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Tuning 2D magnetism in Fe3+XGeTe2 films by element doping

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National Science Review 2022年第6期9卷 163-170页

作者： Shanshan Liu Zihan Li Ke Yang Enze Zhang Awadhesh Narayan Xiaoqian Zhang Jiayi Zhu Wenqing Liu Zhiming Liao Masaki Kudo Takaaki Toriyama Yunkun Yang Qiang Li Linfeng Ai Ce Huang Jiabao Sun Xiaojiao Guo Wenzhong Bao Qingsong Deng Yanhui Chen Lifeng Yin Jian Shen Xiaodong Han Syo Matsumura Jin Zou Yongbing Xu Xiaodong Xu Hua Wu Faxian Xiu State Key Laboratory of Surface Physics and Department of Physics Fudan University Institute for Nanoelectronic Devices and Quantum Computing Fudan University College of Science University of Shanghai for Science and Technology Laboratory for Computational Physical Sciences(MOE) Fudan University Solid State and Structural Chemistry Unit Indian Institute of Science School of Electronic Science and Engineering Nanjing University Department of Physics University of Washington Department of Electronic Engineering Royal Holloway University of London Materials Engineering The University of Queensland Beijing Key Laboratory of Microstructure and Property of Advanced Materials Institute of Microstructure and Property of Advanced Materials Beijing University of Technology The Ultramicroscopy Research Center Kyushu University State Key Laboratory of ASIC and System School of Microelectronics Fudan University Collaborative Innovation Center of Advanced Microstructures Department of Applied Quantum Physics and Nuclear Engineering Kyushu University Centre for Microscopy and Microanalysis The University of Queensland Shanghai Research Center for Quantum Sciences

Two-dimensional（2D） ferromagnetic materials have been discovered with tunable magnetism and orbital-driven nodal-line features. Controlling the 2D magnetism in exfoliated nanoflakes via electric/magnetic fields enables a boosted Curie temperature（TC） or phase transitions. One of the challenges, however, is the realization of high TC2D magnets that are tunable, robust and suitable for large scale fabrication. Here, we report molecular-beam epitaxy growth of wafer-scale Fe3+XGeTe2films with TCabove room temperature. By controlling the Fe composition in Fe3+XGeTe2, a continuously modulated TCin a broad range of 185–320 K has been achieved. This widely tunable TCis attributed to the doped interlayer Fe that provides a 40% enhancement around the optimal composition X = 2. We further fabricated magnetic tunneling junction device arrays that exhibit clear tunneling signals. Our results show an effective and reliable approach, i.e. element doping, to producing robust and tunable ferromagnetism beyond room temperature in a large-scale 2D Fe3+XGeTe2fashion.

关键词： 2D ferromagnetic material Fe3+XGeTe2 film element doping above room temperature, TC tunability

Thermal relaxation error on QKD: Effect and A Probable Bypass

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arXiv 2022年

作者： Aziz, Munsi Afif Gond, Bishwajit Prasad Nandi, Srijita Ray, Soujanya Bhoumik, Debasmita Majumdar, Ritajit Department of Computer Science & Engineering Government College of Engineering and Leather Technology India National Institute of Technology Sikkim India Advanced Computing & Microelectronics Unit Indian Statistical Institute Kolkata India

Quantum cryptography was proposed as a counter to the capacity of quantum computers to break classical cryptosystems. A broad subclass of quantum cryptography, called quantum key distribution (QKD), relies on quantum mechanical process for secure distribution of the keys. Quantum channels are inherently noisy, and therefore these protocols will be susceptible to noise as well. In this paper, we study the performance of two QKD protocols - BB84 and E91 under thermal relaxation error. We show that while E91 protocol loses its security immediately due to loss of entanglement, the performance of BB84 protocol reduces to random guessing with increasing time. Next, we consider the action of an Eve on the BB84 protocol under thermal relaxation noise, who is restricted to guessing the outcome of the protocol only. Under this restriction, we show that Eve can still do better than random guessing when equipped with the characteristics of the noisy channel. Finally, we propose a modification of the BB84 protocol which retains the security of the original protocol, but ensures that Eve cannot get any advantage in guessing the outcome, even with a complete channel information. Copyright © 2022, The Authors. All rights reserved.

关键词： Quantum cryptography

Parking Problem by Oblivious Mobile Robots in Infinite Grids

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arXiv 2023年

作者： Chakraborty, Abhinav Mukhopadhyaya, Krishnendu Department of Computer Science and Engineering Institute of Technical Education and Research Siksha O Anusandhan University Odisha Bhubaneswar India Advanced Computing and Microelectronics Unit Indian Statistical Institute 203 B. T. Road West Bengal Kolkata700108 India

In this paper, the parking problem of a swarm of mobile robots has been studied. The robots are deployed at the nodes of an infinite grid, which has a subset of prefixed nodes marked as parking nodes. Each parking node pi has a capacity of ki which is given as input and equals the maximum number of robots a parking node can accommodate. As a solution to the parking problem, robots need to partition themselves into groups so that each parking node contains a number of robots that are equal to the capacity of the node in the final configuration. It is assumed that the number of robots in the initial configuration represents the sum of the capacities of the parking nodes. The robots are assumed to be autonomous, anonymous, homogeneous, identical and oblivious. They operate under an asynchronous scheduler. They neither have any agreement on the coordinate axes nor do they agree on a common chirality. All the initial configurations for which the problem is unsolvable have been identified. A deterministic distributed algorithm has been proposed for the remaining configurations, ensuring the solvability of the problem. Copyright © 2023, The Authors. All rights reserved.

关键词： Mobile robots

GreyConE: Greybox fuzzing+Concolic execution guided test generation for high level design

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arXiv 2022年

作者： Debnath, Mukta Chowdhury, Animesh Basak Saha, Debasri Sur-Kolay, Susmita Advanced Computing and Microelectronics Unit Indian Statistical Institute Kolkata India Centre for Cybersecurity New York University United States A. K. Choudhury School of It U. of Calcutta India

Exhaustive testing of high-level designs pose an arduous challenge due to complex branching conditions, loop structures and inherent concurrency of hardware designs. Test engineers aim to generate quality test-cases satisfying various code coverage metrics to ensure minimal presence of bugs in a design. Prior works in testing SystemC designs are time inefficient which obstruct achieving the desired coverage in shorter timespan. We interleave greybox fuzzing and concolic execution in a systematic manner and generate quality test-cases accelerating test coverage metrics. Our results outperform state-of-the-art methods in terms of number of test cases and branch-coverage for some of the benchmarks, and runtime for most of them. © 2022, CC BY.

关键词： High level synthesis

MINIMUM CONSISTENT SUBSET IN TREES AND INTERVAL GRAPHS

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arXiv 2024年

作者： Banik, Aritra Das, Sayani Maheshwari, Anil Manna, Bubai Nandy, Subhas C. Krishna Priya, K.M. Roy, Bodhayan Roy, Sasanka Sahu, Abhishek National Institute of Science Education and Research An OCC of Homi Bhabha National Institute Odisha Bhubaneswar752050 India Theoretical Computer Science The Institute of Mathematical Sciences India School of Computer Science Carleton University Canada Department of Mathematics Indian Institute of Technology Kharagpur India Advanced Computing and Microelectronics Unit Indian Statistical Institute Kolkata India

In the Minimum Consistent Subset (MCS) problem, we are presented with a connected simple undirected graph G = (V, E), consisting of a vertex set V of size n and an edge set E. Each vertex in V is assigned a color from the set {1, 2, . . ., c}. The objective is to determine a subset V ′ ⊆ V with minimum possible cardinality, such that for every vertex v ∈ V , at least one of its nearest neighbors in V ′ (measured in terms of the hop distance) shares the same color as v. The decision problem, indicating whether there exists a subset V ′ of cardinality at most l for some positive integer l, is known to be NP-complete even for planar graphs. In this paper, we establish that the MCS problem for trees, when the number of colors c is considered an input parameter, is NP-complete10. We propose a fixed-parameter tractable (FPT) algorithm for MCS on trees running in O(26cn6) time, significantly improving the currently best-known algorithm whose running time is O(24cn2c+3). In an effort to comprehensively understand the computational complexity of the MCS problem across different graph classes, we extend our investigation to interval graphs. We show that it remains NP-complete for interval graphs, thus enriching graph classes where MCS remains intractable. Copyright © 2024, The Authors. All rights reserved.

关键词： Color

Growth rates of the number of empty triangles and simplices

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Computational Geometry 2026年 130卷

作者： Bhaswar B. Bhattacharya Sandip Das Sk Samim Islam Saumya Sen Department of Statistics and Data Science University of Pennsylvania USA Advanced Computing and Microelectronics Unit Indian Statistical Institute Kolkata India

Given a set P of n points in R 2 , in general position, denote by N 2 ( P ) the number of empty triangles with vertices in P . In this paper we investigate by how much N 2 ( P ) changes if a point x is removed from P . By constructing a graph G 2 ( x , P ) based on the arrangement of the empty triangles incident on x , we transform this geometric problem to the problem of counting triangles in the graph G 2 ( x , P ) . We study properties of the graph G 2 ( x , P ) and, in particular, show that it is diamond-free. This relates the growth rate of the number of empty triangles to the famous Ruzsa–Szemerédi problem. We also derive similar bounds for the growth rate of the number of empty simplices for point sets in R d .

关键词： Discrete geometry Empty triangles and simplices Extremal combinatorics Diamond-free graphs

Trace-driven Modeling and Verification of a Mobility-Aware Service Allocation and Migration Policy for Mobile Edge computing

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Trace-driven Modeling and Verification of a Mobility-Aware S...

IEEE International Conference on Web Services (ICWS)

作者： Kaustabha Ray Ansuman Banerjee Advanced Computing and Microelectronics Unit Indian Statistical Institute

ISBN: (数字)9781728187860

ISBN: (纸本)9781728187877

In recent times, Mobile Edge computing (MEC) has emerged as a new paradigm allowing low-latency access to services deployed on edge nodes offering computation, storage and communication facilities. Vendors deploy their services on MEC servers to improve performance and mitigate network latencies often encountered in accessing cloud services. An allocation policy determines how to allocate service requests from mobile users to MEC servers. A number of proposals for binding user service requests to nearby edge servers enroute have been proposed in literature. However, none of these proposals, to the best of our knowledge, provide quantitative performance guarantees on the quality of service metrics. Indeed, the evolving environment, along with a large allocation configuration space makes proving performance guarantees for such allocation policies a challenging task. To address such issues, we propose a trace driven approach to derive a formal model of allocation policies and perform quantitative verification to produce probabilistic guarantees on performance metrics. We use benchmark real world MEC server and user datasets and a mobility aware allocation and migration policy from recent literature to validate our model. Experimental results show our model's effectiveness in quantitatively reasoning about service allocation performance metrics in MEC systems.

关键词： Measurement Web services Computational modeling Resource management Servers Proposals Edge computing

FragQC: An Efficient Quantum Error Reduction Technique using Quantum Circuit Fragmentation

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arXiv 2023年

作者： Basu, Saikat Das, Arnav Saha, Amit Chakrabarti, Amlan Sur-Kolay, Susmita A.K.Choudhury School of Information Technology U. of Calcutta Kolkata India LTIMindtree Ltd. Kolkata India Dept. of Computer Science St. Xavier's University Kolkata India Pune India Advanced Computing and Microelectronics Unit Indian Statistical Institute Kolkata India

Quantum computers must meet extremely stringent qualitative and quantitative requirements on their qubits in order to solve real-life problems. Quantum circuit fragmentation techniques divide a large quantum circuit into a number of sub-circuits that can be executed on the smaller noisy quantum hardware available. However, the process of quantum circuit fragmentation involves finding an ideal cut that has exponential time complexity, and also classical post-processing required to reconstruct the output. In this paper, we represent a quantum circuit using a weighted graph and propose a novel classical graph partitioning algorithm for selecting an efficient fragmentation that reduces the entanglement between the sub-circuits along with balancing the estimated error in each sub-circuit. We also demonstrate a comparative study over different classical and quantum approaches of graph partitioning for finding such a cut. We present FragQC, a software tool that cuts a quantum circuit into sub-circuits when its error probability exceeds a certain threshold. With this proposed approach, we achieve an increase of fidelity by 14.83% compared to direct execution without cutting the circuit, and 8.45% over the state-of-the-art ILP-based method, for the benchmark circuits. © 2023, CC BY.

关键词： Genetic algorithms

Exploiting degeneracy to construct good ternary quantum error correcting code

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arXiv 2020年

作者： Majumdar, Ritajit Sur-Kolay, Susmita Advanced Computing & Microelectronics Unit Indian Statistical Institute India

Quantum error-correcting code for higher dimensional systems can, in general, be directly constructed from the codes for qubit systems. What remains unknown is whether there exist efficient code design techniques for higher dimensional systems. In this paper, we propose a 7-qutrit error-correcting code for the ternary quantum system and show that this design formulation has no equivalence in qubit systems. This code is optimum in the number of qutrits required to correct a single error while maintaining the CSS structure. This degenerate CSS code can (i) correct up to seven simultaneous phase errors and a single bit error, (ii) correct two simultaneous bit errors on pre-defined pairs of qutrits on eighteen out of twenty-one possible pairs, and (iii) in terms of the cost of implementation, the depth of the circuit of this code is only two more than that of the ternary Steane code. Our proposed code shows that it is possible to design better codes explicitly for ternary quantum systems instead of simply carrying over codes from binary quantum systems. Copyright © 2020, The Authors. All rights reserved.

关键词： Quantum optics