Crosstalk is a key obstacle to scaling up quantum computers. It may arise from persistent qubit-qubit couplings or dynamically during gate operation, with the latter being particularly difficult to detect. Here, we introduce the perfect-entangler spectrum as a means to identify dynamic crosstalk leading to undesired entanglement. It leverages the geometric classification of two-qubit gates in terms of perfect entanglers. We exemplify the application of the spectroscopy for fixed-frequency transmons and parametrically driven gates. When scanning the frequency of a spectator qubit, peaks in the perfect-entangler spectrum signal dynamic crosstalk, and analysis of the peaks reveals the mechanisms causing the crosstalk. We discuss the experimental implementation of the crosstalk spectroscopy, which requires two two-qubit gate tomographies.

Using scanning tunneling microscopy-induced luminescence (STML), the optical properties of two-dimensional (2D) semiconductors may be investigated at the nanoscale. This is possible because the tunneling current under the tip is an extremely localized electrical excitation source. However, in most STML applications, the spatial distribution of the emission relative to the excitation point is unresolved. Yet this distribution contains key information about how the interaction of excitons with injected charge carriers affects the luminescence of these materials, and about exciton transport. Resolving this spatial distribution at the nanoscale is relevant both for a fundamental understanding of exciton physics and for device applications; yet it remains a significant challenge. In this work, we resolve the spatial distribution of the emission beyond the diffraction limit of light by deconvolving real-space optical microscopy images of the STML using an iterative algorithm, i.e., Richardson-Lucy (RL) deconvolution. To showcase this technique, we apply it to the STML of monolayer tungsten diselenide (${\text{WSe}}_2$) and tungsten disulfide (${\text{WS}}_2$). Thus, we highlight hitherto ignored or misunderstood aspects of STML on 2D semiconductors related to exciton and charge carrier transport, namely the dependence of the spatial distribution of emission on the tunnel current setpoint and the origin of the emission from hot spots located micrometers from the excitation source.

Imaging polarimetry is becoming an increasingly significant tool, from remote sensing to material characterization. In reactive plasmas, polarimetry is a well-established in situ diagnostic for the size and the complex refractive index of synthesized particles. We present the StokesCam, a self-calibrating, full-Stokes imaging polarimeter based on two micropolarizer cameras. It employs an adapted eigenvalue calibration to address the problem of spatial inhomogeneities and artifacts in polarization optics. A comprehensive uncertainty analysis is provided, using a bootstrapping and Monte Carlo technique to quantify the systematic and statistical errors. The application of the StokesCam to a particle growth process in a reactive plasma is demonstrated as an example of demanding measurement conditions. The device provides high-quality data for scattering modeling and enables not only the spatial monitoring of particle growth but also allows for future studies of the system’s asymmetric multiscattering. This work also serves as a practical guide for readers interested in constructing and deploying their own full-Stokes imaging polarimeter.

Record wall-plug efficiencies in long-wavelength, III-nitride light-emitting diodes (LEDs) have recently been achieved through improvements in electrical efficiency in devices containing V-defects. Numerical modeling suggests this may be due to reduced barrier heights for charge injection in thinned, low-Indium quantum wells parallel to semipolar V-defect facets. To test this proposition, the tip of a scanning tunneling luminescence microscope is used as a local hole injector to map the optoelectronic properties of commercial, green-emitting LED heterostructures around V-defects with nanoscale spatial resolution. A 1 V reduction in the forward bias necessary for current injection at V-defect rims is observed. This, combined with the observation of small (approximately 10 meV) blue shifts in the locally emitted electroluminescence, unambiguously confirms the charge injection mechanism.

Acoustic higher-order topological insulators (AHTIs) hosting topological corner states provide a promising way for the robust localization of acoustic waves. However, energies of prior corner states are localized within a limited area, restricting their applications in the large-area localization of acoustic waves. Meanwhile, despite the critical importance of operating frequency for acoustic device performance, precisely engineering corner states at a specific frequency with a fixed lattice constant remains a challenge. Here, we theoretically propose and experimentally demonstrate an acoustic sandwich metastructure that hosts large-area corner state (LACS) with desired eigenfrequencies by inserting Dirac material layers within two topologically distinct domains. The spatial decay mechanism of LACS is revealed via complex band theory. The frequency of LACS can be finely tuned by modulating the frequency of Dirac material layers via a developed topology optimization algorithm. Furthermore, by spatially separating LACSs with distinct frequencies, we achieve the rainbow LACSs. Our work offers a route to designing AHTIs with tailored LACSs, thereby achieving large-area acoustic trapping with frequency-multiplexed and reconfigurable capabilities.

We demonstrate spin pumping driven by a strongly coupled magnon-photon system using a ferromagnet-coplanar superconducting resonator hybrid system at 1.4 K. Electrical readout via the inverse spin Hall effect reveals characteristic coupling features, including mode splitting and linewidth broadening, demonstrating the electrical detection of strongly coupled microwave photons and magnons. Magnon-photon coupling obtained by combined spin pumping and inverse spin Hall effect measurements is compared to microwave transmission experiments. Furthermore, microwave-power-dependent measurements reveal a decrease in the coupling strength with increasing microwave power alongside the onset of nonlinearities of the superconducting resonator above a critical microwave-power threshold.

We investigate the fracture behavior of precracked triangular beam lattices whose elements have failure stresses drawn from a Weibull distribution. Through a statistical analysis and numerical simulations, we identify and verify the existence of three distinct failure regimes: (i) disorder is effectively suppressed, (ii) disorder manifests locally near the crack tip, modifying the crack morphology, and (iii) disorder manifests globally, leading to initially diffuse failure. Our model naturally reveals the key parameters governing this behavior: the Weibull modulus, quantifying the spread in failure thresholds, and a geometric quantity termed the slenderness ratio. We also reproduce the disorder-induced toughening reported in previous experimental and numerical studies, further demonstrating that its manifestation depends nonmonotonically on disorder. Crucially, our results indicate that this toughening cannot be simply connected to the amount of damage in the lattice, challenging interpretations that attribute increased fracture energy solely to enhanced crack tortuosity or diffuse failure. Overall, our results establish geometry as a powerful control parameter for regulating how disorder is expressed during fracture in beam lattices, with broader implications for the disorder-induced toughening in engineered materials.

Phase-change nanodroplets (PCNDs) are stimuli-responsive agents with growing relevance in applications ranging from materials science and smart systems to microfluidics, decontamination, and biomedical diagnostics and therapy. Targeted activation of PCNDs, where the liquid core transitions into a gas phase to form microbubbles, can be achieved by using external energy sources. While ultrasound and laser-based modalities are typically used for PCND activation, their limited penetration depth in many complex materials and structures poses challenges for deeper targets. In this study, a new microwave-induced nanodroplet activation mechanism is proposed, and its feasibility is demonstrated using an ultrawideband microwave antenna. The experiments were designed to evaluate the effect of microwave exposure on lipid-shell perfluoropentane nanodroplets across a temperature range of 20–70 °C and at varying microwave exposure durations. Findings of this study show that longer duration microwave exposure results in a higher number of PCND activations at lower temperatures without any bulk temperature increase, where statistically significant differences ($p<0.001$) are observed for the 5-min microwave exposure group in comparison with the control group at 50 °C. This statistical significance implies that the microwave exposure reduces the activation threshold of PCNDs, offering a promising approach for noncontact, controlled, and targeted PCND activation in settings where conventional energy-delivery methods are limited.

Recently proposed metastability-induced quantum batteries have shown particular promise for coherent microwave generation. However, achieving high-power coherent microwave generation in quantum batteries remains fundamentally challenging due to quantum correlations, aging, and self-discharging processes. For the cavity-quantum-electrodynamics-based quantum batteries, a further trade-off arises between strong spin-photon coupling for energy storage and sufficient output coupling for power delivery. To overcome these constraints, we introduce dissipation engineering as a dynamic control strategy that temporally separates energy storage and release. By suppressing emission during charging and rapidly enhancing the output coupling during discharging, we realize nanosecond microwave bursts with watt-level peak power. By optimizing three dissipation schemes, we improve work extraction efficiency of the quantum battery by over 2 orders of magnitude and achieve high-power compression factors outperforming the state-of-the-art techniques, establishing dissipation engineering as a pathway toward room-temperature, high-power coherent microwave sources.

Newton’s constant is the least well measured among the fundamental constants of nature, and, indeed, its accurate measurement has long served an experimental challenge. Levitated mechanical systems are attracting growing attention for their promising applications in sensing and as an experimental platform for exploring the intersection between quantum physics and gravitation. Here, we propose a mechanical interferometric scheme of interacting levitated oscillators for the accurate estimation of Newton’s constant. Our scheme promises to beat the current standard by several orders of magnitude.

We present a method to calculate the frequency components of a pump waveform driving a parametric oscillator, which realizes a desired frequency mixing or scattering between frequency modes. The method is validated by numerical analysis, and we study its sensitivity to added Gaussian noise. A series of experiments apply the method and demonstrate its ability to realize complex scattering processes involving many modes at microwave frequencies, including nonreciprocal mode circulation. We also present an approximate method to dynamically control mode scattering, capable of rapidly routing signals between modes in a prescribed manner. These methods are useful tools for encoding and manipulating continuous-variable quantum information with multimodal Gaussian states.

Caloric cooling offers a promising solid-state alternative to conventional refrigeration. A traditional strategy to enhance cooling performance is increasing disorder-related configurational entropy change, which is a phenomenological approach and sometimes fails. Here, we establish a unified phonon-entropy framework applicable to electrocaloric, magnetocaloric, and mechanocaloric systems. By deriving analytical expressions that link entropy to the phonon density of states and mode-specific entropy, we enable mode-level tuning of caloric performance. Under this framework, we propose three key criteria for high-performance mechanocaloric cooling: high low-frequency phonon density of states, large changes in the product of density of states and mode-specific entropy, and low Young’s modulus. Accordingly, we identify PbO as a superior mechanocaloric material, which exhibits a pressure-induced entropy change nearly 2.7 times greater than TiNi, currently among the best-performing mechanocaloric materials. These findings establish a quantitative framework for phonon-entropy-driven caloric cooling and open other avenues for materials design.

Electrons bound to the surface of liquid helium are an emerging quantum computing platform, offering the potential for highly mobile spin qubits that can be manipulated using complementary metal-oxide-semiconductor (CMOS)-fabricated devices. Here, as a step toward realizing this technology, we demonstrate selective two-dimensional shuttling of electrons across a helium film condensed on the surface of a CMOS control chip. The electrons are moved in packets containing, on average, several tens down to single electrons. We perform CCD-style electron shuttling in any of 128 transport microchannels, each of which links electron storage zones and sensing zones in the two-dimensional plane. This shuttling “unit cell” is repeated 32 times across the chip, allowing packet sensing to be performed in parallel. Despite the resulting gain in sensitivity, we find no evidence of electron loss after repeating shuttling sequences at least ${10}^9$ times. The device serves as a prototype quantum information processing platform that is readily scalable to control large monolithically integrated arrays of electron spins.

We propose a scalable dual-species fluxonium-transmon system that utilizes a central transmon to mediate high-fidelity gates and parity checks between two fluxonium qubits without the need for strong nonlocal interactions. This approach suppresses unwanted long-range interactions, which is critical for developing larger quantum processors. First, we analyze the performance of cross-resonance (CR) cnot gates between a fluxonium and a transmon. We show that even in the presence of a spectator qubit, these gates maintain high fidelity with coherent errors on the order of ${10}^{-5}$. We then demonstrate that these gates, when applied sequentially, enable high-fidelity parity checks and logical fluxonium-fluxonium cnot gates. In addition, the central transmon can facilitate the readout of the neighboring fluxoniums, consolidating multiple critical functions into a single ancilla. Our work establishes the viability of a dual-species architecture as a promising path toward fault-tolerant quantum computation.

The surface of three-dimensional topological insulators (TIs) constitutes an intriguing system for hosting Majorana zero modes (MZMs) when rendered superconducting via the proximity effect. To study the peculiar role of MZMs and the accompanied $4\pi$-periodic energy-phase relation in TI-based Josephson junctions (JJs), we constructed a superconducting flux qubit out of a JJ based on ${\text{Sn}}_{0.02}{\text{Bi}}_{1.08}{\text{Sb}}_{0.9}{\text{Te}}_2\mathrm{S}$ (Sn-doped BSTS). In the vicinity of the qubit’s sweet spot, we obtained a two-tone spectrum that differed from that of a conventional flux qubit. The analysis employing different models suggests the existence of 4π-periodic supercurrents in the junction. The results support the fact that superconducting flux qubits incorporating TI-based JJs may serve as a potential platform for the detection and further braiding of MZMs.

The precise measurement of spatial attitude parameters is critical for applications in inertial navigation, industrial monitoring, instrument calibration, and quantum metrology. In this work, we theoretically investigate and experimentally realize the simultaneous measurement of the yaw and pitch angles using a Hermite-Gaussian-postselected double weak-value system integrated with two sets of high-order-mode balanced homodyne detections, thereby achieving a complete characterization of the beam deflection. Signals of the yaw and pitch angles that are involved in ${\text{TEM}}_{10}$ and ${\text{TEM}}_{01}$ modes output from two dark ports of the system can be measured independently. As a result, the obtained minimum measurable yaw and pitch angles of beam deflection are 83 and 89 prad, respectively. This work expands the beam-deflection measurement to two dimensions, providing new insights for future high-precision multiparameter spatial precise detection.

Dynamic atom gravimeters enable absolute gravity measurements on moving platforms. However, their performance is severely degraded due to the complex dynamic environment. This paper finds that the amplitude-modulation noise (AMN) is a key factor contributing to the degradation of gravity- measurement performance. We find that the AMN is induced by the cold atomic cloud trajectory and velocity variation. We build a model to illustrate the principles and magnitude of AMN arising from various experiment processes. Then we propose a method to fit the normalized AMN with respect to the kinematic parameters of the cold atomic cloud and successfully suppress this noise from 0.11 to 0.038 using the fitting result. With this method, we improve the fringe phase resolution from 0.244 to 0.092 rad and reduce the dynamic gravity-measurement noise from 2.69 to 1.68 mGal. This study finds and suppresses a key noise source in dynamic atom gravimeters, which is useful for further improving their precision. The proposed method can also be applied for precision enhancement for other dynamic atom-interferometer-based sensors, such as atom gradiometers and gyroscopes.

The properties of quantum dot–based spin qubits have significant interdevice variability due to the unavoidable presence of various types of disorder in semiconductor nanostructures. A significant source of this variability is charge disorder at the semiconductor-oxide interface, which causes unpredictable, yet, as we show here, correlated fluctuations in such essential properties of quantum dots, such as their mutual tunnel couplings, and electronic confinement energies. This study presents a systematic approach to characterize and mitigate the effects of such disorder. We use finite-element modeling of a $\mathrm{Si}$/$\mathrm{Si}$-$\mathrm{Ge}$ double quantum dot to generate a large statistical ensemble of devices, simulating the impact of trapped interface charges. This work results in a predictive statistical model capable of generating realistic artificial data for training machine-learning algorithms. By applying principal component analysis to this dataset, we identify the dominant modes through which disorder affects the multidimensional parameter space of the device. Our findings show that the parameter variations are not arbitrary, but are concentrated along a few principal axes—i.e., there are significant correlations between many properties of the devices. We finally compare that against control modes generated by sweeping the gate voltages, revealing limitations of the plunger-only control. This work provides a framework for enhancing the controllability and tunability of spin qubit devices, by systematically addressing the nature of electrostatic disorder that leads to statistical correlations in properties of double quantum dots.

Obtaining accurate representations of the eigenstates of an array of coupled superconducting qubits is a crucial step in the design of circuit quantum electrodynamics- (circuit-QED) based quantum processors. However, exact diagonalization of the device Hamiltonian is challenging for system sizes beyond tens of qubits. Here, we employ a tensor network method based on a variant of the density matrix renormalization group (DMRG) algorithm, DMRG-X, to efficiently obtain localized eigenstates of a two-dimensional transmon array without the need to first compute lower-energy states. We also introduce MTDMRG-X, a new algorithm that combines DMRG-X with multitarget DMRG to efficiently compute excited states even in regimes with strong eigenstate hybridization. We showcase the use of these methods for the analysis of long-range couplings in a multitransmon Hamiltonian including qubits and couplers, and we discuss eigenstate localization. These developments facilitate the design and parameter optimization of large-scale superconducting quantum processors.