High-temperature superconductors (HTS) are increasingly being employed to construct electromagnets to generate strong magnetic field for a broad range of applications: from medical devices, through electric motors, to future fusion reactors. These superconductors can experience a quench phenomenon, manifesting as a fast increase of temperature in HTS cables leading to disruption of the magnet operation and even serious damage. In-time, fast quench detection, to prevent operation disruption, is currently one of the most actively developing areas. Currently, the HTS cables have cooling channels to maintain the operating temperature and in this paper a technique based on frequency and time domain reflectometry (FTDR) using electromagnetic microwave signal propagating inside coolant gas channels is suggested and discussed. We demonstrate that the variation of gas permittivity during the heat release can be measured using the reflectometry allowing fast evaluation of the gas temperature. The methods to monitor the heat release and analysis required to recover the information about the gas temperature and heat release location are described. The numerical and experimental studies to demonstrate the application of FTDR to monitor the coolant gas temperature were carried out and the results, as well as the future plans are discussed.

TianQin is a dedicated geocentric mission for space-based gravitational wave (GW) detection. Among its core technologies, the drag-free and pointing control subsystem (DFPCS)—consisting of suspension, drag-free, and pointing controls—keeps the two test masses (TMs) centered and aligned within their housings while maintaining drag-free conditions and precise telescope pointing along the laser-arm directions. This results in orbit-attitude coupled dynamics for the constellation. The coupling is made more prominent through satellite self-gravity, which requires compensation from DFPCS and generally makes the satellites deviate from pure free-fall orbits. In previous studies, it was assumed that the orbit and attitude dynamics could be decoupled in numerical simulation, neglecting the back-action from the closed-loop control to orbit evolution. To address this, we developed a comprehensive model that can propagate the full nine-body (six TMs plus three satellites; orbits and attitudes) dynamics interdependently under intersatellite pointing and drag-free conditions. This paper is threefold. First, we reassess the applicability of the two TMs and telescope pointing scheme to TianQin using the new model, confirming the previous conclusion. Second, to meet the constellation stability requirements, it is found that the dc common self-gravity in the flight direction should be minimized, or kept close, for the three satellites. Finally, we simulate the long-range light path between two TMs or satellites with a precision of sub-$\mathrm{pm}/{\mathrm{Hz}}^{1/2}$; the results support decoupling of the closed-loop dynamics and high-precision orbit for computational efficiency. The method is instrumental to other future missions where the orbit-attitude coupling needs careful consideration.

Aperiodic magnonic crystals, namely magnetic fractals, lack long-range order and produce complex and localized spin-wave spectra. However, to achieve the spin-wave propagation in such magnetic fractals, it is important to enhance the exchange coupling at the interface by introducing two different ferromagnetic materials. In this work, we report the magnetization dynamics of the bicomponent Sierpiński square structure consisting of $\mathrm{Co}\mathrm{Fe}$ inclusions within a $\mathrm{Ni}\mathrm{Fe}$ matrix by solving the Landau-Lifshitz-Gilbert equation using micromagnetic simulations. The time domain magnetization data show the presence of multiple small and wide frequency gaps in the spin-wave spectra. In addition, the spatial profile of the spin-wave mode exhibits a self-similarity at various geometrical scaling for different iterations and a spin-wave channeling along the entire length of the structure, which could further be tuned by varying the azimuthal angle of the external magnetic field. The complex and inhomogeneous demagnetization field arising from aperiodic structuring significantly influences the spin-wave dynamics in these magnetic fractals. These findings demonstrate the potential application of the bicomponent Sierpiński square structure in reconfigurable magnonic device applications.

Quantum batteries, as miniature energy storage devices, have sparked significant research interest in recent years. However, achieving rapid and stable energy transfer in quantum batteries while obeying quantum speed limits remains a critical challenge. In this work, we experimentally optimize the charging process by leveraging the unique energy level structure of a superconducting capacitively shunted flux qubit, using counterdiabatic pulses in the stimulated Raman adiabatic passage. Compared to previous studies, we impose two different norm constraints on the driving Hamiltonian, achieving optimal charging without exceeding the overall driving strength. Furthermore, we experimentally demonstrate a charging process that achieves the quantum speed limit. In addition, we introduce a dimensionless parameter $\mathcal{S}$ to unify charging speed and stability, offering a universal metric for performance optimization. In contrast to metrics such as charging power and thermodynamic efficiency, the $\mathcal{S}$ criterion quantitatively captures the stability of ergotropy while also considering the charging speed. Our results highlight the potential of the capacitively shunted qubit platform as an ideal candidate for realizing three-level quantum batteries and deliver novel strategies for optimizing energy transfer protocols.

In the past decade, the microwave quantum electronics toolbox has been enriched with quantum limited detection devices such as traveling-wave parametric amplifiers (TWPAs). The extreme sensitivity that they provide is not only mandatory for some physics applications within quantum information processing, but is also the key element that will determine the detection limit of quantum sensing setups. In the framework of microwave optomechanical systems, an unprecedented range of small motions and forces is accessible, for which a specific quantitative calibration becomes necessary. We report on near quantum limited measurements performed with an aluminum drumhead mechanical device within the temperature range 4–400 mK. The whole setup is carefully calibrated, especially taking into account the power dependence of microwave absorption in the superconducting optomechanical cavity. This effect is commonly attributed to two-level systems (TLSs) present in the metal oxide. We demonstrate that a similar feature exists in the TWPA, and can be phenomenologically fitted with adapted expressions. If not taken into account, the error on the signal strength can be as large as a factor of about 2, which is unacceptable for quantitative experiments. The power and temperature dependence is studied over the full parameter range, leading to an absolute definition of the phonon population (i.e., Brownian-motion amplitude), with an uncertainty $\pm 20\mathrm{\%}$ limited by sources of noise internal to the optomechanical element.

Efforts to scale up superconducting processors that employ flux qubits face numerous challenges, among which is the crosstalk created by neighboring flux lines, which are necessary to bias the qubits at the zero-field and ${\mathrm{\Phi }}_0/2$ sweet spots. A solution to this problem is to use symmetric gradiometric loops, which incorporate a flux-locking mechanism that, once a fluxon is trapped during cooldown, holds the device at the sweet spot and limits the need for active biasing. We demonstrate this technique by simultaneously locking multiple gradiometric fluxonium qubits in which an aluminum loop retains the trapped fluxon indefinitely. By compensating the inductive asymmetry between the two loops of the design, we are able to lock the effective flux bias within ${\mathrm{\Phi }}_{\mathrm{eff}}=-3\times {10}^{-4}{\mathrm{\Phi }}_0$ from the target, corresponding to only $15\mathrm{\%}$ degradation in $T_{2,E}$ when operated in zero external field. The design strategy demonstrated here reduces integration complexity for flux qubits by minimizing crosstalk and potentially eliminating the need for local flux bias.

Radio-frequency measurements could satisfy DiVincenzo’s readout criterion in future large-scale solid-state quantum processors, as they allow for high bandwidths and frequency multiplexing. However, the scalability potential of this readout technique can only be leveraged if quantum device tuning is performed using exclusively radio-frequency measurements, that is, without resorting to current measurements. We demonstrate an algorithm that performs automatic coarse tuning of double quantum dots with only radio-frequency measurements by exploiting their bandwidth and impedance matching. The tuning was completed within a few minutes with minimal prior knowledge about the device. Our results show that it is possible to eliminate the need for transport measurements for quantum-dot tuning, paving the way for more scalable device architectures.

Cavity-mediated interaction between gate-defined quantum dots (QDs) has emerged as a promising platform to achieve long-distance spin-spin coupling. However, the realization of on-chip quantum networks and scalable quantum computing requires robust and high-fidelity remote quantum operations. In this work, we use Floquet modulation of gate voltages to fine-tune remote couplings between QDs. We show that the long-distance controlled-iswap gate can be well implemented by choosing suitable values of the frequency, amplitude, and phase of Floquet driving. Moreover, we propose a protocol to achieve high-fidelity quantum state transfer using phase modulation and the stimulated Raman adiabatic passage, which exhibits robustness to dephasing noises. Our work provides efficient and feasible solutions to control remote couplings between gate-defined QDs, and will greatly promote related theoretical studies and experimental implementations.

Practical implementations of quantum key distribution (QKD) extending beyond urban areas commonly use satellite links; however, the transmission of quantum states through the Earth’s atmosphere is highly susceptible to noise, restricting its application primarily to nighttime. High-dimensional (HD) QKD offers a promising solution to this limitation by employing high-dimensionally entangled quantum states. Although experimental platforms for HD QKD exist, previous security analyses have been limited to the asymptotic regime and have either relied on impractical measurements or employed computationally demanding convex optimization tasks, restricting the security analysis to low dimensions. In this work, we bridge this gap by presenting a composable finite-size security proof against both collective and coherent attacks for a general HD QKD protocol that uses only experimentally accessible measurements. In addition to the conventional yet impractical “one-shot” key rates, we provide a practical variable-length security argument that yields significantly higher expected key rates. This approach is particularly crucial under rapidly changing and turbulent atmospheric conditions, as encountered in free-space and satellite-based QKD platforms.

Imaging techniques such as functional near-infrared spectroscopy and diffuse optical tomography (DOT) achieve deep, noninvasive sensing in turbid media; however, they are constrained by the photon budget, as most of the injected light is lost to scattering before reaching the detector. Wavefront shaping (WFS) can enhance signal strength via interference at specific locations within scattering media, enhancing light-matter interactions and potentially extending the penetration depth of these techniques. Interpretation of the resulting measurements relies on knowing the optical sensitivity—the relationship between changes in the detected signals and perturbations at a specific location inside the medium; however, conventional diffusion-based sensitivity models rely on assumptions that become invalid under coherent illumination. In this work, we develop a microscopic theory for optical sensitivity that captures the inherent interference effects that diffusion theory necessarily neglects. We show analytically that, under disorder averaging with random illumination, the microscopic and diffusive descriptions coincide. Beyond this limit, our framework identifies WFS strategies that enhance sensitivity. We demonstrate that the input state obtained through phase conjugation at a given point inside the system leads to the largest enhancement of optical sensitivity but requires an input wavefront that depends on the target position. In sharp contrast, the maximum remission eigenchannel, corresponding to the largest eigenvalue of the monochromatic remission matrix, leads to a global enhancement of the sensitivity map with a fixed input wavefront. This global enhancement equals the remission enhancement and preserves the spatial distribution of the sensitivity, making it compatible with existing DOT reconstruction algorithms. Our results, validated through extensive numerical simulations, establish the theoretical foundation for integrating wavefront control with diffuse optical imaging, enabling deeper tissue penetration through improved signal strength in biomedical applications.

Proximity ferroelectricity is a paradigm for inducing ferroelectricity when a nonferroelectric polar material (such as $\mathrm{Al}\mathrm{N}$), which is unswitchable with an external field below the dielectric breakdown field, becomes a practically switchable ferroelectric in direct contact with a thin switchable ferroelectric layer (such as ${\mathrm{Al}}_{1-x}{\mathrm{Sc}}_x\mathrm{N}$). Here, we develop a Landau-Ginzburg-Devonshire approach to study the proximity effect of local piezoelectric response and polarization reversal in wurtzite ferroelectric multilayers under a sharp electrically biased tip. Using finite-element modeling, we analyze the probe-induced nucleation of nanodomains, the features of local polarization hysteresis loops and coercive fields in the ${\mathrm{Al}}_{1-x}{\mathrm{Sc}}_x\mathrm{N}/\mathrm{Al}\mathrm{N}$ bilayers and three-layers. Similar to the wurtzite multilayers sandwiched between two parallel electrodes, the regimes of “proximity switching” (when all layers collectively switch) and the regime of “proximity suppression” (when they collectively do not switch) are the only two possible regimes in the probe-electrode geometry. However, the parameters and asymmetry of the local piezoresponse and polarization hysteresis loops depend significantly on the sequence of the layers with respect to the probe. The physical mechanism of proximity ferroelectricity in the local probe geometry is a depolarizing electric field determined by the polarization of the layers and their relative thickness. The field, whose direction is opposite to the polarization vector in the layer(s) with the larger spontaneous polarization (such as $\mathrm{Al}\mathrm{N}$), renormalizes the double-well ferroelectric potential to lower the steepness of the switching barrier in the “otherwise unswitchable” polar layers. Tip-based control of domains in otherwise nonferroelectric layers using proximity ferroelectricity can provide nanoscale control of domain reversal in memory, actuation, sensing, and optical applications. The ability of the tip-induced proximity switching to differentially switch multilayers, based on the order of the layers, provides a powerful tool for selective domain engineering.

Biphoton states have shown promising applications in quantum information processing, including quantum communications, quantum metrology, and quantum imaging. The generation and manipulation of biphoton entanglement in topologically distinct modes paves the way in this direction. Here we present a comprehensive method for regulating the topological properties of the system by combining the nonlinearity in waveguides, i.e., nonlinearity in the waveguide coupling materials, and the waveguide lattice structure. Our method enables the generation of topological biphoton states with injected pump activation on the topologically trivial modes. This is realized through self-induced manipulation on pump-dependent nonlinear couplings on the defects, which is unable to be realized while there are no such nonlinear couplings. Specifically, by including the nonlinear gain/loss mechanism in the coupling between the nearest-neighbor waveguides and the third-order Kerr nonlinearity effect along the waveguides, the injected pump power will be the controllable parameter for the manipulation of the topology in the defect states and the generation of biphoton entanglement states. We also present an experimental proposal to realize our scheme and its generalization in the contemporaneous “active” topological photonics time-bin platforms. Our method can be used in other Su-Schrieffer-Heeger (SSH) models with various defect configurations. Our method enables the reusability and versatility of SSH lattice chips and their application for fault-tolerant quantum information processing, promoting the industrialization process of quantum technology.

The van der Waals material ${\mathrm{Fe}}_3{\mathrm{Ga}\mathrm{Te}}_2$ (F3GaT) is a promising candidate for spintronic applications due to its high Curie temperature ($T_C$) and strong perpendicular magnetic anisotropy (PMA). In this study, we thoroughly investigate the spin dynamics of F3GaT single crystals using electron spin resonance (ESR) techniques. The temperature-dependent ESR spectra reveal a significant range of magnetic fluctuations from $T_C\sim 362$ K to $T^{\ast }\sim 410$ K. Furthermore, the angle-dependent resonance field $H_r$ of the ESR demonstrates strong PMA, with the maximum $H_r$ in the $ab$ plane indicating the hard direction, while the minimum along the $c$ axis suggesting the easy orientation. Meanwhile, the angle-dependent ESR spectra reveal distinct anisotropic spin couplings. For $H//ab$, spin-spin relaxation predominates between $T_C$ and $T^{\ast }$, whereas spin-lattice relaxation prevails above $T^{\ast }$. In contrast, for $H//c$, the Korringa mechanism, arising from the interaction between localized spins and conduction electrons, dominates above $T_C$. Our findings elucidate the anisotropic spin dynamics in F3GaT, providing insights into its potential application in microwave-based spintronic devices.

An aboveground 60-kg reactor-antineutrino detector prototype, comprising a two-dimensional array of 36 ${}^6\mathrm{Li}$-doped pulse-shape-sensitive plastic scintillator bars, is described. Each bar is 50 cm long with a square cross section of 5.5 cm. Doped with ${}^6\mathrm{Li}$ at 0.1% by mass, the detector is capable of identifying correlated energy depositions for the detection of reactor antineutrinos via the inverse-$\beta$-decay (IDB) reaction. Each bar is wrapped with a specular reflector that directs photons toward photomultiplier tubes mounted at both ends of the bar. This paper highlights the construction, key features, and main performance characteristics of the system. The system, which relies on multiple observables such as pulse-shape discrimination, energy, position, and timing, is capable of detecting IBD-like neutron-correlated backgrounds, long-lived decay chains, and cosmogenic isotopes.

Monoaxial chiral helimagnets (CHMs) host rich helical spin textures, including chiral soliton lattices (CSLs) with tunable periods, arising from the delicate interplay between Dzyaloshinskii-Moriya interaction (DMI), ferromagnetic exchange coupling, uniaxial magnetic anisotropy, and Zeeman energy. However, existing CHMs exhibit spin resonance modes in the gigahertz frequency range, limiting their potential for high-speed signal processing. Here, with the combination of ferromagnetic resonance, electron spin resonance, and magneto-Raman techniques, we gain access to uncover subterahertz CSL phonon modes in a typical CHM ${\mathrm{Cr}}_{1/3}{\mathrm{Ta}\mathrm{S}}_2$. Near the critical field, we identify nontrivial CSL phonon modes reaching 0.15 THz, while a uniform ferromagnetic resonance mode emerges at 0.375 THz in the forced ferromagnetic phase under 9 T. The CSL phonon frequency in ${\mathrm{Cr}}_{1/3}{\mathrm{Ta}\mathrm{S}}_2$ is a factor of five or six higher than that of isostructural ${\mathrm{Cr}}_{1/3}{\mathrm{Nb}\mathrm{S}}_2$ due to larger spin-orbit coupling-induced DMI. Through micromagnetic simulations, we obtain the frequency spectrum and resolve the spatial distribution of amplitudes, phases, and precession trajectories of the CSL modes, providing deep insight into the characteristics of each resonance mode. Furthermore, we demonstrate that physical reservoir computing (RC), which exploits the nonlinear collective spin dynamics and field-controlled hysteresis of these nontrivial spin textures, achieves exceptional performance in time-series prediction tasks. Our findings not only elucidate the intricate dynamic properties of CSL phases but also pave the way for exploring the potential application of CHM materials for subterahertz signal processing and neuromorphic computing.

In this paper, we demonstrate the potential of laser picosecond acoustics for characterizing the averaged mass of nanoparticles distributed on the surface of submicron-thin membranes. Specifically, we investigate guided-wave (GW) propagation in thin membranes covered with silicon oxide nanospheres. By employing picosecond acoustics, we excite and detect GWs, generating spatiotemporal maps of acoustic behavior that visualize the GW dispersion curves. Such dispersion curves are also calculated using a computer model, which implements a semianalytical Green’s-matrix-based solution to the corresponding boundary-value problem. Based on these data, inverse problems are solved to determine the effective elastic parameters of the membrane and the average mass of particles per unit surface. The method exhibits high sensitivity in detecting masses as small as 200 femtograms per square micron. The wide field of view provided by the picosecond technique enables efficient scanning of millimetric surfaces with the potential to detect mass variations at the hundred-femtogram level over large areas.

Bent-core nematic (BCN) liquid crystals (LCs) can form a variety of grating structures under different orientations and exhibit exceptional optical tunability due to their unique flexoelectric effect. Here, we develop a flexoelectric nematic LC (NLC) mixture with broad temperature range (0–65 °C). Based on this material system, we investigate the grating structure formed by the flexoelectric NLCs under different orientations (planar, vertical, and annular photoalignment) and analyze their responses to voltage and temperature. As a result, we achieve one-dimensional, two-dimensional, and annular diffraction patterns with tunable periodicity. Notably, under an external field, we observed the microdomain multidomain phenomenon of NLC gratings in the vertical cell: numerous micrometer-scale segmented gratings spontaneously align in different directions while maintaining a uniform periodicity. This isotropic grating array exhibits an anomalous annular diffraction pattern under laser irradiation: whereas an individual segmented grating produces directional diffraction, the statistically uniform distribution of segmented gratings results in the superposition of diffracted intensities in multiple directions, ultimately forming concentric annular patterns with tunable radius. This tunable diffraction angle grating, applied to spectral scanning, is simple to prepare, low-cost, and can complete a visible light scan in 1.25 s, providing new possibilities for the development of miniaturized spectrometers.

The demand for cryogenic memory components is driven by the need for ultrafast, low-power, and highly reliable computing systems. Phase-slip-based devices promise to fulfill all these requirements, with potential applications in both classical and quantum information processing. However, previous implementations have faced challenges due to inefficient writing and readout schemes. In this work, we address these limitations with a simple device design and measurement techniques inspired by circuit quantum electrodynamics. We present a memory element that stores information in the winding of a high-kinetic inductance superconducting loop, inductively coupled to a coplanar waveguide resonator. Using 2-$\text{μ}\mathrm{s}$ single-shot measurements, we bring the resonator to the steady state and achieve a readout fidelity of 99.698% with an active measurement time of just 25 ns.