Transmitter-side device dependence is a longstanding yet implicit problem in quantum key distribution (QKD), in contrast to the thoroughly addressed measurement-side case. Quantum steering, which intrinsically distinguishes the roles of sender and receiver in entanglement certification, offers a natural route to lifting trust assumptions on the transmitter. Existing one-sided device-independent (1sDI) protocols that exploit quantum steering as the security resource typically operate in a tripartite architecture, whereas adapting them to a transmitter-receiver architecture can introduce a signaling loophole. Here we conceptually formalize the transmitter-device-independence on the basis of faithful quantum steering and propose a practical transmitter-device-independent (TDI) QKD protocol within the 1sDI trust model. The TDI scheme operationalizes the implicit no-signaling condition by enforcing a causal isolation between the input information and the transmitted quantum states, thereby eliminating the associated transmitter-side device vulnerabilities. In a proof-of-principle experiment, we validate the feasibility of the TDI protocol, achieving a key rate in the asymptotic limit of 410 bps over 27 km spool fiber. By delivering TDI security while retaining strong loss tolerance, our approach helps bridge the gap between security and practicality for real-world QKD deployments.

We develop a differential source-pattern protocol for local displacement estimation in a time-reversed Young interferometer, where the source plane is used not merely as a scan coordinate but as a programmable measurement pattern. A signed antisymmetric pattern is implemented by two sequential positive-only source branches, as required by intensity-only source hardware, and the two branch counts are retained as the complete measurement record. Near a quadrature operating point, the local differential signal separates into an envelope-gradient term and a time-reversed-Young interference-gradient term. We connect the localized response kernel to a concrete scanned-excitation measurement of a displaced fluorescent, quantum-dot, or transmissive microfeature and give a representative experimental parameter set. We distinguish the exact finite-spacing response from its derivative approximation, enforce an equal launched-photon budget in all comparisons, and derive the Fisher information both for the full Poisson count pair and for the scalar difference, which follows a Skellam distribution. The numerical results show a clear advantage over a fixed raster sample in the representative regime, while the additional interferometric contribution can enhance, leave unchanged, or suppress the information relative to a matched noninterferometric differential measurement. An optimized direct measurement remains the stronger ideal benchmark when all nuisance quantities are known. The results therefore establish practical design rules for robust local displacement metrology rather than a universal claim of two-feature superresolution.

In contrast to hafnia (${\text{HfO}}_2$) thin films, where the appearance of switchable ferroelectric polarization can be induced by strain or defect engineering, reliable methods for controlling ferroelectricity in ${\text{HfO}}_2$ nanoparticles are absent. Direct experimental observations of ferroelectric hysteresis and ferroelectric domains in these nanoparticles have also not been reported. To the best of our knowledge, stress-induced ferroelectric states in the ${\text{HfO}}_2$ nanoparticles have not been explored. In this work, we study the influence of chemical stress on phase diagrams, dielectric properties, and polar properties of spherical ${\text{HfO}}_2$ core-shell nanoparticles using a Landau-Ginzburg-Devonshire free energy functional that includes trilinear and biquadratic couplings involving polar, antipolar, and nonpolar order parameters. The ferroelectric phase exhibits reentrant behavior as a function of nanoparticle size, such that the spontaneous polarization exists only within a limited range of core radii $R_c$, namely $R_{\mathrm{cr}}^{\min }<R_c<R_{\mathrm{cr}}^{\max }$. The minimal critical radius $R_{\mathrm{cr}}^{\min }$ is primarily determined by the size dependence of the depolarization field and correlation effects, whereas the maximal critical radius $R_{\mathrm{cr}}^{\max }$ is governed mainly by the size dependence of chemical stresses induced by the elastic defects in the shell. Thus, this work identifies a stress-driven mechanism for reentrant ferroelectricity stabilization in nanoscale hafnia systems, arising from the competition between depolarization field-induced suppression of ferroelectricity and its stabilization by shell-induced chemical stress. We revealed that relatively large compressive chemical strains are necessary to induce the ferroelectric phase in the ${\text{HfO}}_2$ nanoparticles. Successful chemical strain engineering opens the way for significant enhancement of nanoscale ${\text{HfO}}_2$ polar properties for applications in advanced memory cells and logic devices.

The development of a highly efficient electrocatalyst for the hydrogen-evolution reaction (HER) plays a vital role in the process of water splitting. Two-dimensional (2D) materials are crucial for the HER due to having a large surface-to-volume ratio, tunable electronic properties, and abundant active sites, which collectively enhance their catalytic efficiency and lower the energy barriers for hydrogen production. Boron oxide (BO) is a recently synthesized light-elements-based 2D material that has not been extensively studied yet. The present work delves into the catalytic performance of pristine and single transition metal-decorated BO monolayer (TM@BO, TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Mo, Ru, Rh, Pd, Ag, Ir, Pt, or Au) for the HER using first-principles density functional theory calculations. The pristine BO monolayer exhibits an indirect band gap with a larger value of Gibbs’ free energy change $\mathrm{\Delta }G=2.33\mathrm{eV}$ as compared with the expected value for an efficient catalyst ($\mathrm{\Delta }G\sim 0\mathrm{eV}$). In contrast, Ti@BO and Fe@BO monolayers exhibit excellent HER performance with extremely low overpotential values around $-0.04\mathrm{eV}$ and 0.004 eV, respectively. The thermal stability of the Ti@BO and Fe@BO systems is confirmed through the AIMD simulations with minimal changes in the bond length and energy. The charge density difference and Bader charge analysis indicate a strong interaction of Ti and Fe on BO due to charge transfer from the metal d orbital to the 2p orbital of oxygen. The room-temperature electron mobility of the Ti@BO exhibits significant enhancement around ($52.96\times {10}^4{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$). The study of the reaction mechanism through the climbing image nudged elastic band method using the Volmer, Heyrovsky, and Tafel scheme under acidic and alkaline media shows that the Volmer–Heyrovsky reaction is the dominant mechanism for both the Fe@BO and Ti@BO monolayers, with the Volmer mechanism as the rate-determining step. However, under an alkaline medium, the HER process is less favorable due to the presence of large energy barriers. Our calculations predict a promising single-atom catalyst-based BO monolayer, which can be useful for its device application in energy conversion and storage.

We investigate the differential voltage generation originating from the direct magnetoelectric effect in nanoscale composite devices during magnetization rotation from the magnetic ground state to an out-of-plane configuration. The devices consist of a magnetostrictive ferromagnetic layer mechanically coupled to a piezoelectric layer. Using finite-element modeling in comsol Multiphysics, we systematically analyze strain transfer mechanisms and the resulting open-circuit voltage generation as a function of material and geometric parameters. At nanoscale dimensions, two distinct strain transfer regimes emerge, with the dominant mechanism governed by both device aspect ratio and magnetic state. Surface clamping effects are found to diminish with decreasing pillar diameter and increasing aspect ratio, while strain transfer to the piezoelectric layer is enhanced by stiffer electrodes or additional clamping layers. Furthermore, magnetostrictive materials with large magnetoelastic coupling and high Poisson ratio substantially increase the voltage output at small dimensions. These results provide design guidelines for material selection and dimensional scaling of magnetoelectric pillars. Output voltages exceeding 200 mV are predicted for scaled devices, highlighting their potential for integration in microelectronic applications.

Achieving broadband sound manipulation within deep-subwavelength, ventilated structures remains a fundamental challenge in acoustics. Here, we introduce a degenerate sandwich architecture that exploits the synergistic coupling of monopoles and dipoles. This platform enables simultaneous broadband control over sound reflection, transmission, and absorption. We experimentally validate this concept using a sandwich-structured device comprising two Fabry-Pérot resonator arrays and a central microperforated plate. Remarkably, featuring a deeply subwavelength cumulative interaction length of merely $\lambda /107$ at 200 Hz, the device achieves near-perfect sound absorption (99%) across an ultrawide spectrum of 200–2000 Hz. Furthermore, the device provides robust sound insulation that significantly outperforms conventional mass-law predictions while maintaining permissible airflow. The industrial viability of this strategy is practically demonstrated through a prototype silencer for a household vacuum cleaner. This work overcomes inherent bandwidth limitations in subwavelength wave manipulation and paves the way for advanced noise-control technologies in open systems.

The adaptive oscillator itself is capable of a type innate neuromorphic processing, as it can dynamically learn and store information about an external signal. When used as a physical reservoir computer, it has been demonstrated that the adaptive oscillator possesses both self-learning and the ability to be used as a multiplex-free morphable logic gate. In addition to these useful traits, the Duffing adaptive oscillator is also a physical unclonable function. Here, a bifurcation diagram is proposed as a novel challenge-response pair. Notably, since the bifurcation diagram is asymptotically approached by the oscillator’s dynamics, it is easily reproducible. Further, small changes to the oscillator’s parameters produce large changes to the bifurcation diagram, which makes it act as a “fingerprint” of the oscillator. From an applied perspective, this means that the Duffing adaptive oscillator could be implemented as a trusted artificial intelligence hardware device.

Exploring the synergy between topological physics and nonlinear dynamics unveils profound insights into emergent states of matter. Inspired by recent experimental demonstrations of topological frequency combs in photonics, we theoretically introduce topological magnon frequency combs (MFCs) in a two-dimensional triangular skyrmion lattice. Computing the Chern numbers of magnon bands reveals robust chiral edge states. The nonlinear four-magnon scattering among the chiral edge modes generates the topological MFCs, activated by dual-frequency microwave driving without an amplitude threshold. The comb spacing is readily tunable through excitation frequency detuning. We finally show that the proposed topological MFCs are robust against disorder, bulk leakage, and thermal fluctuations, although strong nonlinearity exists. This work paves the way for defect-immune magnonic devices exploiting MFCs and sparks investigations into topological-nonlinear phenomena in magnetic systems.

Hole spin qubits based on semiconductor quantum dots are promising for building future large-scale quantum computers owing to their all-electrical manipulation. However, abundant physical mechanisms of valence-band holes lead to anisotropic qubit properties. There is an opportunity to prolong the coherence time and achieve high-fidelity qubit manipulations. Here, we report a single-hole spin qubit in a planar germanium quantum dot and investigate its anisotropic susceptibility to charge noise under an in-plane magnetic field. By correlating the longitudinal spin-electric susceptibility with qubit coherence and control performance, we identify an optimal operating point where the sensitivity to charge noise is minimized. We find that optimizing the magnetic-field orientation reduces the spin-electric susceptibility, resulting in a fivefold enhancement of the Hahn-echo coherence time and a nearly tenfold suppression of control infidelity. At the optimal operating point, gate set tomography demonstrates the maximum gate fidelity of 99.82%. Our finding enhances the prospects of hole spin qubits for scalable quantum information processing.

Arguably, the lamp-pumped vapor-cell atomic clock is the workhorse of precise timekeeping in space. However, the present-day Rb atomic frequency standard (RAFS) has two clear deficiencies: (1) its short-term stability is limited by weak optical pumping, and (2) its long-term stability can be limited by light-shift-induced frequency noise. In both cases, the limitations trace to the use of an rf-discharge lamp for atomic signal generation and monitoring. Though replacement of the lamp by a pulsed diode laser can eliminate these problems, laser use in the RAFS presents space-systems engineers with a dilemma: trading better clock performance against potentially decreased clock reliability. Here, we discuss progress on development of the lamp and laser integrated pulsed optically pumped atomic clock, which is a “bridge technology” that can solve the space-system engineer’s dilemma.

Numerical gate design typically makes use of high-dimensional parametrizations enabling sophisticated, highly expressive control pulses. Developing efficient experimental calibration methods for such gates is a long-standing challenge in quantum control, as on-device calibration requires the optimization of noisy experimental data over high-dimensional parameter spaces. To improve the efficiency of calibrations, we present a systematic method based on singular value decomposition stacking for reducing the dimensionality of the parameter space traversed in gate calibration, starting from an arbitrary high-dimensional pulse representation. We use this approach to design and calibrate an $X_{\pi /2}$ gate robust against amplitude and detuning errors, as well as an $X_{\pi /2}$ gate robust against coherent errors due to a spectator qubit.

We demonstrate single-electron trapping and detection in a dual-plane printed-circuit-board Penning trap. We have performed deterministic single-electron loading, achieved a axial damping rate of ${\gamma }_z/(2\pi )=18(1)\mathrm{Hz}$, measured the axial temperature, and measured the magnetron-radius growth rate at magnetic fields below 0.15 T. These results establish a practical platform for dual-plane Penning traps.

We report an rf parametric amplifier that exploits the gate-tunable quantum capacitance of a semiconductor two-dimensional electron gas at cryogenic temperatures. The prototype amplifier exhibits a gain approximately 30 dB up to an input power of $-66\mathrm{dBm}$ and a noise temperature $T_N\sim 2\mathrm{K}$ at approximately 370 MHz while dissipating approximately a microwatt of power. Operable at tesla-scale magnetic fields and temperatures ranging from millikelvin to a few kelvin, the quantum capacitance parametric amplifier may find utility in the readout circuit of spin qubits. Here, a quantum dot system is used to verify amplifier performance, improving the signal-to-noise ratio of the readout by approximately 9 dB.

Most quantum error-correction (QEC) protocols for superconducting qubits assume spatially and temporally uncorrelated decoherence events; however, recent evidence suggests that cosmic radiation induces spatially correlated errors. We present a platform that sandwiches a superconducting transmon qubit between two microwave kinetic inductance detector (MKID) arrays, enabling real-time detection of radiation-induced phonon bursts. By synchronizing MKID event detection with single-shot measurements of qubit energy relaxation ($T_1$) and phase coherence ($T_2$), we observe statistically significant reductions in both $T_1$ and $T_2$—up to 30.5%—immediately following dual MKID events attributed to penetrating muons. Our findings directly link radiating events to correlated qubit decoherence. Furthermore, our experimental platform provides a foundation for systematic studies of radiation effects, the development of shielding and mitigation techniques, and the refinement of error-correction algorithms tailored to correlated noise sources.

Purpose: Parameter estimation from biexponential models is a notoriously ill-posed problem, often yielding inaccurate estimates that are strongly influenced by noise. We present a simple, nonconventional approach to regularizing nonlinear least-squares (NLLS) parameter estimation and apply it to myelin water fraction (MWF) mapping with magnetic resonance imaging. Motivated by the ridge regression theorem for linear least-squares problems, we introduce a nonlinear extension, which we denote $\lambda$-NL-RR, in which regularization is applied directly to the NLLS estimation of discrete parameters. Methods: We applied $\lambda$-NL-RR to simulated and experimental biexponential magnetic resonance imaging (MRI) data and compared parameter estimates with those obtained using conventional NLLS fitting. The regularization parameter $\lambda$ was selected using generalized cross validation. Results: Under conditions of modest signal-to-noise ratio and closely spaced exponential time constants, regimes in which conventional biexponential analysis performs particularly poorly, $\lambda$-NL-RR was found to reduce mean-square error by up to 80% relative to standard NLLS for simulated data, consistent with the known behavior of regularization in more conventional contexts. Improvements in root-mean-square error in the range of 11%–25% in parameter estimates were seen for in vivo brain data, although there is no true gold standard for underlying values in these experiments. Notably, these results are due to postprocessing only and require no modification of data acquisition strategy or duration. Conclusion: Regularization of the NLLS estimation problem for the biexponential model substantially improves parameter accuracy in MWF mapping. Although related ideas exist in scattered form in the applied mathematics literature, this work recognizes, formalizes, and demonstrates ridge-type regularization for discrete NLLS parameter estimation in MRI. These results establish a foundation for broader application of nonlinear regularization strategies in quantitative MRI and other fields.

We study quantum enhancement of sensitivity using squeezed light in a multiparameter quantum sensor, the hybrid dc and rf optically pumped magnetometer (hOPM) [M. Lipka et al., Multiparameter quantum sensing and magnetic communication with a hybrid dc and rf optically pumped magnetometer, Phys. Rev. Appl. 21, 034054 (2024)]. Using a single spin ensemble, the hOPM acquires both the dc field strength (scalar magnetometry) and resonantly detects one quadrature of the ac magnetic field at a chosen frequency (rf magnetometry). In contrast to the Bell-Bloom scalar magnetometer [C. Troullinou et al., Squeezed-light enhancement and backaction evasion in a high sensitivity optically pumped magnetometer, Phys. Rev. Lett. 127, 193601 (2021)], the backaction evasion in the hOPM is incomplete, leading to a nontrivial interplay of the three quantum noise sources in this system: photon shot noise, spin projection noise, and measurement backaction noise. We observe these interactions using squeezed light as a tool to control the distribution of optical quantum noise between $S_2$ and $S_3$ polarization Stokes components, and the resulting effect on readout quantum noise and measurement backaction. These results demonstrate quantum-enhanced sensitivity in a continuously operating multiparameter sensor and reveal fundamental trade-offs between sensitivity, backaction, and bandwidth.

Parametric resonance provides a versatile mechanism to manipulate wave signals in time-modulated metamaterials, but typically operates within narrow wavelength or frequency ranges. Here, we show that one-dimensional arrays of coupled resonators can generically exhibit parametric amplification across an entire band under standing-wave parametric modulation. We develop a general physical framework to describe the parametric resonance of isolated bands, derive modulation conditions needed to achieve full-band amplification for a given band, and demonstrate their validity in a model of active mechanical metamaterials based on tunable membrane resonator arrays. We numerically demonstrate applications of the proposed strategy in distortion-free amplification and temporal splitting of wave packets, with results in quantitative agreement with our theoretical calculations. Our strategies for broadband amplification can be generalized to other active wave media with nearly flat or cosinelike dispersion relations, with potential applications in loss mitigation, noise squeezing, and programmable wave manipulation.