Physical systems in the time domain may exhibit analogous phenomena in real space, such as time crystals, time-domain Fresnel lenses, and modulational interference in a qubit. Here, we report the experimental realization of time-domain grating using a superconducting qutrit in periodically modulated probe and control fields via two schemes: simultaneous modulation and complementary modulation. Both experimental and numerical results exhibit modulated Autler-Townes (AT) and modulation-induced diffraction (MID) effects. Theoretical results also confirm that the peak positions of the interference fringes of AT and MID effects are determined by the usual two-level relative phases, while the observed diffraction fringes, appearing only in the complementary modulation, are, however, related to the three-level relative phase. Further analysis indicates that such a single-atom time-domain diffraction originates from the correlation effect between the two time-domain gratings. Moreover, we find that the widths of the diffraction fringes are independent of the control-field power. Our results shed light on the experimental exploration of quantum coherence for modulated multilevel systems and may find promising applications in fast all-microwave switches and quantum-gate operations in the strong-driving regime.

To reduce material and processing costs of commercial permanent magnets and to attempt to fill the empty niche of energy products, 10–20 MGOe, between low-flux (ferrites, alnico) and high-flux (${\mathrm{Nd}}_2{\mathrm{Fe}}_{14}\mathrm{B}$- and ${\mathrm{Sm}\mathrm{Co}}_5$-type) magnets, we report the synthesis, structure, magnetic properties, and modeling of $\mathrm{Ta}$-, $\mathrm{Cu}$-, and $\mathrm{Fe}$-substituted ${\mathrm{Ce}\mathrm{Co}}_5$. Using a self-flux technique, we grow single crystals of ${\mathrm{Ce}}_{15.1}{\mathrm{Ta}}_{1.0}{\mathrm{Co}}_{74.4}{\mathrm{Cu}}_{9.5}$, ${\mathrm{Ce}}_{16.3}{\mathrm{Ta}}_{0.6}{\mathrm{Co}}_{68.9}{\mathrm{Cu}}_{14.2}$, ${\mathrm{Ce}}_{15.7}{\mathrm{Ta}}_{0.6}{\mathrm{Co}}_{67.8}{\mathrm{Cu}}_{15.9}$, ${\mathrm{Ce}}_{16.3}{\mathrm{Ta}}_{0.3}{\mathrm{Co}}_{61.7}{\mathrm{Cu}}_{21.7}$, and ${\mathrm{Ce}}_{14.3}{\mathrm{Ta}}_{1.0}{\mathrm{Co}}_{62.0}{\mathrm{Fe}}_{12.3}{\mathrm{Cu}}_{10.4}$. X-ray-diffraction analysis shows that these materials retain a ${\mathrm{Ca}\mathrm{Cu}}_5$ substructure and incorporate small amounts of $\mathrm{Ta}$ in the form of “dumbbells,” filling the $2e$ crystallographic sites within the one-dimensional hexagonal channel with the $1a$ $\mathrm{Ce}$ site, whereas $\mathrm{Co}$, $\mathrm{Cu}$, and $\mathrm{Fe}$ are statistically distributed among the $2c$ and $3g$ crystallographic sites. Scanning-electron-microscopy, energy-dispersive-x-ray-spectroscopy, and scanning-transmission-electron-microscopy examinations provide strong evidence of the single-phase nature of the as-grown crystals, even though they readily exhibit significant magnetic coercivities of approximately 1.6 kOe to approximately 1.8 kOe caused by $\mathrm{Co}$-enriched, nanosized structural defects and faults that can serve as pinning sites. Heat treatments at $1040{}^{\circ }\mathrm{C}$ for 10 h and hardening at $400{}^{\circ }\mathrm{C}$ for 4 h lead to the formation of a so-called composite crystal with a bimodal microstructure that consists of a $\mathrm{Ta}$-poor matrix and $\mathrm{Ta}$-rich laminal precipitates. Formation of the composite crystal during the heat treatment creates a three-dimensional array of extended defects within a primarily single-grain single crystal, which greatly improves its magnetic characteristics. Possible causes for the formation of the composite crystal may be associated with $\mathrm{Ta}$ atoms leaving matrix interstices at lower temperatures and/or matrix degradation induced by decreased miscibility at lower temperatures. $\mathrm{Fe}$ strongly increases both the Curie temperature and magnetization of the system resulting, in $(BH{)}_{max}\approx 13$ MGOe at room temperature.

Testing the limits in performance of device setups with respect to sizes and oscillation frequencies by trying every single combination of the available media can give a set of superior designs with novel properties. This approach is followed for the absorption and scattering of visible light by core-shell nanowires, whose optical thickness is simultaneously large enough to individually perturb the background field and small enough to support coherent collective operation. Numerous maximally performing particles are reported, one for each pair of the bulk materials used, providing a set of limits for the absorbed and scattered power in the presence of realistic losses. This procedure detects the supported resonances at core-shell nanorods, finds the best designs for such a simple geometry, and thus offers additional degrees of freedom in particle or metasurface modeling.

We experimentally study the thermoelectric properties of an ${\mathrm{Au}}_x{\mathrm{Ge}}_{1-x}$ thin-film alloy close to the metal-insulator transition ($x=19.5\mathrm{\%}$). The thermoelectric characterization of the thin-film alloy shows a Seebeck coefficient comparable to that of $\mathrm{Au}$ thin film while preserving good thermal sensor properties, revealing the potential interest in its use in nanoscale thermoelectric systems. In particular, we demonstrate the ability to directly evaporate an ${\mathrm{Au}}_x{\mathrm{Ge}}_{1-x}$ thin film on different nanometric-thick molecular layers. A device engineering is proposed paving the way for investigation of the thermoelectricity of large-area nanometric-thick molecular layers, where the alloy is integrated as a contact electrode, fulfilling the double role of an in situ local heater and a high-resolution thermometer.

We show that engineered diffraction gratings can considerably simplify the design of acoustic ground cloaking devices. Acoustic reflecting gratings are designed in such a way that all the incident energy is channeled toward the diffracted mode traveling in the direction opposite the direction of the incident field (retroreflection effect), and this effect is used to cloak an object placed over an acoustically rigid surface. Axisymmetric gratings consisting of rigid surfaces with just one groove per unit cell are used to design thin acoustic carpet cloaks. Finally, full-wave numerical simulations are performed and a conical carpet cloak is experimentally tested, showing an excellent scattering-cancellation effect.

Strong nonlinear optical effects generally require giant optical fields interacting with the nonlinear media. Doped graphene hosts electrically tunable plasmons with long lifetimes that interact strongly with light. We investigate a graphene plasmonic coupler and explore two mechanisms to pursue highly efficient third-harmonic generation (THG): (1) phase matching of graphene plasmons at fundamental- and third-harmonic frequencies and (2) peak third-order nonlinear susceptibility of doped graphene. The third-harmonic wave is mainly converted from the evanescent mode of the incident light and the THG efficiency is found to be enhanced by over 10 orders of magnitude compared with a bare monolayer graphene. The significantly enhanced nonlinear optical responses in the graphene plasmonic coupler make this configuration an ideal platform for the development of alternative frequency generators and for signal processing at midinfrared and terahertz frequencies.

We demonstrate that interfaces can play a significant role in overcoming the diffusive and subdiffusive nature of exciton transport in organic semiconductors. By designing interfaces with an imbalance between the forward and reverse rates of energy transfer, the interface can act as a gate, thereby directing exciton transport. While previous work has examined from a theoretical perspective the function of multiple exciton gates arranged in series, we provide a combined theory-experiment treatment that permits an assessment of the utility of exciton-permeable gating interfaces in optoelectronic devices. The required asymmetry in interfacial-exciton-transfer rates is realized by engineering a molecular site imbalance. The impact of interfaces on exciton transport is considered by optically injecting excitons into the gating architecture, and detecting those that migrate through the structure using a luminescent sensitizer. For exciton transport in the archetypical organic fluorescent dye 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10(2-benzothiazolyl) quinolizino-[9,9a,1gh] coumarin (C545T) diluted in the wide-gap organic semiconductor p-bis(triphenylsilyl)benzene (UGH2), a more than 200% improvement in transport efficiency is found in an architecture with properly optimized gates compared to a neat film of C545T.

We investigate the impact of the combined diamond heat-spreading layer and microfluidic convection on the performance of a model electronic chip heated locally. Experiments are carried out and a finite element method is used to simulate the thermal response of the device under transient step-wise (without flow) and steady-state (with flow) operation conditions up to heat flux values of 38 and $190\mathrm{W}/{\mathrm{cm}}^2$, respectively. In all cases, the temperature on the heated outer silicon surface did not exceed 100°C. The temperature field contour has an oval shape for transient heating without flow and a funnel shape for steady-state heating with flow. For a step-wise heat flux of $38\mathrm{W}/{\mathrm{cm}}^2$, the differences between temperatures at the center of the resistor and at the outer surface edge after a time interval of 8 s are 5, 3, and 1°C for the chips without a diamond layer, with a 100-µm diamond layer, and only a 400-µm diamond, respectively, which proves the enhanced spreading due to the diamond layer. Under steady-state conditions at a heat flux of $190\mathrm{W}/{\mathrm{cm}}^2$ and volumetric flow rates of water between 2 and 5 ml/min, the surface temperature decreases by approximately15% for silicon wafer with a 100-µm diamond layer and by approximately 22% for a 400-µm diamond as compared to heating without the addition of diamond. Of crucial importance is the proximity of the diamond layer to the heat source, which makes this method advantageous over other thermal management procedures, especially for pulsed operating conditions and hot spots.

Many hydrogen-bonded organic ferroelectrics exhibit low-field switching of large spontaneous polarizations. Although the switchable electric dipoles of π-conjugated organic molecules account for the large spontaneous polarizations, their relevant optoelectronic processes have not been used to probe the ferroelectricity. We show that the variation in electro-optic response enables visualization of the ferroelectric domains and domain walls in single-crystal films of a hydrogen-bonded molecular cocrystal. Highly sensitive and rapid visualization is realized by difference optical image sensing between the forward and reverse field applications. We call this technique “ferroelectrics field modulation imaging (FFMI).” The unique optical-probe nature reveals the existence of two types of domain walls showing different three-dimensional orientations within the films; one is roughly perpendicular to the film plane, whereas the other is considerably tilted from the normal to the plane. We explain that both of the domain walls are stabilized to generate substantial neutrality by being directed parallel to the direction of polarization. This study opens a route for exploring the three-dimensional topological nature of domain walls in ferroelectric materials.

Surface acoustic waves (SAWs) propagating on magnetostrictive ferromagnets can induce magnetization reversal: their weak damping and mature technology make them ideal for remote wave control of magnetic bits. Experimental demonstrations of this spectacular coupling have so far required the simultaneous application of a static magnetic field. We show here SAW-driven all-acoustic switching (AAS) over millimetric distances. It relies on the triggering of magnetization precession of a uniaxial in-plane magnetized film by acoustic ferromagnetic resonance at zero field. Moreover, the absence of a biasing field enables toggling between the two equilibrium magnetic states for over 20 consecutive acoustic pulses. This proof-of-concept opens up an alternative path to magnetic-bit manipulation.

The interfacing of quantum platforms via photonic links is a precursor for establishing scalable quantum networks. The connection of different types of quantum memories for hybrid networking requires the overcoming of the disparate photon wavelengths emitted by each quantum memory. Given achievements in quantum information processing with trapped-ion and neutral-atom architectures, a hybrid system with modular interconnectivity is advantageous. Here, we use a trapped ${}^{138}{\mathrm{Ba}}^{+}$ ion and a periodically poled lithium-niobate (PPLN) waveguide, with a fiber-coupled output, to demonstrate 19% end-to-end efficient quantum frequency conversion (QFC) of single photons from 493 to 780 nm and use fluorescence of the ion to produce light at the ${}^{87}\mathrm{Rb}{D}_2$ transition wavelength. To demonstrate the quantum nature of both the unconverted 493 nm photons and the converted photons near 780 nm, we observe strong quantum statics in their respective second-order intensity correlations. This work extends the range of intralaboratory networking between ions and networking between disparate quantum memories.

Achieving simultaneous control of the amplitude and phase of a metasurface, especially in transmission geometry, is very essential in modern photonic research. An alternative strategy for manipulating the transmissive amplitude and phase is proposed by using a three-layered element. Two outer orthogonal gratings of the element can determine the transmissive polarization while the center modified I-shaped particle achieves a high-efficiency linear polarization conversion. We can control the transmissive phase by modulating the gap size of the modified I-shaped structure, and manipulate the transmissive amplitude by rotating the structure. As a proof of concept, we design a fan-shaped beam metasurface by using a genetic algorithm to obtain the optimal phase and amplitude distributions. The results show that the metasurface can generate a flat top (azimuthal angle range is −40° to 40°) beam under rectangular coordinates within 9.1–10.9 GHz. Our findings offer possibilities to realize arbitrary beam shapes, which not only widen the areas for shaping a wavefront by metasurfaces, but also offer an economical and simple alternative for a beam-forming array antenna.

Three-dimensional (3D) confocal imaging of multiphase flows in a network of microcapillaries is used to conceptualize and quantify the mobilization process of an oleic wetting viscous phase by aqueous nanofluids and surfactant solutions. This microscale visualization reveals that nanoparticles decrease the thickness of wetting-phase film. The efficiency of surfactants in oil mobilization results from their capability to break the wetting phase into smaller ganglia. The type of injectant significantly influences the size of the clusters and the distribution of the wetting phase. We show that the mean size of the wetting phase clusters is a decreasing function of the displacement efficiency for each solution. Incorporation of silica nanoparticles with surfactant solutions hinders the wetting phase break up and decreases the number of clusters. The most frequently occurring cluster size (mode) decreases in the presence of surfactants, but remains unchanged in the presence of silica nanoparticles. Unlike the average cluster size, which is a decreasing function of the nonwetting phase saturation, it is interesting that the mode remains almost unchanged during the displacement process. The reduction of wetting film thickness and the fragmentation of wetting phase have numerous applications in natural and engineering sciences.

We investigate new phenomena in elastic wave propagation in metamaterials characterized by long-range interactions. The kind of waves in this context reveal wave-stopping, negative group velocity, instability, and hypersonic or superluminal effects both for instantaneous and for nonlocal retarded actions. Closed-form results are presented and a universal propagation map synthesizes the expected properties of these materials. Perspectives in physics, engineering, and social dynamics are discussed.

This paper presents experimental evidence for the existence of acoustic valley Hall edge (AVHE) states in topological elastic waveguides. The fundamental lattice is assembled on the basis of a nonresonant unit where space-inversion symmetry (SIS) is broken by our simply perturbing the underlying lattice geometry. This aspect is in contrast with existing elastic AVHE designs that exploit locally resonant units and require the addition of masses to break SIS. The experimental results presented in this study validate findings so far presented only at the theoretical and numerical level. In particular, it is found that edge modes can effectively propagate along domain walls between topologically dissimilar domains and that disorder-induced backscattering is substantially suppressed due to the weak coupling between oppositely-valley-polarized modes. The coupling between valley modes is further investigated and linked to an evident chiral flux of the mechanical energy. Finally, we show that the weak coupling between the valleys can be exploited to achieve selective mode injection at the domain wall, hence realizing a very effective excitation strategy for the chiral edge states.

Digital holographic tomography (DHT) can measure the 3D refractive-index map of a microscopic specimen. To obtain the 3D map using a 2D camera, existing methods scan the angle of illumination, rotate the sample, scan the objective-lens focus, or change the wavelength. Here, we present a snapshot DHT technique that does not rely on a scanning mechanism. Using a technique named snapshot holographic optical tomography (SHOT), we acquire the 3D refractive-index maps of a polystyrene bead and a single Henrietta Lacks (HeLa) cell.

The rapid developments in orbital-angular-momentum-carrying Laguerre-Gaussian ${\mathrm{(LG}}_l^0)$ modes in recent years have facilitated progress in optical communication, micromanipulation, and quantum information. However, it is still challenging to efficiently generate bright, pure, and selectable ${\mathrm{LG}}_l^0$ laser modes in compact devices. We demonstrate a low-threshold solid-state laser that can directly output selected high-purity ${\mathrm{LG}}_l^0$ modes with high efficiency and controllability. Spin-orbital angular momentum conversion of light is used to reversibly convert the transverse modes inside a cavity and determine the output mode index. The generated ${\mathrm{LG}}_1^0$ and ${\mathrm{LG}}_2^0$ laser modes have purities of approximately 97% and approximately 93% and slope efficiencies of approximately 11% and approximately 5.1%, respectively. Our cavity design can also be easily extended to produce higher-order Laguerre-Gaussian modes and cylindrical vector beams. Such a compact laser configuration features flexible control, low threshold, and robustness, making it a practical tool for applications in superresolution imaging, high-precision interferometers, and quantum correlations.

To improve the sensitivity of piezocapacitive pressure sensors, the thickness of the dielectric layer must vary with exposure to a weak force, and the mechanical modulus must be low. We propose a simple method for trapping air bubbles in an elastomer to reduce the modulus of the elastomer. The sensitivity of the pressure sensors fabricated from the air bubble-trapped elastomer is approximately 10 times better than that of a pressure sensor without air bubbles. The pressure sensor with air bubbles has a very high linear response to external pressure changes. We also demonstrate that the pressure sensor fabricated from the air bubble-trapped elastomer can detect the dynamic loading and unloading pressure of a small Lego toy and a small M6 bolt. These results show that our pressure sensor based on the air bubble-trapped elastomer can be used to detect applied pressures or contact forces of electronic skin (e-skin).

In the past decade, it has been demonstrated that surface-enhanced infrared absorption (SEIRA) is a powerful method to enhance vibrational signals of thin molecular layers. Much less attention has so far been given to the possibility of using SEIRA for the detection and characterization of nanometer-sized particles, such as ultrafine dust particles. Here, we report on SEIRA measurements demonstrating that even one single particle with a deeply subwavelength dimension of less than 100 nm can be detected and chemically characterized with standard infrared microspectroscopy. Our approach is based on plasmonic resonances of bowtie-shaped $\mathrm{Au}$ apertures that are designed to extraordinarily enhance the material-specific phononic excitations of a nanometer-sized silica particle. We show that the bowtie geometry is especially suited for single-particle spectroscopy, as it combines the advantage of an intense electromagnetic hot spot, the size of which can be adjusted to the particle dimension, with easy positioning of ultrafine dust particles inside that hot spot. In agreement with numerical calculations, we show that a detection limit in terms of a particle diameter of less than 20 nm can be achieved, which corresponds to a ratio of the diameter to the vacuum wavelength below 0.002. Our approach offers the possibility of analyzing infrared bands from tiniest particles and thus paves the way toward SEIRA-based devices that can sense ultrafine dust.

The lower critical magnetic field, $H_{c1}$, of superconductors is measured by optical magnetometry using ensembles of nitrogen-vacancy centers in diamond. The technique is minimally invasive and allows accurate detection of the vector magnetic field with subgauss sensitivity and submicrometer spatial resolution. These capabilities are used for detailed characterization of the first vortex penetration into superconducting samples from the corners. Aided by the revised calculations of the effective demagnetization factors of actual cuboid-shaped samples, these measurements provide precise determination of $H_{c1}$ and the related absolute value of the London penetration depth, $\lambda$. We apply this method to three well-studied superconductors: optimally doped $\mathrm{Ba}({\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{)}_2{\mathrm{As}}_2$, stoichiometric ${\mathrm{Ca}\mathrm{K}\mathrm{Fe}}_4{\mathrm{As}}_4$, and the high-$T_c$ cuprate ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$. Our results compared well with the values of $\lambda$ obtained with other techniques, thus adding another noninvasive and sensitive method to measure these important parameters of superconductors.