We demonstrate highly efficient control of antiferromagnetic (AFM) magnon spins by the interfacial exchange interaction in heterostructures of ferrimagnetic yttrium iron garnet (YIG) and AFM ${\mathrm{Cr}}_2{\mathrm{O}}_3$. At low temperatures, ${\mathrm{Cr}}_2{\mathrm{O}}_3$ is antiferromagnetically ordered. The interfacial exchange interaction exerted by YIG lifts the degeneracy between the AFM magnon modes in ${\mathrm{Cr}}_2{\mathrm{O}}_3$, resulting in a net spin polarization and a spin current dominated by left-handed magnons, even at zero magnetic field, which is detected by the spin Seebeck effect with a 5-nm-thick $\mathrm{Pt}$ film. In the AFM magnon-dominated region, even if the magnetic field is not sufficiently strong to induce the spin-flop transition in ${\mathrm{Cr}}_2{\mathrm{O}}_3$, the total spin Seebeck signal polarity flips when the YIG magnetization switches. It clearly indicates that the ${\mathrm{Cr}}_2{\mathrm{O}}_3$ magnon polarization is controlled by YIG magnetization through the interfacial exchange interaction. The demonstration of the efficient control of AFM magnon polarization opens a pathway to manipulate AFM magnon quantum states using FM-AFM heterostructures.

We study the entanglement and memristive properties of three coupled quantum memristors. We consider quantum memristors based on conductance-asymmetric superconducting quantum interference device architectures that are coupled via inductors. The three quantum memristors are arranged in two different geometries: linear and triangular coupling configurations. We obtain a variety of correlation measures, including bipartite entanglement and tripartite negativity. For identical quantum memristors, we find that entanglement and memristivity follow the same behavior for the triangular case and the opposite one in the linear case. Finally, we study the multipartite correlations with the tripartite negativity and entanglement monogamy relations, showing that our system has genuine tripartite entanglement. Our results show that quantum correlations in multipartite memristive systems have a nontrivial role and can be used to design quantum memristor arrays for quantum neural networks and neuromorphic quantum computing architectures.

Dynamically modulating the infrared emissivity of materials is of great importance in various applications (e.g., thermal camouflage and radiative cooling). Even though graphene-based materials (such as multilayer graphene, MLG) have shown great potential in active control of emissivity, the device lifetime is rather short, while low-cost large-scale production is difficult to achieve. Herein, graphene aerogels (GAs) with high porosity are prepared by a simple hydrothermal method, and used as electrode in an infrared emissivity modulator with a sandwiched structure. It is demonstrated that the emissivity of GA can be tuned through ion intercalation by electrostatic gating. The modulation depth of GA is comparable to that of MLG, but device lifetime is much longer. This is likely due to the porous structure of GA formed by a continuous three-dimensional MLG network, which makes it easier for ion transport, while allowing effective charge transfer from anions adsorbed on or intercalated into MLG to carbons. Due to a change in surface roughness of GA upon compressing, the emissivity of GA can be further tuned by compressive strain, which provides additional freedom in control of emissivity. The observations offer a promising avenue for the preparation of large-scale emissivity modulators at low cost, which is beneficial for practical applications.

Recently, there have been many developments in domain-wall electronics, such as racetrack memory and domain-wall logic. Here, we show that some of the principles of the control of ferromagnetic and ferroelectric domain walls can be applied to graphene kinks and antikinks, which are topological states of buckled graphene membranes. Using molecular-dynamics simulations, we demonstrate the good properties of graphene kinks for application in a racetracklike memory. Specifically, it is shown that in a sawtooth (ratchetlike) potential, graphene kinks and antikinks are locked into discrete positions on the membrane, and their force-induced unidirectional motion resembles the operation of a digital shift register.

Pentamode material (PM) possesses great potential in underwater acoustic metamaterial device applications due to its broadband and solid-state merits. Previously proposed PM devices are all designed with single materials, where the additional weights for mass adjustment are connected directly to the struts for modulus adjustment. The coupling effects between them severely restrict available fabrication techniques and the realizable range of physical properties of PM devices. A multiphase PM configuration, the additional weights of which are bonded to the struts with interconnecting materials, is proposed, and a waterlike multiphase PM device based on the proposed configuration is developed to assess the validity of the multiphase PM configuration. It is revealed from both simulation and experimental results that the acoustic properties of the proposed multiphase PM device mimics water within the simulation frequency range of 3–24 kHz. The fabrication cost of the proposed multiphase PM device is reduced by 80%, and the duration is only 1/15 when compared to that of a single-phase PM device. Additionally, the multiphase PM has great advantages over single-phase PM for aspects such as withstanding higher hydrostatic pressure due to much more uniform stress distribution and broadening the realizable range of physical properties of PM devices significantly.

We propose the encoding of memristive quantum dynamics on a digital quantum computer. Using a set of auxiliary qubits, we simulate an effective non-Markovian environment inspired by a collisional model, reproducing memristive features between expectation values of different operators in a single qubit. We numerically test our proposal in an IBM quantum simulator with 32 qubits, obtaining a pinched hysteresis curve that characterizes our quantum memristor model. Furthermore, we extend our method to the case of two coupled quantum memristors, opening the door to the study of neuromorphic quantum computing in the current noisy devices.

The magnetocaloric effect of a given material is typically assessed through indirect estimates of the isothermal magnetic entropy change, $\mathrm{\Delta }{S}_M$. While estimating the adiabatic temperature difference, $\mathrm{\Delta }{T}_{\mathrm{ad}}$, is more relevant from the standpoint of refrigeration device engineering, this requires specialized experimental setups. We here present an approach to directly measure $\mathrm{\Delta }{T}_{\mathrm{ad}}$ through time-dependent magnetometry in a commercial superconducting quantum interference device (SQUID) device. We use as reference material gadolinium under a 20-kOe field change, and compare our results with those of the literature. Under nonadiabatic experimental conditions, a remarkably similar $\mathrm{\Delta }{T}_{\mathrm{ad}}(T)$ curve profile is obtained; however, its peak amplitude is underestimated. With a simple compensation methodology we are able to further approximate the profile of the $\mathrm{\Delta }{T}_{\mathrm{ad}}(T)$ curve obtaining the peak amplitude, the maximizing temperature, and the FWHM within relative errors of $-4\mathrm{\%}$, $-0.7\mathrm{\%}$, and 11%, respectively. Our reported approach makes the measurement of both $\mathrm{\Delta }{S}_M(T)$ and $\mathrm{\Delta }{T}_{\mathrm{ad}}(T)$ possible with a single instrument, enabling accelerated progress towards new, competitive, and industry-ready materials.

We consider the magnonic properties of two dipolarly coupled magnetic stripes, both deposited on a normal conductive substrate with strong spin-orbit coupling. A charge current in the substrate acts on the adjacent magnets with spin-orbit torques, which result in magnonic damping or antidamping of the spin waves, and hence a gain-loss coupling of the two magnetic stripes. The whole setup is demonstrated to exhibit features typical for parity-time- ($PT$) symmetric systems. Phenomena are demonstrated that can be functionalized in magnonic devices, including reconfigurable magnonic diodes and logic devices. Alternative stripe designs and $PT$-symmetric, periodic, coupled magnonic textures are studied. Analytical and full numerical analysis identify the conditions for the appearance of exceptional points (EPs), where magnonic gain and loss are balanced and evidence nonreciprocal magnon propagation and enhanced magnon excitation around EPs. Furthermore, the dipolar coupling is shown to bring in a wave-vector-dependent $PT$-symmetric behavior. Proposing and simulating a $PT$-symmetric magnonic crystal, we show how EPs and hence associated phenomena can be steered to a particular wave vector in a gaped spectrum via material design. The phenomena offer additional tools for magnonic based communication and computational devices.

While nitrogen-vacancy ($\mathrm{N}$-$V^{-}$) centers have been extensively investigated in the context of spin-based quantum technologies, the spin-state readout is conventionally performed optically, which may limit miniaturization and scalability. Here, we report photoelectric readout of ground-state cross-relaxation features, which serves as a method for measuring electron-spin resonance spectra of nanoscale electronic environments and also for microwave-free sensing. As a proof of concept, by systematically tuning N-$V$ centers into resonance with the target electronic system, we extract the spectra for the P1 electronic spin bath in diamond. Such detection may enable probing optically inactive defects and the dynamics of local spin environment. We also demonstrate a magnetometer based on photoelectric detection of the ground-state level anticrossings (GSLACs), which exhibits a favorable detection efficiency as well as magnetic sensitivity. This approach may offer potential solutions for determining spin densities and characterizing local environment.

An exact theory is developed with the aim of assessing the properties of the harmonics spectrum of the dynamic magnetization originating from superparamagnetic nanoparticles submitted to a high-frequency driving field. The magnetization is assumed to be always close to equilibrium at the frequencies of interest, so that it can still be described by the anhysteretic Langevin function. The theory, valid for an extended range of values of physical properties and sizes of particles, is aimed at interpreting typical results of magnetic particle spectroscopy and imaging. The analytical framework is exploited to get a deeper knowledge of the spectral properties of nanoparticle magnetization and to assess the persistence of the superparamagnetic behavior at the operating frequencies. The spectral properties of the time-dependent Langevin function are analyzed in detail and compared with experimental results on polydisperse, immobilized nanoparticles. The system function usually exploited in magnetic particle imaging is calculated with precision as a function of both particle size and driving field’s amplitude.

We propose a theoretical protocol to implement multiqubit geometric gates (i.e., the Mølmer-Sørensen gate) using photonic cat-state qubits. These cat-state qubits stored in high-$Q$ resonators are promising for hardware-efficient universal quantum computing. Specifically, in the limit of strong two-photon drivings, phase-flip errors of the cat-state qubits are effectively suppressed, leaving only a bit-flip error to be corrected. Because this dominant error commutes with the evolution operator, our protocol preserves the error bias, and, thus, can lower the code-capacity threshold for error correction. A geometric evolution guarantees the robustness of the protocol against stochastic noise along the evolution path. Moreover, by changing detunings of the cavity-cavity couplings at a proper time, the protocol can be robust against parameter imperfections (e.g., the total evolution time) without introducing extra noises into the system. As a result, the gate can produce multimode entangled cat states in a short time with high fidelities.

Spin torque is a promising tool for driving magnetization dynamics for computing technologies. These torques can be easily produced by spin-orbit effects, but for most conventional spin source materials, a high degree of crystal symmetry limits the geometry of the spin torques produced. Magnetic ordering is one way to reduce the symmetry of a material and allow exotic torques, and antiferromagnets are particularly promising because they are robust against external fields. We present spin torque ferromagnetic resonance (ST-FMR) measurements and second harmonic Hall measurements characterizing the spin torques in antiferromagnetic iron rhodium alloy. We report extremely large, strongly temperature-dependent exotic spin torques with a geometry apparently defined by the magnetic ordering direction. We find the spin torque efficiency of iron rhodium to be (207 ± 94)% at 170 K and (88 ± 32)% at room temperature. We support our conclusions with theoretical calculations showing how the antiferromagnetic ordering in iron rhodium gives rise to such exotic torques.

We report the detection of a gate-tunable kinetic inductance in a hybrid $\mathrm{In}\mathrm{As}$/$\mathrm{Al}$ nanowire. For this purpose, we embed the nanowire into a quarter-wave coplanar waveguide resonator and measure the resonance frequency of the circuit. We find that the resonance frequency can be changed via the gate voltage that controls the electron density of the proximitized semiconductor and thus the nanowire inductance. Applying Mattis-Bardeen theory, we extract the gate dependence of the normal-state conductivity of the nanowire, as well as its superconducting gap. Our measurements complement existing characterization methods for hybrid nanowires and provide a useful tool for gate-controlled superconducting electronics.

Spontaneous symmetry breaking is a source of the phase transition in a variety of physical systems including such as non-Hermitian. It has recently been demonstrated that so-called exceptional points, which are singularities in non-Hermitian systems, separate the areas with symmetrical and asymmetrical eigenstates. Such separation is evidence of phase transitions in non-Hermitian systems taking place at exceptional points. In this paper, we experimentally demonstrate that exceptional-point phase transition in a system of two coupled magnonic waveguides coupled by dipole-dipole interaction occurs. Using infrared laser irradiation to control the spin-wave losses in one of the waveguides covered by a semiconductor $\mathrm{GaAs}$ layer, we observe a change in the wave numbers of the propagating spin waves and a change in the distribution of spin-wave intensity between the waveguides. Retrieving the experimental data, we find the spin-wave propagation parameters and, based on these and the use of coupled mode theory, we argue that in the system of magnonic waveguides the exceptional-point phase transition is observed.

Fragmentation of liquid-metal droplets irradiated by linearly and circularly polarized femtosecond laser pulses is observed in our experiment. The obtained shadowgraph snapshots demonstrate that a circularly polarized pulse may produce several randomly oriented jets effused from the expanding droplets, while a linearly polarized laser pulse generates strictly the cruciform jets. The latter orientation is tied with polarization plane, rotation of which causes rotation of the cruciform jets by the same angle. To shed light on the experimental data we perform molecular dynamics simulation of droplet expansion induced by angle-dependent heating. Our simulation shows that the jet directions are determined by an oriented angle-dependent energy distribution within a frontal hemisphere layer of droplet after absorption of linearly polarized light. As a result, the produced flow velocity field guided by surface tension forms two high-speed opposite jets oriented across the electric field vector as in our experiment. A shock-wave pulse generated in the frontal layer has angle-dependent amplitude inherited from the oriented energy deposition. The release part of shock pulse produces a cavitation zone nearby the droplet center, and thus an expanding spherical shell is formed from the droplet. The flow velocities within a rearside hemisphere of the shell, produced after reflection of the shock wave from the rear side of droplet, generate two low-speed opposite jets oriented along the electric field vector. Thus we find that the cruciform jets are originated independently from the frontal and rear sides of droplet, and a pair of frontal jets is faster than a pair of rearside jets.

We present an antiferromagnetically exchange-coupled composite (soft and hard layers) spin torque oscillator (AF-ECC STO) and demonstrate its operation via both analytical and micromagnetic modeling. The operation exploits the exchange field due to the antiferromagnetic coupling between soft and hard sublayers of the free layer as well as on the easy-plane anisotropy of the soft sublayer. Optimized AF-ECC STO structures can generate large-amplitude magnetization oscillations, which can be tuned over a broad frequency range with precessions mostly generated by the soft layer. We demonstrate that the AF-ECC STO structure offers flexibility in current control of the oscillation frequency and magnetization angle for realistic material parameters.

Airy beams are peculiar beams that are nondiffracting, self-accelerating, and self-healing, and they have offered great opportunities for ultrasound-beam manipulation. However, one critical barrier that limits the broad applications of Airy beams in ultrasound is the lack of simply built devices to generate Airy beams in water. This work presents a family of Airy-beam-enabled binary acoustic metasurfaces (AB BAMs) to generate Airy beams for underwater ultrasound-beam manipulation. AB BAMs are designed and fabricated by three-dimensional (3D) printing with two coding bits: a polylactic acid (which is the commonly used 3D printing material) unit acting as a bit “1” and a water unit acting as a bit “0.” The distribution of the binary units on the metasurface is determined by the pattern of Airy beam. To showcase the wave-front engineering capability of the AB BAMs, several examples of AB BAMs are designed, 3D printed, and coupled with a planar single-element ultrasound transducer for experimental validation. We demonstrate the capability of AB BAMs in flexibly tuning the focal region size and beam focusing in 3D space by changing the design of the AB BAMs. The focal depth of AB BAMs can be continuous and electronical tuned by adjusting the operating frequency of the planar transducer without replacing the AB BAMs. The superimposing method is leveraged to enable the generation of complex acoustic fields, e.g., multifoci and letter patterns (e.g., “W” and “U”). The more complex focal patterns are shown to be also continuously steerable by simply adjusting the operating frequency. Furthermore, the proposed 3D-printed AB BAMs are simple to design, easy to fabricate, and low cost to produce with the capabilities to achieve tunable focal size, flexible 3D beam focusing, arbitrary multipoint focusing, and continuous steerability, which creates unprecedented potential for ultrasound-beam manipulation.