We propose and demonstrate a quantitative noncontact measurement method for the thermal Hall effect (THE) based on magnetic-field-modulated lock-in thermography (LIT). This method enables visualization of THE-induced temperature change and quantitative estimation of the thermal Hall angle θ${}_{\mathrm{THE}}$ by applying periodic magnetic fields to a sample and obtaining the first-harmonic response of thermal images. By combining this method with LIT-based measurement techniques for the longitudinal thermal conductivity κ${}_{xx}$, we also quantify the transverse thermal conductivity κ${}_{xy}$. We validate our measurement methods by estimating θ${}_{\mathrm{THE}}$, κ${}_{xx}$, and κ${}_{xy}$ in a ferromagnetic Heusler alloy ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Ga}$ slab showing large THE.

Superconducting qubits are a key contender for quantum computing elements, but they often face challenges like noise and decoherence from two-level systems (TLSs). Tantalum ($\mathrm{Ta}$) qubits are notable for their long $T_1$ coherence times, nearing milliseconds, presumably due to fewer TLSs, though the cause of this is unclear. We explore this by analyzing the vacuum-oxide interface using density functional theory, particularly comparing $\mathrm{Nb}$ oxide (${\mathrm{Nb}}_2{\mathrm{O}}_5$) and $\mathrm{Ta}$ oxide (${\mathrm{Ta}}_2{\mathrm{O}}_5$). We discover that ${\mathrm{Ta}}_2{\mathrm{O}}_5$ forms a smoother surface with fewer dangling $\mathrm{O}$ atoms and structural TLSs than ${\mathrm{Nb}}_2{\mathrm{O}}_5$. The greater atomic mass of $\mathrm{Ta}$ also lowers the tunnel splittings of these structural TLSs below the qubit’s operating frequency. Furthermore, using external electric fields or ${\mathrm{SO}}_2$ passivation can significantly reduce defect-related TLSs on $\mathrm{Nb}$ surfaces, potentially improving their coherence times.

Nanopillars are widely used for various applications and require accurate shape characterization to enhance their performance and optimize fabrication processes. In this paper, we employ coherent Fourier scatterometry (CFS) combined with rigorous three-dimensional finite-difference time-domain simulations to accurately determine the shapes of nanopillars with various geometries, including cylindrical, triangular, square, and rectangular shapes. The nanopillars considered here have lateral dimensions ($a$) ranging from 100 to 1000 nm. Our methodology utilizes the preferential excitation of the nanostructures by a tightly focused beam and leverages their inherent symmetry to capture far-field signatures that vary periodically with rotation. This approach allows us to distinguish between different nanopillar shapes based on these rotational signatures. Our results demonstrate that the CFS method can reliably characterize nanopillars with lateral dimensions $a\ge 300$ nm, surpassing the conventional diffraction limit of 351 nm. However, the method reaches its fundamental limits for $a\le 200$ nm, as also confirmed by simulations, where we approach the dipole approximation regime ($a\ll \lambda$). This constraint is not observed for rectangular nanopillars, owing to their constant breadth ($b=1000$ nm), which prevents such a regime. Furthermore, our method successfully differentiates nanopillars transitioning from rectangular to square shapes. We also explored the method’s limitations concerning nanostructure height ($h$), finding that triangular and square nanopillars could be characterized accurately for $h\ge 50$ nm and $h\ge 150$ nm, respectively. Furthermore, the method remains robust against shape distortions such as edge roundness. The method is primarily effective in determining the lateral (top-down) shape of nanopillars, it does not resolve longitudinal features. The ability to accurately characterize nanostructure shapes has significant implications in fields such as photonics and biosensing, where geometry critically influences device performance.

Shortcuts to adiabaticity (STA) enables fast and robust coherent control of quantum system, which has been well placed in quantum technologies. In particular, inverse-engineering STA provides much more freedom for the optimization of shortcut, which alleviates the complexity for experimental realization. Here, we implement a STA technique, known as invariant-based inverse engineering, to speed up the adiabatic control of the electron triplet ground state of a single nitrogen-vacancy (N-$V$) center. The microwave pulses to drive inversely engineered STA are obtained with space-curve quantum control, where the evolution of spin transition is mapped to a three-dimensional closed space curve and the design of shortcut is obtained by optimization over the space curve. We demonstrate the fast and high-fidelity drive of dipole-forbidden transition between two spin sublevels of the ground state. Moreover, we demonstrate the robustness of the spin transition by introducing the detuning of driving microwave field. The acceleration and robustness is further confirmed by the comparison with two traditional Raman control schemes. Our results suggest invariant-based inverse engineering is powerful for fast and robust manipulation of N-$V$ system, and thus benefits quantum sensing and quantum computation based on the N-$V$ platform.

Integrated photonics plays a pivotal role in quantum communication devices, offering exceptional robustness, scalability, and performance. The growing maturity of silicon photonics technology offers significant potential for miniaturization and cost-effective implementation of quantum key distribution (QKD). While the practical security of lithium niobate modulators in QKD systems has been extensively examined, the adoption of a new modulation mechanism by silicon photonic modulators necessitates a thorough investigation into their impact on the security of QKD systems. For the first time, we reveal that the two-photon absorption effect in silicon photonic intensity modulators will introduce vulnerabilities, enabling an eavesdropper (Eve) to execute malicious attacks on QKD systems. Through experimental demonstration, we show that by externally injecting femtosecond pulses, Eve can manipulate the intensities of decoy states sent by legitimate users. Based on the experimental results, we find that in the presence of the attack, legitimate users consistently overestimate the secret key rate predicted by the security proof. Our work represents an initial exploration into a new security aspect for the design and standardization of integrated QKD systems.

We present a pair of seismometers capable of measurement in all six axes of rigid motion. The vacuum-compatible devices implement compact interferometric displacement sensors to surpass the sensitivity of typical electrical-readout schemes. Together with the capability to subtract the sensitivity-limiting coupling of ground tilt into horizontal motion, our seismometers can widen the sensing band toward megahertz frequencies. This has notable applications across a range of fields requiring access to low-frequency signals, such as seismology and climate research. We particularly highlight their potential application in gravitational-wave observatories (the Laser Interferometer Gravitational-Wave Observatory, LIGO) in improving their observation capability of intermediate-mass black holes (approximately $1000M_{\odot }$). The sensors are based on a near-monolithic fused-silica design consisting of a fused-silica mass and fiber, showing improved stability and robustness to tilt drifts, alignment, and control compared to all-metal or mixed metal-silica designs. We demonstrate tilt sensitivity that surpasses the best commercial alternatives in a significantly reduced footprint compared to our previous iterations of these sensors.

The rotating-wave approximation (RWA) is ubiquitous in the analysis of driven and coupled resonators. However, the limitations of the RWA seem to be poorly understood and in some cases the RWA disposes of essential physics. We investigate the RWA in the context of electrical circuits. Using a classical Hamiltonian approach, we find that by balancing electrical and magnetic components of the resonator drive or resonator-resonator coupling, the RWA can be made exact. This type of balance, in which the RWA is exact, has applications in superconducting qubits, where it suppresses nutation normally associated with strong Rabi driving. In the context of dispersive readout, balancing the qubit-resonator coupling changes the qubit leakage induced by the resonator drive but does not remove it in the case of the transmon qubit.

Herein, we propose and numerically validate two-dimensional cavity-excited impedance surfaces for full-space beam steering, facilitated by an efficient design framework that combines the idea of baffles and an integral-equation-based formulation. The proposed system directly transforms cavity modes excited by integrated sources, thus achieving a low profile. In contrast to traditional metasurface designs, which often overlook mutual coupling between unit cells, the proposed architecture and its design framework ensure proper consideration of mutual coupling. Specifically, baffles are strategically placed within the 2D cavity to suppress mutual coupling in one direction, while the integral-equation-based formulation manages coupling in the orthogonal direction. Based on the method of moments, the induced surface and volumetric current densities throughout the structure are optimized to produce the desired far-field patterns. In particular, various beam-steering scenarios are considered for ${\theta }_o\in \{0^{\circ },{25}^{\circ },{50}^{\circ }\}$ and ${\varphi }_o\in \{0^{\circ },{45}^{\circ },{90}^{\circ }\}$. Full-wave simulation results show that the system achieves directivities comparable to perfect apertures. Dual-beam steering, which requires independent control over both the amplitude and phase of the aperture fields, is also explored. The proposed architecture and its design framework lend themselves to a wide range of applications in which precise, full-space beam steering and compact design are critical, spanning next-generation communication systems, satellite platforms, radar technologies, and beyond.

Arbitrary energy transfer is only feasible in nondissipative charger-battery systems; in realistic processes, however, energy dissipation prevents this. In this work, we introduce a novel charging technique in which the coherent charger-battery interaction is replaced by a dissipative interaction via an engineered reservoir. We demonstrate that exploiting the collective effects of the engineered reservoir allows for additional optimization, giving rise to an optimal redistribution of energy. This not only significantly enhances the efficiency of the charging process but also remarkably enables the quantum battery to accumulate unlimited energy—limited only by the natural energy scale of the device. This phenomenon cannot occur in conventional charger-battery schemes. The article unveils the intricacies of built-in detuning within the context of a shared environment, offering a deeper understanding of the charging mechanisms involved. These findings apply naturally to quantum circuit battery architectures, suggesting the feasibility of efficient energy storage in these systems. The superoptimal charging mechanism offers a practical avenue for boosting the capacity of the battery through charger-battery configurations.

We develop a comprehensive semiclassical continuum theory of electronic response and structured solvents at electrified metal-solution interfaces. The approach combines an orbital-free density-functional theory of electrons on the metal side with a statistical field theory of a structured electrolyte solution within a grand canonical framework. The resulting grand potential of the entire electrical double layer (EDL) is a hybrid functional of particle density, including metal electrons and classical solution particles, electric potential, and solvent polarization, referred to as density-potential-polarization functional theory (DPPFT). The DPPFT captures major atomistic phenomena within the EDL, including electron spillover, spatially damped oscillations in solvent polarization and electric potential extending toward the bulk solution, and the layered structure of ions. Based on DPPFT, an EDL model for the $\mathrm{Ag}(110)$-${\mathrm{KPF}}_6$ aqueous solution interface is parameterized using experimental data for the double-layer capacitance (C). The calibrated model is employed to study the influence of electronic, ion, and solvent properties on EDL structure. C profiles at different crystal faces and in various electrolyte solutions are rationalized by the model coherently. We reveal that intensified ion layering enhances the capacitance at the potential of zero charge and narrowed ionic peaks in the C profile. Contrary to classical models, the DPPFT allows coions to have appreciable densities near the metal surface, with their magnitudes depending on the local solvent structure and the correlation strength between ions and solvent. All in all, the presented framework provides a holistic and computationally efficient approach for atomistic-level modeling of EDLs under constant-potential conditions.

Microstrip patch antennas are one of the most widely used antennas in communication systems due to their compact size, conformability, ease of implementation, and low cost. The cavity model, which assumes that a microstrip patch antenna is surrounded by four perfect magnetic conducting (PMC) walls on its periphery and perfect electric conducting (PEC) boundaries on the top (patch) and bottom (ground plane), is a well-established analytical method to evaluate its radiated fields and input impedance. In this paper, we extend the traditional cavity model approach to include the response of a microstrip patch antenna with a time-periodic substrate permittivity ${\epsilon }_r(t)={\epsilon }_r(t+T)$. We show that this time-periodic permittivity modulation provides an unprecedented ability to tailor the harmonic response of the antenna. Importantly, we achieve a remarkable 40% fractional bandwidth through such a customized time-periodic permittivity modulation, which is substantially higher than the typical 1–2% fractional bandwidth of conventional microstrip patch antennas.

Reference-frame-independent measurement-device-independent quantum key distribution (RFI MDI QKD) can resist side-channel attacks against detectors and slow variations of reference frames, thus presenting an advantageous approach for long-distance secure quantum communication. Nevertheless, if an eavesdropper implements a Trojan-horse attack (THA) by injecting bright light into sources, the back-reflected light may carry encoding information into the channel, thereby causing serious information leakage. In this paper, we theoretically evaluate the finite-key security of decoy-state RFI MDI QKD against a THA by employing the reference-state technique and a particular concentration inequality. Additionally, dual-parameter optimization and multibasis-estimation strategies are introduced to reduce statistical fluctuations effectively. Our work demonstrates that RFI MDI QKD can maintain a better performance even in the presence of large reference-frame drifts and a THA, representing a key advancement in strengthening the security of quantum communication in real-world implementations.

We present an approach allowing an optically pumped magnetometer (OPM) to be operated within the Earth’s magnetic field as a vector magnetometer, the sensitive axis of which can be freely defined. This approach enables the measurement of any vector component of the Earth’s magnetic field with the same sensitivity. The OPM is realized by a microfabricated cesium-vapor cell with nitrogen buffer gas, which is immersed in a constant homogeneous bias field of approximately $730\text{μ}\mathrm{T}$. Since this bias field is about one order of magnitude stronger than the Earth’s magnetic field, it defines the sensitive axis of the OPM. The bias field is generated by solid-state magnets and has been designed to exhibit a very low relative inhomogeneity ($<\pm {10}^{-4}$ in relative units) within the vapor-cell dimensions as well as a point of vanishing temperature dependence at around ${40}^{\circ }\mathrm{C}$. The OPM utilizes the light-narrowing effect, which enables effective suppression of spin-exchange relaxation even in such a large magnetic field amplitude. Based on this implementation, we demonstrate a white-noise floor of below $60\mathrm{fT}/\sqrt{\mathrm{Hz}}$ in the frequency interval between $100\mathrm{Hz}$ and 600 Hz and a 3-dB sensor bandwidth of $>5\mathrm{kHz}$. Our approach enables unshielded ultrasensitive vectorial measurement capabilities that are relevant in many important applications.

The technology for manufacturing $\mathrm{Ga}\mathrm{N}$-based devices is already very mature, but band engineering in this technology is still limited to mixing group-III elements, while the incorporation of group-V elements into $\mathrm{Ga}\mathrm{N}$ can create possibilities in band-gap engineering. In this work, we report comprehensive experimental studies of the electronic band structure for $\mathrm{As}$-diluted and overdiluted $\mathrm{Ga}\mathrm{N}\mathrm{As}$ supported by computational methods based on the state-of-the-art density-functional-theory (DFT) approach. These studies clearly demonstrated that the incorporation of arsenic into $\mathrm{Ga}\mathrm{N}$ modifies the valence band, while the conduction band remains undisturbed up to 8% arsenic content. For the first time, $\mathrm{As}$-related changes in the valence band are studied with high resolution in electron photoemission spectroscopy. $\mathrm{As}$-related narrowing of the energy gap is also detected in the absorption spectra. These experimental observations are very consistent with the calculations of the electronic band structure for $\mathrm{Ga}\mathrm{N}\mathrm{As}$, and therefore the same DFT approach was used to calculate the electronic band structure for $\mathrm{Ga}\mathrm{N}$ diluted and overdiluted with the remaining group-V elements, i.e., $\mathrm{Ga}\mathrm{NP}$, $\mathrm{Ga}\mathrm{N}\mathrm{Sb}$, and $\mathrm{Ga}\mathrm{N}\mathrm{Bi}$. In this case, it is also clearly visible that adding $\mathrm{P}$, $\mathrm{Sb}$, or $\mathrm{Bi}$ to $\mathrm{Ga}\mathrm{N}$ modifies the valence band, while the conduction band remains undisturbed when the V-group concentration does not exceed 5%.

A discharge with multiply charged ions of a noble gas supported by a powerful infrared laser in a high-pressure jet is considered as a source of extreme ultraviolet (EUV) light radiation in particular narrow bands demanded by next-generation lithography. In a proof-of-principle experiment in krypton, the EUV-emitting region is visualized using a dedicated EUV microscope. Measurements support a basic model of underlying physics that involves expansion of the emitting plasma outside the laser focus. In simulations, we show that using the xenon jet, more optimal for EUV emission, may provide an efficiency competitive to the best commercial EUV sources for lithography.

Cavity magnomechanics is an important hybrid magnonic platform that focuses on the coherent interaction between magnons and phonons. The resulting magnon polarons inherit the intrinsic properties of both magnons and phonons, combining their individual advantages and enabling new physics and functionalities. However, in previous demonstrations the magnon-phonon coupling either had limited bandwidth or could not be efficiently accessed. In this work, we show that by the use of the slow-wave hybrid magnonics configuration based on spoof surface plasmon polaritons (SSPPs), the coherent magnon-phonon interaction can be efficiently observed over a frequency range greater than 7 GHz on an yttrium iron garnet thin film device. In particular, the capability of the SSPPs in exciting short-wavelength magnons reveals a novel size effect when the magnons are coupled with high-overtone bulk acoustic resonances. Our work paves the way towards novel magnomechanical devices.

The increasing demand for high-speed and power-efficient computation, along with progress in photonics, led to extensive investigation of all-optical computation methods in recent years; this is because they have parallel computation ability and high power efficiency compared with their electrically implemented counterparts. As a step toward fiber-based all-optical computing, we present here a proof-of-concept all-optical inference engine implemented using an optomechanical system based on optimization of the shape of a multimode optical fiber. The positions of four points along the fiber are optimized using a genetic algorithm to concentrate light at specific points at the output of the fiber, enabling an optical classification of the pattern of light input to the fiber. We demonstrate recognition of images of a single digit among images of all digits input to the fiber with an average accuracy of $\sim 80\mathrm{\%}$.

The in-plane motion of an electron on helium can couple to superconducting microwave resonators via electrical dipole coupling, offering a robust and rapid readout scheme. In previous efforts, microwave resonator designs for electrons on helium have lacked the coupling strength to reach the strong coupling regime, where coherent quantum effects outlast both electron and resonator decoherence rates. High-impedance superconducting microwave resonators offer a path to strong coupling, but integrating such resonators with electrons on helium remains an outstanding challenge. Here, we introduce a high-impedance resonator design compatible with strong coupling to electrons on helium. We fabricate and measure titanium nitride resonators with median internal quality factors of $3.9\times {10}^5$ and average impedance of 2.5 $\mathrm{k}\mathrm{\Omega }$, promising a sevenfold increase in coupling strength compared with standard 50-$\mathrm{\Omega }$ resonators. In addition, we develop a simplified resonator model from the capacitance matrix and sheet inductance that accurately predicts the mode frequencies, significantly simplifying the design process of future resonators for investigating quantum effects with electrons on helium.

The polarization degree of freedom is an inherent feature of plane waves propagating in an isotropic homogeneous medium. The miniaturization of optical systems leads to the high localization of electromagnetic waves, but also to the loss of polarization control, namely, breaking TE-TM polarization degeneracy. In this work, we discover the near-field polarization degree of freedom for highly localized guided waves propagating along a dielectric metasurface. We demonstrate the opportunity to create a metasurface with the degenerate TE-TM polarization spectrum for the required operating wavelength and different constitutive materials. In particular, we analyze several possible implementations including silicon nitride and ceramic metasurfaces consisting of disk-shaped resonators, and evaluate the impact of substrates. Finally, we experimentally implement one of the metasurface designs and verify its broadband degenerate TE-TM polarization spectrum. The obtained results form an alternative platform for the planar polarization devices utilizing the polarization degree of freedom of localized light.