Annalen der Physik最新文献

Quantum Computing

This cover image, related to article number 2300457 by Selçuk Çakmak and co-workers, illustrates the layers of a soft-core processor to execute RISC (reduced instruction set computer)-V instruction set architecture (RISC-V assembly code) on a quantum processing unit (QPU) based on superconducting qubits. The soft-core processor circuit layer represents a quantum circuit that realizes the example code on the QPU. As a result, the quantum computer (QC) writes the message on the QC terminal screen.

The adaptive voter model is widely used to model opinion dynamics in social complex networks. However, existing adaptive voter models are limited to only pairwise interactions and fail to capture the intricate social dynamics that arises in groups. This paper extends the adaptive voter model to hypergraphs to explore how forces of peer pressure influence collective decision-making. The model consists of two processes: individuals can either consult the group and change their opinion or leave the group and join a different one. The interplay between those two processes gives rise to a two-phase dynamics. In the initial phase, the topology of the hypergraph quickly reaches a new stable state. In the subsequent phase, opinion dynamics plays out on the new topology depending on the mechanism by which opinions spread. If the group always follows the majority, the network rapidly converges to fragmented communities. In contrast, if individuals choose an opinion proportionally to its representation in the group, the system remains in a metastable state for an extended period of time. The results are supported both by stochastic simulations and an analytical mean-field description in terms of hypergraph moments with a moment closure at the pair level.

A proposal is made on how to manipulate photon blockades (PBs) and photon-induced tunneling (PIT) in an optomechanical cavity with a Bose-Einstein Condensate. It is shown that the single-photon blockade (1PB) can emerge with appropriate scattering strength between atoms. Further, by tuning interatomic scattering strength, the switch between 1PB and PIT at the fixed optical detuning can be realized in interatomic repulsion or attraction conditions. The enhancement of 1PB can also be achieved. The scattering control of PBs can be understood from the perspective of the anharmonicity of the energy levels modulated by the interatomic collision. Such a system can be equivalent to a conventional optomechanical system plus an interatomic scattering term. It is found that although there are no PBs in the conventional optomechanical system, in the BEC optomechanical system (BECOMS), PBs can occur at the fixed optical detuning. Moreover, the BECOMS can exhibit stronger 1PB under the same optomechanical coupling intensity. Due to the advantages of intrinsic strong optomechanical nonlinearity and the negligible thermal noise of the mechanical environment, BECOMS is promising for experimental realization of PBs. The results open new possibilities for manipulating few-photon states in quantum regime in cavity optomechanics with a Bose-Einstein Condensate.

Dielectric mirrors comprising thin-film multilayers are widely used in optical experiments because they can achieve substantially higher reflectance compared to metal mirrors. Here, potential problems are investigated that can arise when dielectric mirrors are used at oblique incidence, in particular for focused beams. It is found that light beams reflected from dielectric mirrors can experience lateral beam shifts, beam-shape distortion, and depolarization, and these effects have a strong dependence on wavelength, incident angle, and incident polarization. Because vendors of dielectric mirrors typically do not share the particular layer structure of their products, several dielectric-mirror stacks are designed and simulated, and then the lateral beam shift from two commercial dielectric mirrors and one coated metal mirror is also measured. This paper brings awareness of the tradeoffs between dielectric mirrors and front-surface metal mirrors in certain optics experiments, and it is suggested that vendors of dielectric mirrors provide information about beam shifts, distortion, and depolarization when their products are used at oblique incidence.

Thin ferromagnet/heavy metal multilayer films are considered as prospective media for a magnetic recording and Co/Pd films are a good example of such materials. In this work, the magnetic properties and micromagnetic structure of Co/Pd multilayer films are studied with different bilayer thicknesses ([Co(0.3 × t nm)/Pd(0.5 × t nm)]10), but with the same ratio Co versus Pd. Transmission electron microscope and X-ray diffraction studies allow authors to suppose that the investigated films are highly mixed alloys. Magnetic force microscopy and Lorentz transmission electron microscopy showed the presence of various micromagnetic features in the films. Along with skyrmions that are well-known magnetic topological artifacts some new features are revealed, which are interpreted as 360° domain walls, skyrmioniums and the combination of the above two. It is found that the type and density of micromagnetic features strongly depend on the bilayer thickness parameter (t). The effect is associated with the peculiarities of interfacial magnetic interactions in the samples with highly mixed interfaces. The tooling coefficient represents a useful tool of the electron beam evaporation technique enabling wide manipulation of micromagnetic particles, in particular, skyrmioniums that are currently considered a prospective media for current driven magnetic recording.

Non-Standard Coupling

The back-cover image illustrates the proposed quantum coupling between particles in heterostructures. Unlike standard coupling (the lattice with white squares), where the coupled particles interact only through their potential interaction V(x,y), when dealing with heterostructures (the lattice with colored squares) an additional type of coupling can arise, T(x,y), which shapes the structure of the quantum system by shaping the uncertainty relations followed by the specific type of coupling between the particles. For further details see article 2300363 by Tomer Shushi.

Jumping Platonic Solids

Macroscopic objects excited mechanically by vibrating plates represent simple systems that can exhibit complex dynamics, including quasi-chaotic behavior. Bouncing spheres were investigated for decades. Such mechanical excitation provides a basis for experimental studies of granular gases. The study of bouncing Platonic solids (see article number 2300349 by Ralf Stannarius and co-workers) adds more complexity such as coupling of rotational and translational degrees of freedom. Integrated intelligent sensor chips were employed to analyze the particle trajectories and rotations.

The influence of a a rectangular potential barrier on the quantum transport of fermions in silicene is explored. Specifically, analytical solutions are presented to derive transmission and reflection probabilities together with conductance. It is shown that the transmission is highly sensitive to both the barrier height and incident energy. As a result, the occurrence of Klein and resonant tunnelings is observed, with a significant dependence on the barrier width. Notably, it is found that perfect transmission extends beyond normal incidence, occurring at various oblique angles. Moreover, the transmission pattern exhibits a more fragmented structure with increasing barrier width, reminiscent of Fabry-Pérot resonances. In contrast, the conductance displays a non-monotonic dependence on incident energy and features rapid oscillations with a rising barrier height. However, at a constant barrier height, there is a minimal disparity among conductance profiles for high incident energy values. When incident energy equals the barrier height, the conductance experiences a local minimum. For a thin barrier, a substantial reduction in conductance is observed, unlike the oscillatory behavior seen with a thicker barrier. These findings underscore the progress in silicene research and offer a fresh perspective on the relativistic applications of tunneling in this material.