Annalen der Physik最新文献

Recently, there has been significant interest regarding the regularization of a $��D�\to �4�$ limit of Einstein–Gauss–Bonnet (EGB) gravity. This regularization involves re-scaling the Gauss–Bonnet (GB) coupling constant as $��\alpha �/�(�D�-�4�)�$, which bypasses Lovelock's theorem and avoids Ostrogradsky instability. A noteworthy observation is that the maximally or spherically symmetric solutions for all the regularized gravities coincide in the $��4�D�$ scenario. Considering this, the wormhole solutions in the galactic halos are investigated based on three different choices of dark matter (DM) profiles, such as Universal Rotation Curve, Navarro–Frenk–White, and Scalar Field Dark Matter with the framework of $��4�D�$ EGB gravity. Also, the Karmarkar condition is used to find the exact solutions for the shape functions under different non-constant redshift functions. The energy conditions for each DM profile are discussed and the influence of GB coefficient $�\alpha$ in violating energy conditions are noticed, especially null energy conditions. Further, some physical features of wormholes, viz. complexity factor, active gravitational mass, total gravitational energy, and embedding diagrams, have been explored.

The discovery of the electron in 1897 by J. J. Thomson meant that the atom was no longer the smallest unit of matter. This led to a set of responses both experimental and theoretical which consolidated a new branch of physics—atomic physics. What were the tools available at the time to address atomic physics and how were they deployed? The research begins with Thomson who sought to describe a structure of the atom that accommodates both mechanical and electromagnetic properties, but he had little experimental data to base it on. It was indeed an experimental finding which paved the way for the modern conception of the structure of the atom—Rutherford's scattering experiment. A complex relation between theory and experiment in a new domain of physics is uncovered. While the revolutionary discovery of the electron was the result of a classical propagation experiment, the discovery of the concentrated charge at the center of the atom was an outcome of a scattering experiment—a bombardment technique. This technique has turned out to be the hallmark of experimental atomic physics.

In this work, the role of spin-orbit coupling (SOC) in the physical properties of $�{\mathrm{TlBi}}_2$ is reported. These electronic calculations reveal that the heavy elements Tl and Bi promote strong spin-orbit coupling, lifting some of the degeneracies at the high-symmetry points. The presence of SOC causes significant decreases in both elastic constants and elastic moduli, which in turn improve the compatibility of the calculated Debye temperature ($�{\Theta }_D$ = 80 K) with the recent experimental data of 83 K. Furthermore, our quasi-static harmonic approximation calculation, like this elastic constant calculation, confirms that taking SOC into account improves agreement with the experiment by decreasing value of Debye temperature from 95 to 85 K. Activating the SOC causes significant modifications in the phonon spectrum and the density of phonon states, as well as in the Eliashberg spectral function. As a result of these modifications, the electron–phonon coupling parameter ($�\lambda$) increases from 1.178 to 1.259, by $��\approx �7�\%�$. The calculated values of $�\lambda$ both with and without SOC imply that $�{\mathrm{TlBi}}_2$ can be treated as phonon-mediated superconductor with strong coupling. The SOC-induced increase in $�\lambda$ brings the superconducting transition temperature of $�{\mathrm{TlBi}}_2$ from 6.076 to 6.211 K, which is almost equal to the recent experimental value of 6.2 K.

This study investigates the dynamics of quantum coherence and entanglement in the spin-1 Heisenberg XXZ model. Particularly, the effects of the Heitler-London (HL) coupling and the Dzyaloshinskii-Moriya (DM) interaction are examined. By utilizing tools from quantum information theory, the concept of quantum correlated coherence and negativity are explored. The results show intrinsic decoherence leads to a decay of both correlated coherence and negativity. Interestingly, it is found that a small value of the Dzyaloshinskii-Moriya interaction can significantly enhance coherence and entanglement. Various factors influence the system dynamics, including the initial state, anisotropy parameter, and the coupling distance between spins. It is shown that, by fixing the anisotropy parameter, the isotropic Heisenberg models XX and XXX can be easily recovered. Ultimately, the findings highlight that the system maintains a coherent temporal evolution despite decoherence.

Microstructures, characterized by gain, nonlinearity, internal scattering, and boundary effects, offer an exceptional platform for exploring complex optical phenomena such as random lasing, chaos, and multidimensional speckles. Specifically, complex lasers generated within microcavities and optical fibers, where strong light confinement and scattering play diverse roles, have become a significant branch of laser research. Recently, the rapid advancement of materials, micro-nano technologies, and artificial intelligence has introduced new opportunities and challenges for the generation, control, and application of complex lasers. This review systematically examines various types of microcavity complex lasers from the perspective of microcavity structures with different degrees of disorder. It primarily focuses on the historical development, characteristics, regulation, and applications of disordered microcavity lasers and concludes with a discussion on the future trends in the development of microcavity complex lasers.

Over the past decade, the research on modelocked 2 $��\mu �m�$ fiber lasers has increased rapidly. Conventionally, modelocking is achieved with the existing quantum well structures as well as 2D materials classified as Real Saturable Absorbers. As time progressed and keeping in mind the versatility, stability and robustness, demonstration of 2 $��\mu �m�$ fiber lasers that are modelocked by Artificial Saturable Absorbers (ASA) gained importance. This class of Saturable Absorbers exhibits interesting properties, which can make them the best candidate to replace real material-based Saturable Absorbers. The progress of ASA based modelocking schemes in the 2 $��\mu �m�$ regime is explored and discussed in detail, along with its underlying physics, citing the various uses and the increasing market for ultrafast fiber lasers. Toward the end of this review, a comparison is drawn between different ASAs based modelocking schemes to get the most favorable conditions for desired output parameters as per one's needs. These fiber lasers with an all-fiber ASA foundation have potential uses in the fields of medical, LIDAR, mid-IR generation, environmental sensing, industrial, and defence.

A scheme leveraging reinforcement learning to engineer control fields for generating non-classical states is proposed. It is exemplified by the application to prepare spin-squeezed states for an open collective spin model where a linear control field is designed to govern the dynamics. The reinforcement learning agent determines the temporal sequence of control pulses, commencing from a coherent spin state in an environment characterized by dissipation and dephasing. Compared to the constant control scenario, this approach provides various control sequences maintaining collective spin squeezing and entanglement. It is observed that denser application of the control pulses enhances the performance of the outcomes. However, there is a minor enhancement in the performance by adding control actions. The proposed strategy demonstrates increased effectiveness for larger systems. Thermal excitations of the reservoir are detrimental to the control outcomes. Feasible experiments are suggested to implement this control proposal based on the comparison with the others. The extensions to continuous control problems and another quantum system are discussed. The replaceability of the reinforcement learning module is also emphasized. This research paves the way for its application in manipulating other quantum systems.

The quasiparticle spectrum and transport properties of the double quantum dot (DQD) deposited on a superconducting substrate (Andreev molecule) and side-coupled to a nanowire hosting Majorana zero modes (MZMs) are studied. Placing a DQD on the superconducting substrate induces the trivial Andreev-bound states (ABSs) in quantum dots. However, coupling of DQD with a nanowire causes the leakage of the MZM from the topological nanowire into quantum dots. The relationship between the Andreev states and the Majorana mode for different values of the coupling parameters is analyzed. Additionally, it is shown that the connection point of a metallic tip, treated as an scanning tunneling microscope (STM) tip, affects the measured results of the differential conductance.

Matrix-Product State Approach

The atomic nucleus contains particles that form interacting pairs, mirroring the Cooper pairs observed in superconductors. These pairs are traditionally analyzed using the mean-field technique pioneered by Bardeen, Cooper, and Schrieffer (BCS). However, the matrix-product state (MPS) approach, originally developed for one-dimensional spin chains in condensed-matter physics, offers a significant advancement. This method enables the precise computation of nuclear properties from both simple and more generalized pairing Hamiltonians, eliminating the artifacts commonly associated with mean-field approximations. For further details, see article number 2300436 by Roman Rausch and co-workers.