Achieving both volatile and nonvolatile resistive switching in the same material platform is a key milestone towards the development of dense hardware-based neuromorphic computing. We show that, by suitable choice of electrode metals, a single oxide film can feature both types of behavior. We demonstrate this for two oxides featuring an insulator-to-metal transition: ${\mathrm{Sm}\mathrm{Ni}\mathrm{O}}_3$ and ${\mathrm{Nd}\mathrm{Ni}\mathrm{O}}_3$. When a current is applied across two-terminal $\mathrm{Pt}$ microdevices, the metal/oxide interface is ohmic and most of the voltage drops horizontally along the oxide film, triggering the transition and inducing volatile resistive switching. However, when $\mathrm{Ti}$ electrodes are used, a ${\mathrm{Ti}\mathrm{O}}_x$ layer forms at the metal/oxide interface, across which a strong electric field develops upon application of a current, inducing nonvolatile resistive switching due to vacancy migration. These two electrical behaviors can be observed at the same temperature and coexist at the microscale, leading to different possibilities for implementing neuristors and memristors in the same microcircuit.

We propose a chip analysis method using a fiber-optic quantum sensor based on diamond nitrogen-vacancy ($\mathrm{N}$-V) centers to capture the magnetic field associated with short-pulse currents in chips. The fiber-coupled diamond $\mathrm{N}$-V sensor was precisely positioned at the target region of the chip. We performed real-time monitoring of the $\mathrm{N}$-V center fluorescence responses to pulsing magnetic fields generated by the pulse signals in the test chip through continuous-wave optically detected magnetic resonance. This allowed the accurate reconstruction of the chip internal node signal variations. We successfully achieved a time resolution of 200 ns, which was consistent with the metastable state lifetime of the $\mathrm{N}$-V centers at room temperature. Furthermore, we evaluated the shot noise–limited magnetic sensitivity, which was found to be $6.3\mathrm{nT}/{\mathrm{Hz}}^{1/2}$. The proposed system exhibited swift responsivity to short pulse currents in the chip, providing highly accurate spatial localization of magnetic field variations. It satisfied the demand for rapid response and precise positioning in chip testing. Overall, this study validates the potential application of $\mathrm{N}$-V centers in the domain of chip security analysis, offering a solution for chip diagnostics.

Quantum frequency conversion is a widely used technique to interface atomic systems with the telecom band in order to facilitate propagation over longer distances in fiber. Here, we demonstrate the difference-frequency conversion from 606 nm to 1552 nm of microsecond-long weak coherent pulses at the single-photon level compatible with $\mathrm{Pr}$${}^{3+}$:$\mathrm{Y}$${}_2$$\mathrm{Si}\mathrm{O}$${}_5$ quantum memories, with a high signal-to-noise ratio (SNR). We use a single-step difference-frequency-generation process with a continuous-wave pump at 994 nm in a periodically poled lithium niobate ($\mathrm{Mg}\mathrm{O}$:ppLN) waveguide and ultranarrow spectral filtering down to a bandwidth of 12.5 MHz. With this setup, we achieve the conversion of weak coherent pulses of duration up to 13.6 µs with a device efficiency of about 25 % and an SNR >460 for 10-$\text{μ}\mathrm{s}$-long pulses containing one photon on average. This SNR is large enough to enable a high-fidelity conversion of qubits emitted from an emissive quantum memory based on $\mathrm{Pr}$${}^{3+}$:$\mathrm{Y}$${}_2$$\mathrm{Si}\mathrm{O}$${}_5$ and to realize an interface with quantum processing nodes based on narrow-linewidth cavity-enhanced trapped ions.

Synthetic spin-orbit coupling (SOC) has achieved significant advancements in silicon-based electron spin qubits, positioning it as a promising platform for quantum computation. However, SOC also introduces challenges in coherence and quantum information exchange. To address these challenges and achieve practical scalability, on-demand switchable SOC is crucial. Yet, it remains underexplored due to the nonvolatility of micromagnets. Spin valves, which are known for their ultrafast magnetization switching and have been primarily used in magnetic storage, offer a potential solution. In this paper, we propose an alternative approach by utilizing the stray field of spin valves to enable switchable SOC in silicon. This switchable architecture provides a larger coherent region for spin arrays. It also makes long-sought coherent information exchange via swap operations and resonant quantum state transfer (QST) easily surpasses the fault-tolerance threshold when considering realistic experimental parameters. By leveraging these advantages, we have developed a modular quantum chip that successfully integrates the operation, coherence, and scalability of spin qubits. Combined with recent experimental advancements in spin qubits and spin valves, our proposal demonstrates high feasibility for large-scale silicon quantum computation.

The requirement for ever shorter laser pulses is endless in ultrafast science. Here we propose a mechanism to produce an ultrashort zeptosecond pulse (ZP) to break the attosecond pulse (AP) barrier, where a cascaded coherent synchrotron emission regime of high-order harmonics generation is used for the emission of a giant half-cycle ZP. As an ultraintense laser pulse interacts with the double-foil target, a relativistic electron sheet is formed by the first-foil electrons and accelerated in the transmission direction, by which a half-cycle AP is emitted. The generated half-cycle AP continues to interact with the second foil target, where another relativistic electron sheet is formed by the second-foil electrons and a giant half-cycle ZP is emitted. A theoretical model is proposed for the nanobunching mechanism of the relativistic electron sheet both in the reflection direction and in the transmission direction, and is supported by numerical simulation results. The intensity of the ZP can reach approximately $2.6\times {10}^{21}{\mathrm{W}/\mathrm{cm}}^2$, with a duration of $380\mathrm{zs}$, which corresponds to a power reaching the 100-TW level. This ultraintense ZP will open the door for nuclear excitation, intranuclear dynamics, or vacuum physics studies on the zeptosecond timescale.

Backscattering in microring cavities induces mode mixing and limits device performance. Existing methods to mitigate backscattering often involve complex fabrication processes or are insufficient for complete suppression. In this work, we introduce a method to eliminate backscattering by operating the cavity at an exceptional point (EP). By engineering nonconservative coupling between degenerate clockwise and counterclockwise modes, we achieve chiral transmission that prevents degeneracy lifting and suppresses unwanted mode coupling. Unlike previous approaches that rely on precise gain-loss balance or complex structures, our method utilizes nonconservative coupling between the counterpropgating cavity modes. Using this method, we further show significant enhancement in the cavity performance in Floquet mode conversion efficiency at the EP. Our highly adaptable approach enables seamless integration into various photonic platforms with electro-optic modulators. This advancement mitigates backscattering and improves the precision of light-matter interactions, offering promising applications in quantum communication and information processing.

We present the implementation and performance analysis of a portable rack-mounted stand-alone warm-vapor quantum memory system that also includes the laser package, control electronics, and data-processing hardware. The optical memory is based on long-lived hyperfine ground states of cesium, which are connected to an excited state via the $D_1$ line at 895 nm in a $\mathrm{\Lambda }$-configuration. The memory is operated with weak coherent pulses containing on average $<1$ photons per pulse. The long-term stability of the memory efficiency and storage fidelity is demonstrated at the single-photon level together with operation in a nonlaboratory environment.

Multilayer microperforated panels (MPPs) are highly efficient noise absorbers with simple structures, making them an increasingly popular alternative to porous material-based solutions. However, as the number of MPP layers increases to achieve desirable and broader absorption bandwidths, the complexity of the design process grows significantly, making traditional optimization algorithms inefficient and extremely time-consuming for inversely designing long-sequence MPP structures. In addition, existing inverse-design methods have many drawbacks because they either fail to adapt to different design targets quickly or are difficult to suit different types of structures, e.g., designing for different topologies at each layer. In this work, we introduce AcoustoGPT (Acousto Generative Pretrained Transformer), a transformer-based model for the quick inverse design of long-sequence MPPs to realize a target absorption spectrum, and solve all these drawbacks simultaneously. Our approach employs a transformer encoder to capture a compact latent representation of the absorption spectrum, while a decoder generates the design parameters for each MPP layer. Finally, we integrate a bidirectional long short-term memory (LSTM) model with the transformer to enhance the design accuracy of the absorption spectrum. The trained model is versatile and can easily adapt to various design conditions, such as varying the number of layers and incident angles. This method has potential in designing other sequential or layered structures, including series Helmholtz resonators and higher-dimensional metastructures.

Controlling the streaming flow in acoustically actuated microchannels enables the targeted motion of suspended micro-objects. This can offer novel approaches for rare cell studies or cell sorting in medicine or basic biology. In this work, we utilize the temperature dependence of the acoustic body force, which originates from the interaction of an acoustic field with gradients in compressibility or density. A temperature gradient was optically induced inside an acoustofluidic microchannel by the absorption of light and the resulting streaming flow was measured by particle tracking in three dimensions. Inside a microfluidic channel, two different thermal fields were investigated for a fixed sound field, both in experiments and in simulations. The results show that shifting the location of the heat source from the center to the side of the channel leads to a transition from four streaming rolls to two rolls in the plane normal to the laser incidence. By modulating the optical absorbance of the medium, the streaming velocity can be tuned such that higher absorption leads to faster thermoacoustic streaming. Further, for higher absorbance, we observe increasing velocity components in the direction of the laser due to asymmetric heat generation along the beam.

Ferrimagnetic insulators with perpendicular magnetic anisotropy exhibit unique properties that offer potential for advanced spintronic devices. One of the challenges in exploiting these materials in spintronics lies in the efficient electrical detection of their magnetization. Herein we report the magnetoresistive detection of perpendicular magnetization in insulating ferrimagnetic garnets, enhanced through proximity coupling with an adjacent ultrathin ferromagnetic layer. We design and characterize a hybrid spin-valve device consisting of terbium iron garnet ($\mathrm{Tb}\mathrm{IG}$)$/\mathrm{Co}/\mathrm{Cu}/\mathrm{Tb}$-$\mathrm{Co}$ multilayers where $\mathrm{Tb}\mathrm{IG}$ and $\mathrm{Tb}$-$\mathrm{Co}$ are perpendicularly magnetized soft and hard layers, respectively, while $\mathrm{Co}$ is in-plane magnetized. We reveal through anomalous Hall effect and x-ray magnetic circular dichroism measurements that the interfacial exchange coupling between $\mathrm{Tb}\mathrm{IG}$ and $\mathrm{Co}$ induces a perpendicular magnetization component in the $\mathrm{Co}$ layer, which increases the magnetoresistance readout signal by more than 2 orders of magnitude—reaching 0.2%—compared with the reference system without the $\mathrm{Co}$ layer. A notable but less pronounced enhancement is observed in the $\mathrm{YIG}/\mathrm{Co}$-$\mathrm{Fe}$-$\mathrm{B}/\mathrm{Cu}/\mathrm{Tb}$-$\mathrm{Co}$ spin-valve device compared with the stack without the $\mathrm{Co}$-$\mathrm{Fe}$-$\mathrm{B}$ insertion, demonstrating the applicability of the approach to similar structures. Finally, we show that the magnetoresistive output signal can be effectively used to probe the multidomain state of $\mathrm{Tb}\mathrm{IG}$, opening a path for future insulating spintronic device applications.

The ferroelectric (FE) control of the polarity of spin channels is crucial for designing multifunctional and high-performance spintronic devices. Here, based on first-principles calculations, we propose an effective strategy to achieve full-electrical FE control of the spin-polarized direction of the ${\mathrm{V}\mathrm{Si}}_2{\mathrm{P}}_4$ layer by stacking ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{V}\mathrm{Si}}_2{\mathrm{P}}_4$ heterobilayers van der Waals (vdW) multiferroic structures. Our calculations show that the magnetization direction reversal of the ${\mathrm{V}\mathrm{Si}}_2{\mathrm{P}}_4$ layer can be modulated by FE control due to the polarization-field-induced band-structure shift and interfacial charge transfer. On this basis, we design a lateral multiferroic tunnel junction (MFTJ) device with the ${\mathrm{V}\mathrm{Si}}_2{\mathrm{P}}_4$ monolayer acting as the tunneling barrier, which can realize perfect bipolar spin-polarized current and spin-rectification ratio up to 4.0 × ${10}^5$. The underlying mechanism is attributed to the overlap of the spin-dependent density of states in the two electrodes manipulated by FE polarization. Moreover, using the left and right FE layers as two inputs and considering the inverse spin Hall effect as the output, nonvolatile full-electrical writing and reading of magnetization states as well as multifunction spin-logic operations (and, nor, and xnor) are realized. Besides, we further design another MFTJ with the ${\mathrm{Sc}}_2{\mathrm{CO}}_2$ monolayer acting as the tunneling barrier, which demonstrates the tunneling electroresistance (TER) ratio increases with the tunneling barrier length and a giant TER ratio of up to 4.6 × ${10}^{21}$% is achieved. Our findings provide viable strategies to realize nonvolatile high-performance storage and computing functions for spintronic devices based on the ${\mathrm{Sc}}_2{\mathrm{CO}}_2/{\mathrm{V}\mathrm{Si}}_2{\mathrm{P}}_4$ vdW multiferroic heterostructures.

In the past decade, there has been renewed interest in studying materials with time-dependent constitutive parameters. These structures offer solutions to the major limitations of their spatial counterparts, of which metamaterials are a subclass; however, physically realizing such structures is extremely challenging, as controlling the bulk properties of a material periodically and in a controlled manner is a nontrivial task. In contrast, the temporal modulation of a thin impedance layer is more realistic and achievable. In this work, we demonstrate that one of the most significant effects of active materials—the amplified emission of radiation—can be achieved by enclosing a static material within a time-modulated impedance layer. This effect is shown for both one- and two-dimensional cavities. For the latter, we demonstrate that different multipolar modes can be radiated. Additionally, we incorporate angular dependence into the time-modulated impedance, creating the circular analogue of a spatiotemporally modulated material. This enables the radiation of chiral eigenmodes from a circular cavity due to the coupling of time and cylindrical harmonics of the wave field. Our findings indicate that engineered active surfaces can be utilized to develop a new type of lasing system for various classical waves.

We present the optical properties of epitaxial germanium ($\mathrm{Ge}$) thin films as a function of tensile strain from 0% to 1.96%, measured using variable-angle spectroscopic ellipsometry in the energy range of 0.5–4.1 eV. The band structure of unstrained $\mathrm{Ge}$ is modified using epitaxial tensile strain imparted by the underlying compositionally controlled ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ strain template. The degeneracy of $\mathrm{Ge}$’s light-hole (LH) and heavy-hole (HH) bands near the Γ point is lifted due to tensile strain while the Γ and L valleys descend. Such changes in the band structure impact the optical properties of tensile-strained $\mathrm{Ge},$ such as the dielectric constant, refractive index, and absorption coefficient. At the Γ point, it is noticed that the absorption coefficient gradually increases with tensile strain, indicating a shift in the effective band edge of $\mathrm{Ge}$. Further, it is observed that the indirect transitions are dominated by L-LH, whereas the direct transitions are contributed from the Γ-LH as well as the Γ-HH due to the interplay between the transition energy and joint density of states. In addition, the tensile strain is seen to affect the band structure at different regions in the Brillouin zone (BZ) resulting in the movement of the critical points (CPs) to lower energy in the optical spectrum. The $E_1$ and $E_1$+ Δ${}_1$ CPs in tensile-strained $\mathrm{Ge}$ are redshifted compared with unstrained $\mathrm{Ge}$. The observed movement of the $E_1$, and $E_0$ CP peaks is in close agreement with the first principles calculated band structure. Further, the apparent value of the $E_0$ spin-orbit (SO) energy, Δ${}_0$ is seen to decrease with increasing tensile strain at the Γ point. Interestingly, the $E_1$ SO energy, Δ${}_1$ at the Λ direction in the BZ remains constant, indicating a very low shear deformation-related shift in the band structure due to biaxial tensile strain. As tensile-strained $\mathrm{Ge}$ thin films have a wide range of potential applications in electronics, sensing, and photonics, further understanding of tensile strain in $\mathrm{Ge}$ and its impact on its dielectric and optical properties is essential.

In conventional variational quantum eigensolvers (VQEs), trial states are prepared by applying series of parametrized gates to a reference state, with the gate parameters being varied to minimize the energy of the target system. Recognizing that the gates are intermediates, which are ultimately compiled into a set of control pulses to be applied to each qubit in the lab, the recently proposed ctrl-VQE algorithm takes the amplitudes, frequencies, and phases of the pulse as the variational parameters used to minimize the molecular energy. In this work, we explore how all 3 degrees of freedom interrelate with one another. To this end, we consider several distinct strategies to parametrize the control pulses, assessing each one through numerical simulations of a transmonlike device. For each parametrization, we contrast the pulse duration required to prepare a good ansatz, and the difficulty to optimize that ansatz from a well-defined initial state. We deduce several guiding heuristics to implement practical ctrl-VQE in hardware, which we anticipate will generalize for generic device architectures.

Certain quantum sensing protocols rely on qubits that are initialized, coherently driven in the presence of a stimulus to be measured, then read out. The most widely employed driving sequences act locally in the frequency domain. We introduce and experimentally demonstrate a generalized set of sequences that effect a measurement in any fractional Fourier domain, i.e., along a linear trajectory of arbitrary angle through the time-frequency plane. Combined with linear frequency modulation, this scheme could help separate signal from background in nanoscale spectroscopy and other applications.

“Chirality” refers to the property that an object and its mirror image cannot overlap each other by spatial rotation and translation. Chirality can be found in various research fields. Here we propose chiral chaos and design a chiral chaotic device using whispering gallery mode resonators and tips, where the routes to chaos exhibit pronounced chirality for two pumping directions. The mechanism underlying chirality is that time-reversal symmetry of traveling-wave light fields is regulated by tips, and chaos originates from the nonlinear optomechanical interactions. We propose metrics based on the Lyapunov exponents to quantify the symmetry and chirality between routes to chaos. We show that the proposed chiral chaotic device can be applied to achieve sensing with high sensitivity, a broad detectable range, and strong robustness regarding phase and orientation randomness of weak signals. Our work provides a promising candidate for on-chip sensing and may have applications in chaotic networks and chaotic communications.

Quantum information is very fragile to environmentally and operationally induced imperfections. Therefore, the construction of practical quantum computers requires quantum error-correction techniques to protect quantum information. In particular, encoding a logical qubit into the large Hilbert space of an oscillator is a hardware-efficient way of correcting quantum errors. In this strategy, selective number-dependent arbitrary phase (SNAP) gates are vital for universal quantum control. However, the quality of SNAP gates is considerably limited by the small coupling-induced nonlinearity of the oscillator. Here, to resolve this limitation, we propose a robust scheme based on quantum optimal control via functional theory, by designing an appropriate trajectory for a target operation. Besides, we combine the geometric phase approach with our trajectory design scheme to minimize the decoherence effect, by shortening the gate time. Numerical simulation shows that both errors can be significantly mitigated and that the robustness of the geometric gate against both $X$ and $Z$ errors can be maintained. Therefore, our scheme provides a promising alternative for fault-tolerant quantum computation.