The conjugate variables of angular position and orbital angular momentum have been a toolbox for optical information processing. Here, in order to fully exploit the relationship between the angular position and orbital angular momentum of a partially coherent beam, we propose and generate a new kind of partially coherent beam with angular-correlated coherence structure that can be interpreted as an angular partially coherent beam (APCB). The APCB is generated experimentally by a fast modulated digital micromirror device. The angular diffraction of the generated APCB with the angular analogue of double slits is studied to show the coherent structure of the generated source. We have observed that an APCB with different coherence angles produces different diffraction patterns through the same angular mask, which illustrates an excellent agreement between the numerical simulations and the experimental observations. The specific property of the APCB is important in the optical sensing area, which can be used to identify the angular spacing of objects, to transfer optical information, etc. Our work opens the door for utilizing the photon’s angular degree of freedom in a partially coherent beam modulation technique and raises possibilities for optical sensing with a new toolbox such as for quantum image and object identification.

We show in theory and experiment that in periodically patterned spintronic terahertz emitters (STEs), charge dynamics can modify the emission spectrum in a well-controlled way. Characterization of nanopatterned STEs at frequencies up to 30 THz shows that the STE emission spectrum systematically changes with emitter size. The spectral intensity exhibits significant reductions at frequencies below 4 THz, accompanied by pronounced dips at around 15 and 24 THz. While reduction of the STE size enhances the modulation of all features, it does not alter the dip frequencies. The effect originates from the charging of the structure’s edges by terahertz currents, causing a backflow that interferes with the initially induced current pulse. An analytical model quantitatively reproduces these results and agrees well with the findings of control experiments. Our findings enable a detailed investigation of the charge dynamics in STEs and provide additional means for controlled shaping of STE emission spectra by nanopatterning.

Three-dimensional photoelectron angular distributions (PADs) are measured from an atomic target ionized by ultrafast, elliptical fields of opposite handedness. Comparing these PADs to one another and to numeric simulations, a difficult to avoid systematic error in their orientation is identified and subsequently corrected by imposing the dichroic symmetry by which they are necessarily related. We show that this correction can be directly applied to molecular targets in the same fields. This paves the way for the measurement of enantiosensitive information, which has yet to be accessed experimentally.

Alkaline-earth-like elements play pivotal roles in advanced quantum sensing technologies, notably optical clocks, with unprecedented precision achieved in recent years. Despite remarkable progress, current optical-lattice clocks still face challenges in meeting the demanding size, weight, and power consumption constraints essential for space applications. Conventional atom sources, such as ovens or dispensers, require substantial heating power, which makes up a significant fraction of the overall power consumption of the system. Addressing this challenge, we present a microstructured atomic oven based on fused silica, designed for miniaturization and low-power operation. We characterize the oven by loading a magneto-optical trap with $\mathrm{Yb}$ evaporated from the oven and demonstrate operation with a loading rate above ${10}^8\mathrm{atoms}/\mathrm{s}$ for heating powers below $250$ mW.

Stark systems in which a linear gradient field is applied across a many-body system have recently been proposed for quantum sensing. Here, we explore sensing capacity of Stark probes, in both single-particle and many-body interacting systems, for estimating nonlinear forms of the gradient fields. Our analysis reveals that, this estimation can achieve super-Heisenberg scaling precision that grows linearly by increasing the nonlinearity. Specifically, we find a universal algebraic relation between the scaling of the precision and the degree of the nonlinearity. This universal behavior remains valid in both single-particle and many-body interacting probes and reflects itself in the properties of the phase transition from an extended to a localized phase, obtained through establishing a comprehensive finite-size scaling analysis. Considering a parabolic gradient potential composed of both linear and nonlinear fields, we used multiparameter estimation methodology to estimate the components of the gradient potential. The phase diagram of the system is determined in terms of both linear and nonlinear gradient fields showing how the nonlocalized phase turns into a localized one as the Stark fields increase. The sensing precision of both linear and nonlinear Stark fields follows the same universal algebraic relation that was found for the case of single parameter sensing. We demonstrate that simple and experimentally available measurements can reach the theoretical precision bounds. Finally, we show that quantum enhanced sensitivity is still achievable even when we incorporate the preparation time of the probe into our resource analysis.

Demonstrating the utility of quantum algorithms is a long-standing challenge, where quantum machine learning becomes one of the most promising candidates that can be resorted to. In this study, we investigate a quantum neural compressive-sensing algorithm for ghost imaging to showcase its utility. The algorithm utilizes the variational quantum circuits to reparameterize the inverse problem of ghost imaging and uses the inductive bias of the physical forward model to perform optimization. To validate the algorithm’s effectiveness, we conduct optical ghost-imaging experiments, capturing signals from objects at different physical sampling rates and detection signal-to-noise ratios. The experimental results show that our proposed algorithm surpasses conventional methods in both visual appearance and quantitative metrics, achieving state-of-the-art performance. Of note, we observe that the quantum neural network, guided by prior knowledge of physics, effectively overcomes the challenge of barren plateau in the optimization process. The proposed algorithm demonstrates robustness against various quantum noise levels, making it suitable for near-term quantum devices. Our study leverages a physical inductive-bias-guided variational quantum algorithm, underscoring the potential of quantum computation in tackling a broad range of optimization and inverse problems.

Recent progress has made high-bandwidth electro-optic modulators (EOMs) available. Here we show the cascaded operation of two such modulators driven by custom-built electronics delivering on-demand picosecond pulses and application to a quantum dot–cavity-QED single-photon source. We implement an EOM-based correlation technique and demonstrate light pulses as short as $24\pm 2$ ps with a single EOM. The EOMs can be synchronized and operated in series, and we then produce optical pulses down to $17$ ps. To optimize the pulse contrast, for two different EOM devices, we analyze the transmission as a function of EOM bias, wavelength, and temperature, and we show that, by temperature tuning and stabilization, a pulse contrast above 25 dB can be obtained at the targeted wavelength. With this high contrast, we demonstrate resonant excitation of an $\mathrm{In}\mathrm{Ga}\mathrm{As}$ quantum dot–microcavity-based single-photon source, demonstrating a crucial technology for scalability and synchronization of large-scale photonic quantum applications.

Exploring novel systems with perpendicular magnetic anisotropy (PMA) is vital for advancing memory devices. In this study, we report an intriguing PMA system involving an ultrathin $\mathrm{Fe}$ layer on an antiferromagnetic (AFM) $\mathrm{Co}\mathrm{O}(001)$ surface. The measured perpendicular anisotropy field is inversely proportional to the $\mathrm{Fe}$ thickness, indicating an interfacial origin of PMA. Temperature-dependent measurements reveal that the antiferromagnetism of $\mathrm{Co}\mathrm{O}$ has a negligible effect on the PMA. By leveraging the magneto-optic Kerr effect and birefringence effect, we achieve concurrent visualization of ferromagnetic (FM) and AFM domains. A pronounced coupling effect between these domains is observed near the spin reorientation transition, contrasting sharply with areas of stronger PMA that exhibit weak coupling. This research not only establishes an alternative FM/AFM bilayer PMA system but also significantly advances the understanding of FM/AFM interfacial interactions.

Fast quantum gates are crucial not only for the contemporary era of noisy intermediate-scale quantum devices but also for the prospective development of practical fault-tolerant quantum computing. Leakage errors, which arise from data qubits jumping beyond the confines of the computational subspace, are the main challenges in realizing nonadiabatically driven, fast gates. In this work, we propose and illustrate the usefulness of reinforcement learning (RL) to generate fast two-qubit gates in practical multilevel superconducting qubits. In particular, we show that the RL controller offers great effectiveness in finding piecewise constant gate-pulse sequences that act on two transmon data qubits coupled by a tunable coupler to generate a controlled-$Z$ (cz) gate with a gate time of 10 ns and an error rate of approximately $4\times {10}^{-3}$. Using a gradient-based method to solve the same optimization problem often does not achieve high fidelity for such fast gates. However, we show that using the gate pulses discovered by RL as an ansatz for the gradient-based controller can substantially enhance fidelity compared to using RL alone. While for a 10-ns pulse, this improvement is marginal, the combined RL + gradient approach decreases the gate errors below ${10}^{-4}$ for a gate of length 20 ns.

Recent assessments have enhanced the evaluation of the lattice ac Stark shift in optical clocks to a fractional frequency level below ${10}^{-18}$. With this level of accuracy, meticulous attention is required to address shifts from the background spectrum of the lattice laser. Therefore, it is essential for the lattice laser to exhibit a minimal background spectrum. In this investigation, we employ a system based on sum-frequency generation (SFG) of the fiber-amplified lasers as the source for the strontium optical-clock lattice laser. The spectrum purity of this laser system has been confirmed through a heterodyne measurement involving a titanium:sapphire ($\mathrm{Ti}$:$\mathrm{Sa}$) laser. Consequently, we have characterized the background light shift resulting from its background spectrum, which is more than one order of magnitude lower than that of a tapered amplifier (TA). Through the implementation of carefully selected spectral filtering, the background light shift can be suppressed to a level of mid-${10}^{-20}$. Additionally, the suitability of the SFG laser is also experimentally verified in a strontium clock.

The spin-filtering effect, distinct decaying lengths experienced by oppositely-spin-polarized electrons in a magnetic barrier, generally occurs in ferromagnetic insulators or semiconductors. With the rise of altermagnetic (ALM) materials that exhibit similar capability of spin-polarizing electrons with ferromagnets, it is a natural question to ask whether ALM insulators or semiconductors can also act as unique barriers for the spin-splitting effect. Here, through first-principles calculations, we investigate the complex band structure of the ALM insulator ${\text{FeF}}_2$ and find that it possesses an anisotropic spin-filtering effect: along the [001] direction of ${\text{FeF}}_2$, a current remains spin neutral but has locally nonvanishing spin polarizations in the momentum space; moreover, along the [110] direction of ${\text{FeF}}_2$, a current will be globally spin polarized by different attenuation lengths of oppositely-spin-polarized electrons. Leveraging this anisotropic spin-filtering effect, we designed two types of magnetic tunnel junction with an ALM barrier: ALM-electrode/ALM-insulator-barrier/nonmagnetic-electrode and ferromagnetic-electrode/ALM-insulator-barrier/nonmagnetic-electrode, using ${\text{RuO}}_2(001)/{\text{FeF}}_2/{\text{IrO}}_2$ and ${\text{CrO}}_2(110)/{\text{FeF}}_2/{\text{IrO}}_2$, respectively, as the corresponding prototypes. We found that these two proposed MTJs exhibited tunneling magnetoresistance ratios of 216% and 3956%, by matching the conduction channels of the electrodes and the spin-resolved lowest decay rate of the barrier in the momentum space. Our work deepens and generalizes understanding of the spin-filtering effect for the rising ALM insulators and semiconductors, and broadens applications of antiferromagnetic spintronics.

The ability to fast reset a qubit state is crucial for quantum information processing. However, to actively reset a qubit requires engineering a pathway to interact with a dissipative bath, which often comes at the cost of reduced qubit protection from the environment. Here, we present a multipurpose architecture that enables fast reset and protection of superconducting qubits during control and readout. In our design, two on-chip diplexers are connected by two transmission lines. The high-pass branch provides a flat passband for convenient allocation of readout resonators above the qubit frequencies, which is preferred for reducing measurement-induced state transitions. In the low-pass branch, we leverage a standing-wave mode below the maximum qubit frequency for a rapid reset. The qubits are located in the common stopband to inhibit dissipation during coherent operations. We demonstrate resetting a transmon qubit from its first excited state to the ground state in 100 ns, achieving a residual population of 2.7%. The reset time may be further shortened to 27 ns by exploiting the coherent population inversion effect. We further extend the technique to resetting the qubit from its second excited state. Our approach promises scalable implementation of fast reset and qubit protection during control and readout, adding to the toolbox of dissipation engineering.

The unique properties and potential applications of MXenes, a class of two-dimensional (2D) materials with a distinctive layered structure, have attracted significant research interest in recent years, especially for use in energy-storage systems like metal-ion batteries. However, current theoretical studies ignore the effects of electrode potential and solvation conditions. This study systematically explored the impact of electrode potential on the adsorption, migration, and other behaviors of lithium and potassium ions on ${\mathrm{Ti}}_3{\mathrm{C}}_2{\mathrm{O}}_2$, utilizing an implicit solvation model. The findings demonstrated that electrode potential significantly affected metal-ion adsorption on ${\mathrm{Ti}}_3{\mathrm{C}}_2{\mathrm{O}}_2$, with adsorption strength increasing as the electrode potential decreased. This observation is supported by electronic structure analyses, such as integrated crystal orbital Hamilton population. Additionally, the study investigated the variation in migration energy with changes in electrode potential, revealing that both increases and decreases in electrode potential lead to higher migration energy. These results provide fundamental insights into how electrode potential influences the performance of MXenes and provide a real guide for the development of better MXene materials for metal-ion batteries.

In recent years, higher-order sonic topological insulators have transformed our understanding of how sonic waves are trapped, and have led to the discovery of unique edge and corner states resistant to small perturbations. Programmable coding of a sonic topological insulator realizes sonic logic or and xor gates. Despite the rapid advancements in this field, it has been a significant challenge to achieve programmable binary codes of sonic waves. We propose a solution to this challenge, based on the higher-order states. Using the parity of corner states and the phase difference of two sonic sources, we can realize programming binary coding of the numbers 0–7. More importantly, through meticulous design, we successfully achieve controllable excitation of these corner states and realize programmable binary coding of dual-frequency gaps based on this higher-order sonic topological insulator, such as the binary numbers $000$, $001$, $010$, $011$, $100$, $101$, $110$, and $111$. The corner states enrich our comprehension of higher-order sonic topological insulators and provide an experimental platform for exploring topological corner states. Our results provide an approach for developing new sonic devices that can achieve programmable responses under various operating conditions.