We report on a ${}^{88}{\mathrm{Sr}}^{+}$ single-ion optical clock with an estimated fractional systematic uncertainty of 7.9×${10}^{-19}$. The low uncertainty is enabled by small rf losses, a thorough evaluation of the blackbody-radiation temperature, and our recent measurement of the differential polarizability. A detailed uncertainty evaluation is presented. We also report on two absolute frequency measurements: one against a remote cesium fountain clock, and one against International Atomic Time (TAI). The former lasted 12 d and resulted in a frequency value of 444 779 044 095 485.49(15) Hz. The latter spanned 10 months with monthly optical-clock uptimes between 68% and 99%, and yielded a frequency value of 444 779 044 095 485.373(44) Hz. With a fractional uncertainty of 9.8×${10}^{-17}$, it is, to our knowledge, the most accurate optical frequency measurement reported to date. Both frequency values are in agreement with other recent measurements, providing further evidence that the 2021 CIPM recommended frequency value is too high by 1.6 times its uncertainty.

We present a Josephson traveling-wave parametric amplifier (JTWPA) based on a low-loss lumped-element coplanar waveguide architecture. By employing open-stub capacitors and Manhattan-pattern junctions, our device achieves an insertion loss below 1 dB up to 12 GHz. We introduce windowed sinusoidal modulation for phase matching, demonstrating that a smooth transition in the impedance-modulation strength effectively suppresses intrinsic gain ripples. Using Tukey-windowed modulation with 8% impedance variation, we achieve 20–23-dB gain over 5-GHz bandwidth under ideal matching conditions. In a more practical circuit having impedance mismatches, the device maintains 17–20-dB gain over 4.8-GHz bandwidth with an added noise of 0.18 quanta above standard quantum limit at 20-dB gain and $-99$-dBm saturation power, while featuring zero to negative backward gain below the band-gap frequency.

Networks of nonlinear resonators offer a promising platform for analog computing and the emulation of complex systems. However, realizing such networks remains challenging, as it requires resonators with high quality factors, individual frequency tunability, and strong interresonator coupling. In this work, we present a system that meets all these criteria. Our system is based on metalized silicon nitride membranes that are coupled via their common substrate and controlled capacitively via electrodes. We demonstrate individual frequency tuning and strong parametric driving of each membrane. Notably, we tune membrane frequencies through avoided crossings and demonstrate tunability of the coupled membrane’s parametric response. This platform provides a scalable and controllable setting for exploring collective phenomena, dynamical phase transitions, nonlinear topology, and analog computing.

Enhancing precision sensors for stochastic signals using quantum techniques is a promising emerging field of physics. Estimating a weak stochastic waveform is the core task of many fundamental physics experiments including searches for stochastic gravitational waves, quantum gravity, and axionic dark matter. Simultaneously, noise spectroscopy and characterization (e.g., estimation of various decay mechanisms in quantum devices) are relevant to a broad range of fundamental and technological applications. We consider the ultimate limit on the sensitivity of these devices for Lindblad estimation given any quantum state, fast and precise control sequence, and measurement scheme. We show that it is optimal to rapidly projectively measure and reinitialize the quantum state. We develop optimal protocols for a wide range of applications including stochastic waveform estimation, spectroscopy with qubits, and Lindblad estimation.

Topological Maxwell lattices offer unique functionality as vibration isolators due to their capacity for asymmetrically localizing low-energy vibrational modes to their boundary via the phenomenon of topological polarization. However, existing architectures are difficult to integrate into larger systems while retaining the benefits of their topological polarization because they are not designed to function as self-supporting structures. Here, a topological Maxwell lattice, called the generalized kagome tube, is designed to address this challenge. The topological polarization of the lattice is demonstrated in a spring-and-mass model. Rigid connectors are added to the ends of the kagome tube and a finite-element method is used to determine the displacement transmissibility as a function of frequency as well as the effective stiffness of the lattice under axial and transverse loading conditions. Guidance for experimental validation and continuum-model development is provided.

We present an implementation of multicontrolled (mc) quantum gates that provides significant reductions of cost compared to state-of-the-art methods. The operator applied on the target qubit is a unitary, special unitary, or the Pauli $X$ operator (multicontrolled Toffoli), and requires one clean ancilla, no ancilla, or one dirty ancilla, respectively. We generalize our methods for any number of target qubits, and provide further cost reductions if additional ancilla qubits are available. For each type of mc gate, we provide implementations for unrestricted (all-to-all) connectivity and for linear-nearest-neighbor (LNN) connectivity. All of the methods use a linear cost of gates from the Clifford+$T$ (fault-tolerant) set. In the context of LNN architecture, the cost and depth of our circuits scale linearly irrespective of the position of the qubits on which the gate is applied. Our methods directly improve the compilation process of many quantum algorithms, providing optimized circuits. Given the scale of our improvements, for example, the quadratic-to-linear controlled-not count for LNN, they will naturally result in a large reduction of errors.

We present a SNAIL-based parametric amplifier that integrates a lumped-element impedance matching network for increased bandwidth and an on-chip pump-port filter for efficient pump delivery. The amplifier is fabricated using a single-layer optical lithography step, followed by a single-layer electron-beam-lithography step. We measure a flat 20-dB gain profile with less than 1-dB ripple across a bandwidth of up to 250 MHz on multiple devices, demonstrating robust performance against variations arising from fabrication and packaging. We characterize the amplifier’s linearity by analyzing gain compression and intermodulation distortion under simultaneous multi-tone excitation. We show that the intermodulation products remain suppressed by more than 23 dB relative to the signal tones, even at the 1-dB gain compression point. We further validate its utility by performing simultaneous high-fidelity readout of two transmon qubits, achieving state assignment fidelities of $99.51\mathrm{\%}$ and $98.55\mathrm{\%}$. The combination of compact design, fabrication simplicity, and performance robustness makes this amplifier a practical device for quantum experiments with superconducting circuits.

Wood, plants, and cellulosic materials contain significant amounts of bound water, up to 30% of their dry mass, present as nanoscale inclusions of water molecules within a solid matrix. This bound water is mobile and exchanges readily with vapor and free water; however, its transport dynamics remain poorly understood due to the lack of direct observations. In this study, nuclear magnetic resonance and magnetic resonance imaging were used to characterize bound water diffusion in various wood types and cellulose fibers across different directions and at different temperatures. To isolate bound water dynamics, the accessible pores were filled with oil, and bound water distribution was tracked during desorption. The results demonstrated that bound water diffusivity is independent of both its concentration and its direction, despite the pronounced anisotropy of wood, and exhibits an exponential dependence on the inverse of the temperature. These observations suggest that bound water transport is an activated process, analogous to the diffusion in solids, with an activation energy comparable to the latent heat of liquid water evaporation. These findings show that bound water enables efficient long-distance moisture transport through wood and plant structures, irrespective of whether the voids are closed, empty, or filled with nonaqueous liquid, provided a local bound water deficit exists. Consequently, bound water spontaneously refeeds a desaturated plant system. This phenomenon plays a fundamental role in water extraction, water imbibition, and moisture transport in living plants and cellulosic materials.

Implementing fast and high-fidelity quantum operations using open-loop quantum optimal control relies on having an accurate model of the quantum dynamics. Any deviations between this model and the complete dynamics of the device, such as the presence of spurious modes or pulse distortions, can degrade the performance of optimal controls in practice. Here, we propose an experimentally simple approach to realize optimal quantum controls tailored to the device parameters and environment while specifically characterizing this quantum system. Concretely, we use physics-inspired machine learning to infer an accurate model of the dynamics from experimentally available data and then optimize our experimental controls on this trained model. We show the power and feasibility of this approach by optimizing arbitrary single-qubit operations in detailed numerical simulations of a superconducting transmon qubit. We demonstrate that this framework produces an accurate description of the device dynamics under arbitrary controls, together with the precise pulses achieving arbitrary single-qubit gates with a high fidelity of $\sim 99.99\mathrm{\%}$.

Scalable coherent manipulation of qubit quantum states is crucial for building large-scale superconducting quantum processors towards fault-tolerant quantum computing. Complete coherent manipulation contains quantum gate control and magnetic flux bias for the qubit, especially for quantum processors with frequency-tunable qubits and tunable couplers. In recent years, efforts have been made to propose quantum gate control in a scalable way. However, proposals and experiments for scalable magnetic flux bias for qubits are rarely reported. Here, we propose a scalable scheme to provide magnetic flux for qubits by using an on-chip direct current source (OCDCS). We demonstrate both theoretically and experimentally that only single pulse is needed to deterministically modulate the magnetic flux in the OCDCS, which then provides the qubit with in situ and constant magnetic flux. With the magnetic flux provided by the OCDCS, the experimental results exhibit high-fidelity single-qubit gate and low noise current of the OCDCS, which shows a 15.6 dB reduction compared with that of the RTE scheme. Additionally, we propose a time-division-multiplex (TDM) scheme combining the OCDCS with switch arrays, which could exponentially reduce the number of cables for flux bias from traditional $n$ to ${\log }_2(n)+1$. Our work thus paves the way for scalable flux bias in large-scale superconducting quantum processors.

Light-matter interaction with a squeezed vacuum has received much interest for the ability to increase the native interaction strength between an atom and a photon with a reservoir assumed to have an infinite bandwidth. Here we study a model of parametrically driven cavity quantum electrodynamics (QED) for enhancing light-matter interaction while subjected to a finite-bandwidth squeezed vacuum drive. Our method is capable of unveiling the effect of relative bandwidth as well as squeezing required to observe the anticipated anticrossing spectrum and enhanced cooperativity without the ideal squeezed bath assumption. Furthermore, we analyze the practicality of said models when including intrinsic photon loss due to resonator imperfection. With these results, we outline the requirements for experimentally implementing an effectively squeezed bath in solid-state platforms such as $\mathrm{In}\mathrm{As}$ quantum dot cavity QED such that in situ control and enhancement of light-matter interaction could be realized.

Coupled spins in semiconductor quantum dots are a versatile platform for quantum computing and simulations of complex many-body phenomena. However, on the path of scale-up, crosstalk from densely packed electrodes poses a severe challenge. While crosstalk onto the quantum dot potentials is nowadays routinely compensated for, crosstalk on the exchange interaction is much more difficult to tackle because it is not always directly measurable. Here we propose and implement a way of characterizing and compensating crosstalk on adjacent exchange interactions by following the singlet-triplet avoided crossing in $\mathrm{Ge}$. We show that we can easily identify the barrier-to-barrier crosstalk element without knowledge of the particular exchange value in a $2\times 4$ quantum dot array. We uncover striking differences among these crosstalk elements that can be linked to the geometry of the device and the barrier gate fan-out. We validate the method by tuning up four-spin Heisenberg chains. The same method should be applicable to longer chains of spins and to other semiconductor platforms in which mixing of the singlet and the lowest-energy triplet is present or can be engineered. Additionally, this procedure is well-suited for automated tuning routines as we obtain a standout feature that can be easily tracked and directly returns the magnitude of the crosstalk.

The utility of inertial sensors depends on resilience against real-world dynamics and noise. Atom interferometry offers a sensing technology with the advantages of good long-term stability, high sensitivity, and accuracy. High measurement bandwidth improves an atom interferometer’s ability to reject errors due to dynamics and noise. Here we demonstrate resilience against time-varying environmental noise by rapidly switching the direction of inertial sensitivity in the atom interferometer through a common technique known as k-reversal. We demonstrate sub-interrogation-time k-reversal at 592 Hz in a cold-beam atomic interferometer with an inverse interrogation time of 148 Hz. The interferometer fringe output is read out continuously and postprocessed using nonlinear Kalman filters to determine both the inertial and error contributions to the output phase. The resulting power spectral densities show a significant reduction of phase error due to a noisy magnetic field as the k-reversal frequency increases.

Altermagnetism represents a magnetic phase in which the combination of compensated antiferromagnetic order with an anisotropic crystal field leads to time-reversal symmetry breaking. The resulting combination of properties typically associated with ferromagnets, but with net-zero magnetization, has generated significant interest for both fundamental research and technological applications. With many candidate altermagnetic materials, $\mathrm{Mn}\mathrm{Te}$ has emerged as one of the most promising systems, with growing experimental evidence for altermagnetic phenomena. So far, the majority of measurements have been performed on thin films, or have involved surface measurements. However, the question of altermagnetic order in the bulk system—in the absence of substrate or surface effects—remains. Here we show evidence for bulk altermagnetism in single-crystal $\mathrm{Mn}\mathrm{Te}$ through spectroscopic x-ray microscopy. By performing nanoscale x-ray magnetic circular dichroic (XMCD) imaging in transmission on a $200$-nm-thick lamella, we observe domains and magnetic textures with a spectroscopic signature characteristic of altermagnetic order, thereby confirming the intrinsic nature of altermagnetism in $\mathrm{Mn}\mathrm{Te}$. Quantitative analysis of the XMCD signal reveals excellent agreement with predicted signals, establishing that the altermagnetic order exists throughout the thickness of the lamella and confirming the intrinsic, bulk nature of the state. With these results, we demonstrate that transmission XMCD spectroscopic imaging is a robust, quantitative technique to probe altermagnetic order, providing a means to probe individual altermagnetic domains within complex configurations. This ability to investigate and characterize altermagnetic order in bulk crystals represents an important tool for the exploration of altermagnetism across a wide range of candidate materials, of key importance for the development of future technologies.

Spatial light modulators enable arbitrary control of the intensity of optical light fields and facilitate a variety of applications in biology, astronomy, and atomic, molecular, and optical physics. For coherent light fields, holography, implemented through arbitrary phase modulation, represents a highly power-efficient technique to shape the intensity of light patterns. Here, we introduce and benchmark a spatial light modulator based on a piston micromirror array. In particular, we utilize the reflection-based device to demonstrate arbitrary beam shaping in the ultraviolet (UV) regime at a wavelength of 322 nm. We correct aberrations of the reflected wave front and show that the modulator does not add detectable excess phase noise to the reflected light field. We utilize the intrinsically low latency of the architecture to demonstrate fast switching of arbitrary light patterns synchronized with short laser pulses at an update rate of 1 kHz. Finally, we outline how the modulator can act as an important component of a zone-based architecture for a neutral-atom quantum computer or simulator, including UV wavelengths.

The narrow band gaps of semiconductors allow for thick, uniform Josephson junction barriers, potentially enabling reproducible, stable, and compact superconducting qubits. We study vertically stacked van der Waals Josephson junctions with semiconducting weak links, whose crystalline structures and clean interfaces offer a promising platform for quantum devices. We observe robust Josephson coupling across 2–12 nm (3–18 atomic layers) of semiconducting $\mathrm{WSe}$${}_2$ and, notably, a crossover from proximity- to tunneling-type behavior with increasing weak-link thickness. Building on these results, we fabricate a prototype all-crystalline merged-element transmon qubit with transmon frequency and anharmonicity closely matching design parameters. We demonstrate dispersive coupling between this transmon and a microwave resonator, highlighting the potential of crystalline superconductor-semiconductor structures for compact, tailored superconducting quantum devices.

Characterizing quantum processes is crucial for the execution of quantum algorithms on available quantum devices. A powerful framework for this purpose is the Quantum Model Learning Agent (QMLA), which characterizes a given system by learning its Hamiltonian via adaptive generations of informative experiments and their validation against simulated models. Identifying the incoherent noise of a quantum device in addition to its coherent interactions is, however, as essential. Precise knowledge of such imperfections of a quantum device allows one to devise strategies to mitigate detrimental effects, for example, via quantum error correction. We introduce the open Quantum Model Learning Agent (oQMLA) framework to account for Markovian noise through the Liouvillian formalism. By simultaneously learning the Hamiltonian and jump operators, oQMLA independently captures both the coherent and incoherent dynamics of a system. The added complexity of open systems necessitates advanced algorithmic strategies. Among these, we implement regularization to steer the algorithm toward plausible models and an unbiased metric to evaluate the quality of the results. We validate our implementation in simulated scenarios of increasing complexity, demonstrating its robustness to hardware-induced measurement errors and its ability to characterize systems using only local operations. Additionally, we develop a scheme to interface oQMLA with a publicly available superconducting quantum computer, showcasing its practical utility. These advancements represent a significant step toward improving the performance of quantum hardware and contribute to the broader goal of advancing quantum technologies and their applications.

We experimentally demonstrate the operation of a radiative thermal transistor capable of switching, modulating, and amplifying far-field heat currents. This three-terminal device exploits the metal-insulator transition of ${\mathrm{VO}}_2$ thin films deposited on both surfaces of a substrate using pulsed laser deposition (PLD). This phase transition induces a sharp variation of the infrared emissivity of the ${\mathrm{VO}}_2/\mathrm{substrate}/{\mathrm{VO}}_2$ system, acting as the transistor base placed between two heat flux sensors playing the roles of the emitter and collector. Unlike previous studies, we consider substrates of r-cut and c-cut sapphire, and $\mathrm{Si}/{\mathrm{Si}\mathrm{O}}_2$ to correlate different microstructural properties of ${\mathrm{VO}}_2$ to its emissivity variations and optimize the thermal performance of the developed thermal transistor. By measuring the heat fluxes emitter-base and base-collector, we find that the thermal transistor implemented with a ${\mathrm{VO}}_2/{\mathrm{Si}\mathrm{O}}_2/\mathrm{Si}$ base exhibits the highest thermal switching efficiency (with a value of 3.6) and the largest modulation amplitude (60 W/${\mathrm{m}}^2$), while the ${\mathrm{VO}}_2$ on r-sapphire base yields the highest amplification factor of 126. These record figures of merit underscore the critical role of the ${\mathrm{VO}}_2$ substrate selection and demonstrate the potential of radiative thermal transistors for advanced thermal management applications.

By integrating a dielectric microwave resonator with a piezoelectric-based strain device, we develop an in situ strain-tunable microwave spectroscopy technique that enables contactless measurements of material properties under strain. To demonstrate the capability of this device, we measure the strain-dependent microwave surface impedance of the representative iron-based superconductor ${\mathrm{Ba}\mathrm{Fe}}_2$(${\mathrm{As}}_{1-x}{\mathrm{P}}_x{)}_2$ at the slightly overdoped composition. We successfully control and observe the suppression of superconductivity under both compressive and tensile anisotropic lattice distortions along the tetragonal [110]${}_{\mathrm{T}}$ direction, as manifested by changes in the quality factor and resonance frequency shifts of microwave resonance. Furthermore, strain-induced changes in microwave surface resistivity, an extension of conventional DC-limit transport elastoresistivity to the microwave regime, provide information on electronic anisotropy equivalent to that of DC elastoresistivity, while offering a contactless alternative. Our strain-tunable cavity therefore serves as a powerful, contactless probe of fundamental material properties under strain and may also potentially facilitate the design of hybrid quantum systems with strain-engineered quantum degrees of freedom.

Parametric frequency converters (PFCs) play a critical role in bridging the frequency gap between quantum information carriers. PFCs in the microwave band are particularly important for superconducting quantum processors but their operating bandwidth is often strongly limited. Here, we present a multimode kinetic metastructure for parametric frequency conversion between broadly spanning frequency modes. This device comprises a chain of asymmetric kinetic inductance grids designed to deliver efficient three-wave-mixing nonlinearity. We demonstrate highly efficient coherent conversion among broadly distributed modes and the mode frequency is continuously tunable by controlling the external magnetic field strength, making it ideally suited for quantum computing and communication applications requiring flexible and efficient frequency conversion.