The preparation of quantum states is crucial for enabling quantum computations and simulations. In this work, we present a general framework for preparing ground states of many-body systems by combining the measurement-feedback control process (MFCP) with machine learning techniques. Specifically, we employ Bayesian optimization (BO) to enhance the efficiency of determining the measurement and feedback operators within the MFCP. As an illustration, we study the ground state preparation of the one-dimensional Bose−Hubbard model. Through BO, we are able to identify optimal parameters that can effectively drive the system towards low-energy states with a high probability across various quantum trajectories. Our results open up new directions for further exploration and development of advanced control strategies for quantum computations and simulations.

Motivated by recent realizations of two-dimensional (2D) superconducting-qubit lattices, we propose a protocol to simulate Hofstadter butterfly with synthetic gauge fields in superconducting circuits. Based on the existing 2D superconducting-qubit lattices, we construct a generalized Hofstadter model on zigzag lattices, which has a fractal energy spectrum similar to the original Hofstadter butterfly. By periodically modulating the resonant frequencies of qubits, we engineer a synthetic gauge field to mimic the generalized Hofstadter Hamiltonian. A spectroscopic method is used to demonstrate the Hofstadter butterfly from the time evolutions of experimental observables. We numerically simulate the dynamics of the system with realistic parameters, and the results show a butterfly spectrum clearly. Our proposal provides a promising way to realize the Hofstadter butterfly on the latest 2D superconducting-qubit lattices and will stimulate the quantum simulation of novel properties induced by magnetic fields in superconducting circuits.

A single-photon source with narrow bandwidth, high purity, and large brightness can efficiently interact with material qubits strongly coupled to an optical microcavity for quantum information processing. Here, we experimentally demonstrate a degenerate doubly resonant single-photon source at 852 nm by the cavity-enhanced spontaneous parametric downconversion process with a 100% duty cycle of generation. The single photon source possesses both high purity with a second-order correlation g_h^{\left(2\right)}\left(0\right)=0.021 and narrow linewidth with \mathrm{\Delta }{\nu }_{sp}=\left(800\pm 13\right)\text{kHz}. The single-photon source is compatible with the cesium atom D2 line and can be used for cesium-based quantum information processing.

Recently, nonadiabatic geometric quantum computation has been received great attentions, due to its fast operation and intrinsic error resilience. However, compared with the corresponding dynamical gates, the robustness of implemented nonadiabatic geometric gates based on the conventional single-loop geometric scheme still has the same order of magnitude due to the requirement of strict multi-segment geometric controls, and the inherent geometric fault-tolerance characteristic is not fully explored. Here, we present an effective geometric scheme combined with a general dynamical-corrected technique, with which the super-robust nonadiabatic geometric quantum gates can be constructed over the conventional single-loop geometric and two-loop composite-pulse geometric strategies, in terms of resisting the systematic error, i.e., {\sigma }_x error. In addition, combined with the decoherence-free subspace (DFS) coding, the resulting geometric gates can also effectively suppress the {\sigma }_z error caused by the collective dephasing. Notably, our protocol is a general one with simple experimental setups, which can be potentially implemented in different quantum systems, such as Rydberg atoms, trapped ions and superconducting qubits. These results indicate that our scheme represents a promising way to explore large-scale fault-tolerant quantum computation.

Photogalvanic effect (PGE) occurs in materials with non-centrosymmetric structures when irradiated by linearly or circularly polarized light. Here, using non-equilibrium Green’s function combined with density functional theory (NEGF-DFT), we investigated the linear photogalvanic effect (LPGE) in monolayers of group-V elements (As, Sb, and Bi) by first-principles calculations. First, by designing a two-probe structure based on the group-V elements, we found a giant anisotropy photoresponse of As between the armchair and zigzag directions. Then, we analyzed Sb and Bi’s charge and spin photocurrent characteristics when considering the spin-orbit coupling (SOC) effect. It is found that when the polarization direction of linearly polarized light is parallel or perpendicular to the transport direction (\theta = 0^{\circ } or {90}^{\circ }), the spin up and spin down photoresponse in the armchair direction has the same magnitude and direction, leading to the generation of net charge current. However, in the zigzag direction, the spin up and spin down photoresponse have the same magnitude with opposite directions, leading to the generation of pure spin current. Furthermore, it is understood by analyzing the bulk spin photovoltaic (BSPV) coefficient from the symmetry point of view. Finally, we found that the net charge current generated in the armchair direction and the pure spin current generated in the zigzag direction can be further tuned with the increase of the material’s buckling height |h|. Our results highlight that these group-V monolayers are promising candidates for novel functional materials, which will provide a broad prospect for the realization of ultrathin ferroelectric devices in optoelectronics due to their spontaneous polarization characteristics and high Curie temperature.

The combination of multi-component Bose−Einstein condensates (BECs) and phase imprinting techniques provides an ideal platform for exploring nonlinear dynamics and investigating the quantum transport properties of superfluids. In this paper, we study abundant density structures and corresponding dynamics of phase-separated binary Bose−Einstein condensates with phase-imprinted single vortex or vortex dipole. By adjusting the ratio between the interspecies and intraspecies interactions, and the locations of the phase singularities, the typical density profiles such as ball-shell structures, crescent-gibbous structures, Matryoshka-like structures, sector-sector structures and sandwich-type structures appear, and the phase diagrams are obtained. The dynamics of these structures exhibit diverse properties, including the penetration of vortex dipoles, emergence of half-vortex dipoles, co-rotation of sectors, and oscillation between sectors. The pinning effects induced by a potential defect are also discussed, which is useful for controlling and manipulating individual quantum states.

Few-level systems consisting of a certain number of spin states have provided the basis of a wide range of cold atom researches. However, more developments are still needed for better preparation of isolated few-spin systems. In this work, we demonstrate a highly nonlinear spin-discriminating (HNSD) method for isolating an arbitrary few-level manifold out of a larger total number of spin ground states in fermionic alkaline-earth atoms. With this method, we realize large and tunable energy shifts for unwanted spin states while inducing negligible shifts for the spin states of interest, which leads to a highly isolated few-spin system under minimal perturbation. Furthermore, the isolated few-spin system exhibits a long lifetime on the hundred-millisecond scale. Using the HNSD method, we demonstrate a characteristic Rabi oscillation between the two states of an isolated two-spin Fermi gas. Our method has wide applicability for realizing long-lived two-spin or high-spin quantum systems based on alkaline-earth fermions.

The two-dimensional (2D) bulk photovoltaic effect (BPVE) is a cornerstone for future highly efficient 2D solar cells and optoelectronics. The ferromagnetic semiconductor 2H-FeCl₂ is shown to realize a new type of BPVE in which spatial inversion (P), time reversal (T), and space−time reversal (PT) symmetries are broken (PT-broken). Using density functional theory and perturbation theory, we show that 2H-FeCl₂ exhibits giant photocurrents, photo-spin-currents, and photo-orbital-currents under illumination by linearly polarized light. The injection-like and shift-like photocurrents coexist and propagate in different directions. The material also demonstrates substantial photoconductance, photo-spin-conductance, and photo-orbital-conductance, with magnitudes up to 4650 (nm·μA/V²), 4620 [nm·μA/V² \hslash/(2e)], and 6450 (nm·μA/V² \hslash/e), respectively. Furthermore, the injection-currents, shift-spin-currents, and shift-orbital-currents can be readily switched via rotating the magnetizations of 2H-FeCl₂. These results demonstrate the superior performance and intriguing control of a new type of BPVE in 2H-FeCl₂.

Neuromorphic computing aims to achieve artificial intelligence by mimicking the mechanisms of biological neurons and synapses that make up the human brain. However, the possibility of using one reconfigurable memristor as both artificial neuron and synapse still requires intensive research in detail. In this work, Ag/SrTiO₃(STO)/Pt memristor with low operating voltage is manufactured and reconfigurable as both neuron and synapse for neuromorphic computing chip. By modulating the compliance current, two types of resistance switching, volatile and nonvolatile, can be obtained in amorphous STO thin film. This is attributed to the manipulation of the Ag conductive filament. Furthermore, through regulating electrical pulses and designing bionic circuits, the neuronal functions of leaky integrate and fire, as well as synaptic biomimicry with spike-timing-dependent plasticity and paired-pulse facilitation neural regulation, are successfully realized. This study shows that the reconfigurable devices based on STO thin film are promising for the application of neuromorphic computing systems.

We discover a new wave localization mechanism in a periodic wave system, which can produce a novel type of flat band and is distinct from the known localization mechanisms, i.e., Anderson localization and flat band lattices. The first example we give is a designed electron waveguide (EWG) on 2DEG with special periodic confinement potential. Numerical calculations show that, with proper confinement geometry, electrons can be completely localized in an open waveguide. We interpret this flat band localization (FBL) phenomenon by introducing the concept of self-localized orbitals. Essentially, each unit cell of the waveguide is equivalent to an artificial atom, where the self-localized orbital is a special eigenstate with unique spatial distribution. These self-localized orbitals form the flat bands in the waveguide. Such self-localized orbital induced FBL is a general phenomenon of wave motion, which can arise in any wave systems with carefully engineered boundary conditions. We then design a metallic waveguide (MWG) array to illustrate that similar FBL can be readily realized and observed with electromagnetic waves.

Breaking up bulk crystals of functional materials into nanoscale thinner layers can lead to interesting properties and enhanced functionalities due to the size and interface effects. However, unlike the van der Waals layered crystals, many materials cannot be exfoliated into thin layers by liquid exfoliation. BiFeO₃ is a piezoelectric ceramic material, which is commonly synthesized as bulk crystals, limiting its wider applications. In this contribution, a freeze-drying assisted liquid exfoliation method was adopted to fabricate thin-layered BiFeO₃ nanoplates with lateral sizes of up to 500 nm and thicknesses of 10−20 nm. The freeze-drying process showed a vital role in the preparation process by imposing stress on the dispersed BiFeO₃ crystals during the liquid-to-solid-to-gas transition of the solvent. Such stress resulted in lattice strains in the freeze-dried BiFeO₃ crystals, which enabled their further exfoliation under subsequent ultrasonication. Considering the intrinsic piezoelectric effect of BiFeO₃, pressure sensors based on bulk and thin-layer BiFeO₃ were also fabricated. The pressure sensor based on BiFeO₃ nanoplates exhibited a largely enhanced sensitivity with a wider working range than the bulk counterpart, because of the stronger piezoelectric effect induced and the extra electrical charges at abundant interlayer interfaces. We suggest that the freeze-drying assisted liquid exfoliation method can be applied to other non-van der Waals crystals to bring about more functional material systems.

The effective modulation of the thermal conductivity of halide perovskites is of great importance in optimizing their optoelectronic device performance. Based on first-principles lattice dynamics calculations, we found that alloying at the B and X sites can significantly modulate the thermal transport properties of 2D Ruddlesden−Popper (RP) phase halide perovskites, achieving a range of lattice thermal conductivity values from the lowest ({\kappa }_c = 0.05 W·m⁻¹·K⁻¹@Cs₄AgBiI₈) to the highest ({\kappa }_{a/b} = 0.95 W·m⁻¹·K⁻¹@Cs₄NaBiCl₄I₄). Compared with the pure RP-phase halide perovskites and three-dimensional halide perovskite alloys, the two-dimensional halide perovskite introduces more phonon branches through alloying, resulting in stronger phonon branch coupling, which effectively scatters phonons and reduces thermal conductivity. Alloying can also dramatically regulate the thermal transport anisotropy of RP-phase halide perovskites, with the anisotropy ratio ranging from 1.22 to 4.13. Subsequently, analysis of the phonon transport modes in these structures revealed that the lower phonon velocity and shorter phonon lifetime were the main reasons for their low thermal conductivity. This work further reduces the lattice thermal conductivity of 2D pure RP-phase halide perovskites by alloying methods and provides a strong support for theoretical guidance by gaining insight into the interesting phonon transport phenomena in these compounds.

Photodetectors based on two-dimensional (2D) semiconductors have attracted many research interests owing to their excellent optoelectronic characteristics and application potential for highly integrated applications. However, the unique morphology of 2D materials also restricts the further improvement of the device performance, as the carrier transport is very susceptible to intrinsic and extrinsic environment of the materials. Here, we report the highest responsivity (172 A/W) achieved so far for a PbI₂-based photodetector at room temperature, which is an order of magnitude higher than previously reported. Thermal scanning probe lithography (t-SPL) was used to pattern electrodes to realize the ultrashort channel (~60 nm) in the devices. The shortening of the channel length greatly reduces the probability of the photo-generated carriers being scattered during the transport process, which increases the photocurrent density and thus the responsivity. Our work shows that the combination of emerging processing technologies and 2D materials is an effective route to shrink device size and improve device performance.

Two-dimensional (2D) materials have been considered to hold promise for transistor ultrascaling, thanks to their atomically thin body immune to short-channel effects. The lower channel size limit of 2D transistors is yet to be revealed, as this size is below the spatial resolution of most lithographic techniques. In recent years, chemical approaches such as chemical vapor deposition (CVD) and metalorganic CVD (MOCVD) have been established to grow atomically precise nanostructures and heterostructures, thus allowing for synthetic construction of ultrascaled transistors. In this review, we summarize recent developments on the precise synthesis and defect engineering of electronic nanostructures/heterostructures aiming for transistor applications. We demonstrate with rich examples that ultrascaled 2D transistors are achievable by finely tuning the “growth-as-fabrication” process and could host a plethora of new device physics. Finally, by plotting the scaling trend of 2D transistors, we conclude that synthetic electronics possess superior scaling capability and could facilitate the development of post-Moore nanoelectronics.

Plasmonic resonators are widely used for the manipulation of light on subwavelength scales through the near-field electromagnetic wave produced by the collective oscillation of free electrons within metallic systems, well known as the surface plasmon (SP). The non-radiative decay of the surface plasmon can excite a plasmonic hot electron. This review article systematically describes the excitation progress and basic properities of SPs and plasmonic hot electrons according to recent publications. The extraction mechanism of plasmonic hot electrons via Schottky conjunction to an adjacent semiconductor is also illustrated. Also, a calculation model of hot electron density is given, where the efficiency of hot-electron excitation, transport and extraction is discussed. We believe that plasmonic hot electrons have a huge potential in the future development of optoelectronic systems and devices.

Memristors have received much attention for their ability to achieve multi-level storage and synaptic learning. However, the main factor that hinders the application of memristors to simulate neural synapses is the instability of the formation and breakage of conductive filaments inside traditional memristors, which makes it difficult to simulate the function of biological synapses in practice. However, the resistance change of ferroelectric memristors relies on the polarization inversion of the ferroelectric thin film, thus avoiding the above problem. In this study, a Pd/HfAlO/LSMO/STO/Si ferroelectric memristor is proposed, which can achieve resistive switching properties through the combined action of ferroelectricity and oxygen vacancies. The I−V curves show that the device has good stability and uniformity. In addition, the effect of pulse sequence modulation on the conductance was investigated, and the biological synaptic function and learning behavior were simulated successfully. The results of the above studies provide a basis for the development of ferroelectric memristors with neurosynaptic-like behaviors.

In the framework of the factorization approach we calculate the branching fractions of 100 two-body nonleptonic decay channels in total, including 44 channels of the charm meson decays and 56 channels of the bottom meson decays. For charm meson decays, we test and confirm the previous observation that taking the limit for the number of colors N\to \mathrm{\infty } significantly improves theoretical predictions. For bottom meson decays, the penguin contributions are included in addition. As an essential input, we employ the weak decay form factors obtained in the framework of the relativistic quark model based on the quasi-potential approach. These form factors have well been tested by calculating observables in the semileptonic D and B meson decays and confronting obtained results with experimental data. In general, the predictions for the nonleptonic decay branching fractions are acceptable. However, for a quantitative calculation it is necessary to account for a more subtle effects of the final-state interaction.

The direct observation of gravitational waves (GWs) opens a new window for exploring new physics from quanta to cosmos and provides a new tool for probing the evolution of universe. GWs detection in space covers a broad spectrum ranging over more than four orders of magnitude and enables us to study rich physical and astronomical phenomena. Taiji is a proposed space-based gravitational wave (GW) detection mission that will be launched in the 2030s. Taiji will be exposed to numerous overlapping and persistent GW signals buried in the foreground and background, posing various data analysis challenges. In order to empower potential scientific discoveries, the Mock Laser Interferometer Space Antenna (LISA) data challenge and the LISA data challenge (LDC) were developed. While LDC provides a baseline framework, the first LDC needs to be updated with more realistic simulations and adjusted detector responses for Taiji’s constellation. In this paper, we review the scientific objectives and the roadmap for Taiji, as well as the technical difficulties in data analysis and the data generation strategy, and present the associated data challenges. In contrast to LDC, we utilize second-order Keplerian orbit and second-generation time delay interferometry techniques. Additionally, we employ a new model for the extreme-mass-ratio inspiral waveform and stochastic GW background spectrum, which enables us to test general relativity and measure the non-Gaussianity of curvature perturbations. Furthermore, we present a comprehensive showcase of parameter estimation using a toy dataset. This showcase not only demonstrates the scientific potential of the Taiji data challenge (TDC) but also serves to validate the effectiveness of the pipeline. As the first data challenge for Taiji, we aim to build an open ground for data analysis related to Taiji sources and sciences. More details can be found on the official website (taiji-tdc.ictp-ap.org).

If we approximate light quarks as massless and apply the Schwinger confinement mechanism to light quarks, we will reach the conclusion that a light quark q and its antiquark \overline{q} will be confined as a q\overline{q} boson in the Abelian U(1) QED gauge interaction in (1+1)D, as in an open string. From the work of Coleman, Jackiw, and Susskind, we can infer further that the Schwinger confinement mechanism persists even for massive quarks in (1+1)D. Could such a QED-confined q\overline{q} one-dimensional open string in (1+1)D be the idealization of a flux tube in the physical world in (3+1)D, similar to the case of QCD-confined q\overline{q} open string? If so, the QED-confined q\overline{q} bosons may show up as neutral QED mesons in the mass region of many tens of MeV [Phys. Rev. C 81, 064903 (2010) & J. High Energy Phys. 2020(8), 165 (2020)]. Is it ever possible that a quark and an antiquark be produced and interact in QED alone to form a confined QED meson? Is there any experimental evidence for the existence of a QED meson (or QED mesons)? The observations of the anomalous soft photons, the X17 particle, and the E38 particle suggest that they may bear the experimental evidence for the existence of such QED mesons. Further confirmation and investigations on the X17 and E38 particles will shed definitive light on the question of quark confinement in QED in (3+1)D. Implications of quark confinement in the QED interaction are discussed.

Our knowledge of the properties of dense nuclear matter is usually obtained indirectly via nuclear experiments, astrophysical observations, and nuclear theory calculations. Advancing our understanding of the nuclear equation of state (EOS, which is one of the most important properties and of central interest in nuclear physics) has relied on various data produced from experiments and calculations. We review how machine learning is revolutionizing the way we extract EOS from these data, and summarize the challenges and opportunities that come with the use of machine learning.

In the last decade, chiral symmetry in atomic nuclei has attracted significant attention and become one of the hot topics in current nuclear physics frontiers. This paper provides a review of experimental studies for nuclear chirality in China. In particular, the experimental setups, chiral mass regions, lifetime measurements, and simultaneous breaking of chirality and other symmetries are discussed in detail. These studies found a new chiral mass region (A ≈ 80), extended the boundaries of the A ≈ 100 and 130 chiral mass regions, and tested the chiral geometry of ¹³⁰Cs, ¹⁰⁶Ag, ⁸⁰Br and ⁷⁶Br by lifetime measurements. In addition, simultaneous breaking of chirality and other symmetries have been studied in ⁷⁴As, ⁷⁶Br, ⁷⁸Br, ⁸⁰Br, ⁸¹Kr and ¹³¹Ba.

Heavy meson decays provide an important platform for studies of both QCD and electroweak dynamics, which may contain some portals to understanding of nonperturbative QCD and physics beyond the Standard Model. The factorization-assisted topological-amplitude approach was proposed to study two-body non-leptonic D meson decays, where a promising QCD inspired approach from first principles is still missing. It was also applied to B meson decays whose subleading power contributions are difficult to calculate. By factorizing topological amplitudes into short distance Wilson coefficients and long distance hadronic matrix elements either to be calculated or to be parameterized, it provides an effective framework to extract information of nonperturbative dynamics involved. With important flavor SU(3) breaking effects taken into account, the data of the decay branching ratios (and also CP asymmetries in B decays) can be fitted well. The extracted amplitudes were further applied to make predictions for other observables, such as CP asymmetries in D decays, mixing parameters in the D^0-{\overline{D}}^0 system. By this review, we will describe the formulation of the factorization-assisted topological-amplitude approach and summarize its applications in D and B meson decays and highlight some of its achievements.