Flux avalanche is commonly found in type-II superconductors, and this event is always featured as unpredictable and ultra-fast development with time. It is difficult to be captured dynamically by any experimental method available today. In this letter, we firstly propose a hypervelocity magnetic-optical system with two optical branches; one branch can trigger a dendritic flux avalanche in a superconducting film, and the other is capable of producing continuous multiexposure} to record the lightning avalanche process In contrast with some traditional trigger models, the present method realizes control of the position where the flux avalanche takes place. Second, we study the sensitive dependence on initial conditions} (SDIC) of the present flux avalanche for the first time and find series of positive Lyapunov exponents} between two adjacent trajectories which could be considered direct evidence for the chaotic dynamics in this kind of avalanche. Moreover, we reveal that whether the laser spot is in the Meissner state or the mixed state, avalanches always penetrate from the edge of the superconducting film to the Meissner region instead of occurring around the laser spot. This behavior clearly demonstrates the presented avalanche is driven by the magnetic pressure force}, suggesting that the optically triggered vortex avalanche possesses a new mechanism other than the thermomagnetic avalanches that are commonly found in superconducting films.

To obtain a complete description of a quantum system, one usually employs standard quantum state tomography, which however requires exponential number of measurements to perform and hence is impractical when the system’s size grows large. In this work, we introduce a self-learning tomographic scheme based on the variational hybrid quantum-classical method. The key part of the scheme is a learning procedure, in which we learn a control sequence capable of driving the unknown target state coherently to a simple fiducial state, so that the target state can be directly reconstructed by applying the control sequence reversely. In this manner, the state tomography problem is converted to a state-to-state transfer problem. To solve the latter problem, we use the closed-loop learning control approach. Our scheme is further experimentally tested using techniques of a 4-qubit nuclear magnetic resonance. \red{Experimental results indicate that the proposed tomographic scheme can handle a broad class of states including entangled states in quantum information, as well as dynamical states of quantum many-body systems common to condensed matter physics.

The current practice of manually tuning quantum dots (QDs) for qubit operation is a relatively time-consuming procedure inherently impractical for scaling up and applications. In this work, we report on the {} implementation of a recently proposed auto-tuning protocol that combines machine learning (ML) with an optimization routine to navigate the parameter space. In particular, we show that a ML algorithm trained using exclusively simulated data to quantitatively classify the state of double QD device can be used to replace human heuristics in tuning of gate voltages in real devices. We demonstrate active feedback of a functional double dot device operated at millikelvin temperatures and discuss success rates as a function of initial conditions and device performance. Modifications to the training network, fitness function, and optimizer are discussed as a path towards further improvement in the success rate when starting both near and far detuned from the target double dot range.

We address, using concepts of the microscopic theory of superconductivity, parametric amplifiers and kinetic inductance detectors focusing on the interaction of microwave radiation with the superconducting condensate. This interaction was identified, in recent experiments, as the source of the apparent dissipation in microwave superconducting micro-resonators at low temperatures. Since the evaluation of the performance of practical devices based only on the change in kinetic inductance is not sufficiently informative about the underlying physical processes, we design an experiment with a tunnel-measurement of a microwave-driven superconducting wire, in which the tunnel-process is not affected by the microwaves. We conclude that such an experiment is feasible with the current technology, unfortunately difficult to incorporate in standard superconducting resonators optimized for applied performance. Nevertheless, given the limits of the commonly used phenomenological theories, such an experiment will provide the groundwork for further optimisation of the performance.

We study the performance limit of single-mode operation in low-loss, large-V-number, planar waveguide lasers with transverse spatial hole burning as the dominating mechanism for transverse mode competition. By introducing normalized variables, we develop a simple semi-analytical model to describe universal output characteristics of singlemode emission before the onset of the high-order modes, which can be easily scaled to a wide range of laser configuration parameters. Our model is validated using exact numerical solutions which shows applicability beyond the low-loss approximation. Our analysis establishes a minimum criterion of the loss ratio between the fundamental and 1st higher-order mode for a robust single-mode operation. This criterion is much weaker than the conventional wisdom based on pure wave propagation argument which we attribute to a resonator enhancement effect. Our universal outcome can be denormalized to establish the relationship between single-mode extraction efficiency and optimum output coupling in a multimode laser with arbitrary modal loss ratios over a wide range of single-pass unsaturated gain and loss.

Huygens’ metasurfaces provide a versatile and efficient platform for exotic wave manipulation. Conventional transmissive Huygens’ metasurfaces rely on the interference between different multipole excitations to minimize the undesired reflection, but the different nature between multipoles introduces challenge on the bandwidth and practical applications. Here, we reveal that in contrast to the conventional scheme, exciting congener dipoles within the same multipole catalogue is also possible to realize high-efficiency broadband Huygens’ metasurfaces for linearly polarized light. A theoretical model has been proposed and the required conditions for zero reflection and 2π phase variation have been derived in the dipole approximation. This model has been validated by a silicon dual-nanodisk metasurface, and the beam deflection and focusing functionalities have also been demonstrated with high efficiency and broadband properties.

We study a magneto-granular chain composed of stainless steel beads which are placed inside a properly designed periodic magnetic field. The latter provides attractive forces between the particles, leading to a stable structure, free of mechanical boundaries. Using a scanning laser-based probe at the individual-particle level, we observe experimentally, the propagation of longitudinal as well as transverse/rotation waves. In addition, we obtain the dispersion band diagram. In the linear regime, these observations are well supported by a mass-spring model that takes into account both a normal and a shear mechanical coupling between the beads considering translational and rotational degrees of freedom. In the weakly nonlinear regime, we present experimental results including the beating in amplitude of the second harmonic for the longitudinal waves and propagation under oblique driving excitation. A theoretical model that takes into account the Hertzian contact mechanics, dissipation and the finite size of the system, captures well the results of the second harmonic generation for the longitudinal waves. This magneto-sensitive system offers great freedom to design complex waveguide geometries where the interplay between geometry, wave polarization and nonlinearity may pave the way toward the development of advanced signal processing elastic devices.

As opposed to metasurfaces, which can produce a single output waveform in response to a single input waveform, volumetric metamaterials have the ability to perform independent functions on many distinct input waveforms. Here, we present an experimental demonstration of this multiplexing capability using a volumetric metamaterial designed using the symphotic method. The symphotic method realizes highly efficient multiplexing structures in the strong scattering limit. In contrast to perturbative design methods like volume holography that are only applicable in weakly scattering media, we provide a comprehensive approach that takes into consideration design and fabrication constraints and which can be verified in simulations. We then demonstrate an experimental realization of a symphotic device operating at a frequency of 10 GHz, which has been optimized for three distinct input waveforms corresponding to three distinct output waveforms. The device is realized using a low-loss 3D-printed material. The symphotic device consists of a lattice of dielectric cylindrical elements with varying radii, excited in a parallel-plate waveguide to enforce two-dimensional field symmetry. The experimental results show excellent agreement with analytical coupled-dipole method simulations and finite-element simulations. The experiments further demonstrate the scalability of symphotic metamaterials and their viability for advanced RF and optical devices.

Stochastic behaviour fundamentally limits the performance and reliability of nanomagnetic devices. Typically, stochastic behaviour is assumed to be the result of simple thermal activation, but it may also be “dynamically-induced” i.e. a direct result of the spatial and temporal complexity of magnetisation dynamics. In this paper, we show how materials engineering can be used to comprehensively suppress dynamically induced stochasticity. Using the dynamics of magnetic domain walls in Ni80Fe20 nanowires as a case study we show how manipulation of the Gilbert damping constant via doping with the rare earth element Terbium dramatically simplifies domain wall dynamics. This allows us to obtain quasi-deterministic behaviours from systems that nominally exhibit exceptionally high levels of stochasticity.

We experimentally study the morphology of a radially expanding sheet of liquid tin, formed by nanosecond-pulse Nd:YAG laser impact on a spherical microdroplet. Specifically, the sheet thickness profile and its time evolution are captured in detail over a range of laser-pulse energies and for two droplet sizes. Two complementary methods to determine this thickness are employed and shown to be in excellent agreement. All obtained thickness profiles collapse onto a single self-similar curve. Spatial integration of the thickness profiles allows determining the volume of the sheet. Remarkably, less than half of the initial amount of tin remains in the sheet under conditions relevant for industrial sources of extreme ultraviolet light, where these thin tin sheets serve as target material. Further analysis shows that the dominant fraction of the mass lost from the sheet during its expansion ends up as fine fragments. We propose that such mass loss can be minimized by producing the sheet targets on the shortest possible timescale. These findings are particularly valuable for ongoing developments in state-of-the-art nanolithography.

Transverse mode locking is repaid attention recently due to its combination with the optical vortices’ formation. In the previous investigations, transverse mode locking is only focused on the phase locking of modes in different orders to research the beam pattern dynamics, or between frequency-degenerated transverse modes to form a spatial stationary beam pattern with optical vortices. It’s experimentally shown that phase and frequency locking between transverse modes in non-frequency degenerated families can be obtained by microchip cavities with high nonlinearity. And we also point out that, for a both temporal and spatial stationary composed beam pattern formed by transverse mode locking, not only the frequency but also the propagation parameters of the beam should be coupled.

We demonstrate how noise can be turned into a resource} for optical sensing using a nonlinear cavity. The cavity is driven by a continuous wave laser into the regime of optical bistability. Due to the influence of fluctuations, the cavity randomly switches between two meta-stable} states. By analyzing residence times in these two states, perturbations to the resonance frequency of the cavity can be detected. Here, such an analysis is presented as a function of the strength of the perturbation and of the noise. By increasing the standard deviation of the noise, we find that the detection speed increases monotonically while the sensitivity peaks at a finite value of the noise strength. Furthermore, we discuss how noise-assisted sensing can be optimized in state-of-the-art experimental platforms, relying solely on the minimum amount of noise present in the cavity due to its dissipation. These results open new perspectives for the ultrafast detection of nanoparticles, contaminants, gases, or other perturbations to the resonance frequency of an optical resonator, at low powers and in noisy environments.

Many efforts have been dedicated to enhancing the near-field radiative heat transfer by designing different kinds of geometric shapes or introducing new materials. Besides just improving the heat transfer rate, active and convenient thermal management is also important in micro/nano thermal systems. We show that introducing an intermediate modulator, based on the graphene/hBN/graphene heterostructure, can enhance and manipulate thermal radiative heat transfer without changing the distance or other parameters of the emitter and absorber. Such three-body systems can increase the radiatively exchanged power several times over corresponding two-body counterparts. The introduced modulator can be viewed as a mid-repeater to effectively enhance photon tunneling through evanescent modes. Furthermore, the heat transfer rate could be modulated in a large range and even be lower than two-body systems by applying bias voltages. The mechanism can be explained by the change of energy transmission coefficients between bodies through adjusting the optical properties of graphene. The presented scheme may open a new avenue to actively control near-field heat transfer at the micro/nanoscales.

We introduce chiral gradient metasurfaces that allow perfect transmission of the incident wave into a desired direction and simultaneous perfect rotation of the polarization of the refracted wave with respect to the incident one. In the lossless limit transmission can reach 100% with a single metasurface layer.} Besides using gradient polarization densities which provide bending of the refracted wave with respect to the incident one, using metasurface inclusions that are chiral allows the polarization of the refracted wave to be rotated. We suggest a possible realization of the proposed device by discretizing the required equivalent surface polarization densities, and synthesizing the chiral discrete polarizabilities with properly sized helical inclusions at each discretization point. By using only a single, optically thin, layer of chiral inclusions, we are able to unprecedentedly deflect a normal incident plane wave to a refracted plane wave at $45\lyxmathsym{\textdegree}$ with 72% power efficiency which is accompanied by a 90∘ polarization rotation. The proposed concepts and design method may find practical applications in polarization rotation devices at microwaves as well as in optics, especially when the incident power is required to be deflected.

Identically-sized Co quantum dots (QDs) are constructed on monolayer tungdten disulfide (WS2) forming coupled heterostructures. Topographical images investigated by in situ scanning tunneling microscopy (STM) show a bias-dependent feature. First-principles calculated binding energies combined with the simulated STM images identify that the Co QDs possess a unique magic number, with a tetrahedral Co4 configuration. Numerical differential conductance measured by scanning tunneling spectroscopy (STS) indicates a p-type doping and an Ohmic contact property for the Co4/WS2 system. Mechanism of the novel transport and conduction properties of the coupled heterostructures is further revealed by analyzing the work functions and interfacial interaction. Our findings offer some references for the controlled fabrication of identically-sized zero-dimensional/two-dimensional (0D/2D) heterostructures and propose a feasible strategy for Ohmic interface contact in nanodevices.

How to measure the optical conductivity of atomically thin crystals is an important but challenging issue due to the weak light-matter interaction at the atomic scale. Photonic spin Hall effect, as a fundamental physical effect in light-matter interaction, is extremely sensitive to the optical conductivity of atomically thin crystals. Here, we report a precision measurement of the optical conductivity of graphene, where the photonic spin Hall effect acts as a measurement pointer. By incorporating with the weak-value amplification technique, the optical conductivity of monolayer graphene taken as a universal constant of (0.993±0.005)σ0 is detected, and a high measuring resolution with 1.5×10−8Ω−1 is obtained. For few-layer graphene without twist, we find that the conductivities increase linearly with layer number. Our idea could provide an important measurement technique for probing other parameters of atomically thin crystals, such as magneto-optical constant, circular dichroism, and optical nonlinear coefficient.

Spin wave, the precession of magnetic order in magnetic materials, is a collective excitation that carries spin angular momentum. Similar to the acoustic or optical waves, the spin wave also possesses the polarization degree of freedom. Although such polarization degrees of freedom are frozen in ferromagnets, they are fully unlocked in antiferromagnets or ferrimagnets. Here we introduce the concept of magnetic gating and demonstrate a spin wave analog of the Datta-Das spin transistor in antiferromagnet. Utilizing the interplay between polarized spin wave and the antiferromagnetic domain walls, we propose a universal logic gate of pure magnetic nature, which realizes all Boolean operations in one single magnetic structure.

Individual disk-shaped CoFeB nanodots were driven into a superparamagnetic state by spin transfer torque, and their time-dependent magnetoresistance fluctuations were measured as a function of current. A thin layer of oxidation at the edges has a dramatic effect on the magnetization dynamics. A combination of experimental results and atomistic spin simulations show that pinning to oxide grains can reduce the likelihood that fluctuations lead to reversal, and can even change the easy axis direction. Exchange bias loop shifts and training effects are observed even at room temperature after brief exposure to small fields. The results have implications for studies of core-shell nanoparticles and small magnetic tunnel junctions and spin torque oscillators.

Quantum communication schemes such as quantum key distribution (QKD) and superdense teleportation provide unique opportunities to communicate information securely. Increasingly, optical communication is being extended to free-space channels, but atmospheric turbulence in free-space channels requires optical receivers and measurement infrastructure to support many spatial modes. Here we present a multi-mode, Michelson-type time-delay interferometer using a field-widened design for the measurement of phase-encoded states in free-space communication schemes. The interferometer is constructed using glass beam paths to provide thermal stability, a field-widened angular tolerance, and a compact footprint. The performance of the interferometer is highlighted by measured visibilities of 99.02±0.05%, and 98.38±0.01% for single- and multi-mode inputs, respectively. Additionally, high quality multi-mode interference is demonstrated for arbitrary spatial mode structures and for temperature changes of ±1.0∘C. The interferometer has a measured optical path-length drift of 130nm/∘C near room temperature. With this setup, we demonstrate the measurement of a two-peaked, multi-mode, single-photon state used in time-phase QKD with a visibility of 97.37±0.01%.

Gate leakage current is a crucial issue for the reliability of modern high-κ MOSFETs. Although various physical models describing both direct tunneling and trap-assisted contribution of leakage current have been presented in literature, many of them treats traps in the dielectric as a continuum distribution in energy and position, and trap-to-trap transport of electrons has so far been mostly neglected or not treated three-dimensionally (3D). In this work, we present a mechanistic model for calculation of gate leakage current in high-κ MOSFET multi-layer stacks based on multi-phonon trap-assisted tunneling theory, taking into account the intrinsic 3D discreteness of traps in the dielectric. Our model can to a good approximation reproduce the experimental results at different dielectric thicknesses, gate voltages, temperatures, and different gate materials. We find that in realistic devices, the 3D trap-to-trap transport of electrons contributes a non-negligible part to the gate leakage current. This contribution is more pronounced at low-voltage device operations, which is important for low-power applications. We calculate the intrinsic fluctuation of gate leakage current due to positional and energetic disorder of traps in the dielectric, and conclude that positional disorder is more important than energetic disorder for realistic material parameters. The calculated gate leakage current depends sensitively on temperature, trap energy, and trap density. We provide a computationally efficient 3D master equation approach that enables 3D mechanistic simulation of 103 traps on the order of minutes on a standard desktop computer.

Anisotropy in electronic structures may ignite intriguing anisotropic optical responses, as well demonstrated in various systems including superconductors, semiconductors and even topological Weyl semimetals. Meanwhile, it is well established in metal optics that the metal reflectance declines from one to zero when the photon frequency is above the plasma frequency ωp, behaving as a plasma mirror. However, the exploration of anisotropic plasma mirrors and corresponding applications remains elusive, especially at room temperature. Here, we discover a pronounced anisotropic plasma reflectance edge in the type-II Weyl semimetal WP2, with an anisotropy ratio of ωp up to 1.5. Such anisotropic plasma mirror behavior and its robustness against temperature promise optical device applications over a wide temperature range. For example, the high sensitivity of polarization-resolved plasma reflectance edge renders WP2 an inherent polarization detector. We further achieve a room-temperature WP2-based optical switch, effectively controlled by simply tuning the light polarization. These findings extend the frontiers of metal optics as a discipline and promise the design of multifunctional devices combining both topological and optical features.

Millimeter-wave superconducting devices offer a platform for quantum experiments at temperatures above 1K, and new avenues for studying light-matter interactions in the strong coupling regime. Using the intrinsic nonlinearity associated with kinetic inductance of thin film materials, we realize four-wave mixing at millimeter-wave frequencies, demonstrating a key component for superconducting quantum systems. We report on the performance of niobium nitride resonators around 100GHz, patterned on thin (20-50nm) films grown by atomic layer deposition, with sheet inductances up to 212pH/□ and critical temperatures up to 13.9K. For films thicker than 20nm, we measure quality factors from 1-6$ 10^4$, and explore potential loss mechanisms. Finally we measure degenerate parametric conversion for a 95GHz device with a forward efficiency up to +16dB, paving the way for the development of nonlinear quantum devices at millimeter-wave frequencies.

In a 2016 article [Phys. Rev. Applied 6, 014017 (2016)], Chyba and Hand proposed a new scheme to generate electric power continuously at the expense of Earth’s kinetic energy of rotation, by using an appropriately shaped cylindrical shell of a well chosen conducting ferrite, rigidly attached to the Earth. A recent experimental test [Phys. Rev. Applied 10, 054023 (2018)] gave a null result. In the first part of the present refutation, I use today’s standard electromagnetism and essentially the same model as Chyba and Hand to show in a very simple way that no device of the proposed type can produce continuous electric power, whatever its configuration or size. In the second part, I show that the prediction of nonzero continuous power by Chyba and Hand results from a confusion of frames of reference at a critical step of their derivation. When the confusion is clarified, the prediction becomes exactly zero. In the third part, I comment about the frequent invocation by Chyba and Hand of controversial legacy notions like the existence of an intrinsic velocity of quasi-static magnetic fields.

We propose a new experimental method in microsphere-assisted interference microscopy, making possible to reconstruct surface topographies as much with high quantitative depth accuracy as when the transversal features sizes are smaller than the classical diffraction limit. The full-field super-resolution interference microscope consists not only of one glass microsphere in the object arm, but also of a second similar microsphere in the reference arm. By compensating the sphere aberrations in the two interference arms, the spatial resolution appears to be considerably increased. The increase in 3D spatial resolution allows the topography reconstruction of 300-nm-width grating lines and 200-nm-diameter transparent nanopillars.

In our original article we examined electric power generation from Earth’s rotation through its own nonrotating axisymmetric magnetic field. In a Comment Jeener claims to prove that no such effect is possible. We show that this conclusion results from his failure to recognize a distinction between the corotation with Earth of the non-axially symmetric components of Earth’s magnetic field, and the non-rotation with Earth of the axially symmetric components. We use Earth’s actual geomagnetic field to demonstrate the important consequences of this distinction. Because the distinction has strong empirical support, Jeener’s argument is incorrect.

Due to its superior coherent and optical properties at room temperature, the nitrogen-vacancy (NV) center in diamond has become a promising quantum probe for nanoscale quantum sensing. However, the application of NV containing nanodiamonds to quantum sensing suffers from their relatively poor spin coherence times. Here we demonstrate energy efficient protection of NV spin coherence in nanodiamonds using concatenated continuous dynamical decoupling, which exhibits excellent performance with less stringent microwave power requirement. When applied to nanodiamonds in living cells we are able to extend the spin coherence time by an order of magnitude to the T1-limit of up to 30μs. Further analysis demonstrates concomitant improvements of sensing performance which shows that our results provide an important step towards in vivo quantum sensing using NV centers in nanodiamond.

The performance of many control tasks with Rydberg atoms can be improved via suppression of the motion-induced dephasing between ground and Rydberg states of neutral atoms. The dephasing often occurs during the {} time when the atom is shelved in a Rydberg state before its deexcitation. This work presents two theories to suppress this dephasing. {}, by using laser fields to induce specific extra phase change to the Rydberg state during the gap time, it is possible to faithfully transfer the Rydberg state back to the ground state after the gap. Although the Rydberg state transitions back and forth between different eigenstates during the gap time, it preserves the blockade interaction between the atom of interest and a nearby Rydberg excitation. This simple method of suppressing the motional dephasing of a flying Rydberg atom can be used in a broad range of quantum control over neutral atoms. {}, we find that the motional dephasing can also be suppressed by using a transition in a V'-type dual-rail configuration. The left~(right) arm of thisV’ represents a transition to a Rydberg state |r1(2)⟩ with a Rabi frequency Ωeikz(Ωe−ikz), where z is frozen without atomic drift, but changes linearly in each experimental cycle. Such a configuration is equivalent to a transition between the ground state and a hybrid and time-dependent Rydberg state with a Rabi frequency 2Ω, such that there is no phase error whenever the state returns to the ground state. We study two applications of the second theory: (i) it is possible to faithfully transfer the atomic state between a hyperfine ground state and Rydberg states |r1(2)⟩ with no {} time between the excitation and deexcitation; (ii) by adding infrared laser fields to induce transition between |r1(2)⟩ and a nearby Rydberg state |r3⟩ via a largely detuned low-lying intermediate state in the {} time, the atom can keep its internal state in the Rydberg level as well as adjust the population branching in |r1(2)⟩ during the {} time. This allows an almost perfect Rydberg deexcitation after the {} time, making it possible to recover a high fidelity in the Rydberg blockade gate. The theories pave the way for high-fidelity quantum control over neutral Rydberg atoms without cooling qubits to the motional ground states in optical traps.

The weak value amplification technique has been proved useful for precision metrology in both theory and experiment. To explore the ultimate performance of weak value amplification for multi-parameter estimation, we investigate a general weak measurement formalism with assistance of high-order Hermite-Gaussian pointer and quantum Fisher information matrix. Theoretical analysis shows that the ultimate precision of our scheme is improved by a factor of square root of 2n+1, where n is the order of Hermite-Gaussian mode. Moreover, the parameters’ estimation precision can approach the precision limit with maximum likelihood estimation method and homodyne method. We have also given a proof-of-principle experimental setup to validate the H-G pointer theory and explore its potential applications in precision metrology.

A comparative study for spin-valley splitting of a series of van der Waals (vdW) heterostructures constructed by transition metal dichalcogenides (TMDCs) and magnetic materials has been performed by first principles calculations. It is found that the magnitude of spin-valley splitting is positively correlated the size of magnetic proximity effect closely related to Coulomb interaction, which increases with the increase of interlayer charge transfer. As a result, only when monolayer TMDCs and magnetic materials combined into type-III rather than type-I and type-II band alignment heterostructures, a large spin-valley splitting can be obtained. We demonstrated this criterion in TMDCs/NiY2 (Y=Cl, Br) vdW heterostructures by schematics of level coupling in detail, and then predicted dozens of vdW heterostructures with possible large spin-valley splitting. This discovery can help to quickly determine whether the material can achieve a large spin-valley splitting, and the predicted materials will provide good guidance for the experimentalists.

A phononic crystal formed in a suspended membrane provides full confinement of hypersonic waves and thus realizes a range of chip-scale manipulations. In this letter, we demonstrate the mode-resolved real-space characterization of the mechanical vibration properties in cavities and waveguide systems. Multiple resonant modes are independently characterized in various designed cavities, and wavelength-scale high-Q resonances up to Q= 4200 under atmospheric conditions are confirmed. This also reveals that the waveguide allows us to observe a mode-resolved wave transmission and thereby drive evanescently-coupled cavities. The methods offer a significant tool with which to build compact and low-power microwave phononic circuitry for signal processing and hybrid quantum system applications.

Thermoelectric (TE) materials can convert temperature differences into electricity directly and reversibly without air pollution, which provides a viable route for alleviating global warming and energy crisis. Here we use first-principles calculations combined with semi-classical Boltzmann transport theory to assess the potential of layered LaCuOSe for TE applications. Originating from the layered crystal structure, the electronic and thermal transport properties (i.e. Seebeck coefficient, electrical conductivity and thermal conductivity) are highly anisotropic between the in-plane and out-of-plane directions. The optimal figure of merit of 2.71 is achieved along the out-of-plane direction for electron doping at 900 K. Such excellent TE properties can be attributed to desired La-Se interlayer interaction between adjacent layers and relatively strong coupling between acoustic phonons and optical phonons, resulting in simultaneous enhancement of the electrical conductivity and suppression of the lattice thermal conductivity. This study provides a new route to improve the TE performance of layered LaCuOSe by utilizing anisotropic character of transport propereties and offers implications in promoting related experimental investigations. .

Highly directional and lossless surface wave has significant potential applications in the two-dimensional photonic circuits and devices. Here we experimentally demonstrate a selective Dyakonov surface wave coupling at the interface between a transparent polycarbonate material and nematic liquid crystal 5CB. By controlling the anisotropy of the nematic liquid crystal with an applied magnetic field, a single ray at a certain incident angle from a diverged incident beam can be selectively coupled into surface wave. The implementation of this property may lead to a new generation of on-chip integrated optics and two-dimensional photonic devices. {I.

He+ ion irradiation enables controlled post-deposition modification of layered magnetic thin film systems. The degree of the modification and its depth profile can be tuned by the irradiation dose and energy. Here we use magnetometry and magnetic force microscopy to explore the impact of gentle He+ ion irradiation on synthetic antiferromagnets (SAF) consisting of ferromagnetic (FM) Co/Pt multilayers with perpendicular magnetic anisotropy (PMA), which are antiferromagnetically (AF) coupled via Ru interlayers. This system shows a rich variety of magnetic domain patterns due to the strong competition of the different magnetic energies. We show that AF interlayer exchange and perpendicular interface anisotropy energy are reduced by the ion irradiation, thus resulting in multiple successive magnetic phase transitions.

In laser-solid interactions, electrons may be generated and subsequently accelerated to energies of the order-of-magnitude of the ponderomotive limit, with the underlying process dominated by direct laser acceleration. Breaking this limit, realized here by a radially-polarized laser pulse incident upon a wire target, can be associated with several novel effects. Three-dimensional Particle-In-Cell simulations show a relativistic intense laser pulse can extract electrons from the wire and inject them into the accelerating field. Anti-dephasing, resulting from collective plasma effects, are shown here to enhance the accelerated electron energy by two orders of magnitude compared to the ponderomotive limit. It is demonstrated that ultra-short radially polarized pulses produce super-ponderomotive electrons more efficiently than pulses of the linear and circular polarization varieties.

Antiferromagnets are outstanding candidates for the next generation of spintronic applications, with great potential for downscaling and decreasing power consumption. Recently, the manipulation of bulk properties of antiferromagnets has been realized by several different approaches. However, the interfacial spin order of antiferromagnets is an important integral part of spintronic devices, thus the successful control of interfacial antiferromagnetic spins is urgently desired. Here, we report the high controllability of interfacial spins in antiferromagnetic / ferromagnetic / heavy metal heterostructure devices using spin-orbit torque (SOT) assisted by perpendicular or longitudinal magnetic fields. Switching of the interfacial spins from one to another direction through multiple intermediate states is demonstrated. The field-free SOT-induced switching of antiferromagnetic interfacial spins is also observed, which we attribute to the effective built-in out-of-plane field due to unequal upward and downward interfacial spin populations. Our work provides a precise way to modulate the interfacial spins at an antiferromagnet / ferromagnet interface via SOT, which will greatly promote innovative designs for next generation spintronic devices.

By dissolving sodium chloride (NaCl) into liquid water, we realized the obvious enhancement of stimulated Raman scattering (SRS). Comparing with pure water, the performance improvements included spectrum purification, elevated Raman gain, descending pump threshold, and increased conversion efficiency. In the best SRS results, the pump threshold decreased by 45{%} and the maximum conversion efficiency increased by 10.4{%}. Then, water becomes a typical Raman scattering medium that generates a narrow-band light. Moreover, we found that the bulk structure of water and NaCl solutions could be analyzed in detail by combining the principles of SRS and through analysis of the SRS spectra. In water, the O-H stretching band was proved to be the superposition of stretching modes in different water clusters. For the solution, the O-H stretching vibration of water molecules in hydration shells around Cl− ions can be obtained directly and its variation with respect to solute concentration was investigated using the SRS spectra. The superior SRS properties of solutions originated from the hydration shell around the Cl− ions. This work suggests that the SRS is a promising approach to identifying structures in water and NaCl solutions, and that it can easily be extended to other liquids and solutions. {I.

Superconducting nanowire single-photon detectors promise efficient ($100%)andfast($Gcps) detection of light at the single-photon level. They constitute one of the building blocks to realize integrated quantum optical circuits in a waveguide architecture. The optical response of single-photon detectors, however, is limited to measure only the presence of photons. It misses the capability to resolve the spectrum of a possible broadband illumination. In this work, we propose the optical design for a superconducting nanowire single-photon spectrometer in an integrated optical platform. We exploit a cascade of cavities with different resonance wavelengths side-coupled to a photonic crystal bus waveguide. This allows to demultiplex different wavelengths into different spatial regions, where individual superconducting nanowires that measure the presence of single photons are placed next to these cavities. We employ temporal coupled-mode theory to derive the optimal conditions to achieve a high absorption efficiency in the nanowire with fine spectral resolution. It is shown that the use of a mirror at the end of the cascaded system that terminates the photonic crystal bus waveguide increases the absorption efficiency up to unity, in principle, in the absence of loss. The expected response is demonstrated by full-wave simulations for both two-dimensional and three-dimensional structures. Absorption efficiencies of about 80% are achieved both in two-dimensional structures for four cascaded cavities and in three-dimensional structures for two cascaded cavities. The achieved spectral resolution is about 1nm. We expect that the proposed setup, both analytically studied and numerically demonstrated in this work, offers a great impetus for future quantum nanophotonic on-chip technologies.

Superconductor/Ferromagnets (S/F) hybrids show an interesting magneto-transport that result from the transfer of properties between both constituents. For instance, magnetic memory can be transferred from the F into the S through the pinning of superconducting vortices by ferromagnetic domains. The ability to tailor this type of induced behavior is important to broaden its range of application. Here we show that engineering the F magnetization reversal allows tuning the strength of the vortex pinning (and memory) effects, as well as the field range in which they appear. This is done by using F multilayers in which Co is combined with different heavy metals (Ru, Ir, Pt). By choosing the materials, thicknesses, and stacking order of the layers, we can design the characteristic domain size and morphology, from out-of-plane magnetized stripe domains to much smaller magnetic skyrmions. These changes strongly affect the magneto-transport properties. The underlying mechanisms are identified by comparing the experimental results to a magnetic pinning model.

We establish the angle-resolved thermal emission spectroscopy (ARTES) as a new platform to characterize the intrinsic eigenmode properties of non-Hermitian systems. This method can directly map the dispersion of meta-crystals within the light cone with a high angular resolution. To illustrate its usefulness, we demonstrate the existence of bound states in the continuum (BICs) and non-Hermitian Fermi arcs in a planar corrugated meta-crystal by measuring its angle-resolved thermal emission spectra. We show that change in the thickness of the meta-crystal can induce a band inversion between a BIC and a radiative state, and a pair of exceptional points emerge when the band inversion occurs. With this approach, the band mapping of non-Hermitian photonic systems can become a relatively striaghtforward task.

Transformation theory~has been a powerful tool for material design to control waves in~electromagnetics, acoustics and elastic mechanics. The deformable materials have been demonstrated to guide the propagation of ultrasonic waves freely. Toothed cetaceans such as dolphin may manipulate~directional beams by simply deforming their~foreheads. However, existing materials face great challenges in realizing this bio-acoustic function. Here, we proposed a novel bioinspired semi-analytic conformal transformation acoustics which can predict the evolution of acoustic functions strictly. Based on this method, we designed~series of acoustic steering and collimation models. The sound speed~distribution function~can be strictly determined by conformal mapping, and the acoustic beam shifting and expansion are numerically confirmed. We further fabricated the acoustic steering and collimationdevicesby acoustic metamaterials.~The experimental results show a~good agreement with~theoretical predictions. The proposed bioinspired conformal transformation acoustics may bridge the gap between animal’s~biosonar and artificial materials, and shows potential~application values in underwater acoustics. Maintext Transformation optics [1, 2] is a useful tool to control light path and electromagnetic waves freely, and has drawn great attention recently with various intriguing devices designed. It is based on the form invariance of Maxwell’s equations under coordinate transformations. Pendry et al [1] and Leonhardt [2] firstly designed cloaks that can exclude electromagnetic field outside obstacles, which was later verified by experiments at microwave frequencies with electromagnetic metamaterials [3]. Many other optical functional devices have been further designed, such as field rotators [4, 5], field concentrators [6, 7], illusion devices [8] and so on [9]. The transformation method can be generalized to elastodynamics and acoustics. Milton et al proposed a general elastodynamic equation of motion that is invariant under coordinate transformations and complex transformation elastodynamic was proposed [10]. By comparing the acoustic equation and the dc conductivity equation, the form invariance of acoustics is also confirmed [11]. With that, transformation acoustics was also proposed, and the transformation density tensor and the bulk modulus was found to design acoustic cloaks [11, 12]. Most of the acoustic transformation devices can be calculated theoretically and numerically, but material parameters are difficult to achieve [13]. Fortunately, acoustic metamaterial shows its extraordinary value in several important designs, such as carpet cloaks [14, 15] and Luneburg lenses [16]. Furthermore, acoustics benefit from interesting designs in nature. Recent study indicated that toothed whale can manipulate underwater directional beams and control beam widths by compressing the forehead [17]. A biomimetic projector has been designed based on the gradient sound speed distribution of a pygmy sperm whale [18]. This artificial structure demonstrated the ability in directional acoustic beam control. Meanwhile, the directional beam width and angle of the subwavelength biomimetic emission was verified experimentally [19, 20]. However, complex deformation process can lead to the uncertain transformation of the sound speed. It’s necessary to determine …