A high-$Q$ torsion pendulum suspended by a silica fiber is a very sensitive tool to measure force and torque. Since a torsion pendulum has a weak remanence, it couples with the ambient magnetic field and introduces an additional dissipation and torque to affect the measurement. This work theoretically analyzes the coupling mechanism between the torsion pendulum and the magnetic field: the horizontal magnetic field is the main influence for dissipation. A series of modulation experiments have been performed with an aluminum disk. When dc magnetic fields are modulated, the dissipation coefficient of the horizontal magnetic field is determined to be $(0.9\pm 0.1)\times {10}^4{\mathrm{T}}^{-2}$, and the remanence of the torsion pendulum is $(2.2\pm 0.1)\times {10}^{-7}\mathrm{A}{\mathrm{m}}^2$. For ac magnetic fields, the ratio between the angle change of the torsion pendulum and the horizontal magnetic field is measured to be $<(3.6\pm 0.2)\times {10}^{-7}\mathrm{rad}/\text{μ}\mathrm{T}$ around the millihertz frequency band. In the end, the horizontal magnetic field is shielded from $26.1\pm 0.2$ to $1.8\pm 0.1\text{μ}\mathrm{T}$, and the average $Q$ value is increased from $(3.0\pm 0.2)\times {10}^5$ to $(6.2\pm 1.1)\times {10}^5$; the latter is one of the highest values reached so far. This work is valuable for studying the influence of magnetic field in precision measurement with a torsion pendulum.

A commercial quantum key distribution (QKD) system needs to be formally certified to enable its wide deployment. The certification should include the system’s robustness against known implementation loopholes and attacks that exploit them. Here we ready a fiber-optic QKD system for this procedure. The system has a prepare-and-measure scheme with decoy-state BB84 protocol, polarization encoding, a qubit source rate of 312.5 MHz, and is manufactured by QRate. We detail its hardware and postprocessing. We analyze the hardware for known implementation loopholes, search for possible new loopholes, and discuss countermeasures. We then amend the system design to address the highest-risk loopholes identified. We also work out technical requirements on the certification lab and outline its possible structure.

Transition metal–based quaternary chalcogenides have attracted immense attention for various renewable energy applications, including thermoelectric (TE) devices. While low symmetry and a complex structure help to achieve low thermal conductivity, the TE power-factor and hence the figure of merit ($ZT$) remain low, which hinders use of this class of materials for future TE applications. Here we investigate the TE properties of a system, ${\mathrm{Cu}}_2{\mathrm{Zn}\mathrm{Si}\mathrm{Te}}_4$, with improved electronic transport using first-principles calculations. The presence of a heavy chalcogen such as $\mathrm{Te}$ helps to achieve a relatively low band gap (0.58 eV). This, together with unique electronic band topology, leads to promising values of the power-factor of 5.8 mW ${\mathrm{m}}^{-1}$ ${\mathrm{K}}^{-2}$ ($n$-type conduction) and 3.8 mW ${\mathrm{m}}^{-1}$ ${\mathrm{K}}^{-2}$ ($p$-type conduction) at 900 K. $\mathrm{Te}$ atoms also play a crucial role in mixing the optical and acoustic phonon branches, which, in turn, are responsible for reduced lattice thermal conductivity (approximately $0.86$ W ${\mathrm{m}}^{-1}$ ${\mathrm{K}}^{-1}$ at high temperature). Although the thermal conductivity is not appreciably low, the electronic transport properties (power-factor) are quite favorable and yield a promising TE figure of merit ($ZT\sim 2.40$ for $n$-type conduction and $ZT\sim 1.94$ for $p$-type conduction at 900 K). We propose ${\mathrm{Cu}}_2{\mathrm{Zn}\mathrm{Si}\mathrm{Te}}_4$ as a potential candidate for TE applications, and believe it will attract experimental and theoretical studies.

We develop a hardware-efficient ansatz for variational optimization, derived from existing ansatzes in the literature, that parametrizes subsets of all interactions in the cost Hamiltonian in each layer. We treat gate orderings as a variational parameter and observe that doing so can provide significant performance boosts in experiments. We carried out experimental demonstration runs of a compilation-optimized implementation of fully connected Sherrington-Kirkpatrick Hamiltonians on a 50-qubit linear-chain subsystem of Rigetti’s Aspen-M-3 transmon processor. Our results indicate that, for the best circuit designs tested, the average performance at optimized angles and gate orderings increases with circuit depth (using more parameters), despite the presence of a high level of noise. We report performance significantly better than using a random guess oracle for circuits involving up to $\simeq 5000$ two-qubit and $\simeq 5000$ one-qubit native gates. We additionally discuss various takeaways of our results toward more effective utilization of current and future quantum processors for optimization.

The superposition of frequency-shifted Laguerre-Gauss modes can produce a rotating saddlelike intensity profile. When spinning fast enough, the optical forces produced by this structured light saddle generate a dynamically stable equilibrium point capable of trapping nanoparticles in a high vacuum, akin to a Paul trap but with its unique characteristics. We analyze the stability conditions and center-of-mass motion, dynamics and cooling of a nanoparticle levitated in the optical saddle trap. We expect the optical saddle to find applications in levitated optomechanics experiments requiring fast parametric modulation and inverted squeezing potential landscapes.

High-coherence superconducting cavities offer a hardware-efficient platform for quantum information processing. To achieve universal operations of these bosonic modes, the requisite nonlinearity is realized by coupling them to a transmon ancilla. However, this configuration is susceptible to crosstalk errors in the dispersive regime, where the ancilla frequency is Stark shifted by the state of each coupled bosonic mode. This leads to a frequency mismatch of the ancilla drive, lowering the gate fidelities. To mitigate such coherent errors, we employ quantum optimal control to engineer ancilla pulses that are robust to the frequency shifts. These optimized pulses are subsequently integrated into a recently developed echoed conditional displacement protocol for executing single- and two-mode operations. Through numerical simulations, we examine two representative scenarios: the preparation of single-mode Fock states in the presence of spectator modes and the generation of two-mode entangled Bell-cat states. Our approach markedly suppresses crosstalk errors, outperforming conventional ancilla control methods by orders of magnitude. These results provide guidance for experimentally achieving high-fidelity multimode operations and pave the way for developing high-performance bosonic quantum information processors.

${\mathrm{Al}}_{1-x}{\mathrm{Sc}}_x\mathrm{N}$ thin films have emerged as a technologically important material for several piezoelectric and ferroelectric device applications ranging from acoustic filters and microelectromechanical systems to memories. Such applications require materials to be grown with high structural quality and optimal properties. However, it is challenging to completely eliminate oxygen contamination, which is persistently present in ${\mathrm{Al}}_{1-x}{\mathrm{Sc}}_x\mathrm{N}$ thin films produced by sputtering deposition, particularly with increasing $\mathrm{Sc}$ content. In this study, we examine the role of oxygen in the structure and its effect on the piezoelectric and dielectric properties of ${\mathrm{Al}}_{0.65}{\mathrm{Sc}}_{0.35}\mathrm{N}$ thin film. Our theoretical analysis and experimental results suggest that different oxygen concentrations can have contrasting effects on the piezoelectric properties of ${\mathrm{Al}}_{0.65}{\mathrm{Sc}}_{0.35}\mathrm{N}$ thin films. Oxygen concentration in the range of 1.2 to 4.3 at. % severely degrades the structural coherence of the films and consequently reduces the piezoelectric coefficient from 10.5 to 8.2 pm/V. Electrical characterization and density-functional theory (DFT) calculations indicate the existence of defects of ${\mathrm{O}}_{\mathrm{N}}$ type and $3{\mathrm{O}}_{\mathrm{N}}\text{−}$V${}_{\mathrm{Al}}$ type, depending on oxygen concentration. Our DFT calculations further suggest that at low oxygen concentrations where the substitutional defect of ${\mathrm{O}}_{\mathrm{N}}$ is favored, the piezoelectric coefficient can be nearly 1.5 times higher compared to its counterpart without oxygen.

Ultrafast laser processing is a cutting-edge technology used in three-dimensional nanofabrication owing to its unique multiphoton absorption scheme, making it essential for applications such as microfluidics, photonic devices, and integrated optics. Nevertheless, the precise fabrication of three-dimensional structures within birefringent crystals faces challenges arising from a significantly distorted focused field caused by a refractive index mismatch and birefringence under tightly focused conditions. In this study, we extend the vectorial Debye diffraction theory to incorporate birefringence and deduce an analytical solution to accurately model the distorted focused patterns inside z-cut uniaxial crystals. Practical methods are also proposed to achieve a perfectly focused spot by simultaneously compensating for spherical aberration and birefringence. These findings provide valuable insights for the accurate fabrication of large-scale three-dimensional structures in crystals.

Quantum sensing with solid-state spins offers the promise of high spatial resolution, bandwidth, and dynamic range at sensitivities comparable to more mature quantum sensing technologies, such as atomic vapor cells and superconducting devices. However, despite comparable theoretical sensitivity limits, the performance of bulk solid-state quantum sensors has so far lagged behind these more mature alternatives. A recent review [Barry et al., Rev. Mod. Phys. 92, 015004 (2020)] suggests several paths to improve performance of magnetometers employing nitrogen-vacancy defects in diamond, the most-studied solid-state quantum sensing platform. Implementing several suggested techniques, we demonstrate the most sensitive nitrogen-vacancy-based bulk magnetometer reported to date. Our approach combines tailored diamond growth to achieve low strain and long intrinsic dephasing times, the use of double-quantum Ramsey and Hahn-echo magnetometry sequences for broadband and narrowband magnetometry, respectively, and P1 driving to further extend dephasing time. Notably, the device does not include a flux concentrator, preserving the fixed response of the nitrogen vacancies to magnetic field. The magnetometer realizes a minimum sensitivity of $460\mathrm{fT}{\mathrm{s}}^{1/2}$ in a broadband dc-sensitive mode and $210\mathrm{fT}{\mathrm{s}}^{1/2}$ in a narrowband ac mode. We describe the experimental setup in detail and highlight potential paths for future improvement.

A system in equilibrium keeps “exploring” nearby states in the phase space and consequently, fluctuations can contain information, that the mean value does not. However, such measurements involve a fairly complex interplay of effects arising in the device and measurement electronics, that are nontrivial to disentangle. In this paper, we briefly analyze some of these issues and show the relevance of a two-amplifier cross-correlation technique for semiconductors and thin films commonly encountered. We show that by using home-built very low-cost amplifiers, one can measure spectral densities as low as approximately ${10}^{-18}$–${10}^{-19}{\mathrm{V}}^2\mathrm{H}{\mathrm{z}}^{-1}$. We apply this method to an ionic-liquid-gated Ga:ZnO channel and show that the glass transition of the ionic liquid brings about a change in the exponent of the low-frequency resistance fluctuations of the conducting channel. The variation is absent in ungated devices. Our analysis suggests that a log-normal distribution of the Debye-relaxation times of the fluctuations and an increased weight of the long-timescale relaxations can give a phenomenological but quantitative explanation of the observed change in the exponent.

How to prepare and engineer an orbital angular momentum (OAM) array is crucial for optical micromanipulation, large-alphabet optical communications, and optical image processing. Here, by leveraging nonlinear frequency conversion, we propose a scheme for tailoring an OAM array in the manner of controlling light with light. Specifically, by guiding two fundamental waves into a nonlinear optical crystal, one of which carries a Dammann vortex grating (DVG) and the other carries a Gaussian or vortex mode, we equivalently construct a nonlinear DVG in a nonlinear crystal. Thus, we can prepare a one-dimensional and a two-dimensional vortex array particularly with equal energy distribution. Our present scheme can be directly extended to engineering other spatial modes and enrich the toolkit for light field engineering. Also, this nonlinear manner could inspire more attempts in the fields of structured light nonlinear optics.

Achieving higher precision in quantum metrology demands the optimization of both entangled-state preparation and readout processes. However, direct machine optimization using variational dynamics becomes impractical and time consuming, particularly with a large particle number. Here, we develop a heuristic recursive screening-breeding algorithm designed to efficiently optimize variational dynamics for scalable quantum metrology. Leveraging the similarity between optimal variables for adjacent particle numbers, the algorithm recursively updates variables from few to many particles, significantly reducing computational overhead. This enables the identification of optimized dynamics for entangled state preparation and readout, even with a large particle number. As a proof of concept, we apply the algorithm to efficiently optimize twist-and-turn dynamics for spin cat state preparation, interaction-based readout, and time-reversal metrology. Notably, in well-recursive cases, optimized variables can be approximated via fitting without recursion. Our recursive optimization algorithm establishes an efficient framework for scalable quantum metrology protocols, providing a practical avenue for quantum sensing with many-body systems.

Although $\beta$-${\mathrm{Te}\mathrm{O}}_2$ is a promising $p$-type transparent conducting oxide, due to a large optical gap ($\sim 3.7$ eV) and a light effective hole mass, its hole dopability still remains unexplored. In this work, the electronic structure of $\beta$-${\mathrm{Te}\mathrm{O}}_2$ and its point defects are investigated using the HSEsol functional with the band-gap-tuned mixing parameter. Our calculations reveal that $\beta$-${\mathrm{Te}\mathrm{O}}_2$ exhibits a significant difference between the fundamental and optical band gaps because lower-energy optical transitions are dipole forbidden. Additionally, it has a low hole effective mass, especially in plane. The point-defect calculations show that $\beta$-${\mathrm{Te}\mathrm{O}}_2$ is intrinsically an insulator. From systematic calculations of the trivalent dopants, as well as hydrogen, $\mathrm{Bi}$ doping is suggested as the best candidate for an acceptor dopant. This work paves the way for the material design of $p$-type $\beta$-${\mathrm{Te}\mathrm{O}}_2$.

It is widely known that the magneto-optical Faraday effect is linear in magnetization, and therefore the Faraday angles for the states with opposite magnetizations are of opposite sign but equal in modulus. Here we demonstrate that under certain spatial symmetry-breaking conditions, an asymmetric Faraday effect (AFE) arises, meaning that the Faraday angles for opposite magnetic states differ not only in sign but in absolute value as well. Experimental investigations of AFE are performed in a one-dimensional all-garnet magnetophotonic crystal, where AFE appears in the vicinity of the cavity resonance for an oblique incidence of light with an inclined light polarization plane. The magnitude of the observed asymmetry between Faraday rotations for the two opposite magnetizations is very large and reaches $30\mathrm{\%}$ of the absolute value of the Faraday effect. We confirm the generality of the suggested effect by the numerical analysis of several different configurations in which AFE arises. The discovered AFE is of prime importance for nanoscale magnonics and optomagnetism.

Recent research shows that quasiparticle-induced decoherence of superconducting qubits depends on the superconducting-gap asymmetry originating from the different thicknesses of the top and bottom films in $\mathrm{Al}$/${\mathrm{Al}\mathrm{O}}_x$/$\mathrm{Al}$ junctions. Magnetic field is a key tuning knob to investigate this dependence as it can change the superconducting gaps in situ. We present measurements of the parity-switching time of a field-resilient three-dimensional transmon with in-plane field up to 0.41 T. At low fields, small parity splitting requires qutrit pulse sequences for parity measurements. We measure a nonmonotonic evolution of the parity lifetime with in-plane magnetic field, increasing up to 0.2 T, followed by a decrease at higher fields. We demonstrate that the superconducting-gap asymmetry plays a crucial role in the observed behavior. At zero field, the qubit frequency is nearly resonant with the superconducting-gap difference, favoring the energy exchange with the quasiparticles and so enhancing the parity-switching rate. With a higher magnetic field, the qubit frequency decreases and gets detuned from the gap difference, causing the initial increase of the parity lifetime, while photon-assisted qubit transitions increase, producing the subsequent decrease at higher fields. Besides giving a deeper insight into the parity-switching mechanism in conventional transmon qubits, we establish that $\mathrm{Al}$-${\mathrm{Al}\mathrm{O}}_x$-$\mathrm{Al}$ Josephson junctions could be used in architectures for the parity-readout and manipulation of topological qubits based on Majorana zero modes.

The illusion effect requires the establishment of the same scattering properties. Conventionally, the illusion effect is realized by a device that is larger than the target object, but the minimum size of the illusion device has not been discussed in the literature. Here, we first realize an illusion effect with a metasurface device that is smaller than the target object. This is achieved by obtaining the desired electromagnetic fields inside the target object and constructing a device with a surface-impedance metasurface. Then, more importantly, we discuss the minimum size of such illusion devices. Our results show that the minimum size is related to the size, material, and fine structures of the target objects. Furthermore, we discuss the realization of passive metasurfaces by introducing auxiliary evanescent TM modes. These results are verified with numerical simulations. Our work reveals the size limit of illusion devices, provides guidance for their miniaturization, and has the potential to generalize the application scenarios of illusion devices.

The emerging sliding ferroelectricity engineered by stacking nonpolar two-dimensional materials to form van der Waals (vdW) multilayers has led to the important field of slidetronics, which has attracted broad interest from those working in the fields of condensed matter physics, chemistry, and materials science. Here, we explore the promising territory of sliding ferroelectricity, termed “sliding catalysis,” through extensive first-principles calculations on various two-dimensional bilayer materials for on-off switching of a prototypical chemical process, the hydrogen evolution reaction. It is revealed that, by overcoming a negligible sliding-energy barrier, the two surfaces of the vdW bilayers exhibit reversible Janus catalysis, with one surface presenting enhanced performance and the other degenerate. Moreover, it is found that the larger the dipole moment of the bilayer is, the better the catalytic performance becomes, and importantly, the more effective the on-off switching functionality. The present concept of sliding catalysis is expected to direct the development of high-efficiency, particularly high-selectivity, two-dimensional catalytic platforms.

Activities of radioxenon isotopes are reported from an Advanced Gas-cooled Reactor (AGR) during periods of gaseous release. Xenon isotopes are relevant to the monitoring regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). These releases may affect detections from the International Monitoring System (IMS) by influencing the radioxenon background. Time series activity plots have been produced from both in-core monitoring and direct measurement at the point of release using a stack monitor system. Ratio plots using both data sets have been produced with results compared with a commonly chosen nuclear explosion “discrimination line.” The reported results improve the understanding of radionuclide emissions from civil nuclear power plants. This work is being performed as part of the Xenon Environmental Nuclide Analysis at Hartlepool (XENAH) collaboration between the Atomic Weapons Establishment (AWE, UK), EDF Energy (UK), Pacific Northwest National Laboratory (PNNL, USA), and the Swedish Defence Research Agency (FOI).