Quantum memories play a key role in facilitating tasks within quantum networks and quantum information processing, including secure communications, advanced quantum sensing, and distributed quantum computing. Progress in characterizing large nuclear-spin registers coupled to defect electronic spins has been significant, but selecting memory qubits remains challenging due to the multitude of possible assignments. Numerical simulations for evaluating entangling gate fidelities encounter obstacles, restricting research to small registers, while experimental investigations are time-consuming and often limited to well-understood samples. Here we present an efficient methodology for systematically assessing the controllability of defect systems coupled to nuclear-spin registers. We showcase the approach by investigating the generation of entanglement links between silicon monovacancy or divacancy centers in $\mathrm{Si}\mathrm{C}$ and randomly selected sets of nuclear spins within the two-species (${}^{13}\mathrm{C}$ and ${}^{29}\mathrm{Si}$) nuclear register. We quantify the performance of entangling gate operations and present the achievable gate fidelities, considering both the size of the register and the presence of unwanted nuclear spins. We find that some control sequences perform better than others depending on the number of target versus bath nuclei. This efficient approach is a guide for both experimental investigation and engineering, facilitating the high-throughput exploration of suitable defect systems for quantum memories.

External-quantum-efficiency (EQE) roll-off is a key challenge for perovskite light-emitting diodes (PeLEDs), limiting their applications where high brightness is needed. Auger recombination and Joule heating are considered the main issues behind the EQE roll-off in PeLEDs. Despite intensive efforts to address these issues, roll-off in PeLEDs remains significant, indicating important roles played by other factors. We now investigate the carrier dynamics during the EQE roll-off of PeLEDs by employing in situ time-resolved photoluminescence. We identify that accelerated trap-assisted recombination at high current densities is a key reason behind roll-off. Inspired by this new understanding, we introduce a molecule that successfully restrains the activation of trap states and hence significantly suppresses EQE roll-off. As such, our results pave the way toward the development of high-brightness PeLEDs.

Reinforcement learning is a subfield of machine learning that is having a huge impact in the different conventional disciplines, including physical sciences. Here, we show how reinforcement learning methods can be applied to solve optimization problems in the context of radiative heat transfer. We illustrate their use with the optimization of the near-field radiative heat transfer between multilayer hyperbolic metamaterials. Specifically, we show how this problem can be formulated in the language of reinforcement learning and tackled with a variety of algorithms. We show that these algorithms allow us to find solutions that outperform those obtained using physical intuition. Overall, our work shows the power and potential of reinforcement learning methods for the investigation of a wide variety of problems in the context of radiative heat transfer and related topics.

Gaussian channel simulation is an essential paradigm in understanding the evolution of bosonic quantum states. It allows us to investigate how such states are influenced by the environment and how they transmit quantum information. This makes it an essential tool for understanding the properties of Gaussian quantum communication. Quantum teleportation provides an avenue to effectively simulate Gaussian channels, such as amplifier channels, loss channels, and classically additive noise channels. However, implementations of these channels, particularly quantum amplifier channels and channels capable of performing Gaussian noise suppression, are limited by experimental imperfections and nonideal entanglement resources. In this work, we overcome these difficulties using a heralded quantum teleportation scheme that is empowered by a measurement-based noiseless linear amplifier. The noiseless linear amplification enables us to simulate a range of Gaussian channels that were previously inaccessible. In particular, we demonstrate the simulation of nonphysical Gaussian channels otherwise inaccessible using conventional means. We report Gaussian noise suppression, effectively converting an imperfect quantum channel into a near-identity channel. The performance of Gaussian noise suppression is quantified by calculating the transmitted entanglement.

High-power measurement-induced cavity response is investigated in the $|g⟩$, $|e⟩$, and $|f⟩$ states of a transmon. All the states exhibit photon blockades above a certain critical value, a phenomenon that has previously been understood based on the bistability of semiclassical Duffing oscillators. The measurement-induced state transition (MIST) to high-level transmon states is expected to be one contributor to the bistability; however, the critical values measured in the $|e⟩$ and $|f⟩$ states are not coincident with the MIST. To understand this discrepancy, we utilize the recently developed semiclassical dynamics model of a cavity photon state. The appearance of dim and bright cavity states obtained from the model’s steady-state solution leads to the photon blockades at lower critical photon numbers, and this can explain the response of the bistable region in the $|e⟩$ and $|f⟩$ states.

Precision enhancement is demonstrated in an optical spatial measurement based on a weak-value amplification (WVA) system and splitlike detection, by injecting a ${\mathrm{TEM}}_{10}$ squeezed vacuum beam. We have experimentally realized high-precision optical spatial measurement beyond the shot-noise limit by using squeezing-assisted WVA. Based on the WVA technique, which can amplify the signal by increasing the number of photons that are injected into the interferometer, squeezed-beam injection can reduce the noise level and can further improve the signal-to-noise ratio (SNR). As a result, an SNR improvement of 2 dB, i.e., 1.3 times precision enhancement, can be achieved, and the obtained displacement and tilt sensitivity are $4.96\mathrm{fm}/\sqrt{\text{Hz}}$ and $0.39\mathrm{prad}/\sqrt{\text{Hz}}$, respectively, by using a 2-dB squeezed-beam injection and 2.6% postselection probability in the WVA process. Our work provides an effective method to accomplish higher precision in quantum spatial measurement, which has potential applications in gravitational wave interferometer calibration, super-resolution quantum imaging, etc.

Quantum information processing (QIP) based on high-dimensional quantum systems provides unique advantages and new potentials where high-dimensional quantum correlations (QCs) play vital roles. Exploring the resistance of QCs against noises is crucial as QCs are fragile due to complex and unavoidable system-environment interactions. In this study, we investigate the performance of high-dimensional QCs under local dephasing noise using a single nitrogen-vacancy center in diamond. A freezing phenomenon in the high-dimensional quantum discord dynamics was observed, showing that discord is robust against local dephasing noise. Utilizing a robustness metric known as the freezing index, we find that the discord of qutrits outperforms their qubit counterparts when confronted with dephasing noise. Furthermore, we develop a geometric picture to explain this intriguing freezing phenomenon. Our findings highlight the potential of utilizing discord as a physical resource for advancing QIP in high-dimensional quantum settings.

With the development of nanotechnology, there has been great interest in manipulating nanomaterials. However, the development of manipulating techniques still faces challenges and is slower than that of nanomaterial fabrication techniques. The key to solving this problem is to develop universal nanomotors that can provide energy to overcome the large interfacial resistance caused by the high surface-to-volume ratio at the nanoscale. Photothermal gradient forces generated by photothermal shock have been demonstrated to drive nanomaterials on dry, flat substrates. Yet, the driving mechanism for the motion of semisuspended nanomaterials with a single-point contact remains unclear. In this work, we demonstrate metal nanowire rotation motors that operate on the curved surfaces of silica microfibers. The theoretical analysis proves the unified principle of body and surface forces and confirms that the direct driving power source is the internal stress, a generalized surface force. Experimentally, we achieve pure and stable in situ rotation of single nanowires without axial translation and rotation of multinanowire assemblies. Our work provides a firm foundation for using transient photothermal gradient forces to manipulate nanomaterials at the nanoscale and broadens the potential applications of nanomotors.

The paper describes the means to reveal and characterize slow periodic modulation of the qubit frequency. Such modulation can come from different sources and can impact qubit stability. We show that the modulation leads to very sharp peaks in the power spectrum of outcomes of periodically repeated Ramsey measurements. The positions and shapes of the peaks allow us to find both the frequency and the amplitude of the modulation. We also explore how additional slow fluctuations of the qubit frequency and fluctuations of the modulation frequency affect the spectrum. The analytical results are in excellent agreement with extensive simulations.

Valleytronics, exploring the valley degree of freedom in crystals akin to the charge in electronics and spin in spintronics, holds tremendous potential for information processing and computing in next-generation devices. We investigated the spin and valley manipulation of a $2H$-${\text{VSe}}_2$ monolayer by stacking a ferroelectric substrate, ${\text{AgBiP}}_2{\text{Se}}_6$, to form a van der Waals heterostructure, ${\text{VSe}}_2/{\text{AgBiP}}_2{\text{Se}}_6$, whose lattice mismatch is only 0.44%. Because the band alignment between ${\text{VSe}}_2$ and ${\text{AgBiP}}_2{\text{Se}}_6$ is type I, the valley property at both the valence band and conduction band is well maintained, and the heterostructure exhibits an anomalous valley Hall effect. By switching the ferroelectric polarization direction, valley polarization can be effectively tuned, and the manipulation is nonvolatile because the heterostructure holds the ferroelectric bistability property. When the ferroelectric polarization points to ${\text{VSe}}_2$, interlayer sliding can give rise to obvious valley polarization changes with a small sliding potential, and by interlayer charge transfer, the exchange coupling of $\mathrm{V}$ atoms can be obviously tuned, and therefore the Curie temperature is enhanced from 680 K to 975 K.

Exceptional points, a remarkable phenomenon in physical systems, have been exploited for sensing applications. It has been demonstrated recently that they can also operate as sensory thresholds in which the interplay between exceptional-point dynamics and noise can lead to enhanced performance. Most existing works focused on second-order exceptional points. We investigate the stochastic dynamics associated with higher-order exceptional points with a particular eye towards optimizing sensing performance by developing a theoretical framework based on pseudo-Hermiticity. Our analysis reveals three distinct types of frequency responses to external perturbations. A broad type of stochastic resonance is uncovered where, as the noise amplitude increases, the signal-to-noise ratio reaches a global maximum rapidly, but with a slow decaying process afterwards, indicating achievable high performance in a wide range of the noise level. These results suggest that stochastic higher-order exceptional-point dynamics can be exploited for applications in signal processing and sensor technologies.

Scintillation describes the conversion of high-energy particles into light in transparent media and finds diverse applications such as high-energy particle detection and industrial and medical imaging. This process operates on multiple timescales, with the final radiative step consisting of spontaneous emission, which can be modeled within the framework of quasiequilibrium fluctuational electrodynamics. Scintillation can therefore be controlled and enhanced via nanophotonic effects, which has been proposed and experimentally demonstrated. Such designs have thus far obeyed Lorentz reciprocity, meaning there is a direct equivalence between scintillation emission and absorption by the scintillator. However, scintillators that do not obey Lorentz reciprocity have not been explored, even though they represent an alternative platform for probing emission, which is both nonequilibrium and nonreciprocal in nature. In this work, we propose to harness nonreciprocity to achieve directional control of scintillation emission, granting an additional degree of control over scintillation. Such directionality of light output is useful in improving collection efficiencies along the directions where detectors are located. We present the design of a nonreciprocal scintillator using a one-dimensional magnetophotonic crystal in the Voigt configuration. Our work demonstrates the potential of controlling nonequilibrium such as scintillation by breaking reciprocity and expands the space of nanophotonic design for achieving such control.

We investigate the occurrence of direct and dual Shapiro steps for a Josephson junction coupled to a finite-size-transmission-line resonator. We treat both problems through a circuit-QED approach with a large but finite number of photon modes. For the dual case, we do not assume there is (approximate) charge-phase duality, but include the full multiband dynamics for the Josephson junction. Mean-field equations within such a Hamiltonian approach reproduce the result obtained through a dissipative classical equation when the number of transmission-line modes is large enough. To account for quantum and thermal fluctuations, we go beyond the mean-field treatment within a truncated Wigner approach. The fluctuations are shown to modify both the direct steps and the dual steps. We show how the dual steps are very sensitive to these fluctuations and identify the key physical parameters for the junction and the transmission line controlling their robustness, which is essential for applications to close the quantum metrological triangle.

Heat-assisted magnetic recording (HAMR) is a promising high-density-data-storage technology whose intensive practical deployment requires a perfect balance of many factors, including device reliability, which is challenged by severe writing conditions. In this work, we propose HAMR media composed of $\mathrm{Fe}$-$\mathrm{Pt}$/$\mathrm{Ru}$/$\mathrm{Fe}$-$\mathrm{Pt}$ trilayer nanograins embedded in a carbon segregating matrix. When the $\mathrm{Ru}$ nonmagnetic spacer is thinner than 2 nm, the $\mathrm{Fe}$-$\mathrm{Pt}$ layers were found to be exchange-coupled and to exhibit different Curie temperatures, which is beneficial for lowering the HAMR writing temperature. Given the grain size of 17 nm, sufficient thermal stability was preserved according to the time dependence of coercivity analyzed with use of the Sharrock equation. The granular microstructure of $\mathrm{Fe}$-$\mathrm{Pt}$/$\mathrm{Ru}$/$\mathrm{Fe}$-$\mathrm{Pt}$ films with different $\mathrm{Ru}$ thicknesses was examined in detail, while their magnetic properties were interpreted by micromagnetic simulations distinguishing the properties of individual $\mathrm{Fe}$-$\mathrm{Pt}$ layers. Grain-size reduction, suppression of in-plane variants, and improvement of the degree of ${\mathrm{LI}}_0$ order in the top $\mathrm{Fe}$-$\mathrm{Pt}$ layer are further steps to optimize the developed exchange-coupled $\mathrm{Fe}$-$\mathrm{Pt}$/$\mathrm{Ru}$/$\mathrm{Fe}$-$\mathrm{Pt}$ nanogranular films that would open an avenue for tuning the HAMR media toward their ultimate performance.

Optical clocks represent the most precise experimental devices, finding application in fields spanning from frequency metrology to fundamental physics. Recently, a highly-charged-ion- (HCI) based optical clock was demonstrated using ${\mathrm{Ar}}^{13+}$, opening up a plethora of alternative systems with advantageous atomic properties for high-accuracy clocks. While numerous candidate systems have been explored theoretically, the considerable uncertainty of the clock transition frequency for most species poses experimental challenges. Here, we close this gap by exploring quantum-logic-inspired experimental search techniques for subhertz clock transitions in HCIs confined to a linear Paul trap. These techniques encompass Rabi excitation, an optical dipole force approach, and linear continuous sweeping and their applicability for different types of HCI. Through our investigation, we provide tools to pave the way for the development of exceptionally precise HCI-based optical clocks.

Single-shot ultrafast optical imaging enables the visualization of dynamic scenes at ultrahigh temporal resolution, serving as an indispensable tool for studying nonrepeatable ultrafast phenomena. By employing a time-wavelength mapping within an illumination pulse or pulse train, wavelength-multiplexing ultrafast optical imaging has played a crucial role in observing the ultrafast interactions between laser and materials. However, achieving single-shot wavelength-multiplexing ultrafast imaging with large sequences and high fidelity remains a significant challenge due to spatiotemporal multiplexing in detection. This limitation hinders the accurate analysis of ultrafast phenomena. Here, we report a demosaicing algorithm-based chirped spectral-mapping ultrafast photography, termed DMA-CSMUP, which enables ultrafast imaging with high fidelity and large sequences. DMA-CSMUP can capture up to 42 sequential images in a single shot by combining multiple spectral bands with different hyperspectral cameras. Meanwhile, a joint demosaicing and denoising algorithm is developed to enhance image fidelity significantly and avoid pixel loss caused by mosaic filter arrays. The powerful detection capability of DMA-CSMUP is verified experimentally by imaging the plasma generation and shockwave expansion in glass, as well as the ablation dynamics on a silicon surface induced by a femtosecond laser pulse. DMA-CSMUP provides a well-established tool for observing ultrafast dynamics with high-resolution temporal and spatial information, which is anticipated to facilitate the research of various ultrafast phenomena.

A hitherto unexploited characteristic feature of emerging iontronic devices for information processing is the intrinsic mobility of the medium (water) of dissolved ions in aqueous electrolytes, which therefore respond not only to voltage but also to pressure. Here we study a microfluidic memristor, in the form of a conical channel, exposed to simultaneously applied time-dependent voltage and pressure drops, through numerical solutions of the Poisson-Nernst-Planck-Stokes equations for ion and fluid transport. We show that the channel’s memristive properties can be enhanced, reduced, or instantaneously reset by appropriate pressure, and we leverage this finding with two examples of time series processing of simultaneously applied voltage and pressure pulses. We show not only that the distinction between different voltage time series can be improved by enhancing the conductance response with corresponding pressure pulses, but also that the bandwidth of information transfer through the channel can be doubled by letting the pressure pulses represent a second independent time series.

Spin waves (magnons) are among the prime candidates for building fast yet energy-efficient platforms for information transport and computing. Here we demonstrate theoretically and in state-of-the-art micromagnetic simulation the effects that strategically injected spin-polarized current can have on controlling magnonic transport. We reveal analytically that the Zhang-Li spin-transfer-torque induced by applied current is analogous to the Dzyaloshinskii-Moriya interaction for scattering the magnons in the linear regime, to then provide a generalized Snell’s law that describes the spin-wave propagation across regions with different current densities. We validate the latter in numerical simulations of realistic systems, and exemplify how these findings may help advance the design of spin-wave logic and neuromorphic computing devices.

We show that a self-sustained oscillator with a frequency-selective element operating with two nonlinearly coupled modes can achieve a level of frequency stability well beyond that available using single-mode operation. The system of interest consists of a self-sustained oscillator based on a nonlinear primary mode that is coupled via an internal resonance to a passive secondary mode. Analysis of a generic model for this resonance with both additive and multiplicative noises reveals that the stability improvements accrue from two sources: (i) nonlinear frequency veering in the primary mode, a classical analogue to quantum-level repulsion, that eliminates amplitude-to-frequency noise conversion; and (ii) phase cleaning of the oscillator through an intrinsic phase constraint arising from synchronization of the modes. This latter effect can significantly reduce the effects of intrinsic frequency fluctuations of the primary mode, which are not accessible by any known strategy using single-mode operation. The theoretical predictions are supported by experimental measurements of a microelectromechanical systems-based oscillator that demonstrate a reduction in oscillator line width of several orders of magnitude. This approach offers a means of optimizing frequency stability in self-sustained oscillators, which has direct implications for applications in timekeeping and sensing.

High-dimensional entanglement has been shown to provide significant advantages in quantum communication. One of its most promising implementations is available in the time domain routinely produced in spontaneous parametric down-conversion . While advantageous in the sense that only a single detector channel is needed locally, it is notoriously hard to analyze, especially in an assumption-free manner as required for quantum key distribution (QKD) applications. We develop a complete analysis of high-dimensional entanglement in the polarization-time domain and show how to efficiently certify relevant density matrix elements and security parameters for QKD. In addition to putting past experiments on rigorous footing, we also develop a physical noise model and propose a setup that can further enhance the noise resistance of free-space quantum communication.