An additional normal metal-insulator-superconductor (NIS) junction connects the island to a third superconducting lead, which serves as an input. When the input voltage surpasses the superconducting gap, the resulting injection of quasiparticles increases the electronic temperature of the island, thereby modulating the SINIS current. We perform numerical analyses of the device performance, influenced by input voltage, frequency, and bath temperature. At bath temperatures below $250\mathrm{mK}$, the device shows a transconductance greater than $4\mathrm{mS}$ and a current gain greater than $45\mathrm{dB}$. Both gain and transconductance maintain their levels up to $1\mathrm{MHz}$, but decrease at higher frequencies, with a $-3\mathrm{dB}$ cutoff around $10\mathrm{MHz}$, an input-referred voltage noise of 7.5 $\mathrm{nV}/\sqrt{\mathrm{Hz}}$, and an average power dissipation of approximately 5 nW. Our simulations reveal a fully voltage-controlled, three-terminal, superconducting amplifier characterized by high transconductance and gain, enabled by thermally mediated signal transduction. This architectural design presents a promising avenue for cryogenic amplification with reduced power dissipation and compatibility with current superconducting electronic systems.

The challenge of achieving high thermoelectric (TE) performance is mainly from the entanglement among Seebeck coefficient ($S$), electrical conductivity ($\sigma$), and lattice thermal conductivity (${\kappa }_{\mathrm{L}}$). In this work, we propose a synergetic strategy of enhancing power factor (PF, $S^2\sigma$) and suppressing ${\kappa }_{\mathrm{L}}$ by applying a biaxial tensile strain in two silver chalcogenides ${\mathrm{Sc}\mathrm{Ag}\mathrm{Se}}_2$ and ${\mathrm{Tm}\mathrm{Ag}\mathrm{Te}}_2$ with ${\mathrm{Tl}\mathrm{Cd}\mathrm{S}}_2$-type structure. The forbidden $p$-$d$ orbital coupling at the $\mathrm{\Gamma }$ point and allowed $p$-$d$ orbital coupling at the $A$ point and the middle of $\mathrm{\Lambda }$ line leads to high electronic band dispersion along the $\mathrm{\Gamma }$-$A$ direction and a high-degeneracy valence-band valley (${\mathrm{\Lambda }}_2$). The elongation of the $\mathrm{Ag}$-$\mathrm{Se}$ bond under tensile strain weakens the orbital coupling between $\mathrm{Ag}$-$d$ and $\mathrm{Se}$/$\mathrm{Te}$-$p$ orbitals and reduces the band energy at the $A$ point, which aligns the valence band and achieving a high band degeneracy. Concurrently, the weaker $\mathrm{Ag}$-$\mathrm{Se}$/$\mathrm{Ag}$-$\mathrm{Te}$ bond under a small tensile strain leads to lower phonon group velocity and strong three- and four-phonon scatterings, leading to lower ${\kappa }_{\mathrm{L}}$. Our first-principles calculations combined with electron-phonon coupling analysis as well as phonon and electron Boltzmann transport equations show that applying a 3% (2%) tensile strain can enhance the PF along the $c$ axis of ${\mathrm{Sc}\mathrm{Ag}\mathrm{Se}}_2$ (${\mathrm{Tm}\mathrm{Ag}\mathrm{Te}}_2$) by 243% (246%) at a carrier concentration of $3\times {10}^{20}{\mathrm{cm}}^{-3}$ and reduce the ${\kappa }_{\mathrm{L}}$ by 37% (26%) at 300 K. Consequently, 2–4 times of $ZT$ enhancement is obtained by 3% (2%) tensile strain in ${\mathrm{Sc}\mathrm{Ag}\mathrm{Se}}_2$ (${\mathrm{Tm}\mathrm{Ag}\mathrm{Te}}_2$) at 300 K, achieving a maximum $ZT$ of 3.10 (3.40) at 800 K. Our material design strategy based on molecular orbital analysis reveals an effective route to boosting TE performance, and can be extended to other systems as well.

We report on the internal quality factor of a three-dimensional niobium quarter-wave coaxial cavity that has undergone mid-temperature annealing, exhibiting $Q_{\mathrm{int}}\gtrsim 3\times {10}^9$ at the single-photon level below 20 mK, which corresponds to an internal photon lifetime of ${\tau }_{\mathrm{int}}\sim 90\mathrm{ms}$. Moreover, $Q_{\mathrm{int}}$ of the mid-temperature-annealed cavities remains almost unchanged even after several cooldown cycles and air exposure. These results suggest that stable low-loss niobium oxides are formed by mid-temperature annealing on the surface of a three-dimensional niobium cavity. This surface treatment could be applicable to the fabrication of two-dimensional superconducting circuits and help improve the lifetime of $\mathrm{Nb}$-based superconducting qubits.

As CMOS technology scales down, thermal fluctuations increasingly impact circuit behavior, posing challenges to conventional circuit design. However, the inherent stochasticity introduced by thermal noise is now being explored as a potential resource in the emerging field of probabilistic computing. This work presents a fully CMOS experimental platform that enables direct control over its intrinsic thermal fluctuations. These devices function as programmable multivariate Gaussian samplers, offering a hardware primitive for energy-efficient stochastic computing and serving as an experimental platform for studies in electronic noise and stochastic thermodynamics.

We experimentally observe the generation of magnon harmonics and subharmonics in an on-chip surface-acoustic-wave resonator incorporating a thin ${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ film using microfocused Brillouin light scattering. In our devices, rotating the in-plane magnetic field allows continuous tuning of the magnon-phonon coupling from weak to strong within the same resonator. In the weak-coupling regime, we only observe a fundamental magnetoelastic wave signal at $f_0$. Conversely, in the strong-coupling regime, in addition to the fundamental magnetoelastic wave, we observe subharmonic and harmonic signals at $(3/2)f_0$, $2f_0$, and $3f_0$, which are well reproduced by our analytical model. Our results establish phonons as a means to generate and control nonlinear magnons in the strong-coupling regime, providing a route for magnonic signal processing.

We present bifrost, a first-principles model of polarization mode dispersion (PMD) in optical fibers. Unlike conventional models, bifrost employs physically motivated representations of the PMD properties of fibers, allowing users to computationally investigate real-world fibers in ways that are connected to physical parameters such as environmental temperature and external stresses. Our model, implemented in an open-source Python module, incorporates birefringence from core geometry, material properties, environmental stress, and fiber spinning. We validate our model by examining commercial fiber specifications, fiber-paddle measurements, and published PMD statistics for deployed fiber links, and we showcase bifrost’s predictive power by considering wavelength-division-multiplexed PMD compensation schemes for polarization-encoded quantum networks. bifrost’s physical grounding enables investigations into such questions as the sensitivity of fiber sensors, the evaluation of PMD mitigation strategies in quantum networks, and many more applications across fiber technologies.

Maximizing the computational utility of near-term quantum processors requires predictive noise models that inform robust, noise-aware compilation and error mitigation. Conventional models often fail to capture the complex error dynamics of real hardware or require prohibitive characterization overhead. We introduce a data-efficient framework that first constructs a physically motivated, parameterized noise model, and subsequently employs machine-learning-driven Bayesian optimization to identify its parameters. Our approach circumvents costly characterization protocols by estimating algorithm- and hardware-specific error parameters directly from readily available experimental data derived from existing application and benchmark circuit executions. The generality and robustness of the framework are demonstrated across diverse algorithms and superconducting devices, yielding high-fidelity predictions by estimating an independent parameter set tailored to each specific algorithm-hardware context. Crucially, we show that a model calibrated exclusively on small-scale circuits accurately predicts the behavior of larger validation circuits. Our data-efficient approach achieves up to a 65% improvement in model fidelity quantified by the Hellinger distance between predicted and experimental circuit output distributions, compared to standard noise models derived from device properties. This work establishes a practical paradigm for application-aware noise characterization, enabling compilation and error-mitigation strategies tailored to the specific interplay between quantum algorithms and device-specific noise dynamics.

The development of practical sensors for optical coherence tomography (OCT) with undetected photons requires miniaturization via integration. To be practical, these sensors must exhibit a large spectral bandwidth and a high brightness, which are linked to a high axial resolution and a sufficient signal-to-noise ratio, respectively. Here, we combine these requirements in a scheme for OCT measurements with undetected photons based on nonlinear $\mathrm{Ti}:{\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$ waveguides. We investigate the performance benchmarks of the commonly used SU(1,1) scheme in comparison to an induced-coherence scheme and find that the latter is actually better suited when implementing measurements with undetected photons in integrated systems. In both schemes, we perform pump-gain optimization and OCT measurements with undetected photons with an axial resolution as low as $28\text{μ}\mathrm{m}$.