Annalen der Physik最新文献

Recent advances in experimental quantum platforms have enabled the development of devices capable of generating high-dimensional quantum states, facilitating their use in quantum information processing tasks. High-dimensional entangled states offer significant advantages in areas such as quantum key distribution, quantum communication, and quantum metrology. While the Schmidt rank (SR) characterizes entanglement for pure bipartite states in high-dimensional spaces, its extension to mixed states is the Schmidt number (SN). However, experimentally determining the SN of unknown mixed states remains a significant challenge. Here, we propose an experimentally feasible method to determine the SN of unknown states, constructing a self-guided SN witness scheme. Leveraging techniques from quantum state verification (QSV), this method allows SN estimation using only local measurements, thereby avoiding the need for direct projections onto high-dimensional maximally entangled states. The self-guided aspect is implemented through a Stochastic Gradient Algorithm (SGA) that systematically explores the space of local unitary operations to maximize a fidelity related to Schmidt number witnesses. We numerically demonstrate that for four-dimensional entangled states, our scheme accurately estimates the SN, typically converging within approximately 200 iterations. Our results also show that the method is robust to realistic imperfections, highlighting its potential for practical applications in quantum information processing.

Halide perovskites (HPs) are among the most promising semiconductor candidates for ultrashort pulse generation due to their intrinsic high material gain and ultrafast carrier dynamics. By introducing an ingeniously-designed cavity structure, picosecond (ps) or even femtosecond (fs) laser pulses can be plausibly obtained from the perovskite devices for a wide variety of applications. A comprehensive understand of the carrier density dependence of exciton transport and recombination as well as light‒matter interaction can help researchers gain deeper insight into the ultrashort pulse generation during lasing. Here, an overview of the recent progress on ultrafast charge carrier dynamics in 3D bulk single-crystal perovskites as well as quantum-confined 2D/quasi-2D Ruddlesden–Popper perovskites and 0D perovskite nanocrystals/quantum-dots is provided. Additionally, state-of-the-art developments in pulse generation from various perovskite lasers are summarized, with particular attention paid to gain-switched ultrashort laser pulse emission in different HP microcavities. The physical mechanisms that influence the pulse characteristics of HP lasers based on a rate equation model is also discussed. Finally, the challenges and future prospects of HPs in realizing ultrashort fs-optical pulses for practical applications are discussed emphatically.

$�{\mathrm{CoNb}}_2$$�O_6$ is a unique magnetic material. It features bulk 3D magnetic order at low temperatures, but its quantum critical behavior in a magnetic field is well described by the 1D transverse-field Ising universality class. This behavior is facilitated by the structural arrangement of magnetic $�{\mathrm{Co}}^{�2�+�}$ ions in nearly isolated zig-zag chains. In this work, we investigate the effect of random site dilution on the critical properties of such a quasi-1D quantum Ising system. To this end, we introduce an anisotropic site-diluted 3D transverse-field Ising model. We find that site dilution leads to unconventional activated scaling behavior at the quantum phase transition. Interestingly, the critical exponents of the quantum critical point are in good agreement with those of the disordered 3D transverse-field Ising universality class, despite the strong spatial anisotropy. We discuss the generality of our findings as well as implications for experiments.

The B₁₂ icosahedron serves as the fundamental building block in boron-rich compounds, where the combination of strong multi-center covalent bonding and low atomic mass favors high-frequency phonons and robust electron-phonon coupling, rendering them as promising candidates for high-temperature superconductivity. However, these materials are typically insulating due to the electron-counting rule. Here, we propose a viable strategy to achieve superconductivity in LiB₁₃C₂ by degassing Li and leading to the formation of icosahedron-based B₁₃C₂ superconductor. First-principles calculations demonstrate that the removal of Li alters density of states at the Fermi level ($�N_{E_F}$) while retains its 3D covalent framework. Strikingly, after the complete removal of Li, the resulting B₁₃C₂ is predicted to be an anisotropic single-gap superconductor with a critical temperature (T_c) of 53 K, primarily driven by strong coupling between B₁₂ icosahedral vibrational modes and conduction electrons. This work illustrates a potential route toward achieving high-temperature superconductivity in icosahedron-based boron-rich frameworks.

The susceptibility of second-harmonic generation (SHG) is highly dependent on the symmetry of the material. Constructing a Janus structure by surface modification can break out-of-plane mirror symmetry, leading to asymmetric charge distribution and the generation of a built-in electric field. This study systematically investigates the electronic properties and nonlinear optical responses of Janus derivative of graphane, by one side, fluorinating graphane. Due to the vertical built-in electric field, the out-of-plane SHG response is approximately three times that of the in-plane response, reaching around 60 pm/V. Through the intensity polar plots of the Janus monolayer under different incident lights, the anisotropic response of SHG is further Analyses. This research provides theoretical guidance for further experimental exploration of Janus fluorinated graphane and lays a foundation for its application in nonlinear optical devices.

The high critical temperature (high-T_c) hydride superconductor H₃S has attracted great interest in high-pressure superconductivity research. Finding a strategy to reduce its stabilization pressure while maintaining its high T_c is of great importance for hydrogen-based superconductor studies. In this work, we performed high-throughput calculations for $���F�d��\overline{3}�m�$-H₆SX, P3m1-H₉S₂X and $��P�\overline{3}��m�1��$-H₉S₂X at chosen pressures, where X corresponds to elements from groups IIIA to VIIA. Our results reveal that the difference in covalent radius between S and X atoms is a critical factor influencing the dynamically stable pressure and superconductivity of H₃S. The larger the covalent radius of X relative to S, the lower the dynamically stable pressure required for these hydrides, while still maintaining excellent superconductivity. Based on our analysis, we find that H₉S₂In, H₉S₂Sn, H₉S₂Te, and H₆SIn remain dynamically stable at 20 GPa, with T_c of 54, 72, 5, and 54 K, respectively. Our study proposes a novel strategy of introducing elements with large covalent radii into cubic H₃S to obtain high-T_c superconductors at mild pressure.