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arXiv 2024年

作者： Gowda, Chinmayee Chowde Kartsev, Alexey Tiwari, Nishant Safronov, A.A. Pandey, Prafull Roy, Ajit K. Ajayan, Pulickel M. Galvão, Douglas S. Tiwary, Chandra Sekhar School of Nano Science and Technology Indian Institute of Technology West Bengal Kharagpur721302 India Computing Center of the Far Eastern Branch The Russian Academy of Sciences Khabarovsk680000 Russia MIREA-Russian Technological University Moscow119454 Russia 6 Miklukho-Maklaya St Moscow117198 Russia Department of Metallurgical and Materials Engineering Indian Institute of Technology West Bengal Kharagpur721302 India Materials Engineering Indian Institute of Technology Gandhinagar Gujurat 382055 India Materials and Manufacturing Directorate Air Force Research Laboratory Wright Patterson AFBOH45433-7718 United States Department of Materials Science and NanoEngineering Rice University 6100 S Main Street HoustonTX77005 United States Applied Physics Department and Computational Engineering and Sciences State University of Campinas SP Campinas13083-970 Brazil

Two-dimensional (2D) chromium telluride Cr2Te3 exhibits strong ferromagnetic ordering with high coercivity at low temperatures and paramagnetic behavior when approaching room temperature. The spin states of monolayer Cr2Te3 shows ferromagnetic ordering in the ground state, and in-situ Raman analysis shows reversible structure transformation and hence ferromagnetic to paramagnetic transition during low-temperature heating cycles (0 - 25 °C). The magnetic phase transition near room temperature in the 2D Cr2Te3 prompted the study of these layered material exploration for energy application. We demonstrate that the low-temperature ferromagnetic behavior can be used to magnetically deice material surfaces using an external magnetic source, avoiding the use of harsh chemicals and high temperatures. The hydrophobic nature and dipole interactions of H2O molecules with the surface of the 2D Cr2Te3 coating aid in the condensation of ice droplets formed on the surface. First-principles calculations also confirm the observed crystal structure, surface interaction, and magnetic properties of 2D Cr2Te3 © 2024, CC BY.

关键词： Density functional theory

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Divergence-Free Flux Globalization Based Well-Balanced Path-Conservative Central-Upwind Schemes for Rotating Shallow Water Magnetohydrodynamics

arXiv

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arXiv 2023年

作者： Chertock, Alina Kurganov, Alexander Redle, Michael Zeitlin, Vladimir Department of Mathematics Center for Research in Scientific Computing North Carolina State University RaleighNC27695 United States Department of Mathematics Shenzhen International Center for Mathematics Guangdong Provincial Key Laboratory of Computational Science and Material Design Southern University of Science and Technology Shenzhen518055 China Applied and Computational Mathematics RWTH Aachen University Aachen52062 Germany Department of Mathematics North Carolina State University RaleighNC27695 United States CNRS Paris75231 France Shenzhen International Center for Mathematics Southern University of Science and Technology Shenzhen518055 China

We develop a new second-order flux globalization based path-conservative central-upwind (PCCU) scheme for rotating shallow water magnetohydrodynamic equations. The new scheme is designed not only to maintain the divergence-free constraint of the magnetic field at the discrete level but also to satisfy the well-balanced (WB) property by exactly preserving some physically relevant steady states of the underlying system. The locally divergence-free constraint of the magnetic field is enforced by following the method recently introduced in [A. Chertock, A. Kurganov, M. Redle, and K. Wu, ArXiv preprint (2022), arXiv:2212.02682]: we consider a Godunov-Powell modified version of the studied system, introduce additional equations by spatially differentiating the magnetic field equations, and modify the reconstruction procedures for magnetic field variables. The WB property is ensured by implementing a flux globalization approach within the PCCU scheme, leading to a method capable of preserving both still- and moving-water equilibria exactly. In addition to provably achieving both the WB and divergence-free properties, the new method is implemented on an unstaggered grid and does not require any (approximate) Riemann problem solvers. The performance of the proposed method is demonstrated in several numerical experiments that confirm the lack of spurious oscillations, robustness, and high resolution of the obtained results. © 2023, CC BY.

关键词： Magnetohydrodynamics

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Divergence-Free Flux Globalization Based Well-Balanced Path-Conservative Central-Upwind Schemes for Rotating Shallow Water Magnetohydrodynamics

SSRN

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SSRN 2023年

作者： Chertock, Alina Kurganov, Alexander Redle, Michael Zeitlin, Vladimir Department of Mathematics Center for Research in Scientific Computing North Carolina State University RaleighNC27695 United States Department of Mathematics Shenzhen International Center for Mathematics Guangdong Provincial Key Laboratory of Computational Science and Material Design Southern University of Science and Technology Shenzhen518055 China Applied and Computational Mathematics RWTH Aachen University Aachen52062 Germany Department of Mathematics North Carolina State University RaleighNC27695 United States CNRS Paris 75231 France Shenzhen International Center for Mathematics Southern University of Science and Technology Shenzhen518055 China

关键词： Magnetohydrodynamics

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Quantifying Quantum Entanglement in Two-Qubit Mixed State from Connected Correlator

SSRN

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SSRN 2023年

作者： Guo, Xingyu Ma, Chen-Te Guangdong Provincial Key Laboratory of Nuclear Science Institute of Quantum Matter South China Normal University Guangdong Guangzhou510006 China Guangdong-Hong Kong Joint Laboratory of Quantum Matter Southern Nuclear Science Computing Center South China Normal University Guangdong Guangzhou510006 China Asia Pacific Center for Theoretical Physics Pohang University of Science and Technology Gyeongsangbuk-do Pohang37673 Korea Republic of School of Physics and Telecommunication Engineering South China Normal University Guangdong Guangzhou510006 China The Laboratory for Quantum Gravity and Strings Department of Mathematics and Applied Mathematics University of Cape Town Private Bag Rondebosch7700 South Africa

We quantify Quantum Entanglement using a connected correlation matrix. Quantifying the degree of entanglement between particles requires entanglement measures. The connected correlation matrix is used to quantify Quantum Entanglement, suggesting that it encompasses all necessary entanglement measures. Our study suggests starting with a three-qubit state and obtaining a mixed state by partial tracing over one qubit. By considering the connected correlation, we aim to eliminate the non-connected sector and capture all relevant entanglement degrees. We classify mixed states and demonstrate that separable states exhibit the lowest correlation within each classified class. We then show that the entanglement measure monotonically increases for the correlation measure. This suggests that the connected correlation effectively quantifies Quantum Entanglement. We compare the results to the logarithmic negativity, another measure of entanglement. Our findings indicate that the negativity increases with the correlation measure, but it is not monotonic. Finally, we propose that interpreting Quantum Entanglement from a local perspective is possible, considering that the observable is a vector with locality but violates freedom of choice. © 2023, The Authors. All rights reserved.

关键词： Quantum entanglement

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Anisotropic superconductivity of niobium based on its response to nonmagnetic disorder

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Physical Review B 2022年第22期106卷 224511-224511页

作者： Makariy A. Tanatar Daniele Torsello Kamal R. Joshi Sunil Ghimire Cameron J. Kopas Jayss Marshall Josh Y. Mutus Gianluca Ghigo Mehdi Zarea James A. Sauls Ruslan Prozorov Ames National Laboratory Ames Iowa 50011 USA Department of Physics & Astronomy Iowa State University Ames Iowa 50011 USA Department of Applied Science and Technology Politecnico di Torino I-10129 Torino Italy Istituto Nazionale di Fisica Nucleare Sezione di Torino I-10125 Torino Italy Rigetti Computing 775 Heinz Ave. Berkeley California 94710 USA Center for Applied Physics and Superconducting Technologies Department of Physics and Astronomy Northwestern University Evanston Illinois 60208 USA Hearne Institute of Theoretical Physics Department of Physics and Astronomy Louisiana State University Baton Rouge Louisiana 70808 USA

Niobium is one of the most studied superconductors, both theoretically and experimentally. It is tremendously important for applications, and it has the highest superconducting transition temperature, Tc=9.32 K, of all pure metals. In addition to power applications in alloys, pure niobium is used for sensitive magnetosensing, radio-frequency cavities, and, more recently, as circuit metallization layers in superconducting qubits. A detailed understanding of its electronic and superconducting structure, especially its normal and superconducting state anisotropies, is crucial for mitigating the loss of quantum coherence in such devices. Recently, a microscopic theory of the anisotropic properties of niobium with the disorder was put forward. To verify theoretical predictions, we studied the effect of disorder produced by 3.5 MeV proton irradiation of thin Nb films grown by the same team and using the same protocols as those used in transmon qubits. By measuring the superconducting transition temperature and upper critical fields, we show a clear suppression of Tc by potential (nonmagnetic) scattering, which is directly related to the anisotropic order parameter. We obtain a very close quantitative agreement between the theory and the experiment.

关键词： Impurities in superconductors Irradiation effects Superconducting order parameter Superconductivity Transition temperature Thin films Type-II superconductors Resistivity measurements

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A directional regularization method for the limited-angle Helsinki Tomography Challenge using the Core Imaging Library (CIL)

arXiv

引用

arXiv 2023年

作者： Jørgensen, Jakob Sauer Papoutsellis, Evangelos Murgatroyd, Laura Fardell, Gemma Pasca, Edoardo Department of Applied Mathematics and Computer Science Technical University of Denmark. Richard Petersens Plads Building 324 Kgs. Lyngby2800 Denmark Department of Mathematics The University of Manchester Oxford Road Alan Turing Building ManchesterM13 9PL United Kingdom Finden Ltd Rutherford Appleton Laboratory Harwell Campus DidcotOX11 0QX United Kingdom Scientific Computing Department Science & Technology Facilities Council Rutherford Appleton Laboratory Harwell Campus DidcotOX11 0QX United Kingdom

This article presents the algorithms developed by the Core Imaging Library (CIL) developer team for the Helsinki Tomography Challenge 2022. The challenge focused on reconstructing 2D phantom shapes from limited-angle computed tomography (CT) data. The CIL team designed and implemented five reconstruction methods using CIL (https://***/cil/), an open-source Python package for tomographic imaging. The CIL team adopted a model-based reconstruction strategy, unique to this challenge with all other teams relying on deep-learning techniques. The CIL algorithms showcased exceptional performance, with one algorithm securing the third place in the competition. The best-performing algorithm employed careful CT data pre-processing and an optimization problem with single-sided directional total variation regularization combined with isotropic total variation and tailored lower and upper bounds. The reconstructions and segmentations achieved high quality for data with angular ranges down to 50 degrees, and in some cases acceptable performance even at 40 and 30 degrees. This study highlights the effectiveness of model-based approaches in limited-angle tomography and emphasizes the importance of proper algorithmic design leveraging on available prior knowledge to overcome data limitations. Finally, this study highlights the flexibility of CIL for prototyping and comparison of different optimization methods.1MSC Codes 65R32, 94A08, 65K10 © 2023, CC BY.

关键词： Computerized tomography

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Heisenberg-Limited Adaptive Gradient Estimation for Multiple Observables

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PRX Quantum 2025年第2期6卷 020308-020308页

作者： Kaito Wada Naoki Yamamoto Nobuyuki Yoshioka Graduate School of Science and Technology Keio University 3-14-1 Hiyoshi Kohoku Yokohama Kanagawa 223-8522 Japan Department of Applied Physics and Physico-Informatics Keio University 3-14-1 Hiyoshi Kohoku-ku Yokohama Kanagawa 223-8522 Japan Quantum Computing Center Keio University Hiyoshi 3-14-1 Kohoku Yokohama 223-8522 Japan Department of Applied Physics University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-8656 Japan Theoretical Quantum Physics Laboratory RIKEN Cluster for Pioneering Research (CPR) Wako-shi Saitama 351-0198 Japan JST PRESTO 4-1-8 Honcho Kawaguchi Saitama 332-0012 Japan International Center for Elementary Particle Physics The University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-0033 Japan

In quantum mechanics, measuring the expectation value of a general observable has an inherent statistical uncertainty that is quantified by variance or mean squared error of measurement outcome. While the uncertainty can be reduced by averaging several samples, the number of samples should be minimized when each sample is very costly. This is especially the case for fault-tolerant quantum computing that involves measurement of multiple observables of nontrivial states in large quantum systems that exceed the capabilities of classical computers. In this work, we provide an adaptive quantum algorithm for estimating the expectation values of M general observables within root mean squared error ε simultaneously, using O(ε−1Mlog M) queries to a state preparation oracle of a target state. This remarkably achieves the scaling of Heisenberg limit 1/ε, a fundamental bound on the estimation precision in terms of mean squared error, together with the sublinear scaling of the number of observables M. The proposed method is an adaptive version of the quantum gradient-estimation algorithm and has a resource-efficient implementation due to its adaptiveness. Specifically, the space overhead in the proposed method is O(M), which is independent from the estimation precision ε unlike noniterative algorithms. In addition, our method can avoid the numerical instability problem for constructing quantum circuits in a large-scale task (e.g., ε≪1 in our case), which appears in the actual implementation of many algorithms relying on quantum signal processing techniques. Our method paves a new way to precisely understand and predict various physical properties in complicated quantum systems using quantum computers.

关键词： Quantum computers

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Time-domain methods for quantifying dynamic cerebral blood flow autoregulation: Review and recommendations. A white paper from the Cerebrovascular Research Network (CARNet)

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Journal of Cerebral Blood Flow and Metabolism 2024年第9期44卷 1480-1514页

作者： Kostoglou, Kyriaki Bello-Robles, Felipe Brassard, Patrice Chacon, Max Claassen, Jurgen AHR Czosnyka, Marek Elting, Jan-Willem Hu, Kun Labrecque, Lawrence Liu, Jia Marmarelis, Vasilis Z Payne, Stephen J Shin, Dae Cheol Simpson, David Smirl, Jonathan Panerai, Ronney B Mitsis, Georgios D Department of Electrical and Computer Engineering McGill University Montreal QC Canada Institute of Neural Engineering Graz University of Technology Graz Austria Departamento de Ingeniería Informática Universidad de Santiago de Chile Santiago Chile Department of Kinesiology Faculty of Medicine Université Laval QC Canada Research Center of the Institut universitaire de cardiologie et de pneumologie de Québec Quebec QC Canada Department of Geriatrics Radboud University Medical Center Research Institute for Medical Innovation and Donders Institute Nijmegen Netherlands Cerebral Haemodynamics in Ageing and Stroke Medicine (CHiASM) Department of Cardiovascular Sciences University of Leicester Leicester United Kingdom Department of Clinical Neurosciences Neurosurgery Department University of Cambridge Cambridge United Kingdom Department of Neurology and Clinical Neurophysiology University Medical Center Groningen Groningen Netherlands Medical Biodynamics Program Division of Sleep and Circadian Disorders Brigham and Women's Hospital Harvard Medical School Boston MA United States Division of Sleep Medicine Harvard Medical School Boston MA United States Laboratory for Engineering and Scientific Computing Institute of Advanced Computing and Digital Engineering Shenzhen Institute of Advanced Technology Chinese Academy of Sciences Guangdong Shenzhen China Department Biomedical Engineering Viterbi School of Engineering University of Southern California Los Angeles CA United States Institute of Applied Mechanics National Taiwan University Taipei Taiwan Institute of Sound and Vibration Research University of Southampton Southampton United Kingdom Cerebrovascular Concussion Laboratory Faculty of Kinesiology University of Calgary Calgary AB Canada Sport Injury Prevention Research Centre Faculty of Kinesiology University of Calgary Calgary AB Canada Hotchkiss Brain Institute University of Calgary Calgary AB Canada NIHR Leicester Biomedical Research Centre Bri

Cerebral Autoregulation (CA) is an important physiological mechanism stabilizing cerebral blood flow (CBF) in response to changes in cerebral perfusion pressure (CPP). By maintaining an adequate, relatively constant supply of blood flow, CA plays a critical role in brain function. Quantifying CA under different physiological and pathological states is crucial for understanding its implications. This knowledge may serve as a foundation for informed clinical decision-making, particularly in cases where CA may become impaired. The quantification of CA functionality typically involves constructing models that capture the relationship between CPP (or arterial blood pressure) and experimental measures of CBF. Besides describing normal CA function, these models provide a means to detect possible deviations from the latter. In this context, a recent white paper from the Cerebrovascular Research Network focused on Transfer Function Analysis (TFA), which obtains frequency domain estimates of dynamic CA. In the present paper, we consider the use of time-domain techniques as an alternative approach. Due to their increased flexibility, time-domain methods enable the mitigation of measurement/physiological noise and the incorporation of nonlinearities and time variations in CA dynamics. Here, we provide practical recommendations and guidelines to support researchers and clinicians in effectively utilizing these techniques to study CA. © The Author(s) 2024.

关键词： CARNet cerebral autoregulation cerebral blood flow time-domain methods white paper

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Logical quantum processor based on reconfigurable atom arrays

arXiv

引用

arXiv 2023年

作者： Bluvstein, Dolev Evered, Simon J. Geim, Alexandra A. Li, Sophie H. Zhou, Hengyun Manovitz, Tom Ebadi, Sepehr Cain, Madelyn Kalinowski, Marcin Hangleiter, Dominik Ataides, J. Pablo Bonilla Maskara, Nishad Cong, Iris Gao, Xun Rodriguez, Pedro Sales Karolyshyn, Thomas Semeghini, Giulia Gullans, Michael J. Greiner, Markus Vuletić, Vladan Lukin, Mikhail D. Department of Physics Harvard University CambridgeMA02138 United States QuEra Computing Inc. BostonMA02135 United States Joint Center for Quantum Information and Computer Science NIST University of Maryland College ParkMD20742 United States John A. Paulson School of Engineering and Applied Sciences Harvard University CambridgeMA02138 United States Department of Physics Research Laboratory of Electronics Massachusetts Institute of Technology CambridgeMA02139 United States

Suppressing errors is the central challenge for useful quantum computing [1], requiring quantum error correction [2-6] for large-scale processing. However, the overhead in the realization of error-corrected "logical" qubits, where information is encoded across many physical qubits for redundancy [2-4], poses significant challenges to large-scale logical quantum computing. Here we report the realization of a programmable quantum processor based on encoded logical qubits operating with up to 280 physical qubits. Utilizing logical-level control and a zoned architecture in reconfigurable neutral atom arrays [7], our system combines high two-qubit gate fidelities [8], arbitrary connectivity [7, 9], as well as fully programmable single-qubit rotations and mid-circuit readout [10-15]. Operating this logical processor with various types of encodings, we demonstrate improvement of a two-qubit logic gate by scaling surface code [6] distance from d = 3 to d = 7, preparation of color code qubits with break-even fidelities [5], fault-tolerant creation of logical GHZ states and feedforward entanglement teleportation, as well as operation of 40 color code qubits. Finally, using three-dimensional [[8,3,2]] code blocks [16, 17], we realize computationally complex sampling circuits [18] with up to 48 logical qubits entangled with hypercube connectivity [19] with 228 logical two-qubit gates and 48 logical CCZ gates [20]. We find that this logical encoding substantially improves algorithmic performance with error detection, outperforming physical qubit fidelities at both cross-entropy benchmarking and quantum simulations of fast scrambling [21, 22]. These results herald the advent of early error-corrected quantum computation and chart a path toward large-scale logical processors. Copyright © 2023, The Authors. All rights reserved.

关键词： Qubits

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Picosecond Synchronization of Photon Pairs through a Fiber Link between Fermilab and Argonne National Laboratories

arXiv

引用

arXiv 2022年

作者： Kapoor, Keshav Xie, Si Chung, Joaquin Valivarthi, Raju Peña, Cristián Narváez, Lautaro Sinclair, Neil Allmaras, Jason P. Beyer, Andrew D. Davis, Samantha I. Fabre, Gabriel Iskander, George Kanter, Gregory S. Kettimuthu, Rajkumar Korzh, Boris Kumar, Prem Lauk, Nikolai Mueller, Andrew Shaw, Matthew Spentzouris, Panagiotis Spiropulu, Maria Thomas, Jordan M. Wollman, Emma E. The Fermi National Accelerator Laboratory BataviaIL60510 United States California Institute of Technology PasadenaCA91125 United States The Argonne National Laboratory LemontIL60439 United States The University of Chicago Physics Department ChicagoIL60637 United States The John A. Paulson School of Engineering and Applied Sciences Harvard University CambridgeMA02138 United States The Jet Propulsion Laboratory California Institute of Technology PasadenaCA91109 United States The Center for Photonic Communication and Computing Department of Electrical and Computer Engineering McCormick School of Engineering and Applied Science Northwestern University 2145 Sheridan Road EvanstonIL60208 United States NuCrypt LLC 1460 Renaissance Dr #205 Park RidgeIL60068 United States Department of Physics and Astronomy Northwestern University 2145 Sheridan Road EvanstonIL60208 United States The Division of Engineering and Applied Science The Alliance for Quantum Technologies and the Jet Propulsion Laboratory California Institute of Technology PasadenaCA91125 United States

We demonstrate a three-node quantum network for C-band photon pairs using 2 pairs of 59 km of deployed fiber between Fermi and Argonne National Laboratories. The C-band pairs are directed to nodes using a standard telecommunication switch and synchronized to picosecond-scale timing resolution using a coexisting O-or L-band optical clock distribution system. We measure a reduction of coincidence-to-accidental ratio (CAR) of the C-band pairs from 51 ± 2 to 5.3 ± 0.4 due to Raman scattering of the O-band clock pulses. Despite this reduction, the CAR is nevertheless suitable for quantum networks. Copyright © 2022, The Authors. All rights reserved.

关键词： Quantum communication

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