Quantum repeaters are proposed to overcome exponential photon loss over distance in fibers. One-way quantum repeaters eliminate the need for two-way classical communications, which can potentially outperform quantum m...
详细信息
作者：
Melia, FulvioDepartment of Physics
The Applied Math Program Department of Astronomy The University of Arizona TucsonAZ85721 United States
The conventional picture of supermassive black-hole growth in the standard model had already been seriously challenged by the emergence of ∼ 109 M☉ quasars at z ∼ 7.5, conflicting with the predicted formation of st...
详细信息
Efficient quantum repeaters are needed to combat photon losses in fibers in future quantum networks. Single atom coupled with photonic cavity offer a great platform for photon-atom gate. Here I propose a quantum repea...
详细信息
The support vector machine algorithm with a quantum kernel estimator (QSVM-Kernel), as a leading example of a quantum machine learning technique, has undergone significant advancements. Nevertheless, its integration w...
详细信息
Across many disciplines spanning from neuroscience and genomics to machine learning, atmospheric science, and finance, the problems of denoising large data matrices to recover hidden signals obscured by noise, and of ...
详细信息
Across many disciplines spanning from neuroscience and genomics to machine learning, atmospheric science, and finance, the problems of denoising large data matrices to recover hidden signals obscured by noise, and of estimating the structure of these signals, is of fundamental importance. A key to solving these problems lies in understanding how the singular value structure of a signal is deformed by noise. This question has been thoroughly studied in the well-known spiked matrix model, in which data matrices originate from low-rank signal matrices perturbed by additive noise matrices, in an asymptotic limit where matrix size tends to infinity but the signal rank remains finite. We first show, strikingly, that the singular value structure of large finite matrices (of size ∼1000) with even moderate-rank signals, as low as 10, is not accurately predicted by the finite-rank theory, thereby limiting the application of this theory to real data. To address these deficiencies, we analytically compute how the singular values and vectors of an arbitrary high-rank signal matrix are deformed by additive noise. We focus on an asymptotic limit corresponding to an extensive spike model, in which both the signal rank and the size of the data matrix tend to infinity at a constant ratio. We map out the phase diagram of the singular value structure of the extensive spike model as a joint function of signal strength and rank. We further exploit these analytics to derive optimal rotationally invariant denoisers to recover the hidden high-rank signal from the data, as well as optimal invariant estimators of the signal covariance structure. Our extensive-rank results yield several conceptual differences compared to the finite-rank case: (1) as signal strength increases, the singular value spectrum does not directly transition from a unimodal bulk phase to a disconnected phase, but instead there is a bimodal connected regime separating them; (2) the signal singular vectors can be partiall
Successful applications of complex vision-based behaviours underwater have lagged behind progress in terrestrial and aerial domains. This is largely due to the degraded image quality resulting from the physical phenom...
详细信息
This study aims to clarify the physics of the transition that is observed in Pr3Co4Sn13 (PCS) by specific heat at ∼138 K, which resembles the formation of a charge density wave (CDW). The work is performed using sync...
详细信息
This study aims to clarify the physics of the transition that is observed in Pr3Co4Sn13 (PCS) by specific heat at ∼138 K, which resembles the formation of a charge density wave (CDW). The work is performed using synchrotron radiation based scattering and spectroscopic techniques that include temperature-dependent x-ray diffraction (XRD), x-ray scattering (XRS), x-ray absorption near-edge structure (XANES)/extended x-ray absorption fine structure (EXAFS), resonant inelastic x-ray spectroscopy (RIXS), valence-band photoemission (VB-PES), and first-principles calculation. The appearance of satellite features in the XRD and XRS studies revealed a modulation of the structure along a new q vector (0.5,0.5,0) below 120 K. Phonon calculations suggest softening of a phonon mode and a possible superlattice transition at low temperatures. The XANES spectra of the Sn K, Co L3,2, and Pr M5,4 edge revealed an increase of charge transfer (CT) at low temperatures as a result of an enhancement of Co3d−Sn5p/Pr4f, and Pr4f−Sn5p hybridizations. The EXAFS study at the Sn K edge further suggested local distortion of the Sn sites because of Sn-Sn bond elongation at low temperatures. The VB-PES study and theoretical calculations that are based on spin-polarized density functional theory together confirm the strength of hybridization and the lack of any significant change in the band gap of the PCS with temperatures. The RIXS spectra at the Co L3 edge provide further evidence of the CT process, and the energy level of Co 3d states below the Fermi level were found to be static in the temperature range of 80 to 300 K, implying no change in the band gap of the PCS with temperatures. Based on the relevant results, the appearance of a clear kink around 138 K in the temperature-dependent specific heat measurements is caused by local lattice distortion at the Sn sites by a diffusionless mechanism, resulting in minimal alteration of the electronic structure through Sn-Sn bond elongation and
The enthalpy change involved in metal oxide reduction is a key quantity in various processes related to energy conversion and storage and is of particular interest for computational prediction. Often this prediction i...
详细信息
The enthalpy change involved in metal oxide reduction is a key quantity in various processes related to energy conversion and storage and is of particular interest for computational prediction. Often this prediction involves the simulation of a high-temperature reduction process with a 0-K methodology like density functional theory (DFT), and it is not infrequent for the high temperature and 0-K stable crystal structures to differ. This introduces a conundrum with regard to the choice of crystal structure to utilize in the computation, with approaches in the literature varying and experimental validation remaining scarce. In this work, we address both the crystal structure conundrum and the experimental validation, and then apply the insights we gain to guide a high-throughput search for new materials for solar thermochemical water-splitting applications. By computing the DFT+U oxygen-vacancy formation energy (ΔEvf) of a selection of ABO3 compounds and comparing different crystal structures for each composition, we highlight the issues that arise when the structure utilized in the computation is dynamically unstable at 0 K, namely the presence of an artificial lowering of ΔEvf, and the lack of convergence of ΔEvf with cell size. We solve these limitations by identifying and employing a suitable surrogate dynamically stable structure. We then validate the predictive power of our calculations against appositely generated experimental measurements of reduction enthalpy for a series of Hubbard U values, finding an accuracy ranging between 0.2–0.6 eV/O. In light of such conclusions, we revise and expand a previous a high-throughput DFT study on ABO3 perovskite oxides. We provide a list of candidate STCH materials, highlight trends with redox-active cation and structural distortion, and identify Mn4+, Mn3+, and Co3+ as the most promising redox-active cations.
There has been intense recent interest in the two-dimensional electron gases (2DEGs) that form at the surfaces and interfaces of KTaO3 (KTO), with the discovery of superconductivity at temperatures significantly highe...
详细信息
We study size- and charge-asymmetric oppositely charged colloids driven by an external electric field. The large particles are connected by harmonic springs, forming a hexagonal-lattice network, while the small partic...
详细信息
We study size- and charge-asymmetric oppositely charged colloids driven by an external electric field. The large particles are connected by harmonic springs, forming a hexagonal-lattice network, while the small particles are free of bonds and exhibit fluidlike motion. We show that this model exhibits a cluster formation pattern when the external driving force exceeds a critical value. The clustering is accompanied with stable wave packets in vibrational motions of the large particles.
暂无评论