In the antenna community, there has always been a fundamental question: how can we control antenna behavior, e.g., resonant frequency, bandwidth, and mutual coupling in an array, solely by changing materials surrounding the radiating current? To answer this, we analyze the role of a magneto-dielectric substrate/superstrate in controlling the stored energy, impedance, and radiation properties, showing that the bandwidth of the antennas can be substantially increased by reducing the substrate permittivity or permeability, respectively, in magnetic- and electric-current-driven antennas. These theoretical findings are validated through numerical simulations. The same conceptual framework is applied to investigate the problem of mutual coupling between closely spaced elements. The results show that loading magnetic-current antennas with a magnetic superstrate effectively suppresses surface waves and thereby reduces interelement coupling, whereas for electric-current antennas, a dielectric superstrate provides the most efficient coupling reduction.

We have developed two modular dilution refrigerators with a cooling power on the order of 1 mW at 100 mK and $20\mathrm{\mu }\mathrm{W}$ at 20 mK, and further carried out joint operation by integrating the two modular units. In the integrated configuration, the base temperatures of the mixing chamber cold plates of both refrigerators remained below 10 mK and within the same temperature range; the combined cooling power essentially doubles that of a single module. In this way, a concurrent increase in both cooling power and available experimental space has been realized through the implementation of the modular integration, and the integrated prototype is already being used to conduct superconducting quantum computing experiments. We experimentally verified that, under integrated operation, the load condition of one module has only a negligible effect on the temperature and cooling power of the other refrigerator, demonstrating a certain degree of independence between the two modular units. Finally, we also point out the challenges that the proposed modular integration scheme may face in its further evolution and suggest possible improvement approaches. This study provides a reference for the future development and application of high-cooling power dilution refrigerators. The scalability demonstrated in cooling power and experimental space is expected to offer solutions for future large-scale quantum computing applications.

Systematic Rabi-amplitude and detuning errors remain important sources of infidelity in high-fidelity quantum gates. We develop a robust pulse-engineering scheme for nonadiabatic holonomic quantum computing in a three-level $\mathrm{\Lambda }$-type qutrit, combining inverse engineering with time-dependent perturbative analysis. Pulse shaping eliminates the leading second-order Rabi-amplitude contribution, while static detuning introduces a distinct population-mediated channel that cannot be removed within a single control loop. We therefore introduce a compensation loop that exactly cancels the dominant second-order $O_{13}^{\delta }$ contribution, with the residual $O_{12}^{\delta }$ channel further suppressed by pulse shaping. Using the logical average gate fidelity over the complete computational subspace, the optimized composite sequence reaches closed-system fidelities of 99.88%–99.99% for four representative single-qubit gates at $ϵ=0.2$ and $\delta /2\pi =2\mathrm{MHz}$. With phenomenological decoherence at $T_1=T_2=30\mathrm{\mu }\mathrm{s}$, the NOT and S gates retain fidelities of 99.72% and 99.79%, respectively, with a coherence-time crossover near $0.58\mathrm{\mu }\mathrm{s}$. These results identify the regime in which systematic-error suppression outweighs the decoherence cost of the additional control loop.

This study addresses the persistent multifidelity gap between numerical simulations and experimental observations in the design of elastic metamaterials, specifically focusing on wave transmission spectra of the triply periodic minimal surface lattices. We propose the Dual Elastic Alignment Network (DEAN), a learning framework that uses elastic functional data analysis (EFDA) to separate transmission responses into spectral amplitude and frequency-warping components. DEAN employs a shared geometric encoder with dual probabilistic heads to separately model resonance morphology and frequency shifts across topologies and between fidelity levels. To mitigate experimental data sparsity, we introduce an augmented transfer learning strategy in which the model is first trained on a large set of low-fidelity (LF) simulations and subsequently fine-tuned using a combined dataset of high-fidelity (HF) experimental data and EFDA-generated augmented data. The study uses 72 experimentally evaluated designs together with 510 simulated designs, resulting in a highly sparse experimental regime relative to the broader simulation design space. The baseline discrepancy between the LF and HF datasets corresponds to a normalized mean absolute error (NMAE) of 0.142 and a coefficient of determination ($R^2$) of 0.355. Under the augmented transfer learning strategy, DEAN achieves the strongest aggregate global accuracy among the evaluated models, with the level-set variant reaching a test-set NMAE of 0.055 and an $R^2$ of 0.858, while the multihot variant remains close with an NMAE of 0.059 and $R^2$ of 0.843. Fisher-Rao distance analysis and joint-density evaluation of peak deviations demonstrate improved preservation of resonance morphology and peak characteristics when using the DEAN framework. These findings indicate that explicitly modeling amplitude and frequency-warping variability enhances predictive reliability under sparse experimental data conditions. The proposed framework provides a structured, experimentally grounded surrogate for data-efficient modeling and candidate screening of elastic metamaterials under uncertain constitutive and manufacturing conditions.

Random pulse sequences are a powerful method for qubit noise spectroscopy, enabling efficient reconstruction of sparse noise spectra. Here, we advance this method in two complementary directions. First, we extend the method using a regularizer based on the total generalized variation norm in order to reconstruct a larger class of noise spectra, namely, piecewise-linear noise spectra, which more realistically model many physical systems. We show through numerical simulations that the new method resolves finer spectral features, while maintaining an order-of-magnitude speedup over conventional approaches to noise spectroscopy. Second, we simplify the experimental implementation of the method by introducing Rademacher measurements for reconstructing sparse noise spectra. These measurements use pseudorandom pulse sequences that can be generated in real time from a short random seed, reducing experimental complexity without compromising reconstruction accuracy. Together, these developments broaden the reach of random pulse sequences for accurate and efficient noise characterization in realistic quantum systems.

We present the fabrication of nanoscale superconducting quantum interference devices (SQUIDs) at the apex of wireframe tips on self-aligned superconducting cantilever probes. The probes are made on silicon wafers using molding techniques in combination with corner lithography, which results in a nanowire frame tip with a tunable apex structure. A shadow-effect deposition using magnetron sputtering of niobium creates self-aligned superconducting wireframes on cantilevers with accompanying device circuitry. Superconducting weak links are realized at the apex of the wireframes with the use of focused ion beam nanopatterning. The realized SQUIDs have effective diameters ranging from several micrometers down to 100 nm and can be operated in magnetic fields up to 1 T. Furthermore, the nanowires in the wireframe can be used to flux modulate the SQUID locally. This fabrication process enables the production of wafer-scale templates for probes based on on-tip superconducting devices.

In the transmitter of a quantum key distribution (QKD) system, a wavelength-division multiplexer (WDM) is typically used to combine quantum and synchronization signals and is directly connected to the quantum channel. As a result, it becomes the first optical component exposed to laser-injection attacks. Therefore, understanding the behavior of WDMs under such attacks is essential for assessing the practical security of QKD systems. In this work, we systematically investigate the characteristics of WDMs under high-power laser illumination. Our experimental results show that certain WDM samples exhibit pronounced changes in their spectral features once the injected laser power surpasses a specific threshold. Taking the Trojan-horse attack as an illustrative example, we further perform a theoretical analysis of the resulting spectral side channel and show that it can reduce the maximum secure transmission distance to below 66.9% of its original value. By combining experimental observations with theoretical modeling, this study advances the understanding of the influence of WDMs on the practical security of QKD systems.

We present a low size, weight, and power (SWaP), low-complexity, ytterbium magneto-optical trap (MOT). We demonstrate trapping of $1.4\times {10}^6$ ${}^{171}\mathrm{Yb}$ atoms on the $|{{}^{1}S}_0,F=1/2⟩\leftrightarrow |{{}^{1}P}_1,F^{\prime }=3/2⟩$ transition directly from a hot thermal beam. We explore the effect of trap detuning and oven temperature on trap number, density, loading rate, and sample temperature. The low SWaP and low-complexity design presents a realistic pathway toward portable ytterbium MOTs, allowing cold atom ytterbium systems to escape the confines of the laboratory and perform precision measurements in field environments.

Noisy intermediate-scale quantum (NISQ) devices impose dual challenges on quantum circuit execution: limited qubit connectivity requires extensive SWAP-gate routing, while time-dependent decoherence progressively degrades quantum information. Existing qubit-mapping algorithms optimize for hardware topology and static calibration metrics but systematically neglect transverse relaxation dynamics ($T_2$), creating a fundamental gap between compiler decisions and evolving noise characteristics. We present transverse relaxation time–aware qubit-mapping (TRAM), a coherence-guided compilation framework that elevates decoherence mitigation to a primary optimization objective. TRAM integrates calibration-informed community detection to construct noise-resilient qubit partitions, generates time-weighted initial mappings that anticipate coherence decay, and dynamically schedules SWAP operations to minimize cumulative error accumulation. Evaluated on Qiskit-based simulators with realistic noise models, TRAM outperforms SABRE by 3.29% in fidelity, reduces gate count by 11.47%, and shortens circuit depth by 12.29%, establishing coherence-aware optimization as essential for practical quantum compilation in the NISQ era.

The hot carrier solar cell exhibits a photovoltaic conversion efficiency limit of 85.4%. Among the idealizations necessary to achieve this efficiency, it has traditionally been considered essential that the electrons absorbing sunlight do not end up transferring the captured energy to the crystal lattice. In this work, we argue that such a requirement is not necessary if the absorber is thermally insulated. In our analysis, we also consider the possibility of Ohmic losses in the absorber due to finite electrical conductivity. We also demonstrate that such losses, delivered as heat, can be partially recycled into electrical work with an efficiency that is given by the Carnot factor. The high efficiencies reported here are thermodynamic limits obtained with ideal energy-selective contacts and negligible parasitic contact conductance, not projections of practical device efficiency. Our work includes a sensitivity analysis for finite contact-mediated heat leakage, and the results are presented as design targets.

We present a miniaturized, modular vector magnetometer based on silicon vacancy (${\mathrm{V}}_{\mathrm{Si}}^{-}$) centers in 4H-SiC. While N-$V$-diamond magnetometers can offer high sensitivity, spacecraft integration is often complicated by their requirement for disruptive, mT-scale bias fields. Our silicon carbide (SiC) architecture instead enables a net-zero dc magnetic footprint suitable for magnetically clean payloads, in an integrated demonstrator with a credit-card-scale footprint and a total mass of 185 g. A transmission-geometry SiC-GaAs wafer stack with quartz-rod coupling enables efficient photoluminescence collection while suppressing residual pump light. Resonant rf excitation near 70 MHz is provided by a detuned commercial-off-the-shelf (COTS) NFC coil with tunable capacitance and impedance matching. Modulating the spin energy levels in all three orientations using orthogonal Helmholtz coil pairs enables spin-dependent photoluminescence detection and confirms vector operation. The fully integrated instrument achieves a sensitivity of $4\mathrm{\mu }\mathrm{T}/\sqrt{\mathrm{Hz}}$. A detailed noise budget attributes the performance gap primarily to a 225-fold reduction in optically detected magnetic resonance (ODMR) contrast (1.8% to 0.008%) caused by the poor rf $B_1$ filling factor of the unoptimized COTS coil. With benchtop laser and readout systems, the instrument head reaches $1\mathrm{\mu }\mathrm{T}/\sqrt{\mathrm{Hz}}$, identifying laser and electronic-driver noise as the dominant remaining instrument-level contribution. The modular architecture enables independent subsystem optimization and provides a roadmap toward the single-digit $\mathrm{nT}/\sqrt{\mathrm{Hz}}$ benchtop limit.

Phonon modes within pristine crystalline resonators now routinely reach the quantum ground state. Such systems are attractive for quantum information science applications, as advanced fabrication and processing can enable relatively long quantum coherence times, and precision control can be realized through optical, electrical, or qubit coupling. In many state-of-the-art systems, the phonon lifetime is limited by disorder. In particular, native oxides or damaged “dead layers” at surfaces can host two-level tunneling states (TLS) that lead to a particularly problematic form of dissipation that increases at lower temperatures. As mechanical losses are driven down in systems such as microfabricated bulk acoustic wave resonators, tunneling states are expected to emerge as the dominant mechanism for phonon decoherence. A quantitative description of these mesoscopic systems therefore requires a framework that captures interactions between a selected phonon mode and a large ensemble of TLS. Here, we derive a quantum master equation for this coupled system, permitting the phonon decoherence produced by two-level tunneling states to be calculated. As an example, we estimate the lifetime of several quantum states within quartz microresonators hosting a thin surface layer of tunneling states. We find that the phonon coherence time is maximized at low temperatures, in spite of increased mechanical dissipation, and that phonon-TLS coupling can be reduced for modes with strain nodes at the surfaces.

High-precision, portable, and deployable frequency standards are required for modern navigation and communication technologies. Optical frequency standards are attractive for their improved stability over their microwave counterparts; however, increased complexities have anchored them in the laboratory. Sacrificing the sensitivity of the most stable optical clocks has led to the recent development of deployable and portable optical frequency standards, leveraging hot atomic or molecular vapor. The short-term limit for a majority of previous reports on two-photon rubidium standards is either the shot-noise or intermodulation limit hindering the 1 s fractional frequency stability to around $1\times {10}^{-13}$. The answer for the shot-noise limit is to increase optical power and collected fluorescence, while the intermodulation limit solution requires improvements in laser linewidth, stimulated Brillouin scattering (SBS) lasers are known to reduce frequency noise, suppressing noise of the pump laser. We investigate an optical frequency standard based on the two-photon transition in ${}^{87}\mathrm{Rb}$ probed with a narrow photonic integrated circuit SBS laser with a quality factor over 130 million and instantaneous linewidth $<10\mathrm{Hz}$. The use of a narrow clock laser coupled with operating at higher optical intensities yielded clock instabilities of $2\times {10}^{-14}$ at 1 s, currently the best reported short-term stability for a two-photon rubidium optical frequency standard.

High-resolution imaging of magnetic nanostructures is essential for understanding fundamental spin phenomena and designing advanced devices. Recent developments in three-dimensional (3D) nanomagnetism have highlighted the growing need for imaging techniques that can capture magnetic structures across curved or tilted surfaces with high sensitivity. Though widely used as a powerful technique for imaging magnetization states, conventional magneto-optical Kerr effect (MOKE) microscopy faces inherent limitations in measuring nonplanar systems due to its shallow depth of field (DOF). Here, we present an extended depth-of-field MOKE imaging approach, combining through-focus scanning with image-stitching-based reconstruction, to obtain sharp and well-resolved magnetic domain images across nonplanar sample geometries. The method is validated on both perpendicularly and in-plane magnetized films tilted on purpose for this study, enabling quantitative analysis of domain morphology and detection sensitivity. This laboratory-accessible technique provides a fast and versatile route for 3D magnetic imaging, complementing large-scale x-ray-based methods and offering a practical tool for investigating nonplanar magnetic samples with tilted or curved 3D geometries.