We study ballistic transport in bilayer graphene junctions and show how electrostatic gating, interlayer bias, and homogeneous strain provide complementary control over electron transmission. In the absence of strain, transport is governed by symmetry constraints that suppress transmission at specific incidence angles despite the availability of states. An interlayer bias lifts this suppression through mode mixing and opens a tunable transport gap. Within a full four-band description, we identify a distinct conductance threshold that marks the onset of propagation of the upper band inside the barrier. This produces a clear change in the slope of the conductance and serves as an experimentally accessible transport fingerprint of the multiband structure and interlayer coupling. Homogeneous in-plane strain acts as a geometric control mechanism. By reshaping the band structure in momentum space, it redistributes the angular transmission window and suppresses conductance without introducing disorder. Notably, strain preserves the underlying symmetry-based decoupling responsible for transmission suppression while shifting its condition away from normal incidence. These results provide a unified framework for interpreting angle-resolved transport in bilayer graphene and establish multiband ballistic transport as a practical probe of band-structure geometry.

We demonstrate a dissipative protocol for ground-state preparation of a quantum spin chain on a trapped-ion quantum computer. As a first step, we derive a Kraus representation of a dissipation channel for the protocol recently proposed by Ding et al. [Single-ancilla ground state preparation via lindbladians, Phys. Rev. Res. 6, 033147 (2024)] that still holds for arbitrary temporal discretization steps, extending the analysis beyond the Lindblad dynamics regime. The protocol guarantees that the fidelity with the ground state monotonically increases (or remains unchanged) under repeated applications of the channel to an arbitrary initial state, provided that the ground state is the unique steady state of the dissipation channel. Using this framework, we implement dissipative ground-state preparation of a transverse-field Ising chain for up to 19 spins on the trapped-ion quantum computer Reimei provided by Quantinuum. Despite the presence of hardware noise, the dynamics consistently converges to a low-energy state far away from the maximally mixed state even when the corresponding quantum circuits contain as many as 4110 entangling gates, demonstrating the intrinsic robustness of the protocol. By applying zero-noise extrapolation, the resulting energy expectation values are systematically improved to agree with noiseless simulations within statistical uncertainties.

Two-dimensional (2D) van der Waals (vdW) ferromagnet ${\text{Fe}}_5{\text{GeTe}}_2$ (F5GeT2) is a promising candidate for spintronic applications due to its intrinsic near-room-temperature ferromagnetism, magnetic anisotropy, excellent tunability, and emergent topological magnetic textures. However, the delicate ferromagnetic order and moderate magnetic anisotropy hinder its practical implementation in next-generation spin-based devices. Doping with specific elements has been demonstrated to be an effective strategy for enhancing ferromagnetism and elevating the Curie temperature ($T_C$) in such systems. In this work, we synthesized lightly Ni-doped $({\text{Fe}}_{5-x}{\text{Ni}}_x{)}_5{\text{GeTe}}_2({\text{Ni}}_x\text{−}\mathrm{F}5\text{GeT}2)$ single crystals and conducted a comprehensive investigation into their magnetic properties. We found that even a small amount of Ni-doping can significantly elevate $T_C$ and enhance the easy in-plane anisotropy (EPA) compared with pristine F5GeT2. By employing the modified Arrott plot (MAP) method and critical isotherm (CI) analysis, the critical exponents for two distinct magnetic field orientations are obtained. For ${\text{Ni}}_{0.05}\text{−}\mathrm{F}5\text{GeT}2$, we determine $\beta =0.385(7)$, $\gamma =1.303(4)$, and $\delta =4.696(5)$ for $H//ab$, and $\beta =0.359(1)$, $\gamma =1.195(7)$, and $\delta =4.455(1)$ for $H//c$. For ${\text{Ni}}_{0.1}\text{−}\mathrm{F}5\text{GeT}2)$, we find $\beta =0.354(9)$, $\gamma =1.342(5)$, and $\delta =4.764(6)$ for $H//ab$, and $\beta =0.368(2)$, $\gamma =1.242(1)$, and $\delta =4.561(1)$ for $H//c$. These derived exponents exhibit excellent self-consistency and adhere to the Widom scaling relation. However, the critical exponents do not conform to any single theoretical universality class, which indicates the presence of anisotropic magnetic exchanges induced by the Ni-doping. The magnetic interactions of ${\text{Ni}}_{0.05}\text{−}\mathrm{F}5\text{GeT}2$ and ${\text{Ni}}_{0.1}\text{−}\mathrm{F}5\text{GeT}2$ fall between the short-range and long-range limits, suggesting that low-concentration Ni-doping modulates the spin decay distances of the system. Our findings establish a pathway for tailoring the magnetic properties of 2D-vdW ferromagnets through doping engineering, expanding the prospects for developing high-performance room-temperature spintronic devices.

Magnetic skyrmions are topologically distinct spin textures that hold significant potential for applications in information storage and processing. In this study, we investigate the transformation of various dipolar-stabilized spin textures present in amorphous ferrimagnetic Gd/Fe multilayers under the influence of in-plane magnetic field components. Using Lorentz transmission electron microscopy, we observe the nucleation of three different types of magnetic spin objects in the presence of an out-of-plane magnetic field. By tilting the sample up to 18°, the relative contribution of the in-plane field is varied, enabling controlled transformations between topologically trivial and topologically protected types of spin objects. We find that the in-plane field component plays a critical role in determining the topological nature of the stabilized spin objects. Additionally, local variations in spin texture appearance are observed and linked to intrinsic membrane wrinkling, which induces a tilted anisotropy axis and effective in-plane fields. These findings, supported by micromagnetic simulations, highlight the tunability of spin objects through controlled field application, paving the way for alternative strategies in spintronic device engineering.

In this study, we report a robust cryptographic scheme operating over noisy channels, enabled by a nonlinear detection architecture that intrinsically mitigates channel-induced phase aberrations. Difference-frequency generation (DFG) in a nonlinear crystal is employed to automatically compensate channel-induced phase aberrations, providing intrinsic noise mitigation. Spatial modes in the orbital angular momentum basis are used as high-dimensional information carriers, providing enhanced capacity and improved security. As a classical proof-of-principle, our results demonstrate that the DFG correction mechanism reliably restores the spatial mode transfer matrix to near-ideal fidelity across a broad range of aberration types and strengths, recovering projected secret key rates and mutual information metrics consistent with a secure high-dimensional channel. These findings establish nonlinear wave mixing as a viable tool for noise-resilient, high-dimensional communication, with a clear pathway toward quantum implementation using single-photon sources and detectors.

Coherent ferrons, the quanta of polarization waves, can potentially be hybridized with many other quasiparticles for achieving novel control modalities in quantum communication, computing, and sensing. Here, we theoretically demonstrate a new hybridized state resulting from the strong coupling between fundamental-mode (wavenumber is zero) coherent ferrons and cavity bulk acoustic phonons. Using a van der Waals ferroelectric ${\text{CuInP}}_2{\mathrm{S}}_6$ membrane as an example, we predict an ultrastrong ferron-phonon coupling at room temperature, where the coupling strength $g_c$ reaches over 10% of the resonant frequency ${\omega }_0$. We also predict an in situ bistable electric-field control of mode-specific ferron-phonon hybridization via ferroelectric switching. We further show that ${\text{CuInP}}_2{\mathrm{S}}_6$ allows for reaching the fundamentally intriguing but challenging deep-strong coupling regime (i.e., $g_c/{\omega }_0>1$) near the ferroelectric-to-paraelectric phase transition. Our findings establish the theoretical basis for exploiting coherent ferron as a new contender for a hybrid quantum system with strong and highly tunable coherent coupling.

The rapid development of machine learning and quantum computing has placed quantum machine learning (QML) at the forefront of research. However, existing QML algorithms based on quantum variational algorithms face challenges in trainability and noise robustness. To address these challenges, we introduce a gradient-free, noise-robust quantum reservoir computing algorithm that harnesses discrete time crystal dynamics as a reservoir. We characterize the memory, nonlinear, and information scrambling capacities of the quantum reservoir, revealing their correlation with dynamical phases and nonequilibrium phase transitions. For ten-class classification, both noisy simulations and experimental results on superconducting quantum processors match ideal simulations, demonstrating that accuracy increases with system size and confirming topological robustness against noise. Our work presents the first experimental demonstration of quantum reservoir computing for image classification based on digital quantum simulation. Besides, it also experimentally demonstrates the relationship between many-body nonequilibrium dynamical phase transitions and QML performance. These findings introduce noise-robust and efficient design principles for quantum reservoir computing and broader quantum machine learning algorithms in the NISQ era.

Processing steps, such as thermal oxidation, creation of p- and n-doped regions via ion implantation, and postoxidation and postimplantation annealing, are essential for successful and reliable fabrication of devices based on $4H$-SiC. These processing steps are known to introduce crystalline defects or even modifications within the SiC base material that can potentially compromise device operation and reliability. In this work, we systematically study the strain introduced in the $4H$-SiC crystal by SiC-specific manufacturing methods. The results show that tensile strain is present after ion implantation, thermal oxidation, and subsequent annealing processes. Interestingly, aluminum implanted samples show compressive strain near the surface in addition to the presence of an additional Raman signature, while nitrogen and phosphorus implanted samples experience tensile strain. Density functional theory calculations were performed to corroborate the experimental data and connect the type of strain to the microscopic impact that different dopants have on the SiC lattice. These results contribute to the understanding of processing-induced modifications within the crystal and show that Raman spectroscopy is a powerful tool to assess modifications to the $4H$-SiC crystal.

Optical and acoustic communications based on orbital angular momentum (OAM) offer an additional degree of freedom for enhancing information capacity, yet practical implementations of broadband space-time-frequency division multiplexing (STFDM) remain challenging due to system complexity and limited tunability, particularly at low frequencies. Here, we demonstrate a compact and efficient method for broadband STFDM using acoustic rotating point sources (ARPS). We show that a single ARPS can generate multiple high-purity OAM modes with tunable topological charges, whose frequencies are intrinsically linked to the rotational Doppler effect. This mechanism enables simultaneous space, time, and frequency multiplexing within a single transmission path, while significantly reducing the number of required transmitters compared with conventional active array-based approaches. Of note, the proposed method operates continuously from low to high frequencies, extending broadband STFDM to low-frequency acoustic regimes that are particularly relevant for underwater communication. Moreover, we experimentally reveal, for the first time, the coherence properties of multiple acoustic OAM modes with identical topological charges and exploit this property to enhance the stability of high-order modes and mitigate mode crosstalk in OAM-based communication. This work provides a compact and versatile approach for OAM-based acoustic communication, paving the way for future high-capacity multiplexing systems.

Accurate characterization of nonlinear photonic integrated circuits is fundamentally limited by the inability of linear transmission measurements to distinguish input and output on/off-coupling efficiencies, which enter only through their product. We show that this degeneracy arises from an inherent input-output symmetry of linear optics and can be broken by exploiting the directional asymmetry of nonlinear processes. We introduce bidirectional nonlinear optical tomography (BNOT), which combines forward and backward pumping of complementary nonlinear interactions to uniquely infer individual on/off-coupling efficiencies from off-chip measurements. By jointly modeling the nonlinear response and detection statistics, BNOT enables unbiased reconstruction of on-chip nonlinear figures of merit with significantly reduced uncertainty, whereas conventional calibration yields systematically biased estimates. Monte Carlo simulations demonstrate reliable convergence of the inferred efficiencies across realistic noise and fluctuation regimes. Our results establish nonlinear directionality as a general symmetry-breaking resource for coupling-resolved characterization in integrated photonics, with immediate implications for scalable quantum light sources, frequency conversion, and precision optical metrology.

Thermoelectric efficiency benefits from suppressing lattice thermal conductivity (${\kappa }_l$), yet the microscopic origin of the glasslike ultralow ${\kappa }_l$ in ${\text{AgSbTe}}_2$ remains debated. Here we combine first-principles simulation of anharmonic lattice dynamics with the unified theory of thermal transport to quantify how Ag-Sb cation disorder controls heat conduction. We find that compared with cation-ordered $\mathrm{L}{1}_1$ and D4 phases, disordered structures exhibit a strongly reduced ${\kappa }_l$ across a wide temperature range [approximately equal to $0.48\text{W}/(\mathrm{m}\mathrm{K})$ at 300 K] and a much weaker temperature dependence ($\propto T^{-0.40}$). Our detailed analysis of the phonon spectrum and mode-resolved transport properties reveals that cation disorder disrupts the Te-centered octahedral network, softens phonons, lowers group velocities, and enhances low-frequency scattering, thus dramatically suppressing the diagonal (particlelike) contribution [approximately equal to $0.07\mathrm{W}/(\mathrm{m}\mathrm{K})$] while making the off-diagonal (wavelike) term dominant. Moreover, we performed a statistical analysis of ${\kappa }_l$ of 434 dynamically stable cation-disordered configurations, which reveals a robust positive correlation between ${\kappa }_l$ and the average frequency of acoustic modes. In addition, acoustic softening further correlates with increased Ag and Te participation and reduced participation ratios, indicating disorder-induced localization of heat-carrying modes. These results identify cation-disorder-driven localization and low-frequency scattering as key to the phonon-glass behavior of ${\text{AgSbTe}}_2$, and suggest disorder engineering as a route to tune ${\kappa }_l$ in multication thermoelectrics.

We present a variational quantum algorithm that solves the one-dimensional diffusion problem with a space-dependent diffusion constant $D(x)$. This problem is relevant for the exchange of hydroxide ion across a two-layer membrane in an alkaline electrolyzer, where the concentration of ${\text{OH}}^{-}$ ion determines the chemical stability for longer time periods. We use 16 to 64 grid points across the membrane, resulting from $n=4$ to 6 data qubits for the ideal statevector and shot-based quantum simulations implemented using Qiskit. For these qubit numbers, the depth of the parametric quantum circuit has been chosen to ensure sufficient expressibility. The state preparation requires particular attention since the diffusivity $D$ is piecewise constant in the different layers with discontinuities at the interface. Furthermore, we compare different classical optimization schemes with respect to their convergence in the variational quantum algorithms (VQA) method. We demonstrate the applicability of the quantum algorithm to a problem with nontrivial boundary conditions and jump conditions of the diffusion constant and outline possible extensions of the proof-of-concept application case of quantum computing. Our simulations show that pronounced hydroxide-ion concentration gradients, and thus chemical instabilities, can occur only when the ratio of diffusivity in both layers of the membrane exceeds approximately 50.

We present an approach to the molecular beam epitaxy of high-$Q$ planar GaAs-based microcavities in which the AlGaAs high-index layers of the distributed Bragg reflectors are replaced by short-period GaAs/AlAs superlattices (digital alloys) engineered to provide the same effective Al content. This design enables a significant reduction of interface roughness, precise control of both the $\lambda /4$ optical thickness and the effective Al content, suppression of the propagation of certain structural defects, and efficient tuning of the intrinsic absorption at the polariton emission wavelength through optimization of the superlattice parameters. Using this approach, we have grown a microcavity with a low polariton lasing threshold of $P_{\mathrm{th}}\approx 570\pm 90\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$ and a high experimental quality factor of $Q_{\mathrm{expt}}\approx (5.4\pm 0.1)\times {10}^4$. This value exceeds by a factor of 2 the theoretical estimate obtained within a model in which the digital alloy is replaced by a ternary AlGaAs alloy with the same effective Al content. We demonstrate that accurate modeling of the stop-band characteristics and the $Q$ factor requires incorporation of the modified electronic density of states in the superlattice, including quantum-confinement and excitonic effects.

We present a gradient-based method to construct memory-efficient, high-fidelity, single-qubit gates for fluxonium qubits. These gates are constructed using a sequence of single-flux quantum (SFQ) pulses that are sent to the qubit through either capacitive or inductive coupling. The schedule of SFQ pulses is constructed with an on-ramp and an off-ramp applied prior to and after a pulse train, where the pulses are spaced at intervals equal to the qubit period. We reduce the optimization problem to the scheduling of a fixed number of SFQ pulses in the on-ramp and solve it by relaxing the discretization constraint of the SFQ clock as an intermediate step, allowing the use of the Broyden-Fletcher-Goldfarb-Shanno optimizer. Using this approach, gate fidelities of 99.99% can be achieved for inductive coupling and 99.9% for capacitive coupling, with leakage being the main source of coherent errors for both approaches.

The microscopic coexistence of ferroelectricity and ferromagnetism in solids remains a fundamental challenge in condensed matter physics, with far-reaching implications for multifunctional materials and next-generation electronic devices. Using first-principles calculations, we predict emergent sliding ferroelectricity and doping-mediated ferromagnetism in bilayer (BL) InSe. The energetically favored AB-stacked BL-InSe spontaneously breaks the out-of-plane mirror symmetry, resulting in a switchable polarization with a saturated component of 0.089 pC/m and a low transition barrier of 28.8 meV per unit cell. Strikingly, low-concentration electrostatic doping enhances rather than suppresses the ferroelectric polarization due to the abnormal layer-dependent electronic occupation in BL-InSe, in contrast to the conventional screening paradigm. In addition, the characteristic Mexican-hat-shaped valence band enables doping-induced itinerant half-metallic ferromagnetism, where the interlayer spin density difference scales linearly with doping concentration and can be reversed by switching the polarization direction, revealing a direct coupling between polarization and spin degrees of freedom. These results demonstrate the coexistence of ferroelectric and ferromagnetic orders in BL-InSe and establish a viable platform for realizing voltage-tunable multiferroicity through stacking and carrier doping in otherwise nonpolar and nonmagnetic semiconductors.

Decoders, which function as the “precision translators” in digital systems, have traditionally required external memory to integrate storage and computation, leading to high circuit complexity and component counts. This work presents a novel nonvolatile decoding mechanism that exploits the ferroelectric polarization reversal and electron transport anisotropy of two-dimensional materials. Based on a $\text{GaTe}/{\text{In}}_2{\text{Se}}_3$ two-dimensional van der Waals heterostructure, we designed a four-terminal, dual-channel ferroelectric tunnel junction. First-principles calculations demonstrate that the device can be stabilized into four distinct resistance states through the synergistic control of polarization direction and charge transport path, thereby fully enabling the binary decoding of “00”, “01”, “10”, and “11”. This design integrates combinational logic and memory within a single ferroelectric device, which not only minimizes data movement but also enhances storage density, offering a promising pathway for designing low-power, high-density integrated circuits in the post-Moore era.

We investigate the effects of alloying and growth orientation on the electronic properties of the ultrawide bandgap semiconductor $\beta {\text{-Ga}}_2{\mathrm{O}}_3$ and pseudomorphic $({\text{Al}}_x{\text{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$ alloy heterojunctions. Band offsets are computed from first principles using density functional theory with the Heyd-Scuseria-Ernzerhof hybrid functional for different aluminum concentrations and four growth orientations, namely, (100)B, (010), (001)B, and ($\overline{2}01$). Significant variations are found and ascribed to the strained pseudomorphic alloys. The values of the band offsets are fed into technology computer-aided design (TCAD) models of Schottky barrier diodes (SBD). $I$-$V$ and $C$-$V$ characteristics from the TCAD models show reasonable agreement with recent experimental measurements in the forward bias region. Discrepancies in the negative bias region are expected due to the ideality of the Schottky junctions considered in this study. Our findings underscore the critical role of growth orientation and strain in the accurate modeling of $\beta {\text{-Ga}}_2{\mathrm{O}}_3$-based SBD.

Phononic nanodevices offer a promising route toward quantum technologies, as phonons combine strong confinement within matter with broad coupling capabilities to various quantum systems. In particular, the piezoelectric response of materials, such as lithium niobate, enables coupling between superconducting qubits and gigahertz-frequency phonons. However, bulk lithium niobate phononic devices typically rely on surface acoustic waves and are therefore inherently subject to leakage from the surface into the bulk substrate. Here, we explore the acoustic behavior of resonator cavities supporting GHz-frequency Lamb waves in a 200-nm-thick suspended lithium niobate layer. We characterize the acoustic response at both room and millikelvin temperatures. We find that our resonator cavities with strong confinement reach intrinsic quality factors of approximately 6000 at the single phonon level. We use the measured parameters of the resonators to model their coupling to a superconducting transmon qubit, allowing us to evaluate their potential as quantum acoustic devices.

Privacy is a fundamental requirement in distributed quantum sensor networks, where multiple clients estimate spatially distributed parameters using shared quantum resources while interacting with potentially untrusted servers. Despite its importance, existing privacy conditions rely on idealized quantum bounds and do not fully capture the operational constraints imposed by realistic measurements. Here, we introduce a universal operational privacy framework for distributed quantum sensing, formulated in terms of the experimentally accessible Fisher information matrix and applicable to arbitrary protocols characterized by singular information structures. The proposed condition provides a protocol-independent criterion, ensuring that no information about individual parameters is accessible to untrusted parties. We further experimentally demonstrate that a distributed quantum sensing protocol employing fewer photons than the number of estimated parameters simultaneously satisfies the universal privacy condition and achieves Heisenberg-limited precision. Our results establish universal operational constraints governing privacy in distributed quantum sensor networks and provide a foundation for practical, privacy-preserving quantum sensing beyond full-rank regimes.