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The challenges of measuring spin Seebeck noise

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arXiv 2023年

作者： Luo, Renjie Zhao, Xuanhan Legvold, Tanner J. Chen, Liyang Liu, Changjiang Hong, Deshun Bhattacharya, Anand Natelson, Douglas Department of Physics and Astronomy Rice University HoustonTX77005 United States Applied Physics Program Smalley-Curl Institute Rice University HoustonTX77005 United States Materials Science Division Argonne National Laboratory LemontIL60439 United States Department of Electrical and Computer Engineering Rice University HoustonTX77005 United States Department of Materials Science and NanoEngineering Rice University HoustonTX77005 United States

Just as electronic shot noise in driven conductors results from the granularity of charge and the statistical variation in the arrival times of charge carriers, there are predictions for fundamental noise in magnon currents due to angular momentum being carried by discrete excitations. The inverse spin Hall effect as a transduction mechanism to convert spin current into charge current raises the prospect of experimental investigations of such magnon shot noise. Spin Seebeck effect measurements have demonstrated the electrical detection of thermally driven magnon currents and have been suggested as an avenue for accessing spin current fluctuations. Using spin Seebeck structures made from yttrium iron garnet on gadolinium gallium garnet, we demonstrate the technical challenges inherent in such noise measurements. While there is a small increase in voltage noise in the inverse spin Hall detector at low temperatures associated with adding a magnetic field, the dependence on field orientation implies that this is not due to magnon shot noise. We describe theoretical predictions for the expected magnitude of magnon shot noise, highlighting ambiguities that exist. Further, we show that magnon shot noise detection through the standard inverse spin Hall approach is likely impossible due to geometric factors. Implications for future attempts to measure magnon shot noise are discussed. Copyright © 2023, The Authors. All rights reserved.

关键词： Shot noise

Single-Shot Readout of a Solid-State Spin in a Decoherence-Free Subspace

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Physical Review Applied 2021年第3期15卷 L031002-L031002页

作者： D. Farfurnik R. M. Pettit Z. Luo E. Waks Department of Electrical and Computer Engineering Institute for Research in Electronics and Applied Physics and Joint Quantum Institute University of Maryland College Park Maryland 20742 USA Intelligence Community Postdoctoral Research Fellowship Program University of Maryland College Park Maryland 20742 USA

The efficient single-photon-emission capabilities of quantum dot molecules position them as promising platforms for quantum information processing. Furthermore, quantum dot molecules feature a “decoherence-free” subspace that enables spin qubits with long coherence times. To efficiently read out the spin state within this subspace requires the optical cycling of isolated transitions that originate from a triplet manifold within the quantum dot molecule. We propose and theoretically study a two-stage spin-readout protocol within this decoherence-free subspace that allows single-shot readout performance. The process incorporates a microwave π pulse and optical cycling of the isolated transitions, which induces fluorescence that allows us to identify the initial spin state. This protocol offers enhanced readout fidelity compared to previous schemes that rely on the excitation of transitions that strongly decay to multiple ground states or require long initialization via slow optically forbidden transitions. By simulating the performance of the protocol, we show that an optimal spin-readout fidelity of over 97% and single-shot readout performance are achievable for a photon-collection efficiency of just 0.12%. This high readout performance for such realistic photon-collection conditions within the decoherence-free subspace expands the potential of quantum dot molecules as building blocks for quantum networks.

关键词： Optoelectronics Quantum information with solid state qubits Quantum networks Single photon sources Double quantum dots Coherent control Microwave techniques Quantum master equation

Parameter-free differential evolution algorithm for the analytic continuation of imaginary time correlation functions

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Physical Review E 2022年第2期106卷 025312-025312页

作者： Nathan S. Nichols Paul Sokol Adrian Del Maestro Data Science and Learning Division Argonne National Laboratory Argonne Illinois 60439 USA Department of Physics University of Vermont Burlington Vermont 05405 USA Materials Science Program University of Vermont Burlington Vermont 05404 USA Department of Physics Indiana University Bloomington Indiana 47408 USA Department of Physics and Astronomy University of Tennessee Knoxville Tennessee 37996 USA Min H. Kao Department of Electrical Engineering and Computer Science University of Tennessee Knoxville Tennessee 37996 USA

We report on differential evolution for analytic continuation: a parameter-free evolutionary algorithm to generate the dynamic structure factor from imaginary time correlation functions. Our approach to this long-standing problem in quantum many-body physics achieves enhanced spectral fidelity while using fewer compute (CPU) hours. The need for fine-tuning of algorithmic control parameters is eliminated by embedding them within the genome to be optimized for this evolutionary computation-based algorithm. Benchmarks are presented for models where the dynamic structure factor is known exactly and experimentally relevant results are included for quantum Monte Carlo simulations of bulk He4 below the superfluid transition temperature.

关键词： Nonequilibrium statistical mechanics Helium-4 superfluids Genetic algorithm Neutron scattering Numerical techniques Path-integral Monte Carlo Quantum Monte Carlo

Quantum Atomic Matter Near Two-Dimensional Materials in Microgravity

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arXiv 2023年

作者： Maestro, Adrian Del Kim, Sang Wook Bigelow, Nicholas P. Thompson, Robert J. Kotov, Valeri N. Department of Physics and Astronomy Min H. Kao Department of Electrical Engineering and Computer Science Institute for Advanced Materials and Manufacturing University of Tennessee KnoxvilleTN37996 United States Department of Physics and Materials Science Program University of Vermont BurlingtonVT05405 United States Department of Physics and Astronomy Institute of Optics Center for Coherence and Quantum Optics University of Rochester RochesterNY14627 United States Jet Propulsion Laboratory California Institute of Technology PasadenaCA91109 United States

Novel two-dimensional (2D) atomically flat materials, such as graphene and transition-metal dichalcogenides, exhibit unconventional Dirac electronic spectra. We propose to effectively engineer their interactions with cold atoms in microgravity, leading to a synergy between complex electronic and atomic collective quantum phases and phenomena. Dirac materials are susceptible to manipulation and quantum engineering via changes in their electronic properties by application of strain, doping with carriers, adjustment of their dielectric environment, etc. Consequently the interaction of atoms with such materials, namely the van der Waals / Casimir-Polder interaction, can be effectively manipulated, leading to the potential observation of physical effects such as Quantum Reflection off atomically thin materials and confined Bose-Einstein Condensate (BEC) frequency shifts. Copyright © 2023, The Authors. All rights reserved.

关键词： Transition metals

Deep Automatic Alignment of Mpox Dermatological Hand Photography

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Deep Automatic Alignment of Mpox Dermatological Hand Photogr...

IEEE International Symposium on Biomedical Imaging

作者： Bohan Jiang Andrew McNeil Yihao Liu Gaurav Rudravaram Inga Saknite Placide Mbala-Kingebeni Olivier Tshiani Mbaya Tyra Silaphet Rachel Weiss Lori E. Dodd Veronique Nussenblatt Daniel Moyer Bennett A. Landman Benoit M. Dawant Eric R. Tkaczyk Department of Electrical and Computer Engineering Vanderbilt University Nashville TN USA Department of Dermatology Vanderbilt University Medical Center Nashville TN USA Department of Veterans Affairs Dermatology Service and Research Service Nashville TN USA Biophotonics Laboratory University of Latvia Riga Latvia Institut National de Recherche Biomedicale Kinshasa Democratic Republic of the Congo Clinical Monitoring Research Program Directorate Frederick National Laboratory for Cancer Research Frederick MD USA Clinical Trials Research Section Division of Clinical Research National Institute of Allergy and Infectious Disease Bethesda MD USA Laboratory of Clinical Immunology and Microbiology National Institute of Allergy and Infectious Diseases Bethesda MD USA Department of Computer Science Vanderbilt University Nashville TN USA

ISBN: (数字)9798331520526

ISBN: (纸本)9798331520533

Mpox is a viral illness with heavy cutaneous involvement. Automatic tracking of mpox lesion progression is critical in determining the resolution of evolving lesions. This work introduces a novel application of deep learning for lesion monitoring through alignment of dermatological hand photographs. By adapting the VoxelMorph framework for 2D photographic data, we explore key point alignment across serial images. We trained our neural network model on a unique dataset of 1,658 hand images and evaluated its performance on a test set of 254 images. Additionally, we validated the method's generalizability with a supplementary set of 500 images, which included extensive Mpox infection. Our findings indicate modest yet significant improvements in key points and lesion center registration across different regularization strengths. Although promising, the complexity of hand structure presents challenges, requiring cautious application and further refinement, especially in regions with intense spatial discontinuities, such as interdigital areas.

关键词： Hands Photography Deep learning Training Three-dimensional displays Image resolution Neural networks Parametric statistics Lesions Monitoring

Enhanced nonlinearity in a functionalized whispering gallery mode microcavity

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Enhanced nonlinearity in a functionalized whispering gallery...

2020 Frontiers in Optics Conference, FiO 2020

作者： Pampel, Steven K. Bae, Kyuyoung Horning, Thomas M. Zohrabi, Mo Grayson, Michael Park, Wounjhang Gopinath, Juliet T. Department of Physics University of Boulder Colorado BoulderCO80309 United States Department of Electrical Computer and Energy Engineering University of Boulder Colorado BoulderCO80309 United States Materials Science and Engineering Program University of Colorado BoulderCO80309 United States

We report a ~3x increase in third-harmonic generation conversion efficiency using indium tin oxide (ITO) nanoparticles on the surface of a silica microsphere. This establishes ITO-microresonators as a promising tool f... 详细信息

ISBN: (纸本)9781943580804

关键词： Microresonators

CONVERGENCE SPEED AND APPROXIMATION ACCURACY OF NUMERICAL MCMC

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arXiv 2022年

作者： Cui, Tiangang Dong, Jing Jasra, Ajay Tong, Xin T. School of Mathematics Monash University Australia Graduate School of Business Columbia University United States Applied Mathematics and Computational Science Program Computer Electrical Mathematical Sciences and Engineering Division King Abdullah University of Science and Technology Saudi Arabia Department of Mathematics National University of Singapore Singapore

When implementing Markov Chain Monte Carlo (MCMC) algorithms, perturbation caused by numerical errors is sometimes inevitable. This paper studies how perturbation of MCMC affects the convergence speed and Monte Carlo estimation accuracy. Our results show that when the original Markov chain converges to stationarity fast enough and the perturbed transition kernel is a good approximation to the original transition kernel, the corresponding perturbed sampler has similar convergence speed and high approximation accuracy as well. We discuss two different analysis frameworks: ergodicity and spectral gap, both are widely used in the literature. Our results can be easily extended to obtain non-asymptotic error bounds for MCMC estimators. We also demonstrate how to apply our convergence and approximation results to the analysis of specific sampling algorithms, including Random walk Metropolis and Metropolis adjusted Langevin algorithm with perturbed target densities, and parallel tempering Monte Carlo with perturbed densities. Finally we present some simple numerical examples to verify our theoretical claims. Copyright © 2022, The Authors. All rights reserved.

关键词： Inverse problems

Effective Suppression of Leakage Current in SnO x Thin Films Enabled by Low-Concentration Al Doping

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Optical Materials 2025年

作者： Junzhe Zhang Zhong Pan Yumeng Guo Yunhui Jang Mengmeng Chu Jangkun Song Yongsang Kim Muhammad Quddamah Khokhar Junsin Yi Department of Electrical and Computer Engineering Sungkyunkwan University Suwon 16419 Gyeonggi-do Republic of Korea Department of Display Engineering Sungkyunkwan University Suwon 16419 Republic of Korea Interdisciplinary Program in Photovoltaic System Engineering Sungkyunkwan University Suwon 16419 Gyeonggi-do Republic of Korea

SnO 2 inherently exhibits a high carrier concentration, which, while beneficial for conductivity, poses reliability challenges in electronic devices, including leakage current, threshold voltage drift, and overall performance degradation. To address these issues and enhance device stability, this study demonstrates that low-concentration Al doping via atomic layer deposition (ALD) effectively modulates the carrier density of SnO x thin films, leading to improved electrical properties. Optimized 2% Al-doped SnO x thin films, annealed at 600°C in oxygen for 1 hour, exhibit enhanced device performance, achieving a mobility of 2.87 cm 2 /V·s, a leakage current reduction from 10 -8 A to 10 -10 A, and an on-off ratio of 10 6 . X-ray photoelectron spectroscopy (XPS) analysis reveals a significant reduction in oxygen vacancies after Al doping, which plays a crucial role in suppressing leakage pathways and stabilizing the threshold voltage. These improvements contribute to enhanced device reliability and electrical stability. Furthermore, the tailored Al doping strategy not only effectively controls the carrier concentration but also preserves the intrinsic conductivity of SnO x , making it a promising approach for high-performance thin-film transistors (TFTs) and optoelectronic applications. This work highlights the effectiveness of precise dopant engineering in optimizing metal oxide semiconductors, providing a scalable strategy to enhance device longevity and functionality.

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More Optimal Fractional-Order Stochastic Gradient Descent for Non-Convex Optimization Problems

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arXiv 2025年

作者： Partohaghighi, Mohammad Marcia, Roummel Chen, YangQuan Electrical Engineering and Computer Science Graduate Program University of California Merced United States Department of Applied Mathematics University of California Merced MercedCA United States Lab Department of Mechanical Engineering School of Engineering University of California MercedCA95343 United States

Fractional-order stochastic gradient descent (FOSGD) leverages fractional exponents to capture long-memory effects in optimization. However, its utility is often limited by the difficulty of tuning and stabilizing these exponents. We propose 2SED Fractional-Order Stochastic Gradient Descent (2SEDFOSGD), which integrates the Two-Scale Effective Dimension (2SED) algorithm with FOSGD to adapt the fractional exponent in a data-driven manner. By tracking model sensitivity and effective dimensionality, 2SEDFOSGD dynamically modulates the exponent to mitigate oscillations and hasten convergence. Theoretically, for onoconvex optimization problems, this approach preserves the advantages of fractional memory without the sluggish or unstable behavior observed in naïve fractional SGD. Empirical evaluations in Gaussian and α-stable noise scenarios using an autoregressive (AR) model highlight faster convergence and more robust parameter estimates compared to baseline methods, underscoring the potential of dimension-aware fractional techniques for advanced modeling and estimation tasks. © 2025, CC BY.

关键词： Convex optimization