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.

We theoretically study the electromagnetic wave radiation of magnons driven by acoustic phonons in systems with strong magnon-phonon interaction. We evaluate the field dependence of radiation intensity spectra that exhibits the avoided crossing, a characteristic of strongly coupled systems. At the crossover where the magnon and phonon eigenstates are hybridized, we demonstrate the existence of two resonant radiation frequencies with circular polarization and the enhancement of antenna radiation efficiency by over 100 times. We can also reconfigure the ellipticity of the antenna polarization by changing the applied out-of-plane magnetic field. Our results open up possibilities of developing ultracompact antennas by using the hybridized magnon-phonon mode.

Generation of circularly polarized high harmonics with the same helicity to all orders is indispensable for chiral-sensitive spectroscopy with attosecond temporal resolution. Solid-state samples have added a valuable asset in controlling the polarization of emitted harmonics. However, maintaining the identical helicity of the emitted harmonics to all orders is a daunting task. In this work, we demonstrate a robust recipe for efficient generation of circularly polarized harmonics with the same helicity. For this purpose, a nontrivial tailored driving field, consisting of two co-rotating laser pulses with frequencies $\omega$ and $2\omega$, is utilized to generate harmonics from graphene. The Lissajous figure of the total driving pulse exhibits an absence of rotational symmetry, which imposes no constraint on the helicity of the emitted harmonics. Our approach to generating circularly polarized harmonics with the same helicity is robust against various perturbations in the setup, such as variation in the subcycle phase difference or the intensity ratio of the $\omega$ and $2\omega$ pulses, as rotational symmetry of the total driving pulse remains absent. Our approach is expected to be equally applicable to other two-dimensional materials, among others, transition-metal dichalcogenides and hexagonal boron nitride, as our approach is based on the absence of rotational symmetry of the driving pulse. Our work paves the way for establishing compact solid-state chiral extreme ultraviolet sources, opening a realm for chiral light-matter interaction on its intrinsic timescale.

The hot-carrier solar cell (HCSC) has the potential for converting solar energy into electrochemical energy with an efficiency of 85.4%. For this, in addition to an idealized light absorber, the HCSC has to be connected to the external load by means of the so-called monoenergetic energy-selective contacts (ESCs). However, the thermodynamic properties that these types of contact have to exhibit, such as their electric, thermal conductivity, and Seebeck coefficient, have not been explored. This paper aims to fill this gap. In this respect, we model electron transport in nonideal ESCs using the transport theory proposed by Datta and Landauer, which has allowed us to calculate the value of these parameters as a function of the temperature and electrochemical potential of operation. Our findings also reveal that, to preserve the HCSC efficiency above 82%, the ESCs could require in the order of $3\times {10}^{19}{\mathrm{cm}}^{-3}$ electron states. As the ESCs depart from ideality, the temperature of the hot carriers at which optimum efficiency is obtained increases to above 2540 K. The monoenenergetic selective contact characterized by the highest energy demands an electric, thermal conductivity, and Seebeck coefficient that, when combined, are characterized by a high thermoelectric figure of merit $(ZT\approx 8)$. We are not aware of any material exhibiting this figure of merit, which illustrates the difficulty in putting the HCSC concept into practice. Conversely, our work supports the idea that pursuing materials capable of transporting electrons ballistically through monoenergetic electron channels can provide the key for achieving materials characterized by high $ZT$.

The emergence and development of acoustic artificial materials stimulate a large number of applications for the manipulation of ultrasonic and elastic waves. Most of the reported metasurfaces and metamaterials only work effectively at a given frequency and target a fixed functionality. Reconfigurable designs may solve this problem, to a certain extent, but require the introduction of complex active control components. Here, by integrating multiple functionalities on a conformally mapped Mikaelian lens with a hyperbolic secant refractive-index distribution, a broadband passive lens is presented and accomplished on an elastic plate. Just by adjusting the location and type of source, different regulations of flexural waves can be switched from one sort to another. Through projecting the refractive-index profile onto the thickness of the plates, the proposed Mikaelian lens is designed and fabricated. Theoretical prediction and experimental results demonstrate beam scanning at an angle of up to 120° from 30 to 180 kHz and achromatic subwavelength focusing with a full width at half maximum of around 0.3λ from 30 to 120 kHz. Without using locally resonant materials or active control elements, this work provides a feasible way to construct multifunctional flexural-wave devices.

This paper proposes a scheme and design of a cryogenic multiplexing control chip (MCC), which enables one microwave cable to control many superconducting qubits. Designed based on an adjustable inductor, the MCC is a nonreciprocal device that generates microwave signals between 4 and 8 GHz and constructs a $XY$ control circuit to operate qubits. The effects of filters, isolators, power splitters, qubits, and load impedance on the MCC are analyzed in the frequency-domain simulation. And in the time-domain simulation, the response time, Gaussian pulses, single sideband, amplitude, and frequency compensation of the MCC are examined. The MCC can be integrated with the superconducting qubits on the same package at the 20-mK temperature stage with insertion loss of $-6$ dB and isolation of $-26$ dB. The time-domain simulation has revealed that the output specific microwave pulses of the MCC can be used for driving the superconducting qubits with crosstalk of about $-80$ dB. This is much less than $-40$ dB of the physical requirements on crosstalk, which can meet fidelity on single-qubit (99.92%) and two-qubit gates (99.40%). The power dissipation for each qubit control is less than 1 pW. The MCC can greatly reduce the number of microwave control lines and is beneficial to the development of a large-scale superconducting quantum processor.

Hybrid superconducting-photonic microresonators are a promising platform for realizing microwave-to-optical transduction. However, the absorption of scattered photons by the superconductors leads to unintended microwave resonance-frequency variation and line-width broadening. Here, we experimentally study the dynamics of this effect and its impact on microwave-to-optics conversion in an integrated lithium niobate–superconductor hybrid-resonator platform. We unveil an adiabatic frequency shifting of the intracavity microwave photons induced by the fast photoresponses of the thin-film superconducting resonator. As a result, the temporal and spectral responses of electro-optics transduction are modified and well described by our theoretical model. This work provides insights into the light-induced conversion dynamics that must be considered in future designs of hybrid superconducting-photonic system.

Driven quantum nonlinear oscillators, while essential for quantum technologies, are generally prone to complex chaotic dynamics that fall beyond the reach of perturbative analysis. By focusing on subharmonic bifurcations of a harmonically driven oscillator, we provide a recipe for the choice of the oscillator’s parameters that ensures a regular dynamical behavior independently of the driving strength. We show that this suppression of chaotic phenomena is compatible with a strong quantum nonlinear effect reflected by the confinement rate in the degenerate manifold spanned by stable subharmonic orbits.