We present the concept of the optomagnonic logic gate, where interference of spin waves excited by femtosecond laser pulses at multiple points by the inverse Faraday effect in a bismuth-substituted yttrium iron garnet film plays a decisive role. The resulting spin-wave distribution is determined by constructive and destructive interference, which is controlled by the polarization of laser sources. A variable platform with a spatial light modulator is used to control the overall spin-wave distribution by manipulating the arrangement of the local spin-wave sources. We demonstrate the experimental optical excitation of backwards volume magnetostatic spin waves at multiple points and use wavelet analysis and micromagnetic numeric simulations to analyze them. Simulations provide an excellent agreement with the experimental data and are further used to model the magnon logical gate (xnor) based on optically excited spin-wave interference.

We propose a scheme to implement the phase-robust topological router based on a one-dimensional dimerized superconducting circuit lattice with long-range hopping. We show that the proposed dimerized superconducting circuit lattice can be mapped into an extended chiral-symmetric Su-Schrieffer-Heeger (SSH) model with long-range hopping, in which the existence of long-range hopping induces a special zero-energy mode. The peculiar distribution of the zero-energy mode enables us to engineer a phase-robust topological router, which can achieve quantum state transfer (QST) from one site (input port) to multiple sites (output ports). Benefiting from the topological protection of chiral symmetry, we demonstrate that the presence of the mild disorder in nearest-neighbor and long-range hopping has no appreciable effects on QST in the lattice. Particularly, after introducing another long-range hopping into the extended SSH lattice, we propose an optimized protocol of the phase-robust topological router, in which the number of the output ports can be efficiently increased. Resorting to the Bose statistical properties of the superconducting circuit lattice, the input port and output ports assisted by the zero-energy mode can be detected via the mean distribution of the photons. Our work breaks the traditional QST form with only one outport by the zero-energy mode and opens a pathway to construct large-scale quantum information processing in the SSH chains with long-range hopping.

MXene has emerged as one of the frontier two-dimensional materials. In this work, ${\mathrm{Ti}}_3{\mathrm{C}}_2{T}_2(T=-\mathrm{O},-\mathrm{Cl},-\mathrm{OH}$, or $-\mathrm{F})$ MXene-${\mathrm{Cs}}_3{\mathrm{Bi}}_2{\mathrm{Br}}_9$ perovskite heterostructures are constructed, and the various surface terminations of ${\mathrm{Ti}}_3{\mathrm{C}}_2{T}_2$ can achieve functionalized perovskite optoelectronic applications in the heterostructures. Lattice-mismatch rates of the ${\mathrm{Ti}}_3{\mathrm{C}}_2{T}_2$ and ${\mathrm{Cs}}_3{\mathrm{Bi}}_2{\mathrm{Br}}_9$ heterostructures are only about 1%, which makes the electronic properties of ${\mathrm{Cs}}_3{\mathrm{Bi}}_2{\mathrm{Br}}_9$ independent of lattice stress in the heterostructures. The binding energies of the ${\mathrm{Ti}}_3{\mathrm{C}}_2{T}_2/{\mathrm{Cs}}_3{\mathrm{Bi}}_2{\mathrm{Br}}_9$ interfaces are quite low, especially at the ${\mathrm{Ti}}_3{\mathrm{C}}_2(\mathrm{OH}{)}_2/{\mathrm{Cs}}_3{\mathrm{Bi}}_2{\mathrm{Br}}_9$ interface. Due to the adjustable work function (WF) of ${\mathrm{Ti}}_3{\mathrm{C}}_2{T}_2$, the types of interface contacts are different, including n- and p-type Schottky contacts and an ohmic contact. The ${\mathrm{Ti}}_3{\mathrm{C}}_2(\mathrm{OH}{)}_2/{\mathrm{Cs}}_3{\mathrm{Bi}}_2{\mathrm{Br}}_9$ interface is an ohmic contact; this is attributed to the big difference in the WFs of ${\mathrm{Ti}}_3{\mathrm{C}}_2(\mathrm{OH}{)}_2$ and ${\mathrm{Cs}}_3{\mathrm{Bi}}_2{\mathrm{Br}}_9$, which could greatly boost the charge-carrier separation and transfer efficiency. In addition, the constructed heterostructures enhance the optical absorption coefficient and reduce charge-carrier effective masses. These results indicate that the ${\mathrm{Ti}}_3{\mathrm{C}}_2{T}_2/{\mathrm{Cs}}_3{\mathrm{Bi}}_2{\mathrm{Br}}_9$ heterostructures, especially ${\mathrm{Ti}}_3{\mathrm{C}}_2(\mathrm{OH}{)}_2/{\mathrm{Cs}}_3{\mathrm{Bi}}_2{\mathrm{Br}}_9$, can significantly improve the optoelectronic performance of the lead-free perovskite.

The possibility of controlling Josephson vortices and fluxon states has always been an attractive area of research that can influence the development of superconducting devices and quantum computing. Here we demonstrate the capability of magnetic force microscopy to detect and manipulate Josephson vortices (JVs) and fluxons below the critical current in complex superconducting systems on the example of a dc superconducting quantum interference device. The simultaneous magnetic force microscopy and transport investigation method make it possible to generate JVs by direct current in Josephson junctions and simultaneously analyze their dynamics under various external conditions. Our results show a dynamic process of transition of $2\pi$-phase singularities of JVs and fluxons from one to another. Finally, we demonstrated that the magnetic force microscopy method could distinguish the difference in critical currents between several Josephson junctions in complex superconducting circuits without the need of direct electron transport measurements.

What is the fate of an oscillator when its inductance and capacitance are varied while its frequency is kept constant? Inspired by this question, we propose a protocol to implement parity-time ($\mathcal{P}\mathcal{T}$) symmetry in a lone oscillator. Different forms of constrained variations lead to static, periodic, or arbitrary balanced gain and loss profiles, that can be interpreted as purely imaginary gauge fields. With a state-of-the-art, dynamically tunable $LC$ oscillator comprising synthetic circuit elements, we demonstrate static and Floquet $\mathcal{P}\mathcal{T}$ breaking transitions, including those at vanishingly small gain and loss, by tracking the circuit energy. Concurrently, we derive and observe conserved quantities in this open, balanced gain-loss system, both in the static and Floquet cases. Lastly, by measuring the circuit energy, we unveil a giant dynamical asymmetry along exceptional-point contours that emerge symmetrically from the Hermitian degeneracies at Floquet resonances. Distinct from material or parametric gain and loss mechanisms, our protocol enables on-demand parity-time symmetry in a minimal classical system—a single oscillator—and may be ported to other realizations including metamaterials and optomechanical systems.

In this work, we develop upper bounds on key rates for device-independent quantum key distribution (DI-QKD) protocols and devices. We study the reduced $\mathrm{cc}$-squashed entanglement and show that it is a convex functional. As a result, we show that the convex hull of the currently known bounds is a tighter upper bound on the device-independent key rates of the standard Clauser-Horne-Shimony-Holt (CHSH)-based protocol. We further provide tighter bounds for DI-QKD key rates achievable by any protocol applied to the CHSH-based device. This bound is based on reduced relative entropy of entanglement optimized over decompositions into local and nonlocal parts. In the dynamical scenario of quantum channels, we obtain upper bounds for device-independent private capacity for the CHSH-based protocols. We show that the device-independent private capacity for the CHSH-based protocols on depolarizing and erasure channels is limited by the secret key capacity of dephasing channels.

Optical cavities find diverse uses in lasers, frequency combs, optomechanics, and optical signal processors. Complete reconfigurability of the resonant frequency as well as the loss enables development of generic field programmable cavities for achieving the desired performance in these applications. Conventional reconfigurable cavities are generally limited to specific material platforms or specific optical tuning methods and require sophisticated fabrication. Furthermore, the tuning of the loss is coupled to the resonance shift in the cavity. We propose and demonstrate a simple and generic interferometer in a cavity structure that enables quasiperiodic modification of the internal cavity loss and the cavity resonance to reconfigure the $Q$ factor, transmission characteristics, and group delay of the hybrid cavity, with simple tuning of the optical phase in the interferometer. We also demonstrate methods to decouple the tuning of the loss from the resonance shift, that enables resonance-locked reconfigurability. This structure also enables resonance shift to both shorter and longer wavelengths using the same phase-tuning technique, which is challenging to achieve in conventional reconfigurable cavities. These devices can be implemented in any guided-wave platform (on-chip or fiber-optic) with potential applications in programmable photonics and reconfigurable optomechanics.

Increasing the energy density in electric double-layer capacitors (EDLCs), also known as supercapacitors, remains an active area of research. Specifically, there is a need to design and discover electrode and electrolyte materials with enhanced electrochemical storage capacity. Here, using fully atomistic molecular dynamics (MD) simulations, we investigate the performance of hyper-branched “poly(amidoamine) (PAMAM)” dendrimer as an electrolyte and an electrode coating material in a graphene-based supercapacitor. We investigate the performance of the capacitor using two different modeling approaches, namely the constant charge method (CCM) and the constant potential method (CPM). These simulations facilitated the direct calculation of the charge density, electrostatic potential, and field, and hence the differential capacitance. We found that the presence of the dendrimer in the electrodes and the electrolyte increased the capacitance by about $65.25\mathrm{\%}$ and $99.15\mathrm{\%}$, respectively, compared with the bare graphene electrode-based aqueous EDLCs. Further analysis revealed that these increases were due to the enhanced electrostatic screening and reorganization of the double-layer structure of the dendrimer-based electrolyte.

Piezoelectric optomechanical platforms present one of the most promising routes towards efficient transduction of signals from the microwave to the optical frequency domains. While there has been significant recent progress particularly on the materials front, alternative device architectures that can potentially meet the stringent efficiency requirements of quantum transducers need to be continuously explored. In this work, we utilize the mechanical supermode principle to improve the overall microwave-to-optical transduction efficiency, by fabricating Lamb-wave resonators that are hybridized with the mechanical breathing modes of a rib waveguide in a suspended gallium arsenide ($\mathrm{Ga}\mathrm{As}$) photonic-integrated-circuit platform. Combining the strong elasto-optic interactions available in $\mathrm{Ga}\mathrm{As}$ with the increased phonon injection efficiency enabled by this architecture, we demonstrate signal transduction up to 7 GHz, and an increase in transduction efficiency of approximately 25 times for the hybridized mode ($f_m\approx 2$ GHz), using this approach. We also outline routes for improving device performance to enable quantum transduction within this platform.

A topological Fano resonance with ultrasharp asymmetric line shape is sensitive to external parameters and is immune to structural disorder, and thus, acts as a robust sensor. Here, an ultracompact tunable on-chip integrated topological Fano resonance is designed based on graphene-based nanomechanical phononic crystals. The Fano resonance comes from the interference between topologically protected even and odd edge modes at the interface between trivial and nontrivial insulators. The two edge modes have different edge-mode widths, resulting in distinct resonant lifetimes. The resonant frequency can be adjusted by employing different gate voltages, which can vary the tension of the graphene membrane. Such tunable topological Fano resonances can be applied to design a wide variety of highly sensitive and accurate robust sensors, including extremely tiny forces, masses, and spatial positions.

We propose a high-resolution label-free two-dimensional imaging method by introducing second-harmonic generation (SHG) and structured illumination in quantitative phase microscopy (QPM), termed ${\mathrm{S}}^2\mathrm{QPM}$, which can achieve a fourfold lateral resolution improvement compared with normal incident illumination for noncentrosymmetric structures. Unlike traditional QPM only obtaining information about the optical path difference, ${\mathrm{S}}^2\mathrm{QPM}$ can additionally recover structural information from the ${\chi }^{(2)}$ distribution. Analytical solutions for SHG fields are obtained by solving the inhomogeneous and nonlinear Helmholtz equation in the $\mathit{k}$-space in a both concise and accurate way. With the $\mathit{k}$-space SHG field solutions for different structured illumination patterns, an object reconstruction model is developed to retrieve the high-resolution normalized ${\chi }^{(2)}$ distributions and quantitative phase maps. We simulate high-resolution reconstructions of the normalized ${\chi }^{(2)}$ distributions and quantitative phase maps using various resolution targets. The lateral resolution improvement is quantified by synthesizing the object spectrum function and profiling resolution targets.

Drying plays a central role in various fabrication processes and applications of functional nanoporous materials, most prominently in relation to energy storage and conversion. During such processes, liquid coexists with air inside the sample, leading to transport as a result of concentration gradients of vapor and/or liquid. Experimentally, it is extremely challenging to unravel this transport phenomenology inside the hidden geometry of porous media. Here, we observe the drying of a model nanoporous material (monolithic mesoporous silica glass, Vycor) with magnetic resonance imaging. We show that, for various boundary conditions (air-flux intensities), no dry region develops, but the sample desaturates in depth. This desaturation is almost homogeneous throughout the sample for weak air flux, while saturation gradients can be observed for sufficiently strong air flux. We demonstrate that the transport of water is mainly ensured by liquid flow towards the free surface, resulting from a gradient of vapor pressure, associated with local saturation (via the desorption curve), leading to a gradient of liquid pressure (via the Kelvin law). Assuming otherwise standard hydrodynamic characteristics of the nanoconfined liquid, this results in a diffusionlike model, which appears to represent experimental data very well in terms of the spatial distribution of water over time inside the sample for various boundary conditions (air-flux intensities). Finally, we propose a predictive model of the detailed drying characteristics of a nanomaterial from knowledge of its pore size, permeability, and desorption curve. This provides an insight into the rational design of drying-based processes employing functional nanoporous materials and allows for a mechanistic understanding of drying phenomenologies in natural nanoporous media.

Quantum key distribution (QKD) allows two remote parties to share information-theoretically secure keys. In recent years, a revolutionary breakthrough called twin-field (TF) QKD has been developed to overcome the linear key-rate constraint and greatly increases the achievable distance. Phase randomization and subsequent postselection play roles in its security proof. Later, no-phase-postselection TF QKD was proposed and became a popular variant, since the removal of phase postselection leads to a higher key rate. However, the achievable distance is decreased compared to the original one. Here, we propose a TF QKD protocol with partial phase postselection. Namely, its code mode is still free from global phase randomization and postselection to make sure the advantage of the high key rate remain. On the other hand, phase postselection is introduced in the decoy mode to improve the performance. Applying an operator dominance condition, we prove universal security of the proposed protocol in the finite-key case under coherent attacks, and numerical simulations confirm its potential advantages in terms of key rate and achievable distance.

We experimentally investigate the properties of hyperentangled states displaying simultaneous entanglement in multiple degrees of freedom and find that Bell tests beyond the standard Clauser-Horne-Shimony-Holt inequality can reveal a higher-dimensional nature in a device-independent way. Specifically, we show that hyperentangled states possess more than just simultaneous entanglement in separate degrees of freedom but also entanglement in a higher-dimensional Hilbert space. We also verify the steerability of hyperentangled quantum states by steering different photonic degrees of freedom.

We devise nanoscale-designed ferromagnetic thin films with graded exchange-coupling (J) profiles that allow us to obtain constant coercivities over a very extended temperature range. The magnetic structure designed here is composed of two ferromagnetic layers, which are separated by a spacer layer with a linear exchange-graded profile. Our detailed magnetometry analysis on single-crystal $\mathrm{Co}\text{−}\mathrm{Ru}$ alloy thin films reveals a coercivity plateau with a relative change of less than 2% over a temperature range of 75 K, whereas conventional films exhibit changes larger than 20%. This remarkable behavior is achieved by means of a strongly temperature-dependent exchange bias between adjacent ferromagnetic portions of our film structures, which are designed to fully compensate for the conventional temperature dependence of the coercive field. This strongly temperature-dependent bias field is mediated by a paramagnetic interlayer in our film design and can be adjusted by a suitable choice of both the spacer-layer composition profile and thickness. Our particular design can be applied to a large variety of magnetic materials and adapted to relevant temperature ranges that are needed to maintain stable coercive field values over a wide operation range in real applications.

Ionic gating is a powerful technique for tuning the physical properties of a material via electric-field-induced charge doping, but is prone to introduce extrinsic disorder and undesired electrochemical modifications in the gated material beyond pure electrostatics. Conversely, reversible, volatile, and electrostatic modulation is pivotal in the reliable design and operation of novel device concepts enabled by the ultrahigh induced charge densities attainable via ionic gating. Here we demonstrate a simple and effective method to achieve reversible and volatile gating of surface-sensitive ultrathin niobium nitride films via controlled oxidation of their surface. The resulting niobium oxide encapsulation layer exhibits a capacitance comparable to that of nonencapsulated ionic transistors, withstands gate voltages beyond the electrochemical stability window of the gate electrolyte, and enables a fully reversible tunability of both the normal-state resistivity and the superconducting transition temperature of the encapsulated films. Our approach should be transferable to other materials and device geometries where more standard encapsulation techniques are not readily applicable.

${\mathrm{Bi}}_2{\mathrm{Te}}_3$ is a widely used thermoelectric material with strong anharmonicity. Determination of its thermal conductivity requires consideration of the high-order phonon scattering process, which makes it extremely time consuming and challenging to accurately calculate its thermal conductivity by obtaining high-order force constants based on density-functional theory. In this work, a deep-neural-network potential is developed to reproduce phonon dispersion and predict the lattice thermal conductivity of ${\mathrm{Bi}}_2{\mathrm{Te}}_3$. The equilibrium molecular dynamics simulations combined with this potential are performed to calculate the lattice thermal conductivity and the results nicely match the experimental values. Meanwhile, we find the generalized gradient approximation with the DFT-D3 functional can accurately reproduce the experimental lattice constants of ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ and provide a description of the phonon dispersion in ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ as well as the local density approximation. Furthermore, we explore the influence of the native point defects on thermal conductivity, and find that $\mathrm{Te}$ vacancies have the most significant effect on the reduction of thermal conductivity, owing to the appreciable inhibition of phonon propagation speed by $\mathrm{Te}$ vacancies, and the additional scattering among original low-frequency optical phonons and the fresh low-frequency optical phonons moving downward from high frequency region, which provides some theoretical guidance for reducing thermal conductivity in experimental research.

Bound states in the continuum (BICs) provide a viable way of achieving high-Q resonances in both photonics and acoustics. In this work, we propose a general method of constructing Friedrich-Wintgen (FW) BICs and accidental BICs in a coupled acoustic waveguide-resonator system. We demonstrate that FW BICs can be achieved with arbitrary two degenerate resonances in a closed resonator, regardless of whether they have the same or opposite parity. Moreover, their eigenmode profiles can be arbitrarily engineered by adjusting the position of the attached waveguide. This suggests an effective way of continuously switching the nature of the BICs from FW BICs to symmetry-protected BICs or accidental BICs. Also, such BICs are sustained in the coupled waveguide-resonator system with shapes such as rectangles, ellipses, and rhomboids. These interesting phenomena are well explained by the two-level effective non-Hermitian Hamiltonian, where two strongly coupled degenerate modes play a major role in forming such FW BICs. Additionally, we find that such an open system also supports accidental BICs in geometry space instead of momentum space via tuning the position of the attached waveguide, which is attributed to the quenched coupling between the waveguide and eigenmodes of the closed cavity. Finally, we fabricate a series of three-dimensional coupled resonator waveguides and experimentally verify the existence of FW BICs and accidental BICs by measuring the transmission spectra. Our results complement the current BIC library in acoustics and provide nice routes for designing acoustic devices, such as acoustic absorbers, filters, and sensors.

The lack of certain crystalline symmetries in strong spin-orbit-coupled nonmagnetic materials allows for the existence of unconventional spin Hall responses, with electrically generated transverse spin currents possessing collinear flow and spin directions. The injection of such spin currents into an adjacent ferromagnetic layer can excite magnetization dynamics via unconventional spin-orbit torques, leading to deterministic switching in ferromagnets with perpendicular magnetic anisotropy. We study the interplay between conventional and unconventional spin-orbit torques on the magnetization dynamics of a perpendicular ferromagnet in the small intrinsic damping limit, and identify a rich set of dynamical regimes that includes deterministic and probabilistic switching, precessional and pinning states. Contrary to common belief, we find that there exists a critical conventional spin Hall angle, beyond which deterministic magnetization switching transitions to a precessional or pinned state. Conversely, we show that larger unconventional spin Hall angle is generally beneficial for deterministic switching. We derive an approximate expression that qualitatively describes the state-diagram boundary between the full deterministic switching and precessional states and discuss a criterion for searching symmetry-broken spin Hall materials in order to maximize switching efficiency. Our work offers a roadmap towards energy-efficient spintronic devices, which might open the door for applications in advanced in-memory computing technologies.