We demonstrate that the time-averaged far-field thermal radiation between macroscopic bodies can be different from the Planck limit when their temperature difference is periodically modulated. This difference arises from the nonlinear dependence of the radiative heat flux on temperature and persists even for temperature-independent emissivities. By contrast, when the material emissivity depends on temperature, the modulated thermal radiation is driven by the second temperature derivative of emissivity and increases with the square of the amplitude of the temperature oscillations. These temperature fluctuations generate thermal radiation even without a mean temperature difference. Our findings thus reveal a mechanism to control and modulate far-field radiation with potential applications in thermal management and energy harvesting.

We have developed a simple detection scheme to study spin waves excited by surface acoustic waves (SAWs) in ferromagnetic thin films. Metallic antennas made of $\mathrm{Ta}$ and a ferromagnetic element are placed along the SAW propagation path. The SAW excites spin waves in the ferromagnetic element and induces acoustoelectric current in the antennas: the latter is detected as a dc voltage. The dc voltage takes an extremum at the spin-wave resonance condition. The antennas placed before and after the ferromagnetic element along the SAW propagation path can probe spin-wave excitation from reflected and transmitted SAWs, respectively. Interestingly, we find characteristics of spin-wave excitations that are different for the reflected and transmitted SAWs: the former excites spin waves with larger frequency with broader linewidth compared to the latter. The results show that the antennas act as a nonlocal spin-wave-power detector and can be used to map out the spin-wave spectra in a unique way, providing insights into the magnon-phonon coupling in magnetic nanostructures fabricated on phononic SAW devices.

Optical interferometers are extensively used in fundamental physics studies, gravitational wave detection, quantum metrology, topological photonics, and quantum information processing. Fiber-based interferometers are compact, mechanically robust, and cheap, and thus are ubiquitously deployed. However, the optical phase in fiber interferometers is sensitive to ambient perturbation, resulting in compromised phase-sensing precision. Therefore, phase control, shifting, and stabilization of fiber interferometers are essential. Methods to create stable interference patterns and to lock a fiber interferometer at arbitrary phase have been shown, which however are sophisticated, bulky, and delicate, preventing wider application in harsh environments outside laboratories or in space. Here we demonstrate an innovative method for arbitrary-phase locking of fiber unbalanced Mach-Zehnder interferometers. Compared with existing methods, our method is much simpler. We showcase the preparation and characterization of a narrow-band, energy-time-entangled photon state generated in integrated nonlinear microresonators, where two-photon interference visibility reaches 0.993(6). Our method constitutes a critical building block for photonic quantum networks, and is useful to emerging single-photon interference in curved space-time that facilitates exploration of the interface of quantum mechanics and general relativity.

Spin selection is explored for a quantum dot spin qubit with spin accumulations $\mathrm{\Delta }{\mu }_S$ and $\mathrm{\Delta }{\mu }_D$ in the source and drain reservoir, created by ferromagnetic contacts. If $\mathrm{\Delta }{\mu }_S$ and $\mathrm{\Delta }{\mu }_D$ have opposite signs, a single electron can be trapped on the quantum dot in two opposite spin states, depending on the source-drain voltage. The selected spin is then electrically reversible and with low error rates for temperatures up to above 4 K. If $\mathrm{\Delta }{\mu }_S$ and $\mathrm{\Delta }{\mu }_D$ have the same sign, the spin selectivity is enhanced and persists up to even higher temperature than for a spin qubit with spin accumulation in only one of the reservoirs. These results offer opportunities to improve and electrically control spin qubit initialization and readout at elevated temperature.

The rapid advancement of quantum information technology has spurred the need for establishing hybrid quantum systems (HQSs) capable of providing complementary functionalities and multitasking capabilities. Recently, there has been growing interest in HQSs that leverage magnons and other discrete quantum systems. However, the realization of high-fidelity quantum logic on an HQS incorporating both a single spin and coherent magnons has remained elusive at room temperature. In this study, we successfully demonstrate the high-fidelity quantum control of a single spin’s state and present the experimental implementation of a quantum game on an HQS through flexible coherent magnon driving. This accomplishment is made possible through the use of nitrogen-vacancy centers and yttrium-iron-garnet film. Our findings not only underscore the advantages of single-spin coherence for implementing high-fidelity quantum logic but also highlight the absence of heat generation of magnon driving resulting from reducing the energy cost by two orders of magnitude. This, in turn, opens up exciting avenues for further research focused on entangling spin qubits with a quantum data bus of magnons within the context of quantum networks.

Magnetic skyrmions have attracted extensive attention as information carriers for building future power-efficient and ultradense memory or logic devices because of their nanoscale size, topological protection, and current-induced high mobility. The critical issue for realizing the above applications is manipulating skyrmion in a controlled way. Here, we demonstrate a voltage-induced spatial varying channel-like strain in a multiferroic heterostructure to control the trajectory of the current-driven skyrmions. The electromechanical simulation results show that by applying a voltage crossing the piezoelectric thickness, a strain-shaped channel is created as a result of the inverse piezoelectric effect. The voltage-controlled strained channel can modulate the skyrmion Hall effect (SkHE) due to magnetoelastic coupling. We analytically and numerically demonstrated that the compressive and tensive strain inside the channel would lead to a lateral repulsive and attractive force on the skyrmion, respectively, and guide the skyrmion moving straight along the channel. In addition, the skyrmion tunneling effect between two adjacent strained channels with the help of SkHE can be further exploited in developing the demultiplexer (demux) logic gates that work with the voltage-selected region as the selector input and the skyrmion as the information carrier. Furthermore, based on the cascading of demux, the design of programmable logic gates, which were controlled by the voltage-induced strain gates, has been proposed. We also confirmed the operation schematic of the half-adder and full-adder implemented by demux and programmable gates. These results indicated an effective method for guiding the skyrmion motion behavior by voltage-controlled strain, which paved the way to develop skyrmion-based logic gates with reconfigurable and programmable features for information processing and computing systems.

Cloaking has key applications but entails sophisticated control of signal propagation and scattering characteristics. Here, we show that invisibility for magnon signals is achievable in a nonreciprocal and electrically controlled way by engineering the magnonic channels such that they exhibit parity-time ($PT$) symmetry. This is accomplished by attaching current-carrying heavy-metal contacts to the magnon waveguides and exerting fields from an attached bias layer. Tuning the current density in the metal layer, the magnons in this setup experience electrically controlled, compensated gain and loss due to spin-orbit torque, which renders the setup $PT$ symmetric. The magnon dynamics is then shown to be pseudo Hermitian with exceptional points (EPs) determined actively by an external electric field. We analyze the magnon scattering from single and periodic $PT$-symmetric regions and identify the conditions necessary for the formation of unidirectional invisibility, which can be steered by specific combinations of bias layers and current amplitudes in the heavy metal as to reach the EP. The unidirectional invisibility at EP is found to be extended for a periodic $PT$-symmetric region. Intrinsic damping on $PT$-symmetric unidirectional invisibility is shown to be marginal confirming the experimental feasibility. It is shown how the unidirectional magnons can be utilized to amplify and generate magnonic orbital angular-momentum states in coupled magnetic rings demonstrating an alternative path for manipulating magnon propagation and processing.

The assessment of channel resources is critical in the implementation of quantum teleportation (QT), however, an accurate evaluation approach remains elusive in high-dimensional systems. In this paper, we present a general approach for achieving the optimal $d$-dimensional QT fidelity of arbitrary mixed-channel states, and perform an experimental verification of three-dimensional QT to demonstrate its validity. Compared with the previous method, our approach is more precise in determining the optimal QT fidelity with a wider range, which improves the identification of channel resource effectiveness, and eliminates the divergence between different estimation methods for high-dimensional fully entangled fraction (FEF, which has a close connection with the optimal QT fidelity). Our approach can be further applied in the resource design and allocation in high-dimensional quantum networks.

Epitaxial lattice matching is an important condition for the formation of coherent interfaces with low defect densities. However, lattice-matched substrates with the same crystal structure as the active layer are often not available, suggesting opportunities for utilizing heterostructural interfaces. For example, at high $\mathrm{Al}$ contents that are interesting for ultrawide-gap applications in power electronics, ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ semiconductor alloys in the (0001) orientation of the wurtzite (wz) structure become lattice-matched to (111)-oriented rocksalt (rs) $\mathrm{Ta}\mathrm{C}$ substrates. To predict the expected interface atomic structures under different synthesis conditions, we perform high-throughput density-functional-theory calculations, using an algorithm for systematic sampling of the possible stacking sequences of the atomic layers on the in-plane hexagonal lattice. The approach considers octahedral, tetrahedral, and prismatic coordination motifs, and is generally applicable for the modeling of commensurate rs/wz heterostructural interfaces. Our results provide guidance for synthesis control of substrate-film bonding and the polarity of ultrawide-gap ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ alloys on $\mathrm{Ta}\mathrm{C}$ substrates.

Traditional polarized photodetectors have faced critical challenges, such as limited functionality, integration complexities, and subpar photosensitivity. In this study, we propose a kind of multifunctional coupled polarized photodetector based on an anisotropic $\mathrm{MnSSe}/{\mathrm{Ta}\mathrm{Ir}\mathrm{S}}_4/\mathrm{MnSSe}$ lateral magnetic tunnel junction (MTJ) that integrates self-powered, near-infrared photodetection, spin valve, pure spin current, and multichannel optical communication induced by the photogalvanic effect. Profiting from the synergistic interplay between optical transition and spin-tunneling selection rules within the MTJ, seamless toggling between perfect spin filtering and pure spin current can be achieved in the self-powered mode. Furthermore, the remarkable performance metrics, including an anisotropy ratio of 481.84, an extinction ratio of 725.43, and a tunneling magnetoresistance ratio of 100%, underscore the exceptional capabilities of the multifunctional polarized photodetector. Building upon these achievements, a proof-of-concept three-channel optical communication scheme is shown to amplify the output efficiency of binary signals by an additional 50%. Our research provides insights into the development of multifunctional and high-performance photodetectors and presents an interesting platform for advancing coupled optoelectronic and spintronic applications.

Using the ferromagnetic resonance technique, a localized resonance mode was experimentally discovered in an array of out-of-plane magnetized nanosized circular dots with an aspect ratio $L/R$ (thickness/radius) close to unity. The frequency of this mode is lower than the frequency of the main Herring-Kittel quasiuniform spin excitation mode. Micromagnetic modeling reproduces the measured dependencies of the resonance frequencies on magnetic field and confirms that the localized mode is a superposition of two modes localized at the top and bottom faces of the dot. An analytical model based on the Schrödingerlike equation of magnetization dynamics was developed. This model accounts for the inhomogeneity of the demagnetizing field, predicts the presence of such a localized mode, and provides a good estimate of its frequency. Unlike the frequency of the main mode, which predominantly depends only on the aspect ratio of the dot, the frequency of the localized mode explicitly depends on the dot thickness. This offers an opportunity to solve the inverse problem of estimating the average dot sizes on the basis of the patterned film ferromagnetic resonance curves.

Reducing optical losses is crucial for reducing quantum noise in gravitational-wave detectors. In fact, with equal input power, a lower level of round-trip losses in the arm cavities allows more power to be stored. Moreover, losses are the main source of degradation of the squeezed vacuum, which, along with increasing the power, is the most effective strategy to reduce quantum noise. Frequency-dependent squeezing obtained via a filter cavity is currently used to reduce quantum noise over the whole detector bandwidth. Such filter cavities are required to have high finesse in order to produce optimal squeezing angle rotation, and the presence of losses is particularly detrimental for the squeezed beam, as it does multiple round trips within the cavity. Characterizing such losses is crucial to assess the achievable quantum noise reduction. Here we present an in situ measurement of the optical losses, for different positions of the beam on the mirrors of the Virgo filter cavity. We implemented an automatic system to map the losses with respect to the beam position on the mirrors, finding that optical losses depend clearly on the position at which the beam hits the input mirror, varying from 42 to 87 ppm (parts per million), while they are much more uniform when we scan the end mirror (53 to 61 ppm). We repeated the measurements on several days, finding a statistical error less than $\pm 4$ ppm. The lowest measured losses are not much different from those estimated by individual mirror characterization performed before installation (30.3–39.3 ppm). This means that no major loss mechanism has been neglected in the estimation presented here. The larger discrepancy found for some beam positions is likely to be due to contamination. In addition to a thorough characterization of the losses, the methodology described herein allowed an optimal cavity axis position to be found for which the cavity round-trip losses are among the lowest ever measured. This work can contribute to achieving the very challenging loss goals for the optical cavities of future gravitational-wave detectors, such as the Einstein Telescope and Cosmic Explorer.

Recent higher-order topological insulators in topological crystalline insulators that go beyond the conventional bulk-edge correspondence principle have drawn extensive attention. However, the acoustic source that excites corner states must be near the corner’s position due to the acoustic source in the domain of the band gap, which is an unfavorable manipulation of acoustic waves. If we place the acoustic source far from the position of the corner state, we cannot detect the higher-order topological insulators. Here, we design an acoustic crystal based on Kekulé-like Lattice modulations to crack this tough nut and achieve the long-distance mutual excitation of acoustic topological interface and helical corner states. In addition, the corner states can appear in the interface states due to the charge accumulation at the boundary that ensures the presence of the corner states. Our findings enrich applications of topological corner states and interface states and share the potential to broaden the possibilities for acoustic higher-order topological states and interface states, which can extend to other classical wave systems.

The concept of skyrmions, which refers to topologically stable vector textures and was originally introduced in particle physics, has recently been transferred to various types of fields, including electromagnetic ones. Its potential in optics and photonics stimulates the development of sophisticated strategies for skyrmionic beam shaping, but these are limited to bulky systems, thus hindering the emergence of practical applications. Here we propose and experimentally report on the realization of compact flat-optics skyrmion generators based on the spin-orbit interaction of light. Our approach highlights how the use of unitary wave plates beyond the uniform-retardance condition opens new avenues for the preparation of topological optical states.

We propose a faster digital quantum algorithm for portfolio optimization using the digitized counterdiabatic quantum optimization paradigm in the impulse regime, that is, where the counterdiabatic terms are dominant. Our approach notably reduces the circuit depth requirement of the algorithm and enhances the solution accuracy, making it suitable for current quantum processors. We apply this protocol to a real-case scenario of portfolio optimization with 20 assets, using purely quantum and hybrid classical-quantum paradigms. We demonstrate the advantages of our protocol using up to 20 qubits on an IonQ trapped-ion quantum computer. By benchmarking our method against the standard quantum approximate optimization algorithm and finite-time digitized adiabatic algorithms, we obtain a significant reduction in the circuit depth by factors of 2.5 to 40, while minimizing the dependence on the classical optimization subroutine. Besides portfolio optimization, the proposed method is applicable to a large class of combinatorial optimization problems.

State tomography allows quantum states to be characterized, and was recently applied to reveal the dynamic magnetization state of a parametrically driven magnet. The identification of nonclassical states, such as squeezed states, relies on a careful analysis of their emission and their distinction from thermal and vacuum fluctuations. A technique allowing detection of equilibrium magnetization fluctuations is a crucial first step in this regard. In this paper, we show that inductive magnon noise spectroscopy (iMNS) allows characterization of the thermal magnetization fluctuations of a ferromagnetic thin film in a broadband coplanar waveguide-based scheme. Relative to a cold microwave background, the microwaves emitted by the equilibrium magnetization fluctuations can be detected via spectrum analysis. We provide a comprehensive picture of our microwave system by quantitatively modeling its response, including the thermalizing influence of the cables. The model allows for direct comparison to low-power broadband ferromagnetic resonance measurements with excellent agreement, corroborating the equilibrium character of the iMNS measurement by probing the linear response of the equilibrium state. Our work thus demonstrates broadband access to the equilibrium properties of magnetization fluctuations using a purely inductive approach.

We investigate the emergence and optimization of conventional exchange bias (EB) in ultrathin (<10 nm) ferroelectric (FE) ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_3$ (BTO)/ferromagnetic (FM) ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{Mn}\mathrm{O}}_3$ (LSMO) epitaxial bilayers without an antiferromagnetic (AFM) material. The EB originates from the electronic orbital reconstruction at the FE-FM interface due to the ferroelectric polarization. We achieve maximum EB of approximately 42 Oe with single-domain polarization in nine-unit-cell-thick BTO, setting the BTO thickness above the critical threshold for ferroelectricity yet below the thickness of strain relaxation and multidomain breakdown. Furthermore, the LSMO layer needs to be thick enough to sustain both the FM layer and polarization-induced AFM spin configuration at the LSMO/BTO interface, yet as thin as possible to enable the EB loop shift. The temperature, training, field, and thickness dependence of the EB confirm that the LSMO/BTO interface exhibits conventional EB despite its unconventional origin. Using x-ray magnetic circular dichroism, scanning transmission electron microscopy, and density-functional-theory calculations, we confirm that the macroscopic EB effect originates from the interfacial AFM spin configuration in LSMO driven by FE-induced d-orbital modifications in interfacial $\mathrm{Mn}$ ions. Thus, we engineer strong interfacial EB coupling in artificial multiferroics without a conventional AFM material by controlling FE polarization, highlighting the potential for advanced spintronic applications.

Superconducting diodes are recently-discovered quantum analogues of classical diodes. The superconducting diode effect relies on the breaking of both time-reversal and inversion symmetry. As a result, the critical current of a superconductor can become dependent on the direction of the applied current. The combination of these ingredients naturally occurs in proximitized semiconductors under a magnetic field, which is also predicted to give rise to exotic physics such as topological superconductivity. In this work, we use InSb nanowires proximitized by Al to investigate the superconducting diode effect. Through shadow-wall lithography, we create short Josephson junctions with gate control of both the proximitized weak link as well as the proximitized leads. When the magnetic field is applied perpendicular to the nanowire axis, the superconducting diode effect depends on the out-of-plane angle. In particular, it is strongest along a specific angle, which we interpret as the direction of the spin-orbit field in the proximitized leads. Moreover, the electrostatic gates can be used to drastically alter this effect and even completely suppress it. Finally, we also observe a significant gate-tunable diode effect when the magnetic field is applied parallel to the nanowire axis. Due to the considerable degree of control via electrostatic gating, the semiconductor-superconductor hybrid Josephson diode emerges as a promising element for innovative superconducting circuits and computation devices.