Despite extensive research interests in perovskite oxides, low-energy consumption, nondestructive, and manoeuverable methods for phase transition in perovskite oxides are still under exploration, and the underlying mechanisms remain ambiguous. Here, optical susceptibility, including electron and anharmonic phonon contributions, is used to evaluate Gibbs free-energy variations of ${\mathrm{Pb}\mathrm{Ti}\mathrm{O}}_3$ and ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_3$ under terahertz irradiation. This corresponds to an off-resonant light-controlled phase transition, rather than the resonant approaches that excites hot carriers over electronic band or infrared-active vibrations in the phonon band. We show that intermediate terahertz light can trigger polarization change between ferroelectric orientation variants of ${\mathrm{Pb}\mathrm{Ti}\mathrm{O}}_3$ at room temperature. Similarly, the phase transformation from low-symmetric ferroelectric phase to high-symmetric paraelectric structure in ${\mathrm{Pb}\mathrm{Ti}\mathrm{O}}_3$ can be driven by changing the polarization and intensity of the incident light. Analogous results are obtained in ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_3$. In detail, the phonon spectrum and optical susceptibility exhibit strong temperature dependence, in which we show significant effects of anharmonic vibration. In order to explicitly show its nonlinear optical nature, we perform an alternating electric field dressed ab initio molecular dynamics simulation, which maps onto the Raman-active phonon excitation under off-resonant terahertz irradiation.

Understanding the computational overheads imposed by classical control systems on quantum computing platforms becomes critically important as these quantum machines grow in scale and complexity. In this work, we calculate the overheads imposed by the implementation of real-time graph traversal algorithms needed to find computational paths through incomplete cluster states for the implementation of one-qubit gates; a necessary requirement for a realistic implementation of photonic measurement-based quantum computing. By implementing two different algorithms, a global breadth-first search that searches the entire cluster state and an incremental version that traverses a narrow subsection of the cluster state, we analyze the trade-off between the accuracy of finding viable paths and the speed at which this operation can be performed, which constrains the overall photonic clock cycle of the system. We also outline the broader implications of our results for implementing classical control systems for measurement-based photonic quantum computing.

Optically levitated microspheres are an excellent candidate for force and acceleration sensing. Here, we propose an acceleration-sensing protocol based on an optically levitated microsphere array (MSA). The system consists of an $N$-microsphere array levitated in a driven optical cavity via holographic optical tweezers. By positioning the microspheres suitably relative to the cavity, the center-of-mass (COM) mode of the collective motion of the MSA is coupled to the cavity mode. The optomechanical interaction encodes the information of acceleration that acts on the MSA onto the intracavity photons, which can then be detected directly at the output of the cavity. The optically levitated MSA distributes its mass into multiple optical traps, which not only circumvents the problem of levitating a large-mass microsphere but also leads to a significant improvement in sensitivity. Compared with the traditional single-microsphere measurement scheme, our method presents an improvement in sensitivity by a factor of $\sqrt{N}$.

We theoretically predict and experimentally observe the onset of weak-link physics in the dynamical response of transition-edge sensors (TESs). We develop a theoretical framework based on a Fokker-Planck description that incorporates both the TESs electrical response, stemming from Josephson phenomena, and the electrothermal effects due to coupling to a thermal bath. Our measurements of a varying dynamic resistance are in excellent agreement with our theory, thereby establishing weak-link phenomena as the main mechanism underlying the operation of TESs. Furthermore, our description enables the calculation of power spectral densities, paving the way for a more thorough investigation of the unexplained “excess noise” in long diffusive junctions and TESs reported in recent experiments.

By performing density-functional calculations, we find a giant magnetocrystalline anisotropy (MCA) constant in abundant element cerium ($\mathrm{Ce}$) substituted M-type hexaferrite, in the energetically favorable strontium site, assisted by a quantum confined electron transfer from $\mathrm{Ce}$ to a specific iron ($2a$) site. Remarkably, the calculated electronic structure shows that the electron transfer leads to the formation of ${\mathrm{Ce}}^{3+}$ and ${\mathrm{Fe}}^{2+}$ at the $2a$ site producing an occupied $\mathrm{Ce}$($4f^1$) state below the Fermi level that adds a significant contribution to MCA and magnetic moment. A half $\mathrm{Ce}$ substitution forms a metallic state, while a full substitution retains the semiconducting state of the strontium hexaferrite (host). In the latter, the band gap is reduced due to the formation of charge-transferred states in the gap region of the host. The optical absorption coefficient shows an enhanced anisotropy between light polarization in parallel and perpendicular directions. Calculated formation energies, including the analysis of probable competing phases, and elastic constants confirm that both compositions are chemically and mechanically stable. With successful synthesis, the $\mathrm{Ce}$ hexaferrite can be an alternative high-performing critical-element-free permanent magnet material adapted for use in devices such as automotive traction drive motors.

Acoustic beam-shaping techniques have a variety of application scenarios. Traditional phase-only modulation techniques are unable to accurately shape ultrasonic beams that require precise modulation of both amplitude and phase, such as nondiffracting beams. To provide more flexible, simple, and efficient shaping methods, we have developed the Fourier-transform acoustic beam-shaping system. Our proposed system enables the phase-only acoustic beam to reconstruct wave front and optimize its shape for achieving amplitude and phase modulation. We conducted experiments on generating different types of beams using the system. The feasibility of the system was established by generating multifocal beams. Additionally, nondiffracting Weber beams were constructed, with the findings showing that the beam possesses self-healing capability and can travel along a parabolic trajectory. Furthermore, by extending the Fourier transform to the two-dimensional space, we have successfully generated a perfect acoustic vortex beam, which has the same annular intensity profile for any given integer value of the order. Experiments showed that the perfect vortex beam enables the flexible and accurate manipulation of single and multiple particles. We conclude that the Fourier-transform acoustic system is a convenient way for acoustic beam shaping and has broad application prospects, such as drug delivery and high-speed acoustic communication.

Recently, much attention has been paid to second-order photonic topological insulators (SPTIs), because of their support for highly localized corner states with excellent robustness. SPTIs have been implemented in either transverse-magnetic (TM) or transverse-electric (TE) polarizations in two-dimensional photonic crystals (PCs), and the resultant topological corner states are polarization dependent, which limits their application in polarization-independent optics. However, to achieve polarization-independent corner states is not easy, since they are usually in-gap and the exact location in the topological band gap is not known in advance. Here we report on an SPTI based on a two-dimensional square-lattice PC made of an elliptic metamaterial, and we report that whether the band gap is topological or trivial depends on the choice of the unit cell. It is found that locations of topological band gaps of TM and TE polarizations in the frequency spectrum can be independently controlled by the out-of-plane permittivity ${\epsilon }_{\perp }$ and the in-plane permittivity ${\epsilon }_{\parallel }$, respectively, and more importantly, the location of in-gap corner states can also be separately manipulated by them. From this, we achieve topological corner states for both TM and TE polarizations with the same frequency in the PC by adjusting ${\epsilon }_{\perp }$ and ${\epsilon }_{\parallel }$, and their robustness with regard to disorders and defects is numerically demonstrated. The proposed SPTI provides a potential application scenario for polarization-independent topological photonic devices.

We experimentally verified our prior theoretical work [J. Opt. Soc. Am. B 39, 3012 (2022)] by employing matter-wave interference to measure the ultranarrow momentum width of an optically trapped Bose-Einstein condensate (BEC) in situ. Splitting the BEC wave packet into various diffraction orders through double stand-wave pulses, we calibrated the momentum width by fitting the oscillation curve of the population of the zero-momentum state. The observed interference fringes exhibited slight deviations from our simplified theory. We numerically calculated the Gross-Pitaevskii equation and utilized Wigner function to gain insight into the impact of the external trap potential and nonlinear term of BEC. We found that the discrepancy was caused by the combined effects of the mean-field interaction and spatial density modulation of BEC. This quantum thermometry is straightforward to apply and is especially well suited for temperature calibration in deep cooling experiments. For atomic samples at the pK level after deep cooling, interatomic interactions can be safely disregarded, enabling momentum-width calibration in a single shot.

The steering and the focusing of acoustic beams are of increasing interest for personalized-sound-zone applications. Sound zones require the generation of a strong contrast in sound pressure level between different regions of the space. A way to do so is to control and steer the acoustic field radiated from a source with use of metamaterial-based acoustic lenses. Predictive models based on numerical approaches such as the finite-element method are commonly used, but they are generally cumbersome and time-consuming. In contrast, explicit models rely on Snell’s law of refraction and phase gratings but do not account for the couplings between the metamaterial atoms. In this work, a metamaterial-based acoustic lens is proposed as a solution to steer and focus acoustic sources, with use of slits loaded with periodic Helmholtz resonators. We control the radiation of a baffled duct by a metalens located at the output of the waveguide and excited at the other end by a loudspeaker. A fully explicit two-dimensional predictive model is developed on the basis of the mode-matching technique, accounting for thermoviscous losses, interslit evanescent coupling, and high-order modes in the baffled duct. The pressure radiated by the metalens outside the baffled duct is then explicitly derived. The semianalytical results show excellent agreement when compared with the solutions obtained by the finite-element method, both in the near field and in the far field over a wide frequency range. An optimization strategy is then proposed, and the beam steering and focusing are reported experimentally on a three-dimensionally-printed prototype.

The superconducting fluxonium qubit has a great potential for high-fidelity quantum gates with its long coherence times and strong anharmonicity at the half-flux-quantum sweet spot. However, current implementations of two-qubit gates compromise fluxonium’s coherence properties by requiring either a temporary population of the noncomputational states or tuning the magnetic flux off the sweet spot. Here we realize a fast all-microwave cross-resonance gate between two capacitively coupled fluxoniums with the qubit dynamics well confined to the computational space. We demonstrate a direct controlled not (cnot) gate in 70 ns with fidelity up to $\mathcal{F}=0.9949(6)$ despite the limitations of a suboptimal measurement setup and device coherence. Our results project a possible pathway towards reducing the two-qubit error rate near to or below ${10}^{-4}$ with present-day technologies.

The propagation of magnetostatic surface spin waves in permalloy stripes was observed by high-resolution wide-field magneto-optical Kerr microscopy using the stroboscope technique. A long-time stable semiconductor-laser light source was employed and uniform illumination using a fiber speckle reducer and active stabilization of the focus and the sample position were achieved. These enabled the measurement of spin waves at a frequency of 5.6 GHz in a minimum stripe width of $2\text{μ}\mathrm{m}$ with a sensitivity of 1% saturation magnetization. A pronounced self-focusing effect was observed, which is explained by the peculiar dispersion relation of the spin wave. The capability of measuring all three vector components of magnetization allows direct observation of spin waves as a propagation of precessional motion.

We present all-electrical operation of a ${\mathrm{Fe}}_x{\mathrm{Cr}}_{1-x}$-based Curie switch at room temperature. More specifically, we study the current-induced thermally driven transition from ferromagnetic to antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) indirect coupling in a ${\mathrm{Fe}/\mathrm{Cr}/\mathrm{Fe}}_{17.5}{\mathrm{Cr}}_{82.5}/\mathrm{Cr}/\mathrm{Fe}$ multilayer. Magnetometry measurements at different temperatures show that the transition from the ferromagnetic to the antiferromagnetic coupling at zero field is observed at approximately $325$ K. Analytical modeling confirms that the observed temperature-dependent transition from indirect ferromagnetic to indirect antiferromagnetic interlayer exchange coupling originates from the modification of the effective interlayer exchange constant through the ferromagnetic-to-paramagnetic transition in the ${\mathrm{Fe}}_{17.5}{\mathrm{Cr}}_{82.5}$ spacer with minor contributions from the thermally driven variations of the magnetization and magnetic anisotropy of the Fe layers. Room-temperature current-in-plane magnetotransport measurements on the patterned ${\mathrm{Fe}/\mathrm{Cr}/\mathrm{Fe}}_{17.5}{\mathrm{Cr}}_{82.5}/\mathrm{Cr}/\mathrm{Fe}$ strips show the transition from the “low-resistance” parallel to the “high-resistance” antiparallel remanent magnetization configuration, upon increased probing current density. Quantitative comparison of the switching fields, obtained by magnetometry and magnetotransport, confirms that the Joule heating is the main mechanism responsible for the observed current-induced resistive switching.

Quasibrittle materials endowed with (statistically) self-similar hierarchical microstructures show distinct failure patterns that deviate from the standard scenario of damage accumulation followed by crack nucleation and growth. Here we study the failure of paper sheets with hierarchical slice patterns as well as nonhierarchical and unpatterned reference samples, considering both uncracked samples and samples containing a macroscopic crack. Failure is studied under displacement-controlled tensile loading as well as under creep conditions. Acoustic emission records and surface strain patterns are recorded alongside stress-strain and creep curves. The measurements demonstrate that hierarchical patterning efficiently mitigates against strain localization and crack propagation. In tensile loading, this results in a significantly increased residual strength of cracked samples. Under creep conditions, for a given range of lifetimes, hierarchically patterned samples are found to sustain larger creep strains at higher stress levels; their creep curves show unusual behavior characterized by multiple creep rate minima due to the repeated arrest of emergent localization bands.

In parametric down-conversion, a nonlinear crystal is pumped by a laser and spontaneous emission takes place in signal and idler modes according to the phase-matching conditions. A seed laser can stimulate the emission in the signal beam if there is mode overlap between them. This also enhances the emission in the idler beam, affecting its coherence properties. While the degree of coherence of the idler field as a function of the seed power has already been studied, the transverse coherence length has not yet been properly investigated. The transverse coherence length is a key parameter of optical beams that determines the beam divergence, for example. Here, we present a theoretical and experimental investigation of the transverse coherence length in stimulated down-conversion. In addition, we make a connection between stimulated down-conversion and partially coherent sources like the Gaussian-Schell model beams, and show that in general the idler field cannot be described with this model.

The design of easy-to-operate high-fidelity two-qubit gates remains an area of ongoing research. Many of the common schemes require dedicated control lines, while others are vulnerable to issues of frequency crowding. Here, we propose a scheme for coupling a chain of transmons acting as logical qubits via a quantum bus of auxiliary qubits. The auxiliary array is made of floating transmons and through the use of mediated interactions we generate effective capacitance between them beyond the nearest neighbor. Logical qubits are not directly coupled to each other but they can be coupled by bringing them closer in frequency to the far-detuned auxiliary arrays. This allows for tunable coupling between non-neighboring logical qubits and for the application of entangling gates to three or more qubits at once.

The commercial and industrial demand for the solution of hard combinatorial optimization problems pushes forward the development of efficient solvers. One of them is the Ising machine, which can solve combinatorial problems mapped to Ising Hamiltonians. In particular, spintronic hardware implementations of Ising machines can be very efficient in terms of area and performance, and are relatively low cost considering the potential to create hybrid CMOS-spintronic technology. Here, we perform a comparison of oscillator-based and probabilistic paradigms of Ising machines on several hard max-cut instances, analyzing their scalability and performance at software level. We show that probabilistic Ising machines outperform oscillator-based Ising machines in terms of the number of iterations required to achieve the problem’s solution. Nevertheless, high-frequency spintronic oscillators with subnanosecond synchronization times could be very promising as ultrafast Ising machines. In addition, considering that a oscillator-based Ising machine acts better for max-cut problems because of the absence of the linear term in the Ising Hamiltonian, we introduce a procedure to encode max-3SAT to max cut. We foresee potential synergic interplays between the two paradigms.

The generation, propagation, and control of twisted light in a photonic chip has developed to meet the demands of modern optics, contributing to different research fields such as classical and quantum information technologies and integrated microfluidics. Here, we show how a single Gaussian illumination can excite different twisted-light modes into a buried annular waveguide, including that carrying orbital angular momentum (OAM) or superpositions of its constituents. We show that is possible to encode one-by-multiple information of independent OAM modes, unveiling the dynamics of the generation of OAM modes in a photonic chip. Owing to the degree of freedom of OAM light, OAM-circuit photonics can be explored to enhance high-capacity data processing for quantum or classical networking.

A wideband vibration energy harvester with multiple nonlinear forces is investigated. The nonlinearities are due to repulsive magnets and hardening springs, which gives rise to multistabilities between a number of energy branches. Not all branches are accessible by a simple up or down sweep of the driving frequency and in particular the highest energy branch is often hidden, requiring a suitable frequency schedule to be accessed. Detailed theoretical understanding of the energy branch structure along with robust experimental methods are essential for characterizing each of the energy branches to enhance the energy output from such a vibration energy harvesting system. We introduce a graphical representation in the form of eye diagrams based on time-resolved measurements of acceleration and output voltage to study the dynamical features of the different branches. This generic approach allows us to optimize the design, which results in 1.3 mW of power generated at 1 g over the 44-Hz frequency bandwidth while maintaining a small footprint of $1.23{\mathrm{cm}}^3$. The energy conversion ratio of the energy harvester at 120-Hz drive frequency is 0.52 for the high-energy branch.