Characterization of quantum devices generates insights into their sources of disturbances. State-of-the-art characterization protocols often focus on incoherent noise and eliminate coherent errors when using Pauli or Clifford twirling techniques. This approach biases the structure of the effective noise and adds a circuit and sampling overhead. We motivate the extension of an incoherent local Pauli noise model to coherent errors and present a practical characterization protocol for an arbitrary gate layer. Notably, the coherent noise estimation is robust to Pauli noise. We demonstrate our protocol on a superconducting hardware platform and identify the leading coherent errors. To verify the characterized noise structure, we mitigate its coherent and incoherent components using a gate-level coherent noise mitigation scheme in conjunction with probabilistic error cancelation. The proposed characterization procedure opens up possibilities for device calibration, hardware development, and improvement of error mitigation and correction techniques.

Quantized surface acoustic waves (SAWs) in piezoelectric media have been studied recently, and they can be used to control the electric dipoles of quantum systems via the electric field produced through the piezoelectric effect. However, it is not easy nor convenient to manipulate magnetic moments directly by an electric field. Here we study a quantum theory of SAWs in a piezomagnetic medium. We show that the intrinsic properties of the piezomagnetic medium enable the SAW in the piezomagnetic medium to interact directly with magnetic moments of quantum systems via the magnetic field induced by the piezomagnetic effect. By taking a strip SAW waveguide made of a piezomagnetic medium as an example, we further study the coupling strengths between different magnetic quantum systems with magnetic moments and the quantized single-mode SAW in the waveguide. Based on this, we discuss the interaction between magnetic quantum systems mediated by a quantized multimode SAW in a piezomagnetic waveguide. Our study provides a convenient way to directly control magnetic quantum systems by quantized SAWs, and offers potential applications to on-chip information processing based on solid-state quantum systems via quantized acoustic waves.

The extrinsic stacking sequence based on intrinsic crystal symmetry in multilayer two-dimensional materials plays a significant role in determining their electronic and optical properties. Compared with Bernal-stacked (ABA) multilayer graphene, rhombohedral (ABC) multilayer graphene hosts stronger electron-electron interaction due to its unique dispersion at low-energy excitations and has been utilized as a unique platform to explore strongly correlated physics. However, discerning the stacking sequence via scanning mapping methods has always been a fairly time-consuming process. Here, we report a rapid recognition method for ABC-stacked graphene with high accuracy by infrared imaging based on the distinct optical responses in the infrared range. The optical contrast of the image between ABC- and ABA-stacked graphene is strikingly clear, and the discernibility is comparable to traditional optical Raman microscopy but with higher consistency and throughput. We demonstrate that the infrared imaging technique can be integrated with dry transfer techniques commonly used in the literature. This rapid and convenient infrared imaging technique will significantly improve the sorting efficiency for differently stacked multilayer graphene, thereby accelerating the exploration of the novel emergent correlated phenomena in ABC-stacked graphene.

Invertible logic is an unconventional computing paradigm that enables bidirectional logic operations between inputs and outputs, and holds significant promise for solving critical complex problems. Here we propose a network of coupled chaotic systems that function as deterministic analogues of probabilistic “$p$-bits,” to implement parallel invertible logic. In the forward mode, the network has the capability to process inputs to implement the fundamental logic operations NOR/NAND, and their complementary operations OR/AND, in parallel. In the reverse mode, the states of the input nodes yield all possible logical inputs consistent with the truth table of the logic functions for a given output, with the network again having the capacity to implement inverse logic operations in parallel. Our basic idea leverages the existence of distinct attractor geometries, with varying residence times in state-space partitions, and exploits the transitions between these attractors to consistently mirror the logic operations, both in direct and inverse mode. Lastly, we provide proof-of-principle electronic circuit experiments to verify the concept, demonstrate the robustness of the architecture and its potential to be realized in physical implementations.

Feedback-based control of nano- and micromechanical resonators can enable the study of macroscopic quantum phenomena and also sensitive force measurements. Here, we demonstrate the feedback cooling of a low-loss and high-stress macroscopic SiN membrane resonator close to its quantum ground state. We use the microwave optomechanical platform, where the resonator is coupled to a microwave cavity. The experiment utilizes a Josephson traveling-wave parametric amplifier, which is nearly quantum-limited in added noise, and is important for mitigating resonator heating due to system noise in the feedback loop. We reach a thermal phonon number as low as 1.6, which is limited primarily by microwave-induced heating. We also discuss the sideband asymmetry observed when a weak microwave tone for independent readout is applied in addition to other tones used for the cooling. In a typical situation, the asymmetry can be attributed to the quantum-mechanical imbalance between emission and absorption. In specific situations, however, we find that the asymmetry is an artifact due to coupling of different sideband processes by cavity nonlinearity under multitone irradiation.

Magnetic field detection plays an important role in various fields, such as scientific research and industrial applications. Increasing attention has been paid to magnetometers based on quantum systems due to their capacity to achieve high sensitivity and precision. The nitrogen-vacancy center in diamond is recognized to be a promising candidate for quantum sensing due to its potential in realizing high sensitivity, nanoscale spatial resolution, good biocompatibility, and the capability of working under room-temperature conditions. However, implementing a comprehensively miniaturized and low-power-consumption nitrogen-vacancy magnetometer with subnanotesla sensitivity, which leads to practical applications, is still a challenge. Here, we present a compact magnetometer with full integration of all the required functional modules. The magnetometer can achieve a sensitivity of $390\mathrm{pT}/\sqrt{\mathrm{Hz}}$ within a volume of $10.5\times 9.3\times 4.5{\mathrm{cm}}^3$, and the total power consumption is 10.2 W. This work shows the way to realize practical $\mathrm{N}$-$V$ magnetometry.

Continuous evolution of superconducting properties as a function of carrier density is difficult to investigate experimentally, unlike the properties of a “gated” semiconductor. This is because superconductors, in general, have carrier densities that are too high for a dielectric insulated gate (as in field-effect transistors) to work. Using an ionic liquid gate, we demonstrate that the modulation of carrier density can alter the superconducting transition temperature by up to 204 mK in epitaxial indium nitride on gallium nitride, accounting for $\ge 10\mathrm{\%}$ of the transition temperature in ungated conditions. Our devices are in the metallic regime, in the moderately clean limit ($k_{F}l\approx 3$–$6$) throughout the gate voltage range, and their properties are therefore not primarily governed by strong localization, granularity, etc. The primary determinants of the transition temperature in $\mathrm{In}\mathrm{N}$, which is a degenerate semiconductor, are carrier density, screening, and interaction, rather than disorder scattering. We show that the observed behavior is consistent with Bardeen-Cooper-Schrieffer s-wave superconductivity, as corroborated by the superconducting parameters we measure. Furthermore, we observe up to $60\mathrm{\%}$ suppression of the supercurrent in our experiments. Both positive and negative gate voltages result in suppression of the critical current. Ionic liquid-gated $\mathrm{In}\mathrm{N}$ thus presents a platform in which s-wave superconductivity can be tuned at low carrier densities, almost 1000–10 000 times lower than in other systems such as niobium nitride. We point out potential areas where low carrier (superfluid) density can find useful applications.

The ionization-energy (IE) offset significantly impacts exciton dissociation and charge transfer in organic solar cells (OSCs). However, the optimal IE offset for efficient hole transfer remains uncertain. Herein, we explored the effect of IE offset on exciton dissociation and charge transfer in bilayer OSCs using simulations and experiments, focusing on PM6 as the donor and BTP-based acceptors (eC9-0Cl, eC9-2Cl, and eC9-4Cl). Varying the number of chlorine substitutions in the acceptors’ terminal groups results in IE offsets of 0.23, 0.30, and 0.47 eV for PM6/eC9-0Cl, PM6/eC9-2Cl, and PM6/eC9-4Cl, respectively. With the IE offset of 0.47 eV, a power conversion efficiency (PCE) of 17.7% was achieved, while a 0.3 eV offset still attained a modest 16.4%. Simulations reveal three key findings: the IE offset directly influences the maximum PCE a device potentially achieves; the PCE is affected by the mobility of charge carriers but not by their type; and lower bimolecular recombination rates correlate with higher PCE. We found a minimum IE offset of 0.3 eV, carrier mobility of $1\times {10}^{-8}{\mathrm{m}}^2/\mathrm{V}\mathrm{s}$, and bimolecular recombination rate of $1\times {10}^{-13}{\mathrm{cm}}^3/\mathrm{s}$ to achieve a PCE of over 20%. Our results provide guidelines for designing novel materials for high-efficiency bilayer OSCs.

Diamondlike-carbon (DLC) films are widely used as nanocoatings in devices such as in hard disk drives. However, the narrow spacing causes collisions between the head and disk and leads to wear of the nanocoatings. Herein, the nanoscale wear estimation approach during DLC head sliding is investigated. The molecular dynamics (MD) method is applied to create a systematic interface model that explores how the wear mechanisms of the DLC head transform. The mechanisms of wear debris formation are discussed by analyzing the corresponding spatial distributions. Based on the clear fundamental debris-level origins of the MD simulation, an improved wear law is proposed for time-resolved adhesive wear estimation at the nanoscale. The proposed law establishes a connection between the measurable quantity, that is, normal stress, and the height loss. It is applied to quantify the head’s height loss and additional simulations involving different external loads are performed to verify the applicability of the proposed wear law.

Detection of radioactive material at distances greater than the radiated particle range is an important goal with applications in areas such as national defense and disaster response. Here, we demonstrate avalanche-breakdown-based remote detection of a 3.6 mCi α-particle source at a standoff distance of 10 m, using 70 ps, long-wave infrared (λ = 9.2 µm) ${\mathrm{CO}}_2$ laser pulses. This is ∼10 times longer than our previous results using a mid-IR laser. The primary detection method is direct backscatter from microplasmas generated in the laser focal volume. The backscatter signal is amplified as it propagates back through the ${\mathrm{CO}}_2$ laser chain, enhancing sensitivity by >100 times. We also characterize breakdown plasmas with fluorescence imaging, and present a simple model to estimate backscattered signals as a function of the seed density profile in the laser focal volume. All of this is achieved with a relatively long-drive laser focal geometry (f/200) that is readily scalable to >100 m.

Chalcogenide is an essential construction material for emerging nanoelectro-optical memories and radio-frequency (rf) switches, yet the latter still lacks comprehensive insights from theoretical mechanisms to device components. Here, we conceive of a directly heated chalcogenide-based phase-change rf switch with two-dimensional constrained $\mathrm{Sb}$, a pivotal component of microwave switches capable of low energy consumption and ultrafast responses. In their quasi-two-dimensional amorphous counterparts, Peierls distortion is consolidated with highly localized electrons elevating the electrical resistivity of the scale-shrinking $\mathrm{Sb}$ that originates from quantum confinement effects, favoring low-Joule-heat energy barriers. The fabricated $\mathrm{Sb}$-based phase-change rf switch operates with insertion loss of less than 1.2 dB and isolation of greater than 18 dB (up to 67 GHz). The total switch energy consumption can be as low as $1.1\text{μ}\mathrm{J}$, with over 3 orders of magnitude switching ratio. The ultrafast recrystallization process in the dimensional limit benefits from glass homogeneity along with the topological rearrangement of the three- to fourfold rings, explaining the 300-ns ultrafast response of the rf switch regarding geometrical-physical relevance. This work provides insights into chalcogenide-based assembly for rf switches that allow for future reconfiguration of wireless and 6G communication systems.

Differential carrier lifetime (DCL) measurements were performed on c-plane ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}/\mathrm{Ga}\mathrm{N}$ single-quantum-well (QW) light-emitting diodes (LEDs) with varying indium-content QWs (x = 13.5%, 16%, 22%), emitting with violet, blue, and green wavelengths. The recombination lifetimes of LEDs were found to increase with increasing indium composition, resulting in increased carrier densities n measured by DCL. Extraction of the A coefficients, which are assumed to not vary with n, and of the effective B(n) and C(n) coefficients of the ABC model of the internal quantum efficiency (IQE) of QWs showed no significant changes in the A coefficient with increasing indium content [$\mathrm{In}$] in the ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ QW, and a reduction in the B(n) and C(n) coefficients with increasing [$\mathrm{In}$]. When looking at the Shockley-Read-Hall (SRH) recombination rate An, the radiative recombination rate B(n)$n^2$, and the Auger-Meitner (AM) recombination rate C(n)$n^3$, we observed that at any given n, the SRH rate is the same for the three [$\mathrm{In}$] measured, while the radiative rate decreases (by up to approximately 9 times) and the AM rate decreases (by up to approximately 7 times) with increasing indium content. This shows that the larger reduction in radiative recombination rates relative to nonradiative recombination rates with increasing [$\mathrm{In}$] is the largest contributor to the decreased quantum efficiencies of LEDs (the “green gap”) at any given n. While some of the reduction in the effective recombination coefficients B(n) and C(n) can be explained by the reduced wave-function overlaps of the QW with increasing indium content, the larger reduction of B(n) relative to C(n) motivates further study of the intrinsic recombination coefficients $B_0$ and $C_0$ of bulk ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ alloys and how they are related to the effective recombination coefficients B(n) and C(n) in QWs. The relative contributions of nonradiative recombination are enhanced at any given current density due to the sublinear relationship between the carrier density n and the current density. Thus, the solution to the green gap, up to any intrinsic limitations set by the indium content of the QW, from an IQE perspective, requires the design of long-wavelength $(\mathrm{In},\mathrm{Ga})\mathrm{N}$ LEDs with improved wave-function overlaps that can operate with a lower carrier density at any given current density.

In piezoacoustic drop-on-demand inkjet printing, a single droplet is produced for each piezoelectric actuator driving pulse. This droplet is typically multicomponent, including surfactants to control the spreading and drying of the droplet on the substrate. However, the role of these surfactants in the droplet formation process remains rather elusive. Surfactant concentration gradients may manifest themselves across microsecond-to-second timescales, spanning both the rapid ejection of ink from the nozzle exit and the comparatively slower idling timescale governing the firing of successive droplets. In the present work, we study the influence of surfactants on droplet formation across 6 orders of magnitude in time. To this end, we visualize the microsecond droplet formation process using stroboscopic 8 ns laser-induced fluorescence microscopy while we vary the nozzle idle time. Our results show that increasing the idle time up to $\mathcal{O}$(1) s affects only the breakup dynamics of the inkjet but not its velocity. By contrast, for idle times greater than $\mathcal{O}$(1) s, both the breakup dynamics are altered and the velocity of the inkjet increases. We show that the increased velocity results from a decreased surface tension of the ejected droplet, which we observed from the shape oscillations of the jetted droplets in flight. The measured decrease in surface tension is surprising as the microsecond timescale of droplet formation is much faster than the typical millisecond-to-second timescale of surfactant adsorption. By varying the bulk surfactant concentration, we show that the fast decrease in surface tension results from a local surfactant concentration increase to more than 200 times the critical micelle concentration. Numerical simulations then show that the evaporation-driven increased surfactant concentration present at the nozzle exit results in the surface of the droplet being fully coated during its ejection. Altogether, our results suggest that a local high concentration of surfactant allows surfactant adsorption to the interface of an inkjet on the microsecond-to-millisecond timescale, which is much faster than the typical millisecond-to-second timescale associated with surfactant adsorption.

Superresolution focusing has wide applications in ultrasonics. Here, we propose a modified Fresnel-spiral lens (MFSL) consisting of Fresnel spiral (FS) slits and embedded phase gratings to achieve superresolution ultrasonic focusing. The FS slits can push low spatial frequency components of the transmitted ultrasonic wave into high spatial frequencies with minimal energy loss, while the phase gratings exert additional phase lag that the overall topological charge is zero. Then, a subdiffraction hot spot with tiny sidelobes is obtained at the focal plane. The focusing resolution of the MFSL can approach the theoretical limit of 0.38λ with the increasing numerical aperture (NA). It is also found that the focusing resolution of the MFSL is robust to structure features and that the focusing efficiency is influenced by both the slit width and the number of spiral arms. Finally, we demonstrate the superresolution ultrasonic focusing capability of the proposed MFSL through experiments. Our work offers an alternative strategy to realize high-efficiency subdiffraction ultrasonic focusing, which may have important implications for medical imaging and treatment, remote sensing and communication, and particle manipulation.

A scalable and programmable quantum computer holds the potential to solve computationally intensive tasks that classical computers cannot accomplish within a reasonable time frame, achieving quantum advantage. However, the vulnerability of the current generation of quantum processors to errors poses a significant challenge towards executing complex and deep quantum circuits required for practical problems. Quantum error-correction codes such as stabilizer codes offer a promising path forward for fault-tolerant quantum computing; however, their realization on quantum hardware is an on-going area of research. In particular, fault-tolerant quantum processing must employ logical gates on logical qubits with error suppression with realistically large size codes. This work has implemented a transversal controlled-not (cnot) gate between two logical qubits constructed using the repetition code with flag qubits, and demonstrated error suppression with increasing code size under multiple rounds of error detection and correction. Our results conducted on IBM quantum devices through cloud access show that despite the potential for error propagation among logical qubits during the transversal cnot gate operation, scaling the code distance as we increase the number of physical qubits from 21 to 39 and 57 can suppress errors, which persists over ten rounds of error detection and correction. Our work establishes the feasibility of employing logical cnot gates alongside error detection on a superconductor-based processor using current generation quantum hardware.

Performing parallel-gate operations while retaining low crosstalk is an essential step in transforming neutral-atom arrays into powerful quantum computers and simulators. Tightly focusing control beams in small areas for crosstalk suppression is typically challenging and can lead to imperfect polarization for certain transitions. We tackle such a problem by introducing a method to engineer single-qubit gates through phase-modulated continuous driving. Distinct qubits can be individually addressed to high accuracy by simply tuning the modulation parameters, which significantly suppresses crosstalk effects. When arranged in a lattice structure, optimal crosstalk suppression can be achieved by choosing the appropriate modulation parameters. With the assistance of additional addressing light or multiple modulation frequencies, we develop two parallel-gate schemes with efficient and easy experimental implementations compared to existing light-shift methods. Our results pave the way to scaling up atom-array platforms and achieving individual-atom control of a three-dimensional array with low-error parallel-gate operations, without requiring complicated wavefront design or high-power laser beams.

The longitudinal optical confinement factor (${\mathrm{\Gamma }}_z$) in vertical-cavity surface-emitting lasers (VCSELs) is typically negatively correlated with the lasing threshold ($P_{\mathrm{th}}$), but is commonly small due to the limited distribution of the active layer in a cavity. To enhance ${\mathrm{\Gamma }}_z$ and reduce $P_{\mathrm{th}}$, we introduce a novel design for colloidal quantum-dot (CQD) VCSELs based on the gain medium integrated distributed Bragg reflector (GI-DBR). The CQDs integrated into these VCSELs not only act as the high-index medium of the DBR that supports a high reflectivity but also as the active medium for amplifying the emission. The overlap between the electric field antinodes and the gain region is significantly improved, leading to a ${\mathrm{\Gamma }}_z$ up to 83%, which is 108% higher than that of the control sample with a traditional dielectric DBR-based structure. Consequently, the $P_{\mathrm{th}}$ is expected to be 59% lower according to the simulation result. Moreover, this GI-DBR-based structure reveals excellent general applicability to enable low-threshold lasing from VCSELs composed of diverse materials.