Imaging is indispensable for nearly every field of science, engineering, technology, and medicine. However, measurement noise and stochastic distortions pose fundamental limits to accessible spatiotemporal information despite impressive tools such as structured-illumination microscopy (SIM), stochastic optical reconstruction microscopy or photoactivated localization microscopy (STORM or PALM), and stimulated-emission-depletion (STED) microscopy. How to combat this challenge ideally has been an open question for decades. Inspired by a virtual-gain technique to compensate losses in metamaterials, active convolved illumination (ACI) has recently been proposed to significantly improve the signal-to-noise ratio and hence the data acquisition. In this technique, the light pattern of the object is superimposed with a correlated auxiliary pattern, the function of which is to reverse the adverse effects of losses, noise, and random distortion based on their spectral characteristics. Despite enormous implications in statistics, any experimental evidence verifying the theory of this novel technique has been lacking to date. We find experimentally that ACI boosts not just the resolution limit and image contrast but also the resistance to pixel saturation. The results confirm the previous theories and may open up horizons in a wide range of disciplines from atmospheric sciences, seismology, biology, statistical learning, finance, and information processing to quantum noise beyond the fundamental boundaries.

We demonstrate non-Hermitian topological phase transitions induced solely by imaginary disorder. Starting from the trivial phase in the well-known Benalcazar, Bernevig, and Hughes model, we find that adding sufficient imaginary disorder to the trivial bulk can lead to a higher-order topological insulator supporting topological corner-localized states. In experiments, we elaborately design a two-dimensional reconfigurable acoustic lattice with a loss configuration that can be randomly set. By increasing the strength of lossy disorder, we observe the transitions from a trivial to a higher-order topological phase and subsequently to a gapless phase. To further show that imaginary disorder offers an alternative degree of freedom for controlling topological phases, we propose a non-Hermitian topological disclination state induced by imaginary disorder. Our work demonstrates an example of a non-Hermitian higher-order topological Anderson insulator and offers a reconfigurable platform to study the interplay between non-Hermitian disorder and topological phases.

A method is presented for the determination of complex-valued compression and shear elastic moduli of polymers for ultrasound applications. The resulting values, which are scarcely reported in the literature, are found with uncertainties typically around 1% (real part) and 6% (imaginary part). The method involves a setup consisting of a cm-radius, mm-thick polymer ring glued concentrically to a disk-shaped piezoelectric transducer. The ultrasound electrical-impedance spectrum of the transducer is computed numerically and fitted to measured values as an inverse problem in a wide frequency range, typically from 500 Hz to 5 MHz, both on and off resonance. The method is validated experimentally by ultrasonic through transmission around 1.9 MHz. The method is low cost, not limited to specific geometries and crystal symmetries, and, given the developed software, easy to execute. The method has no obvious frequency limitations before severe attenuation sets in above 100 MHz.

Acoustic holography is widely used in particle manipulation. However, previous methods focus on modulating the amplitude and phase of the target sound field. In general, the amplitude gradient and phase gradient of the sound field correspond to the gradient force and the scattering force, respectively. But the relationship between the force and the aforementioned gradient is nonlinear even for a Rayleigh particle (whose radius is much smaller than the wavelength), not to mention the Mie particle(whose radius is comparable with the wavelength). If we want to control the continuous motion of a Mie particle quantitatively, we need to design force based on the relationship among the force, acceleration, and velocity. Here we propose to design radiation force along the path of a particle directly in holography methods. Compared to the usual modulation of amplitude and phase, the method designing radiation force directly can control the acceleration and orbital limiting velocity of a two-dimensional orbit rotation of a Mie particle with radius $a=0.4\mathrm{mm}$ (approximately $2/3$ wavelength) in simulation. The experiment verified its feasibility in controlling the continuous motion of particle quantitatively. This work shows its superiority over the pure acoustic holography methods in quantitative particle manipulation.

Machine learning finds application in the quantum control and readout of qubits. In this work we apply artificial neural networks to assist the manipulation and the readout of a prototypical molecular spin qubit-an oxovanadium(IV) moiety-in two experiments designed to test the amplitude and the phase recognition, respectively. We first successfully use an artificial network to analyze the output of a storage-retrieval protocol with four input pulses to recognize the echo positions and, with further post selection on the results, to infer the initial input pulse sequence. We then apply an artificial neural network to ascertain the phase of the experimentally measured Hahn echo, showing that it is possible to correctly detect its phase and to recognize additional single-pulse phase shifts added during manipulation.

The concept of birefringence, commonly treated as a property resulting from more than one polarization, is associated with different refractive indices, depending on polarization. Here, we propose a two-dimensional elastic metamaterial engineered to demonstrate birefringence of single polarization for flexural waves. By adopting a network of beams with “overpass” structures to upset the topology of unit cells from a conventional elastic plate, birefringence of single polarization at low frequencies can be realized and confirmed through measured band structures and double refraction of the flexural waves; this is further supported by full-wave simulations and models. Our approach can engineer birefringence at low frequencies in which the wavelength is at least a few times larger than the lattice constant, further allowing efficient control of beam splitting, filtering, and multiplexing with applications for elastic wave devices.

We study the stabilization and electrical manipulation of skyrmions in magnetic ultrathin films in the absence of an applied magnetic field. We show that this requires an increased magnetic anisotropy, controlled by the sample thickness, as compared to usual skyrmionic samples, so that the uniform state corresponds to the zero-field ground state and the skyrmions to metastable excitations. Although skyrmion stabilization at zero field is demonstrated over a broad range of thicknesses, electrical control appears to be more demanding to avoid skyrmion deformation. In the thinnest samples, the large magnetic anisotropy prevents skyrmion deformations and we show that they can be nucleated progressively by current pulses, which underlines that the only possible transition occurs between uniform and skyrmion states. The solitonic skyrmions in zero applied magnetic field have the same properties as compared to field-stabilized ones, with a long-term stability and high mobility when excited by a spin-orbit torque.

Electron spin transport in a two-dimensional $\mathrm{Si}$ inversion channel is experimentally and theoretically studied in terms of electron distribution in the subbands, electron momentum scattering processes, electron momentum lifetime, and spin lifetime. The electrical properties, electron charge transport, and spin transport are investigated by measuring a $\mathrm{Si}$-based spin metal-oxide-semiconductor field-effect transistor with a 10­-μm channel length under various bias and temperature conditions (4, 77, 150, and 295 K). In particular, in our unique procedure, the same device is measured before and after annealing to quantitatively clarify the change in the spin transport with lower and higher electron mobilities, by excluding device-to-device variability. Even when the distribution of electrons in the subbands, electron mobility, and temperature are significantly changed, the spin-flip probability, which is defined as the ratio of electron momentum lifetime to spin lifetime, is nearly constant at approximately 1/25 000, probably due to the Elliot-Yafet mechanism. The estimated spin conservation lengths at various temperatures are increased 2–50 times with increases in both the electron mobility and spin drift. With a high electron mobility of $3065{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ at 4 K, spin transport with a spin conservation efficiency of 94% is achieved through the 10-μm-long channel.

Passively mode-locked semiconductor disk lasers have received tremendous attention from both science and industry. Their relatively inexpensive production combined with excellent pulse performance and great emission-wavelength flexibility make them suitable laser candidates for applications ranging from frequency-comb tomography to spectroscopy. However, due to the interaction of the active medium dynamics and the device geometry, emission instabilities occur at high pump powers and thereby limit their performance potential. Hence, understanding those instabilities becomes critical for an optimal laser design. Using a delay-differential equation model, we are able to detect, understand, and classify three distinct instabilities that limit the maximum achievable pump power for the fundamental mode-locking state and link them to characteristic positive-net-gain windows. We furthermore derive a simple analytic approximation in order to quantitatively describe the stability boundary. Our results enable us to predict the optimal laser-cavity configuration with respect to positive-net-gain instabilities and therefore may be of great relevance for the future development of passively mode-locking semiconductor disk lasers.

We combine soliton dynamics in gas-filled hollow-core photonic crystal fibers with a state-of-the-art fiber laser to realize a turnkey system producing few-femtosecond pulses at 8-MHz repetition rate at pump energies as low as 220 nJ. Furthermore, by exploiting the soliton self-frequency shift in a second hydrogen-filled hollow-core fiber, we efficiently generate pulses as short as 22 fs, continuously tunable from 1100 to 1474 nm.

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.