We propose silicon nitride ($\mathrm{S}{\mathrm{i}}_3{\mathrm{N}}_4$) nanowaveguide-based CMOS-compatible integrated sources of spectrally pure visible-telecom photon pairs. Our designs are intrinsically devoid of spectral correlations, eradicating the need for narrow-band filtering that reduces the source brightness. Further, the signal photons lie in the visible–near-infrared (vis-NIR) band, which can provide increased heralding efficiency of the idler photon in the telecom band using high-efficiency single-photon detectors. For example, a rectangular-cross-section silica-clad $\mathrm{S}{\mathrm{i}}_3{\mathrm{N}}_4$ nanowaveguide with dimensions $680\text{~nm}\times 840\text{~nm}$ and length 7 cm provides a heralded single-photon purity of approximately $91\mathrm{\%}$ for a pump wavelength of 956.8 nm and a pump bandwidth of 1200 GHz, with the signal and idler lying in the visible and telecom bands at approximately $701$ nm and approximately $1505$ nm, respectively, demonstrating a peak spectral brightness of approximately $1.2\times {10}^4$ photon $\mathrm{pairs}/\mathrm{s}/\mathrm{nm}/{\mathrm{mW}}^2$ for a linear propagation loss of 0.5 dB/cm. The effect of propagation losses on the purity is also studied for such source designs. We also propose some designs capable of generating high-purity photon pairs to address various specific vis-NIR quantum memory transitions with telecom-band interfacing for long-distance hybrid quantum networks. Such compact on-chip sources could have potential applications in various quantum technologies, such as sensing, simulation, computing, communication, and networking.

Coherent acoustic phonon generation and detection assisted by optical resonances are at the core of efficient optophononic transduction processes. However, when one is dealing with a single optical resonance, the optimum generation and detection conditions occur at different laser wavelengths, i.e., different detunings from the cavity mode. In this work, we theoretically propose and experimentally demonstrate the use of elliptical micropillars to reach these conditions simultaneously at a single wavelength. Elliptical micropillar optophononic resonators present two optical modes with orthogonal polarizations at different wavelengths. By using a cross-polarization-scheme pump-probe experiment, we exploit the mode splitting and couple the pump beam to one mode while the probe is detuned from the other mode. In this way, at a particular micropillar ellipticity, the phonon-generation and phonon-detection processes are both enhanced. We report an enhancement of the coherent-phonon-generation-detection process by a factor of approximately 3.1 when comparing the highest achievable signals from elliptical and circular micropillars. Our findings constitute a step forward in tailoring light-matter interaction for more-efficient ultrahigh-frequency optophononic devices.

Quantum entanglement is a fundamental property commonly used in various quantum information protocols and algorithms. Nonetheless, the problem of identifying entanglement has still not reached a general solution for systems larger than $2\times 3$. In this study, we use deep convolutional NNs, a type of supervised machine learning, to identify quantum entanglement for any bipartition in a three-qubit system. We demonstrate that training the model on synthetically generated datasets of random density matrices excluding challenging positive-under-partial-transposition entangled states (PPTES), which cannot be identified (and correctly labeled) in general, leads to good model accuracy even for PPTES states, that were outside the training data. Our aim is to enhance the model’s generalization on PPTES. By applying entanglement-preserving symmetry operations through a triple Siamese network trained in a semisupervised manner, we improve the model’s accuracy and ability to recognize PPTES. Moreover, by constructing an ensemble of Siamese models, even better generalization is observed, in analogy with the idea of finding separate types of entanglement witnesses for different classes of states.

We investigate the electrical properties of nominally undoped, 10–40-nm-thick $\mathrm{Sc}\mathrm{N}$(111) layers grown on nearly lattice-matched $\mathrm{Ga}\mathrm{N}$:$\mathrm{Fe}$/${\mathrm{Al}}_2{\mathrm{O}}_3$(0001) templates by plasma-assisted molecular beam epitaxy. Hall-effect measurements yield electron concentrations of $0.7\text{--}3.1\times {10}^{19}{\text{cm}}^{-3}$ and mobilities of 50–160 ${\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ at room temperature. The temperature-dependent (4–360 K) conductivity exhibits two distinct regimes, suggesting two-band conduction in an impurity band and the conduction band. Assuming a single shallow donor in $\mathrm{Sc}\mathrm{N}$ and employing the standard two-band conduction model, we extract the carrier density and mobility in these bands. The results reveal nondegenerate characteristics for a 40-nm-thick layer, while thinner layers are weakly degenerate. For the nondegenerate layer, the donor ionization energy amounts to approximately 12 meV. The electron mobility of the layers is limited by ionized-impurity scattering and phonon scattering at low and high temperatures, respectively. Fits with an expression for optical phonon scattering developed for weakly degenerate semiconductors return an effective phonon energy of $(61\pm 5)\mathrm{meV}$, a value in between the energies of the longitudinal optical ($\approx 84\mathrm{meV}$) and transverse optical ($\approx 45\mathrm{meV}$) phonon modes in $\mathrm{Sc}\mathrm{N}$.

We observe strongly anisotropic third-harmonic generation mediated by resonant sum-frequency driving of Raman-active phonons with terahertz light, extending light-induced dual control of structural and optical properties in solids. Either strong enhancement or strong suppression of the third harmonic can be achieved, covering six orders of magnitude, a result of interference between purely electronic and phonon-mediated contributions to the polarization field. These findings enrich capabilities for tailoring nonlinear optics via phononics and for the spectroscopy of crystalline structural dynamics.

Phase engineering plays a pivotal role in various scientific research and industrial applications including microwaves, optics, and acoustics. However, traditional phase engineering methods lack the flexibility for arbitrary programming due to the absence of digitization. Conversely, while broadband digitization technology holds promise, its utilization in wave engineering has been constrained by narrowband transmission capabilities. In this study, we introduce a novel approach to broadband digital phase encoding spanning frequencies from 50 to 500 kHz. Our methodology is exemplified through the development of an acoustic soft metacollimator with simulations and experiments conducted underwater across different frequency ranges. Our findings demonstrate that the soft metacollimator significantly enhances transmission intensity by 7.7 dB and improves spatial resolution by a factor of 10. Moreover, the soft metacollimator enables novel functionalities such as long-distance energy enhancement and broadband coding properties in underwater acoustics. This pioneering broadband digital phase encoding technique holds promise for advancing next-generation phase engineering and offers versatile applications in biomedical ultrasonics, acoustic communications, and the development of underwater broadband acoustic antennas.

Two-dimensional (2D) metal halide perovskites have garnered significant attention in the field of light-emitting diodes due to their high photoluminescence quantum yield and tunability. In comparison with the widely studied 2D Ruddlesden-Popper (RP) perovskites, the 2D Dion-Jacobson (DJ) double perovskites, which offer higher stability and nontoxicity, have received relatively less attention. In addition, the regulatory effects of halogens on the luminescence mechanisms and performance of 2D DJ double perovskites remain unknown. Utilizing density functional theory, the stability and luminescence properties of 2D DJ double-perovskite $({\mathrm{C}}_6{\mathrm{H}}_{16}{\mathrm{N}}_2{)}_2\mathrm{Ag}\mathrm{Bi}{X}_8\cdot {\mathrm{H}}_2\mathrm{O}$ ($X$ = $\mathrm{Cl},\mathrm{Br},\mathrm{I}$) are effectively modulated through halogen substitution. The findings indicate that the dissociation energy incrementally increases as the halogen changes from $\mathrm{I}$ to $\mathrm{Br}$ to $\mathrm{Cl}$, suggesting that the incorporation of lighter halogens enhances structural stability. The minimal self-trapping formation energy (i.e., 0.08 eV) of $({\mathrm{C}}_6{\mathrm{H}}_{16}{\mathrm{N}}_2{)}_2{\mathrm{Ag}\mathrm{Bi}\mathrm{I}}_8\cdot {\mathrm{H}}_2\mathrm{O}$ facilitates easy detrapment of self-trapped excitons, leading to a tendency toward free exciton luminescence. The self-trapping formation energies of $({\mathrm{C}}_6{\mathrm{H}}_{16}{\mathrm{N}}_2{)}_2{\mathrm{Ag}\mathrm{Bi}\mathrm{Br}}_8\cdot {\mathrm{H}}_2\mathrm{O}$ and $({\mathrm{C}}_6{\mathrm{H}}_{16}{\mathrm{N}}_2{)}_2{\mathrm{Ag}\mathrm{Bi}\mathrm{Cl}}_8\cdot {\mathrm{H}}_2\mathrm{O}$ are 0.77 eV and 0.96 eV, respectively, indicating substantial self-trapping depths; thus, favoring self-trapped exciton luminescence. In addition, the transition dipole moments of $({\mathrm{C}}_6{\mathrm{H}}_{16}{\mathrm{N}}_2{)}_2{\mathrm{Ag}\mathrm{Bi}\mathrm{Br}}_8\cdot {\mathrm{H}}_2\mathrm{O}$ and $({\mathrm{C}}_6{\mathrm{H}}_{16}{\mathrm{N}}_2{)}_2{\mathrm{Ag}\mathrm{Bi}\mathrm{Cl}}_8\cdot {\mathrm{H}}_2\mathrm{O}$ are substantially higher than those of $({\mathrm{C}}_6{\mathrm{H}}_{16}{\mathrm{N}}_2{)}_2{\mathrm{Ag}\mathrm{Bi}\mathrm{I}}_8\cdot {\mathrm{H}}_2\mathrm{O}$, suggesting that substituting I with $\mathrm{Cl}$ and $\mathrm{Br}$ enhances the luminous efficiency of 2D DJ double-perovskite $({\mathrm{C}}_6{\mathrm{H}}_{16}{\mathrm{N}}_2{)}_2\mathrm{Ag}\mathrm{Bi}{X}_8\cdot {\mathrm{H}}_2\mathrm{O}$ ($X$ = $\mathrm{Cl},\mathrm{Br},\mathrm{I}$). These results indicate that halogen substitution can not only affect the stability of 2D DJ perovskites but also modulate their luminescent properties. Our research provides theoretical insights for the experimental design of superior luminescent materials.

Two-level system (TLS) loss typically limits the coherence of superconducting quantum circuits. The loss induced by TLS defects is nonlinear, resulting in quality factors with a strong dependence on the circulating microwave power. We observe frequency mixing due to this nonlinearity by applying a two-tone drive to a coplanar waveguide resonator and measuring the intermodulation products using a multifrequency lock-in technique. This intermodulation spectroscopy method provides an efficient approach to characterizing TLS loss in superconducting circuits. Using harmonic balance reconstruction, we recover the nonlinear parameters of the device-TLS interaction, which are in good agreement with the standard tunneling model for TLSs.

Overdamped Josephson junctions usually do not exhibit chaotic behavior in their phase dynamics, either because the phase-space dimension is less than $3$ (as in the case of a single overdamped ac-driven junction) or due to the general tendency of systems to become less chaotic with increasing dissipation (as in the case of coupled overdamped junctions). Here we consider the so-called ${\phi }_0$ superconductor/ferromagnet/superconductor Josephson junction in which the current flowing through the junction may induce magnetization dynamics in the ferromagnetic interlayer. We find that due to the induced magnetization dynamics, even in the overdamped limit (i.e., for a junction without capacitance), the junction may exhibit chaos and hysteresis that in some cases leads to multiple branches in its current-voltage characteristics. We also show that pulsed current signals can be used to switch between the different voltage states, even in the presence of added thermal noise. Such switching could be used in cryogenic memory components.

Recent progress shows that a surface-acoustic-wave (SAW) cavity can not only induce quantum acoustic dynamics, but can also form optomechanical-like systems. Its operating frequencies in the microwave band make it resistant to the thermal noise of surrounding environments, while its radiation-pressure couplings make it susceptible to weak forces. Based on these advantages, we propose a gyroscope comprising coupled microwave-SAW cavities. In this paper we systematically consider the range, signal-to-noise ratio, and sensitivity, which are the three most important indices to gyroscopes, but only partially considered in existing works. Additionally, we establish the fundamental limits of sensitivity when the quantum input is in the vacuum state and the squeezed vacuum state. We find that squeezing improves sensitivity and can surpass the standard quantum limit. However, this improvement can only reach up to $\sqrt{2}/2$ even as the squeezed parameter approaches infinity, which is rarely noted in recent works. Finally, we also offer analytical constraints for cooperativity and squeezed parameters. These constraints can be utilized to design gyroscopes based on coupled cavities in experiments.

Universal robust quantum control is essential for large-scale quantum computation. The geometric phase, as a key element with intrinsic error-resilient features, can be well integrated into a quantum control process to enhance control robustness. However, due to the inability to optionally avoid some trajectory segments seriously affected by systematic errors, the robust universality of current geometric quantum control based on some special geometric evolution trajectories is still lacking, resulting in unsatisfactory performance of arbitrary geometric gate. Here, we propose another scheme for universal robust geometric control based on geometric trajectory correction, where enough available evolution parameters are introduced, without more experimental demands, to ensure the effective reduction of sensitivity to systematic errors. Numerical simulation shows that our implemented arbitrary geometric gates have error-resilient features better than conventional ones. In addition, we also verify the feasibility of the high-fidelity physical implementation of our scheme on superconducting quantum circuits. Therefore, our theoretical work is expected to offer an attractive avenue for realizing practical quantum computation in existing experimental platforms.

We analyze the experimental error budget of parametric resonance gates in a tunable coupler architecture. We identify and characterize various sources of errors, including incoherent, leakage, amplitude, and phase errors. By varying the two-qubit gate time, we explore the dynamics of these errors and their impact on the gate fidelity. To accurately capture the impact of incoherent errors on gate fidelity, we measure the coherence times of qubits under gate operating conditions. Our findings reveal that the incoherent errors, mainly arising from qubit relaxation and dephasing due to white noise, limit the fidelity of the two-qubit gates. Moreover, we demonstrate that leakage to noncomputational states is the second largest contributor to the two-qubit gates infidelity, as characterized using leakage-randomized benchmarking. The error budgeting methodology we develop here can be effectively applied to other types of gate implementations.

In this work, we investigate optical properties of inorganic and organic metal halide perovskites (${\mathrm{Cs}\mathrm{Pb}\mathrm{X}}_3$ and ${\mathrm{MAPb}\mathrm{X}}_3$ with $X=\{\mathrm{Cl},\mathrm{Br},\mathrm{I}\}$). We use the eight-band $k\cdot p$ model to calculate the electronic band structures for perovskite materials of cubic and pseudocubic phase. In order to find respective parameters, the band structures of considered materials were obtained within state-of-the-art density-functional theory and used next as targets to adjust the $k\cdot p$ bands and determine the values of $k\cdot p$ parameters. The calculated band structures were used to obtain the material gain for bulk crystals (${\mathrm{Cs}\mathrm{Pb}\mathrm{Cl}}_3$, ${\mathrm{Cs}\mathrm{Pb}\mathrm{Br}}_3$, ${\mathrm{Cs}\mathrm{Pb}\mathrm{I}}_3$, ${\mathrm{MAPb}\mathrm{Cl}}_3$, ${\mathrm{MAPb}\mathrm{Br}}_3$, and ${\mathrm{MAPb}\mathrm{I}}_3$), which is compared with the material gain in well-established III-V semiconductors. It was found that for these perovskites a positive material gain appears at lower carrier density than for the reference materials ($\mathrm{Ga}\mathrm{As}$ and $\mathrm{In}\mathrm{P}$). We demonstrate that from the point of view of the electronic band structure, the studied perovskites are very promising gain medium for lasers.

Atom spin sensors occupy a prominent position in the landscape of quantum technology, as they can combine precise measurements with appealing miniature packages that are crucial for many applications. In this work, we report on the design and realization of miniature silicon-wafer cells, with a double-chamber configuration and integrated heaters. The cells are tested by our systematically studying the dependence of the spin dynamics on the main pump parameters, temperature, and bias magnetic field. The results are benchmarked against centimeter-sized paraffin-coated cells, which allows optimization of the operating conditions of a radio frequency–driven atomic magnetometer. In particular, we observe that, when indirect optical pumping is performed on the two cells, an analogous line-narrowing mechanism appears in otherwise-very-different cell conditions. Competitive results are obtained, with magnetic resonance linewidths of roughly 300 Hz at the maximum signal-to-noise ratio, in a nonzero-magnetic-field setting, and in an atomic shot noise–limited regime.

Quantum simulators offer the potential to utilize the quantum nature of a physical system to study another physical system. In contrast to conventional simulation, which experiences an exponential increase in computational complexity, quantum simulation cost increases only linearly with increasing size of the problem, rendering it a promising tool for applications in quantum chemistry. The variational-quantum-eigensolver algorithm is a particularly promising application for investigating molecular electronic structures. For its experimental implementation, spin-based solid-state qubits have the advantage of long decoherence time and high-fidelity quantum gates, which can lead to high accuracy in the ground-state finding. This study uses the nitrogen-vacancy-center system in diamond to implement the variational-quantum-eigensolver algorithm and successfully finds the eigenvalue of a specific Hamiltonian without the need for error-mitigation techniques. With a fidelity of 98.9% between the converged state and the ideal eigenstate, the demonstration provides an important step toward realizing a scalable quantum simulator in solid-state spin systems.

With an explosive increase in demand for efficient luminescent materials in integrated optical systems, research on lanthanide ion-doped cubic sesquioxide ceramics has become important and attractive. Because of the large doping capability of lanthanide atoms and a low preparation temperature that is much lower than the melting point, sesquioxides have demonstrated promising potential as a host matrix in solid-state laser gain media. Here, for the first time, we demonstrate that two types of cation sites with different symmetries in cubic sesquioxides could empower effective manipulation of the luminescence properties of lanthanide dopants, leading to either magnetic dipole (MD) or electrical dipole (ED) emission, respectively. Using rigorous first-principle calculations, the luminescence properties of $\mathrm{Eu}$-doped sesquioxide $M_2{\mathrm{O}}_3$ ($M$ = $\mathrm{Sc},\mathrm{Y},\mathrm{La}$) are systematically investigated, unveiling the underlying competition mechanisms between MD and ED spontaneous emission. Through analyzing the formation energies of $\mathrm{Eu}$ dopants and intrinsic defects, the impact of strain and temperature on the doping concentration and dopant sites of $\mathrm{Eu}$ in sesquioxide is unambiguously elucidated, facilitating effective and selective manipulation of MD and ED emission.

A ternary cold source field effect transistor (T-CSFET) is proposed based on source density-of-state engineering, using a narrow-band-gap semiconductor at the source region. A current plateau at the subthreshold region is obtained in the transfer characteristics of T-CSFETs, namely an intermediate state with a constant current between on and off states. We meticulously study a two-dimensional T-CSFET based on a graphene-${\mathrm{Mo}\mathrm{S}}_2$ heterojunction by quantum transport simulations. It is shown that ternary states can be well distinguished with a current ratio between two adjacent states of over ${10}^3$ at a low overall supply voltage of 0.6 V. The intermediate state is stable with a constant current in a gate voltage region over 0.2 V and can be modulated by varying the doping density. We also obtain ternary transfer curves for T-CSFETs based on one-, two-, and three-dimensional materials. Based on T-CSFETs, a two-bit ternary adder with hybrid logic is implemented and verified by circuit simulations. The proposed T-CSFETs exhibit excellent properties for multivalue logic, including high drive current, tunable multivalue states, stable and reliable operation, energy and area efficiency, and a variety of material systems.

Recently, great progress has been made in the entanglement of multiple photons at various wavelengths and with different degrees of freedom for optical quantum information applied in diverse scenarios. However, multiphoton entanglement in the transmission window of green light under water has not yet been reported. Here, by combining femtosecond-laser-based multiphoton entanglement and entanglement-maintaining frequency up-conversion techniques, we successfully generate a green two-photon polarization-entangled Bell state and a green three-photon Greenberger-Horne-Zeilinger state, whose state fidelities are $0.893\pm 0.002$ and $0.595\pm 0.023$, respectively. Our result provides a scalable method to prepare green multiphoton entanglement, which may have wide applications in underwater quantum information.

In this work, we propose a deep convolutional attention neural network to realize the recognition of acoustic vortex fields. Convolutional attention mechanisms are introduced into the network together with the residual idea. The deep neural network is trained and then evaluated, and the performance is compared with those of several typical convolutional neural networks, including AlexNet, GoogLeNet, and ResNet. The results show that the improved neural network model based on the convolutional attention mechanism proposed here has better classification performance and stronger stability. The classification accuracy of the improved model on the whole test set reaches more than 95%, indicating that the model has a stable classification ability. Our work helps further study the detection and recognition of acoustic vortex fields, which will find many applications in scientific research and industry.