We study the local quantum Fisher information (LQFI) in the mixed-spin Heisenberg XXZ chain. Both the maximal and minimal LQFI are studied and the former is essential to determine the accuracy of the quantum parameter estimation, the latter can be well used to characterize the discord-type quantum correlations. We investigate the effects of the temperature and the anisotropy parameter on the maximal LQFI and thus on the accuracy of the parameter estimation. Then we make use of the minimal LQFI to study the discord-type correlations of different site pairs. Different dimensions of the subsystems cause different values of the minimal LQFI which reflects the asymmetry of the discord-type correlation. In addition, the site pairs at different positions of the spin chains have different minimal LQFI, which reveals the influence of the surrounding spins on the bipartite quantum correlation. Our results show that the LQFI obtained through a simple calculation process provides a convenient way to investigate the discord-type correlation in high-dimensional systems.

Optimization problems are prevalent in various fields, and the gradient-based gradient descent algorithm is a widely adopted optimization method. However, in classical computing, computing the numerical gradient for a function with d variables necessitates at least d+1 function evaluations, resulting in a computational complexity of O(d). As the number of variables increases, the classical gradient estimation methods require substantial resources, ultimately surpassing the capabilities of classical computers. Fortunately, leveraging the principles of superposition and entanglement in quantum mechanics, quantum computers can achieve genuine parallel computing, leading to exponential acceleration over classical algorithms in some cases. In this paper, we propose a novel quantum-based gradient calculation method that requires only a single oracle calculation to obtain the numerical gradient result for a multivariate function. The complexity of this algorithm is just O(1). Building upon this approach, we successfully implemented the quantum gradient descent algorithm and applied it to the variational quantum eigensolver (VQE), creating a pure quantum variational optimization algorithm. Compared with classical gradient-based optimization algorithm, this quantum optimization algorithm has remarkable complexity advantages, providing an efficient solution to optimization problems.The proposed quantum-based method shows promise in enhancing the performance of optimization algorithms, highlighting the potential of quantum computing in this field.

Recently universal dynamic scaling is observed in several systems, which exhibit a spatiotemporal self-similar scaling behavior, analogous to the spatial scaling near phase transition. The latter one arises from the emergent continuous scaling symmetry. Motivated by this, we investigate the possible relation between the scaling dynamics and the continuous scaling symmetry in this paper. We derive a theorem that the scaling invariance of the quenched Hamiltonian and the initial density matrix can lead to the universal dynamic scaling. It is further demonstrated both in a two-body system analytically and in a many-body system numerically. For the latter one, we calculate the dynamics of quantum gases quenched from the zero interaction to a finite interaction via the non-equilibrium high-temperature virial expansion. A dynamic scaling of the momentum distribution appears in certain momentum-time windows at unitarity as well as in the weak interacting limit. Remarkably, this universal scaling dynamics persists approximately with smaller scaling exponents even if the scaling symmetry is fairly broken. Our findings may offer a new perspective to interpret the related experiments. We also study the Contact dynamics in the BEC−BCS crossover. Surprisingly, the half-way time displays a maximum near unitarity while some damping oscillations occur on the BEC side due to the dimer state, which can be used to detect possible two-body bound states in experiments.

Creation of stable intrinsically anisotropic self-bound states with embedded vorticity is a challenging issue. Previously, no such states in Bose−Einstein condensates (BECs) or other physical settings were known. Dipolar BEC suggests a unique possibility to predict stable two dimensional anisotropic vortex quantum droplets (2D-AVQDs). We demonstrate that they can be created with the vortex axis oriented perpendicular to the polarization of dipoles. The stability area and characteristics of the 2D-AVQDs in the parameter space are revealed by means of analytical and numerical methods. Further, the rotation of the polarizing magnetic field is considered, and the largest angular velocities, up to which spinning 2D-AVQDs can follow the rotation in clockwise and anti-clockwise directions, are found. Collisions between moving 2D-AVQDs are studied too, demonstrating formation of bound states with a vortex−antivortex−vortex structure. A stability domain for such stationary bound states is identified. Unstable dipolar states, that can be readily implemented by means of phase imprinting, quickly transform into robust 2D-AVQDs, which suggests a straightforward possibility for the creation of these states in the experiment.

We present a novel class of Rydberg-mediated nuclear-spin entanglement in divalent atoms with global laser pulses. First, we show a fast nuclear-spin controlled phase gate of an arbitrary phase realizable either with two laser pulses when assisted by Stark shifts, or with three pulses. Second, we propose to create an electrons−nuclei-entangled state, which is named a super bell state (SBS) for it mimics a large Bell state incorporating three small Bell states. Third, we show a protocol to create a three-atom electrons-nuclei entangled state which contains the three-body W and Greenberger−Horne−Zeilinger (GHZ) states simultaneously. These protocols possess high intrinsic fidelities, do not require single-site Rydberg addressing, and can be executed with large Rydberg Rabi frequencies in a weak, Gauss-scale magnetic field. The latter two protocols can enable measurement-based preparation of Bell, hyperentangled, and GHZ states, and, specifically, SBS can enable quantum dense coding where one can share three classical bits of information by sending one particle.

Non-orthogonality in non-Hermitian quantum systems gives rise to tremendous exotic quantum phenomena, which can be fundamentally traced back to non-unitarity. In this paper, we introduce an interesting quantity (denoted as \eta) as a new variant of the Petermann factor to directly and efficiently measure non-unitarity and the associated non-Hermitian physics. By tuning the model parameters of underlying non-Hermitian systems, we find that the discontinuity of both \eta and its first-order derivative (denoted as \mathrm{\partial }\eta) pronouncedly captures rich physics that is fundamentally caused by non-unitarity. More concretely, in the 1D non-Hermitian topological systems, two mutually orthogonal edge states that are respectively localized on two boundaries become non-orthogonal in the vicinity of discontinuity of \eta as a function of the model parameter, which is dubbed “edge state transition”. Through theoretical analysis, we identify that the appearance of edge state transition indicates the existence of exceptional points (EPs) in topological edge states. Regarding the discontinuity of \mathrm{\partial }\eta, we investigate a two-level non-Hermitian model and establish a connection between the points of discontinuity of \mathrm{\partial }\eta and EPs of bulk states. By studying this connection in more general lattice models, we find that some models have discontinuity of \mathrm{\partial }\eta, implying the existence of EPs in bulk states.

Rare-earth orthoferrite REFeO₃ (where RE is a rare-earth ion) is gaining interest. We created a high-entropy orthoferrite (Tm_0.2Nd_0.2Dy_0.2Y_0.2Yb_0.2)FeO₃ (HEOR) by doping five RE ions in equimolar ratios and grew the single crystal by optical floating zone method. It strongly tends to form a single-phase structure stabilized by high configurational entropy. In the low-temperature region (11.6‒ 14.4 K), the spin reorientation transition (SRT) of Γ₂ (F_x, C_y, G_z)‒Γ₂₄‒Γ₄ (G_x, A_y, F_z) occurs. The weak ferromagnetic (FM) moment, which comes from the Fe sublattices distortion, rotates from the a- to c-axis. The two-step dynamic processes (Γ₂‒Γ₂₄‒Γ₄) are identified by AC susceptibility measurements. SRT in HEOR can be tuned in the range of 50‒60000 Oe, which is an order of magnitude larger than that of orthoferrites in the peer system, making it a candidate for high-field spin sensing. Typical spin-switching (SSW) and continuous spin-switching (CSSW) effects occur under low magnetic fields due to the strong interactions between RE‒Fe sublattices. The CSSW effect is tunable between 20‒50 Oe, and hence, HEOR potentially can be applied to spin modulation devices. Furthermore, because of the strong anisotropy of magnetic entropy change (-\mathrm{\Delta }{S}_{\text{m}}) and refrigeration capacity (RC) based on its high configurational entropy, HEOR is expected to provide a novel approach for refrigeration by altering the orientations of the crystallographic axes (anisotropic configurational entropy).

Recent studies have shown that the construction of nanophononic metamaterials can reduce thermal conductivity without affecting electrical properties, making them promising in many fields of application, such as energy conversion and thermal management. However, although extensive studies have been carried out on thermal conductivity reduction in nanophononic metamaterials, the local heat flux characteristic is still unclear. In this work, we construct a heat flux regulator which includes a silicon nanofilm with silicon pillars. The regulator has remarkable heat flux regulation ability, and various impacts on the regulation ability are explored. Surprisingly, even in the region without nanopillars, the local heat current is still lower than that in pristine silicon nanofilms, reduced by the neighboring nanopillars through the thermal proximity effect. We combine the analysis of the phonon participation ratio with the intensity of localized phonon modes to provide a clear explanation. Our findings not only provide insights into the mechanisms of heat flux regulation by nanophononic metamaterials, but also will open up new research directions to control local heat flux for a broad range of applications, including heat management, thermoelectric energy conversion, thermal cloak, and thermal concentrator.

Exciton physics in atomically thin transition-metal dichalcogenides (TMDCs) holds paramount importance for fundamental physics research and prospective applications. However, the experimental exploration of exciton physics, including excitonic coherence dynamics, exciton many-body interactions, and their optical properties, faces challenges stemming from factors such as spatial heterogeneity and intricate many-body effects. In this perspective, we elaborate upon how optical two-dimensional coherent spectroscopy (2DCS) emerges as an effective tool to tackle the challenges, and outline potential directions for gaining deeper insights into exciton physics in forthcoming experiments with the advancements in 2DCS techniques and new materials.

Valleytronic materials can provide new degrees of freedom to future electronic devices. In this work, the concepts of the ferrovalley metal (FVM) and valley gapless semiconductor (VGS) are proposed, which can be achieved in valleytronic bilayer systems by electric field engineering. In valleytronic bilayer systems, the interaction between out-of-plane ferroelectricity and A-type antiferromagnetism can induce layer-polarized anomalous valley Hall (LP-AVH) effect. The K and −K valleys of FVM are both metallic, and electron and hole carriers simultaneously exist. In the extreme case, the FVM can become VGS by analogizing spin gapless semiconductor (SGS). Moreover, it is proposed that the valley splitting enhancement and valley polarization reversal can be achieved by electric field engineering in valleytronic bilayer systems. Taking the bilayer \mathrm{R}\mathrm{u}\mathrm{B}{\mathrm{r}}_2 as an example, our proposal is confirmed by the first-principle calculations. The FVM and VGS can be achieved in bilayer \mathrm{R}\mathrm{u}\mathrm{B}{\mathrm{r}}_2 by applying electric field. With appropriate electric field range, increasing electric field can enhance valley splitting, and the valley polarization can be reversed by flipping electric field direction. To effectively tune valley properties by electric field in bilayer systems, the parent monolayer should possess out-of-plane magnetization, and have large valley splitting. Our results shed light on the possible role of electric field in tuning valleytronic bilayer systems, and provide a way to design the ferrovalley-related material by electric field.

Two-dimensional transition metal dichalcogenides (TMDs) exhibit promising application prospects in the domains of electronic devices, optoelectronic devices and spintronic devices due to their distinctive energy band structures and spin−orbit coupling properties. Cr-based chalcogenides with narrow or even zero bandgap, covering from semiconductors to metallic materials, have considerable potential for wide-band photodetection and two-dimensional magnetism. Currently, the preparation of 2D CrX_n (X = S, Se, Te) nanosheets primarily relies on chemical vapor deposition (CVD) and molecule beam epitaxy (MBE), which enable the production of high-quality large-area materials. This review article focuses on recent progress of 2D Cr-based chalcogenides, including unique crystal structure of the CrX_n system, phase-controlled synthesis, and heterojunction construction. Furthermore, a detailed introduction of room-temperature ferromagnetism and electrical/optoelectronic properties of 2D CrX_n is presented. Ultimately, this paper summarizes the challenges associated with utilizing 2D Cr-based chalcogenides in preparation strategies, optoelectronics devices, and spintronic devices while providing further insights.

With the emergence of the Internet of Things (IoT) and the rapid growth of big data generated by edge devices, there has been a growing need for electronic devices that are capable of processing and transmitting data at low power and high speeds. Traditional Complementary Metal-Oxide-Semiconductor (CMOS) devices are nonvolatile and often limited by their ability for certain IoT applications due to their unnecessary power consumption for data movement in von Neuman architecture-based systems. This has led to a surge in research and development efforts aimed at creating innovative electronic components and systems that can overcome these shortcomings and meet the evolving needs of the information era, which share features such as improved energy efficiency, higher processing speeds, and increased functionality. Memristors are a novel type of electronic device that has the potential to break down the barrier between storage and computing. By storing data and processing information within the same device, memristors can minimize the need for data movement, which allows for faster processing speeds and reduced energy consumption. To further improve the energy efficiency and reliability of memristors, there has been a growing trend toward diversifying the selection of dielectric materials used in memristors. Halide perovskites (HPs) have unique electrical and optical properties, including ion migration, charge trapping effect caused by intrinsic defects, excellent optical absorption efficiency, and high charge mobility, which makes them highly promising in applications of memristors. In this paper, we provide a comprehensive overview of the recent development in resistive switching behaviors of HPs and the underlying mechanisms. Furthermore, we summarize the diverse range of HPs, their respective performance metrics, as well as their applications in various fields. Finally, we critically evaluate the current bottlenecks and possible opportunities in the future research of HP memristors.

Quasi-two-dimensional (2D) Ruddlesden‒Popper (RP) halide perovskites, as a kind of emerged two-dimensional layered materials, have recently achieved great attentions in lasing materials field owing to their large exciton binding energy, high emission yield, large optical gain, and wide-range tuning of optical bandgap. This review will introduce research progresses of RP halide perovskites for lasing applications in aspects of materials, photophysics, and devices with emphasis on emission and lasing properties tailored by the molecular composition and interface. The materials, structures and fabrications are introduced in the first part. Next, the optical transitions and amplified spontaneous emission properties are discussed from the aspects of electronic structure, exciton, gain dynamics, and interface tailoring. Then, the research progresses on lasing devices are summarized and several types of lasers including VCSEL, DFB lasers, microlasers, random lasers, plasmonic lasers, and polariton lasers are discussed. At last, the challenges and perspectives would be provided.

The application of the semiclassical description to a particle-core system with imbued chiral symmetry is presented. The classical features of the chiral geometry in atomic nuclei and the associated dynamics are investigated for various core deformations and single-particle alignments. Distinct dynamical characteristics are identified in specific angular momentum ranges, triaxiality and alignment conditions. Quantum observables will be extracted from the classical picture for a quantitative description of experimental data provided as numerical examples of the model’s performance.

Progress in the studies of chirality in atomic nuclei at iThemba LABS is reviewed. New regions of chirality, around mass 80 and 190 have been discovered using the AFRODITE array, specifically in the nuclei ⁷⁴As, ^78,80,82Br, ⁸¹Kr, and ^193,194,198Tl. Many phenomena have been observed, including multiple chiral bands in the same nucleus, the coexistence of octupole correlations and nuclear chirality, and the coexistence of pseudo spin and nuclear chirality. The best example of chiral degeneracy to date was found in ¹⁹⁴Tl. The level scheme of ¹⁰⁶Ag has been revisited and interpreted in terms of two- and four-quasiparticle bands. Investigations using the particle-rotor model have shown that the fingerprints of chirality in the two-quasiparticle system only can occur in an idealised model description. For systems with a higher number of quasiparticles, the calculations showed that nuclear chirality can persist.

A simple semi-analytical collective model that takes into account the limitations of the variation interval of the collective variable is suggested to describe the chiral dynamics in triaxial odd−odd nuclei with a fixed particle−hole configuration. The collective Hamiltonian is constructed with the potential energy obtained using the postulated ansatz for the wave function symmetric with respect to chiral transformation. By diagonalizing the collective Hamiltonian the wave functions of the lowest states are obtained and the evolution of the energy splitting of the chiral doublets in transition from chiral vibration to chiral rotation regime is demonstrated.