Frontiers of Physics最新文献

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.

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 Green-berger–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.

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.

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.

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.

Engineering phonon transport in low-dimensional materials has great significance not only for fundamental research, but also for thermal management applications of electric devices. However, due to the difficulties of micro and nano processing and characterization techniques, the work on tuning phonon transport at nanoscale are scarce. In this work, by introducing Ar⁺ plasma, we probed the phonon transport in two-dimensional (2D) layered semiconductor PdSe₂ under different defect concentrations. By using thermal bridge method, the thermal conductivity was measured to decrease by 50% after a certain Ar⁺ irradiation, which implied a possible phase transition. Moreover, Raman characterizations were performed to show that the Raman sensitive peaks of PdSe₂ was red-shifted and finally became disappeared with the increase of defect concentration. “Defect engineering” proves be a practical strategy in tuning the phonon thermal transport in low-dimensional materials, thus providing guidance for potential application in designing thermoelectric devices with various emerging materials.

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.

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.

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.

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.