We consider nanoflakes of van der Waals ferrielectric ${\mathrm{Cu}\mathrm{In}\mathrm{P}}_2{\mathrm{S}}_6$ covered by an ionic surface charge and reveal the appearance of polar states with a relatively large polarization of approximately 5 µC/${\mathrm{cm}}^2$ and stored free charge of around 10 µC/${\mathrm{cm}}^2$, which can mimic “midgap” states associated with a surface-field-induced transfer of $\mathrm{Cu}$ and/or $\mathrm{In}$ ions in the van der Waals gap. The change in the ionic screening degree and mismatch strains induce a broad range of the transitions between paraelectric phase, antiferroelectric, ferrielectric, and ferri-ionic states in ${\mathrm{Cu}\mathrm{In}\mathrm{P}}_2{\mathrm{S}}_6$ nanoflakes. The states’ stability and/or metastability is determined by the minimum of the system free energy consisting of electrostatic energy, elastic energy, and a Landau-type four-well potential of the ferrielectric dipole polarization. The possibility of governing the transitions by strain and ionic screening can be useful for controlling the tunneling barrier in thin-film devices based on ${\mathrm{Cu}\mathrm{In}\mathrm{P}}_2{\mathrm{S}}_6$ nanoflakes. Additionally, we predict that the ${\mathrm{Cu}\mathrm{In}\mathrm{P}}_2{\mathrm{S}}_6$ nanoflakes reveal features of the controllable negative capacitance effect, which make them attractive for advanced electronic devices, such as nanocapacitors and gate oxide nanomaterials with reduced heat generation.

Efficient quantum sensing technologies rely on the precise control of quantum sensors, particularly two-level systems or qubits, to optimize estimation processes. We here exploit the quantum Zeno effect (QZE) as a tool for maximizing information obtainable by quantum sensors, with a specific focus on the level avoided-crossing (LAC) phenomenon in qubit systems. While the estimation of the LAC energy splitting has been extensively studied, we emphasize the crucial role that the QZE can play in estimating the coupling strength. We introduce the concept of information amplification by the QZE for a LAC system under off-resonant conditions. The proposed approach has implications for ac magnetic field sensing and the characterization of complex systems, including many-spin systems requiring the estimation of spin-spin couplings. Overall, our findings contribute to the advancement of quantum sensing by leveraging the QZE for improved control and information extraction.

Solution-processed molybdenum disulfide (${\mathrm{Mo}\mathrm{S}}_2$) shows promise for tunable photonics and optoelectronics development. However, though scalable, it often leads to devices with inferior performance as a result of its random, discrete nature. In this study, we show via density-functional-theory calculations that the electronic structure of the individual solution-processed nanosheets can be modulated collectively by external electric fields. Particularly, the nanosheets can form Stark ladders, giving variations in the underlying optical processes and thus tunable collective optical properties. We confirm this electro-optical modulation experimentally using solution-processed ${\mathrm{Mo}\mathrm{S}}_2$ films with ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] incorporated, and prove that the local polarization fields from P(VDF-TrFE) can modulate the collective optical properties of the ${\mathrm{Mo}\mathrm{S}}_2$, specifically, the optical absorption and photoluminescence. Given the scalability of solution processing, our results underpin the potential of electro-optical modulation of solution-processed ${\mathrm{Mo}\mathrm{S}}_2$ for tunable photonics and optoelectronics development. To illustrate this potential, we demonstrate solution-processed electroabsorption modulators.

Defects in semiconductors have in recent years been revealed to have interesting properties in the venture towards quantum technologies. In this regard, silicon carbide has shown great promise as a host for quantum defects. In particular, the ultrabright AB photoluminescence lines in $4H\text{−}\mathrm{Si}\mathrm{C}$ are observable at room temperature and have been proposed as a single-photon quantum emitter. These lines have previously been studied and assigned to the carbon–antisite-vacancy (CAV) pair. In this paper, we report on new measurements of the AB lines’ temperature dependence, and carry out an in-depth computational study on the optical properties of the CAV defect. We find that the CAV defect has the potential to exhibit several different zero-phonon luminescences with emissions in the near-infrared telecom band, in its neutral and positive charge states. However, our measurements show that the AB lines only consist of three nonthermally activated lines instead of the previously reported four lines; meanwhile, our calculations on the CAV defect are unable to find optical transitions in full agreement with the AB-line assignment. In light of our results, the identification of AB lines and the associated room-temperature emission require further study.

Polar skyrmions are unique particlelike swirling polarization textures with nontrivial topology. So far, they have mainly been discovered in ferroelectric-insulator superlattices and multilayers, showing a densely packed and liquidlike state that suffers strong interactions with neighbors. This makes it challenging to develop storage and logic devices based on polar skyrmions, and limits the exploration of the potentially unique properties of polar skyrmion lattices. An important and interesting question, therefore, is the following: Can we construct artificial polar skyrmion arrays with regular spatial distribution and weak correlation in ferroelectrics? Here, via phase-field simulations, we demonstrate a spatial modulation strategy for the construction of regularly distributed and weakly correlated artificial polar skyrmion arrays in ferroelectric thin film. The crossbar electrode pattern on the top surface of the ferroelectric thin film is introduced in the simulated model to create the spatial modulation effect. The stability of the artificial polar skyrmion arrays is summarized by the use of phase diagrams. These polar skyrmions are illustrated to be individually controllable by local electric and mechanical stimuli. Moreover, a mechanism of weak correlation between the skyrmions is elucidated, and a dimerization phenomenon of artificial polar skyrmion arrays akin to the antiferroelectric distortion is revealed. Our work, therefore, provides a new approach to constructing intriguing polar topological textures in ferroelectrics and offers promising possibilities for developing devices based on polar topology.

Error suppression to the experimental imperfections is a central challenge for useful quantum computing. Recent studies have shown the advantages of using single-modulated pulses based on optimal control, which can realize high-fidelity two-qubit gates in neutral-atom arrays. However, typical optimization minimizes only the ideal gate error in the absence of any decay, which allows the gate to be passively influenced by all error sources leading to an exponential increase of the insensitivity when error becomes larger. In the present work, we propose the realization of two-qubit $C_Z$ gates with active robustness against two-photon detuning errors. Our method depends on a modified cost function in numerical optimization for shaping gate pulses, which minimizes, not only the ideal gate error but also the fluctuations of gate infidelity over a wide error range. We introduce a family of Rydberg blockade gates with active robustness towards the impacts of versatile noise sources such as Doppler dephasing and ac Stark shifts. The resulting gates with robust pulses can significantly increase the insensitivity to any type of errors acting on the two-photon detuning, benefiting from a relaxed requirement of colder atomic temperatures or more stable lasers for current experimental technology.

Dissipation engineering offers a powerful tool for quantum technologies. Recently, new superconducting devices have achieved an engineered two-photon dissipation rate exceeding all other relevant timescales. In particular, they have proven most useful in preventing transitions between the logical states $|\pm \alpha ⟩$ of a cat qubit. Here, we present three key applications of strong two-photon dissipation for quantum measurement and control, beyond cat qubit stabilization. Firstly, we demonstrate its efficacy in overcoming limitations encountered in Wigner tomography at high photon numbers. Secondly, we showcase its potential for realizing universal gates on cat qubits, exploiting the coherent mapping between cat qubit states and superpositions of 0 and 1 photons. Finally, we harness the transient dynamics of a cat state under two-photon dissipation to prepare squeezed cat states with a squeezing factor exceeding $3.96\pm 0.07$ dB.

The writing energy for reversing the magnetization of the free layer in a magnetic tunnel junction (MTJ) is a key figure of merit for comparing the performances of magnetic random-access memories with competing technologies. Magnetization switching of MTJs induced by spin torques typically relies on square voltage pulses. Here, we focus on the switching of perpendicular MTJs driven by spin-orbit torque (SOT), for which the magnetization reversal process consists of sequential domain nucleation and domain-wall propagation. By performing a systematic study of the switching efficiency and speed as a function of pulse shape, we show that shaped pulses achieve up to 50% reduction of writing energy compared to square pulses without compromising the switching probability and speed. Time-resolved measurements of the tunneling magnetoresistance reveal how the switching times are strongly impacted by the pulse shape and temperature rise during the pulse. The optimal pulse shape consists of a preheating phase, a maximum amplitude to induce domain nucleation, and a lower amplitude phase to complete the reversal. Our experimental results, corroborated by micromagnetic simulations, provide diverse options to reduce the energy footprint of SOT devices in magnetic memory applications.

Quantum communication and quantum metrology are widely compelling applications in the field of quantum information science, and quantum remote sensing is an intersection of both. Despite their differences, there are notable commonalities between quantum communication and quantum remote sensing, as they achieve their functionalities through the transmission of quantum states. Here we propose a quantum integrated sensing and communication (QISAC) protocol, which achieves quantum sensing under the Heisenberg limit while simultaneously enabling quantum secure communication through the transmission of entanglements. We have theoretically proven its security against eavesdroppers. The security of QISAC is characterized by the secrecy capacity for the information bit as well as asymmetric Fisher information gain for sensing. Through simulations conducted under the constraints of limited entanglement resources, we illustrate that QISAC maintains high accuracy in the estimation of phase. Hence, our QISAC offers a fresh perspective for applications of future quantum networks.

Inks deposited in conventional direct ink writing need to be able to support their own weight and that of the upper layers with minimal deformation to preserve the structural integrity of the three-dimensional (3D) printed parts. This constraint limits the range of usable inks to high-viscosity materials. Embedded printing enables the use of much softer inks by depositing the materials in a bath of another fluid that provides external support, thus diversifying the types of 3D printable structures. The interactions between the ink and bath fluids, however, give rise to a unique type of defect: spreading of the dispensed ink behind the moving nozzle. By printing horizontal threads made of dyed water in baths of Carbopol suspensions, we demonstrate that the spreading can be attributed to the pressure field generated in the viscous bath by the relative motion of the nozzle. As the pressure gradient increases with the viscosity of the bath fluid while the viscosity of the ink resists the flow, a larger bath-to-ink viscosity ratio results in more spreading for low-concentration Carbopol baths. For high-concentration, yield-stress-fluid baths, we find that the steady-state viscosity alone cannot account for the spreading, as the elastic stress becomes comparable to the viscous stress and the bath fluid around the dispensed ink undergoes fluidization and resolidification. By parameterizing the transient rheology of the high-concentration Carbopol suspensions using a simple viscoelastic model, we suggest that the ink spreading is exacerbated by the elasticity, but is mitigated by the yield stress as long as the yield stress is low enough to allow steady injection of the ink. These results help illuminate the link between the bath rheology and the printing quality in embedded 3D printing.

This study systematically explores the mechanical, transport, and thermoelectric properties of the alkali antimonide compounds $M_3\mathrm{Sb}$ ($M$ = $\mathrm{Na}$, $\mathrm{K}$, $\mathrm{Rb}$, $\mathrm{Cs}$) using first-principles calculations and the Boltzmann transport equation. We found that considering quartic anharmonic effects leads to temperature-dependent phonons undergoing a frequency shift and overall phonon spectrum hardening, thereby increasing the phonon group velocity. Additionally, this study reveals that alkali-metal atoms play an important role in the phonon frequency of $M_3\mathrm{Sb}$ ($M$ = $\mathrm{Na}$, $\mathrm{K}$, $\mathrm{Rb}$, $\mathrm{Cs}$). The quartic anharmonicity strengthens as the mass of the alkali-metal atom increases. Moreover, as the atomic number of alkali-metal atoms increases, the interaction between atoms weakens, resulting in a gradual decrease in bulk modulus ($B$), shear modulus ($G$), and Young’s modulus ($E$). We also observe that, beyond 400 K, the lattice thermal conductivity ${\kappa }_L$ of ${\mathrm{Rb}}_3\mathrm{Sb}$ is lower than that of ${\mathrm{Cs}}_3\mathrm{Sb}$, which is mainly attributed to the larger scattering rate of ${\mathrm{Rb}}_3\mathrm{Sb}$. By considering various scattering mechanisms, we obtain reasonable electron relaxation times and electron transport properties. Because of the large electronic dispersion band at the conduction-band minimum, $p$-type $M_3\mathrm{Sb}$ exhibits high electron mobility. Finally, owing to the low lattice ${\kappa }_L$ and good power factor, these four $p$-type alkali antimonide compounds demonstrate excellent thermoelectric performance.

The identification of nonclassical features of multiphoton quantum states represents a crucial task in the development of many quantum photonic technologies. Under realistic experimental conditions, a photonic quantum state gets affected by its interaction with several nonideal optoelectronic devices, including those used to guide, detect, or characterize it. The result of such noisy interaction is that the nonclassical features of the original quantum state get considerably reduced or are completely absent in the detected, final state. In this work, the self-learning features of artificial neural networks are exploited to experimentally show that the nonclassicality of multiphoton quantum states can be assessed and fully characterized, even in the cases in which the nonclassical features are concealed by the measuring devices. Our work paves the way toward artificial-intelligence-assisted experimental-setup characterization, as well as smart quantum state nonclassicality identification.

Satellite-based quantum communication is a promising approach for establishing global-scale quantum networks. In free-space quantum channels, single-mode-fiber coupling plays a crucial role in increasing the signal-to-noise ratio of daylight quantum key distribution (QKD) and ensuring compatibility with standard fiber-based QKD protocols. However, consistently achieving high efficiency and stable single-mode-fiber coupling under strong atmospheric turbulence remains an ongoing experimental challenge. In this study, we experimentally demonstrate an adaptive method based on convolutional neural networks capable of directly estimating phase information from a single defocused image. We developed a convolutional neural network to establish the relationship between intensity distribution and phase information of turbulent distortions. We demonstrate the real-time performance of our deep-learning adaptive method in increasing single-mode-fiber coupling efficiency across various turbulence scales and quantify turbulence frequencies. Notably, the method proved highly effective in strong-turbulence scenarios, with frequencies reaching up to 200 Hz, leading to a significant increase in single-mode-fiber coupling efficiency. We demonstrate the corrective capability of our adaptive method for strong turbulence, enabled by the generalization of the convolutional neural network. Our results offer an efficient solution for daytime free-space QKD applications.

Nonreciprocity of propagation of surface acoustic waves (SAWs) in the microwave frequency band can be achieved using the magnetoelastic interaction of SAWs with spin waves (SWs) propagating in magnetic heterostructures. Recent works have shown that the ultimate isolation of a counterpropagating hybridized SAW/SW is achieved in heterostructures consisting of a synthetic antiferromagnet—a ferromagnetic (FM) bilayer with antiferromagnetic Ruderman-Kittel-Kasuya-Yosida interlayer coupling—placed on top of a piezoelectric acoustic waveguide. In this work, we study in detail a more practical and technologically simpler system based on an FM bilayer, where layers are coupled by only dipole-dipole interaction, and having noncollinear magnetizations of the FM layers. A weak in-plane anisotropy with noncollinear easy axes in the layers is shown to be the only essential factor for the realization of strongly nonreciprocal propagation of a hybridized SAW/SW. We formulate requirements for the relative orientation of the layer’s magnetizations and wave propagation direction necessary to realize an efficient SAW isolator, and demonstrate examples of SAW transmission characteristics which prove the possibility of achieving an isolation exceeding 50 dB for a submillimeter-long FM bilayer with insertion losses of just a few decibels more than those of a pure SAW device. In addition to relative fabrication simplicity, the proposed magnetoelastic heterostructure exhibits a reasonable robustness in respect to deviations in the anisotropy axes and/or bias field directions—an important benefit for device mass production.

Using modulation transfer spectroscopy, we achieve the frequency stabilization of a high-power 3-W blue laser at the wavelength of 420 nm to the $\mathrm{Rb}$ $5S_{1/2}$–$6P_{3/2}$ transition. The in-loop frequency stability of this laser is $1.8\times {10}^{-11}/\sqrt{\tau }$, reaching $1.7\times {10}^{-12}$ at 100 s and $7\times {10}^{-13}$ at 1000 s. An external power feedback loop is established using an acousto-optic modulator, employing the zeroth-order diffracted light for power stabilization, achieving an in-loop power stability of $1.0\times {10}^{-6}$ at 1 s. Moreover, the continuous mode-hop free interval of this high-power laser can simultaneously cover the $5S_{1/2}$–$6P_{3/2}$ transitions of ${}^{85}\text{Rb}$ and ${}^{87}\text{Rb}$, with successful locking achieved for both isotopes, providing a comprehensive analysis of the $\mathrm{Rb}$ atomic transitions in the blue spectral region. As an application, this 3-W 420-nm laser with excellent power and frequency stabilities is used as a repumping source for diffuse laser cooling of ${}^{87}\text{Rb}$ atoms, realizing a one-meter-long cold-atom cloud. This paves the way for using blue-light cooling to realize a cold-$\mathrm{Rb}$-atom active optical clock. In addition, the ultrahigh-stability 420-nm laser also finds applications in various fields such as the Rydberg atom experiment, Bose-Einstein condensation, ultranarrow-bandwidth Faraday atomic filter, and so on.

Optical illumination of quantum dot qubit devices at cryogenic temperatures, while not well studied, is often used to recover operating conditions after undesired shocking events or charge injection. Here, we demonstrate systematic threshold-voltage shifts in a dopant-free $\mathrm{Si}$/$\mathrm{Si}$${}_{0.7}$$\mathrm{Ge}$${}_{0.3}$ field-effect transistor using a near-infrared (780-nm) laser diode. We find that illumination under an applied gate voltage can be used to set a specific, stable, and reproducible threshold voltage that, over a wide range in gate bias, is equal to that gate bias. Outside this range, the threshold voltage can still be tuned, although the resulting threshold voltage is no longer equal to the applied gate bias during illumination. We present a simple and intuitive model that provides a mechanism for the tunability in the gate bias. The model presented also explains why cryogenic illumination is successful at resetting quantum dot qubit devices after undesired charging events.

We propose and demonstrate a static quantum dot on a potential hilltop to generate and analyze ballistic hot electrons along a quantum Hall edge channel well above the chemical potential. High-energy resolution associated with discrete energy levels is attractive for studying hot-electron dynamics. In particular, the energy distribution function of hot electrons weakly coupled to cold electrons is investigated to reveal spectral diffusion with energy relaxation. The analysis allows us to estimate the maximum energy exchange per scattering, which is a key parameter to describe interacting electrons in the edge channel.

We address the photonic spin-orbit coupling known from nano-optics and plasmonics in the microwave regime. The spin $\mathbf{S}$ and momentum $\mathbf{q}$ of microwaves emitted by an excited magnetic particle are locked by $\mathbf{q}\cdot \mathbf{S}=0$ with a fixed chirality $\hat{\mathbf{n}}\cdot (\hat{\mathbf{S}}\times \hat{\mathbf{q}})=1$ when evanescent along $\hat{\mathbf{n}}\perp \mathbf{q}$. This field excites magnons in a nearby magnetic film in the form of directional beams that rotate with the magnetization direction. The exchange of these magnons between two distant nanomagnets leads to a highly tunable strong coupling and entangles their excited states.

Machine learning is becoming a widely used technique with impressive growth due to the diversity of problems of societal interest for which it can offer practical solutions. This increase of applications and required resources start to become limited by present-day hardware technologies. Indeed, novel machine learning subjects such as large language models or high-resolution image recognition raise the question of large computing time and energy cost of the required computation. In this context, optical platforms have been designed for several years with the goal of developing more efficient hardware for machine learning. Among different explored platforms, optical free-space propagation offers various advantages: parallelism, low energy cost, and computational speed. Here, we present a new design combining the strong and tunable nonlinear properties of a light beam propagating through a hot atomic vapor with an extreme learning machine model. We numerically and experimentally demonstrate the enhancement of the training using such free-space nonlinear propagation on an MNIST image classification task. We point out different experimental hyperparameters that can be further optimized to improve the accuracy of the platform.