Measuring the height of steplike features in samples has become important in many scientific and industrial applications. It is routinely done using both tactile and optical methods, the latter being preferable due to their noncontact nature and improved speed capabilities. Nevertheless, techniques less sensitive to instabilities or without calibration or reference sample requirements would be advantageous. Here, we propose a method to measure nanometric step heights based on a modal analysis of the reflected or transmitted field. Our approach requires a minimum of four single-point measurements by detectors with no spatial resolution (photodiodes) and yet can reconstruct spatial structure with nanometric resolution. It has the benefits of not requiring a reference measurement or calibration and it is completely digital, thus offering high reliability and real-time measurement. As proof of principle, we perform measurements on reflective samples, finding excellent agreement between the set and measured values, with uncertainties comparable to those of scanning-force microscopes.

Superatomic materials are newly emerging candidates for high-performance thermoelectric (TE) devices due to their intrinsic ultralow thermal conductivities. However, the low TE power factor becomes a huge obstacle to reaching the required dimensionless figure of merit (ZT) values for practical applications. Here, motivated by the recently synthesized superatomic ${\mathrm{Re}}_6{\mathrm{Se}}_8{\mathrm{I}}_2$ monolayer [He et al. J. Am. Chem. Soc. 144, 74 (2022)], we study its superior TE properties by using density functional theory combined with phonon Boltzmann transport theory and deep potential molecular dynamics. We show that the large mass and anharmonic $\mathrm{Re}—\mathrm{I}$ bonds introduce strong phonon scattering and result in a low lattice thermal conductivity of 1.20 W m${}^{-1}$ K${}^{-1}$ at 300 K, while the strong and harmonic $\mathrm{Re}—\mathrm{Se}$ network ensures a high TE power factor of 4344 µW m${}^{-1}$ K${}^{-2}$ in the b direction for n-type doping. This is an order of magnitude higher than those of other cluster-based materials. Owing to the low thermal conductivity and high TE power factor, ${\mathrm{Re}}_6{\mathrm{Se}}_8{\mathrm{I}}_2$ exhibits higher ZT values of 1.20 (500 K) and 1.43 (900 K) with n-type doping along the b direction compared with other cluster-based TE materials reported so far.

Nonreciprocal transport of electromagnetic waves within magnetized plasma is a powerful building block towards understanding and exploiting the properties of more general topological systems. Much recent attention has been paid to the theoretical issues of wave interaction within such a medium, but there is a lack of experimental verification that such systems can be viable in a lab or industrial setting. This work provides an experimental proof of concept by demonstrating nonreciprocity in a unit component, a microwave plasma circulator. We design an $E$-plane $Y$ junction plasma circulator operating in the range of 4 to 6 GHz using standardized waveguide specifications. From both simulations and experiments, we observe wide band isolation for the power transmission through the circulator. The performance and the frequency band of the circulator can be easily tuned by changing the plasma density and the magnetic field strength. By linking simulations and experimental results, we estimate the plasma density for the device.

Highly efficient elastic wave manipulation is crucial in the materials and physical engineering communities. Recently, coupling-interaction theory has attracted extensive attention to enhance the efficiency of traditional metamaterials. Here, experimental demonstrations of an elastic focusing metasurface with a dual-coupled resonator for high-efficient energy harvesting are exhibited. An easy-to-implement optimized elastic metasurface with bridged coupling, which is higher efficiency than traditional elastic metasurfaces, is proposed. Results show that a significantly enhanced efficiency, up to 239% is achieved, compared with a conventional metasurface. Furthermore, the robustness of the enhanced efficiency against variation of the focal point and frequency fluctuations of the incident waves is observed. The suggested device provides a simple feasible method for high-efficient energy harvesting.

We theoretically propose and experimentally demonstrate acoustic metasurfaces that exhibit undistorted transmission and configurable reflection, therefore serving as remarkable veil structures with camouflage effects for sonars, hereby denoted as acoustic metaveils. The metaveil is composed of a configurable array of two acoustic meta-atoms, which are the flipped counterparts of each other. Reciprocity and space inversion guarantee distortion-free transmission in an ultrabroad spectrum, irrespective of the arrangement of the array, while the reflection can be conveniently manipulated by changing the arrangement to produce the desired acoustic camouflage. Three types of unusual reflection behaviors are demonstrated, including diffuse reflection, multibeam reflection, and reflective focusing. The acoustic metaveils open a way to independently manipulate the reflection without influencing the acoustic transmission wave front, which is a crucial step for sonar stealth and camouflage.

Spin-based computing, combining logic and nonvolatile magnetic memory, is promising for emerging information technologies. However, the realization of a universal spin logic operation, representing a reconfigurable building block with all-electrical spin-current communication, has so far remained challenging. Here, we experimentally demonstrate reprogrammable all-electrical multifunctional spin logic operations in a nanoelectronic device architecture, utilizing graphene buses for spin communication and mixing and nanomagnets for writing and reading information at room temperature. This device realizes a multistate spin-majority logic operation, which is reconfigured to achieve (n)and, (n)or, and xnor Boolean operations, depending on the magnetization of inputs. The results are in good agreement with the predictions from a spin-circuit model, providing an experimental demonstration of a spin-based logic unit that takes advantage of the vector nature of spin, as opposed to conventional scalar charge-based devices. These spin logic operations in large-area graphene are fully compatible with industrial fabrication processes and represent a promising platform for scalable all-electric spin-based logic-in-memory computing architecture.

Superconducting flux qubits are promising candidates for the physical realization of a scalable quantum processor. Indeed, these circuits may have both a small decoherence rate and a large anharmonicity. These properties enable the application of fast quantum gates with high fidelity and reduce scaling limitations due to frequency crowding. The major difficulty of flux qubits’ design consists of controlling precisely their transition energy—the so-called qubit gap—while keeping long and reproducible relaxation times. Solving this problem is challenging and requires extremely good control of e-beam lithography, oxidation parameters of the junctions, and sample surface. Here we present measurements of a large batch of flux qubits and demonstrate a high level of reproducibility and control of qubit gaps ($\pm 0.6\mathrm{GHz}$), relaxation times ($15$–$20\text{μ}\mathrm{s}$), and pure echo dephasing times ($15$–$30\text{μ}\mathrm{s}$). These results open the way for potential applications in the fields of quantum hybrid circuits and quantum computation.

We report the implementation of energy-dispersive x-ray spectroscopy for high-resolution inspection of layered semiconductors in the form of atomically thin transition metal dichalcogenides down to the monolayer limit. The technique is based on a scanning electron microscope equipped with a silicon drift detector for energy-dispersive x-ray analysis. By optimizing operational parameters in numerical simulations and experiments, we achieve layer-resolving sensitivity for few-layer crystals down to the monolayer, and demonstrate elemental composition profiling in vertical and lateral heterobilayers of transition metal dichalcogenides. The technique can be straightforwardly applied to other layered two-dimensional materials and van der Waals heterostructures, thus expanding the experimental toolbox for quantitative characterization of layer number, atomic composition, or alloy gradients for atomically thin materials and devices.

A family of optical speckles with propagation-invariant annular morphology are generated via a phase-only mask and free-space evolution, termed vortex speckles, for which phase design is inspired by the vortex beam’s helical wave front carrying orbital angular momentum. Vortex beams’ graceful symmetry (central and/or axial) can be naturally inherited into vortex speckles by adjusting the parity of the topological value $\ell$ and the consistency of the initial phase angle ${\varphi }_0$. By sequentially imprinting such a series of phase profiles onto a spatial light modulator, the resultant stochastically fluctuating vortex speckles naturally constitute an annular pseudothermal light field, and the customized symmetry in intensity profiles leads to spatial correlations, which are exploited for Hanbury Brown and Twiss interferometry and beam-splitter-free lensless ghost imaging and diffraction experiments. Symmetric annular pseudothermal light also has diverse phase correlations, so in a proposed vortex self-interferometer, we can manipulate photon correlations (parity-induced anticorrelation) and observe intriguing correlation states (spatially varying photon correlation oscillations). This work not only presents a flexible light-source option for applications requiring ring-shaped speckle illumination, but it also paves the way for the customization of nontrivial classical correlation modes.

We propose a general approach to implement ultrafast nonadiabatic geometric single- and two-qubit gates by employing counter-rotating effects. This protocol is compatible with most optimal control methods used in previous rotating-wave approximation (RWA) protocols; thus, it is as robust as (or even more robust than) the RWA protocols. Using counter-rotating effects allows us to apply strong drives. Therefore, we can improve the gate speed by 5–10 times compared to the RWA counterpart for implementing high-fidelity ($\ge 99.99\mathrm{\%}$) gates. Such an ultrafast evolution (nanoseconds, even picoseconds) significantly reduces the influence of decoherence (e.g., the qubit dissipation and dephasing). Moreover, because the counter-rotating effects no longer induce a gate infidelity (in both the weak and strong driving regimes), we can achieve a higher fidelity compared to the RWA protocols. Therefore, in the presence of decoherence, one can implement ultrafast geometric quantum gates with $\ge 99\mathrm{\%}$ fidelities.

This paper presents numerical and experimental investigations of negative refraction at the interface between two mechanical rotator lattices, adding to the recent body of anomalous wave behavior reported for such simple lattices. Each lattice implements easily reconfigured interrotator coupling which determines whether the lattice’s passband is acoustic (with positive group velocity) or optic (with negative group velocity). Since the group velocities have opposite signs over the entirety of both lattices’ Brillouin zones, the negative refraction at their interface is inherently broadband. The numerical study constructs a large lattice structure for full-wave simulation and quantitatively analyzes the linear and nonlinear negative refraction. The experimental study documents robust negative refraction in a smaller-scale fabricated system and serves as validation for the numerical findings. We observe frequency-dependent transmission in both simulations and experiments. A linear analysis captures the observed phenomenon at low amplitude. At larger amplitudes, numerical simulations are used to document amplitude-dependent transmission. This phenomenon is explained by a nonlinear dispersion shift and transitional evanescent waves analyzed using a perturbation method. A sensitivity test demonstrates the robustness of negative refraction in the proposed rotator lattice structure.

Ventilated acoustic insulation currently represents one of the most promising research directions in applied acoustics. With the ongoing development and application of acoustic metamaterials, tremendous progress has been made in this space. In this work, we propose a ventilated acoustic insulator based on a labyrinthine metamaterial, a design that consists of a peripheral, circumferential labyrinthine region and a central ventilated, open region. Herein, we demonstrate the potential for this design to yield high-performance wide-band acoustic insulation, a performance metric currently lacking in this class of acoustic silencers, in combination with ventilation. The silencing effect of the labyrinthine acoustic insulator is theoretically and experimentally verified in the frequency range from 1025 to 2000 Hz. Our reported design establishes the foundation for the development of increasingly broadband ventilated acoustic insulators.

As progress is made towards the first generation of error-corrected quantum computers, robust characterization and validation protocols are required to assess the noise environments of physical quantum processors. While standard coherence metrics and characterization protocols such as $T_1$ and $T_2$, process tomography, and randomized benchmarking are now ubiquitous, these techniques provide only partial information about the dynamic multiqubit loss channels responsible for processor errors, which can be described more fully by a Lindblad operator in the master equation formalism. Here, we introduce and experimentally demonstrate Lindblad tomography, a hardware-agnostic characterization protocol for tomographically reconstructing the Hamiltonian and Lindblad operators of a quantum noise environment from an ensemble of time-domain measurements. Performing Lindblad tomography on a small superconducting quantum processor, we show that this technique naturally builds on standard process tomography and $T_1/T_2$ measurement protocols, characterizes and accounts for state-preparation and measurement errors, and allows one to place bounds on the fit to a Markovian model. Comparing the results of single- and two-qubit measurements on a superconducting quantum processor, we demonstrate that Lindblad tomography can also be used to identify and quantify sources of crosstalk on quantum processors, such as the presence of always-on qubit-qubit interactions.

The exceptional point (EP), a non-Hermitian degeneracy at which eigenvalues and eigenvectors coalesce simultaneously, is investigated in mechanical oscillators involving a time-varying mass. A dynamic modulation mechanism is employed to create the time-varying mass, which can potentially develop an EP by acting as an energy source and drain. To fully demonstrate the existence of EPs, the eigenvalue problem for the modulated system is theoretically formulated through two different schemes, based on the state-space and harmonic balance methods. A second-order EP is confirmed by both methods and exists as a result of the coalescence of fundamental and harmonic eigenmodes. As a salient property of this second-order EP, the square-root behavior of the eigenfrequency subject to small perturbations of the system parameters is theoretically demonstrated, and utilized to devise a proof-of-concept model for mechanical sensors with high sensitivity to void defects in elastic solids. The EP behavior induced by a time-varying mass may find potential applications in damage assessment and health monitoring of engineering structures.

Ultrashort terahertz pulse generation is essential for a range of proven terahertz applications, from time-resolved spectroscopy of fundamental excitations to nondestructive testing and imaging. Recently, it has been shown that semiconductor-based terahertz quantum cascade lasers (QCLs) can be used to generate pulses as short as a few picoseconds through active mode locking. However, further progress for subpicosecond and high peak power pulse generation is hampered by poor knowledge on how the electric field actually forms in these lasers. Here, we theoretically and experimentally show the amplitude- and phase-resolved buildup of pulse generation through active mode locking, from initiation of pulse generation to the nanosecond steady state. The experimental results, using an ultrafast coherent seeding technique to probe the laser from femtosecond to nanosecond time scales, are in full agreement with the theoretical calculations based on a theoretical model using multimode reduced rate equations. In particular, we show that the electric field buildup to achieve short pulse operation is extremely fast, requiring only a few photon round trips, owing to the ultrafast gain dynamics of the lasers. Further, this shows a gain recovery time of the order of a few picoseconds, an order of magnitude smaller than the photon round-trip time, highlighting that terahertz QCLs are categorically class-A lasers. This demonstration marks an important formulism for future progress towards exploring the ultrafast pulse generation buildup dynamics of these complex semiconductor lasers.

Efficient manipulation of magnetic materials is essential for spintronics. In conventional spin-current-generator/magnet (SCG/M) bilayers, interfacial spin-orbit torques (SOTs) lose effectiveness in applications that require large magnetic layer thicknesses to maintain magnetic anisotropy and stability at lateral sizes of tens of nanometers (e.g., magnetic tunnel junctions and racetrack nanowires). Here, we develop a universally workable three-dimensional spin-orbit material scheme in which the SOT efficiency can be remarkably boosted towards infinity by stacking [SCG/M/oxide]${}_n$ superlattices, with the oxide layers breaking inversion symmetry. We demonstrate that this superlattice scheme promotes not only perpendicular magnetic anisotropy for an effectively rather thick magnetic layer but also enables switching of such thick magnetic layers by interfacial SOTs with $n^2$ times lower power consumption than the corresponding conventional bilayer scheme with the same total thicknesses for the SCG and M. In contrast, we find that spin torque diminishes in second-type superlattices, [SCG/M]${}_n$, lacking inversion-symmetry breaking. These results provide an in-depth understanding of SOTs in magnetic multilayers and establish [SCG/M/oxide]${}_n$ superlattices as advantageous building blocks for the development of low-power, high-stability, and high-endurance spintronic memory and computing.

Current quantum computers are limited in the number of qubits and coherence time, constraining the algorithms executable with sufficient fidelity. The variational quantum eigensolver (VQE) is an algorithm to find an approximate ground state of a quantum system and is expected to work on even such a device. The deep VQE [K. Fujii, et al., arXiv:2007.10917] is an extension of the original VQE algorithm, which takes a divide-and-conquer approach to relax the hardware requirement. While the deep VQE is successfully applied for spin models and periodic material, its validity on a molecule, where the Hamiltonian is highly nonlocal in the qubit basis, is still unexplored. Here, we discuss the performance of the deep VQE algorithm applied to quantum chemistry problems. Specifically, we examine different subspace-forming methods and compare their accuracy and complexity on a 10 $\mathrm{H}$-atom treelike molecule as well as a 13 $\mathrm{H}$-atom version. Additionally, we examine the performance on the natural occurring molecule retinal. This work also proposes multiple methods to lower the number of qubits required to calculate the ground state of a molecule. We find that the deep VQE can simulate the electron-correlation energy of the ground state to an error of below 1%, thus helping us to reach chemical accuracy in some cases. The accuracy differences and qubits’ reduction highlights the basis creation method’s impact on the deep VQE.