Annalen der Physik最新文献

In this work, a scheme to protect quantum entanglement from a non-Markovian noisy environment is proposed. By applying two quantum weak measurements before and after sending the quantum state into the noisy channel, the quantum state can be “pushed” closer to a decoherence-free state, reducing decoherence during the time evolution. Then, the second weak measurement can partially retrieve the initial quantum state from the state corrupted by the noisy environment. The study involves a non-Markovian dynamic equation to examine the impact of the memory effect on the protection scheme's performance. Various factors affecting the residual entanglement and the success probability are analyzed. The results suggest that two measurement strengths shall be chosen approximately in a linear relation, with the best ratio determined by the memory time of the environment. Additionally, it is demonstrated that the memory effect significantly enhances the protection efficiency. Lastly, the scheme's robustness against systematic errors is evaluated. 

Despite the extensive applications of perovskite compounds, the precise nature of non-Hermitian bonding in these materials remains poorly understood. In this study, density functional theory calculations are performed to determine the electronic structures of perovskite compounds. In particular, the bandgaps of Ba₂ScNbO₆ and Ba₂LuNbO₆ are found to be 2.617 and 2.629 eV, respectively, and the deformation bond energies and non-Hermitian bonding of these compounds are calculated. The relationship between the non-Hermitian zeros of the O-Nb bond of Ba₂ScNbO₆ and the non-Hermitian zeros of the Sc-O bond is found to be similar but with varying sizes. Further, in-depth research on non-Hermitian chemistry verified that precise control of atomic bonding and electron states can be achieved, providing new insights into the study of chemical bonds.

Quantitative climate mobility research has, so far, focused primarily on climate change impacts on migration outcomes. This focus has led to a separation between quantitative climate migration research and the broader field of migration studies. In this paper ways are proposed for quantitative research to better address the complexity in the relationship between climate change and mobility. First technical suggestions are presented to improve upon migration model setups and designs and highlight promising developments. Then it is argued that quantitative methodologies can broaden the scope of research inquiries by examining how climate mitigation and adaptation efforts influence mobility, as well as assessing how mobility itself impacts vulnerability.

In the realm weak force sensing, an important issue is to suppress fundamental noise (quantum noise and thermal noise), as they limit the accuracy of force measurement. In this study, a weak force sensing scheme that combines a degenerate optical parametric amplifier (OPA) and an auxiliary mechanical oscillator into a cavity optomechanical system to reduce quantum noise is investigated. It is demonstrated that the noise reduction of two coupled oscillators depends on their norm mode splitting. and provide a classic analogy and quantum perspective for further clarification. Besides, the noise reduction mechanism of OPA is to reduce the fluctuation of photon number and enhance the squeezing of the cavity field. A specific design is proposed that aimed at enhancing the joint effect of both, beyond what can be achieved using OPA alone or two series coupled oscillators. This scheme provides a new perspective for deeper understanding of cavity field squeezing and auxiliary oscillator in force sensing.

High-field superconductors are characterized by a spin splitting of the density of states, giving rise to spin transport phenomena. This includes spin-polarized tunneling, spin-dependent thermoelectric effects, long-range quasiparticle spin transport, and spin-dependent coupling of supercurrents and quasiparticles. This review gives a brief overview of the theory background, recent experimental progress in the field, and an outlook on open problems and possible applications.

The additivity properties for both bipartite and multipartite systems are investigated by using entropic uncertainty relations (EUR) defined in terms of the joint Shannon entropy of probabilities of local measurement outcomes. In particular, state-independent and state-dependent entropic inequalities are introduced. Interestingly, the violation of these inequalities is strictly connected with the presence of quantum correlations. It is shown that the additivity of EUR holds only for EUR that involve two observables, while this is not the case for inequalities that consider more than two observables or the addition of the von Neumann entropy of a subsystem. They are applied to bipartite systems and to several classes of states of a three-qubit system.

Feature dimensionality plays an important role for modern medical diagnosis and image processing. In this work, the study introduces an optoelectronic neural network for multimodal image segmentation, which dramatically improves computing speed and decreases imaging acquisition cost in brain tumor diagnostics. Multi-layer metasurfaces are utilized as an image preprocessor that reduces image dimensionality at the physical layer. The low-dimensional image is then processed to a U-Net semantic segmentation network, to handle the complex and heterogeneous nature of brain image data. By using diffractive neural network, the metasurface encoder is optimized and physically constructed with high-efficiency transmission metasurfaces. The entire optoelectronic network attains a structural similarity index measure (SSIM) of 96%, demonstrating its potential to revolutionize on-site medical image processing with its high precision in segmenting brain imaging data.

The transmissions of fermions are investigated through gapped graphene structures by employing a combination of double barrier tilting and a time-oscillating potential. The latter introduces additional sidebands into the transmission probability that manifest at energy levels determined by the frequency and incident energy. These sidebands arise from the absorption or emission of photons generated by the oscillating potential. It is demonstrated that the tilting and positioning of the scattering events within the barriers play a crucial role in determining the peak of tunneling resistance. In particular, the presence of a mid-barrier-embedded scatter leads to a transition from a peak to a cusp when the incident energy reaches the Dirac point within a barrier. Additionally, it is that introducing a time-varying potential results in transmissions dispersing across both the central band and the sidebands.

From the perspective of resource theory, it is interesting to achieve the same quantum task using as few quantum resources as possible. Semiquantum key distribution (SQKD), which allows a quantum user to share a confidential key with a classical user who prepares and operates qubits on only one basis, is an important example for studying this issue. To further limit the quantum resources used by users, in this paper, the first SQKD protocol is constructed, which restricts the quantum user to prepare quantum states on only one basis and removes the classical user's measurement capability. Furthermore, it is proven that the constructed protocol is secure against the restricted attack by deriving a key rate expression of the error rate in the asymptotic scenario. The work in this paper provides inspiration for achieving quantum superiority with minimal quantum resources.

The functional integral formulation of the Hubbard model when treated in its Kotliar-Ruckenstein representation in the radial gauge involves fermionic, as well as complex and radial slave boson fields. In order to improve on the understanding of the interplay of the three types of fields, and on the nature of the latter, a comprehensive investigation of an exactly solvable two-site cluster is performed, as it entails all pitfalls embodied in this approach. It is first shown that the exact partition function is recovered, even when incorporating in the calculation the square root factors that are at the heart of the representation, when suitably regularized. It is shown that using radial slave boson fields allows to overcome all hurdles following from the normal ordering procedure. It is then demonstrated that this applies to the Green's function as well, and to the correlation functions of physical interest, thereby answering the criticisms raised by Schönhammer [K. Schönhammer, Phys. Rev. B 1990 42, 2591]. In addition, the investigation generalizes the calculations to the Hubbard model extended by a non-local Coulomb interaction.