检索结果-内蒙古大学图书馆

Magnetic anisotropy reversal driven by structural symmetry-breaking in monolayer α-RuCl3

学校读者我要写书评

暂无评论

arXiv 2022年

作者： Yang, Bowen Goh, Yin Min Sung, Suk Hyun Ye, Gaihua Biswas, Sananda Kaib, David A.S. Dhakal, Ramesh Yan, Shaohua Li, Chenghe Jiang, Shengwei Chen, Fangchu Lei, Hechang He, Rui Valentí, Roser Winter, Stephen M. Hovden, Robert Tsen, Adam W. Institute for Quantum Computing University of Waterloo WaterlooONN2L 3G1 Canada Department of Physics and Astronomy University of Waterloo WaterlooONN2L 3G1 Canada Department of Physics University of Michigan Ann ArborMI48109 United States Department of Materials Science and Engineering University of Michigan Ann ArborMI48109 United States Department of Electrical and Computer Engineering Texas Tech University LubbockTX79409 United States Institut für Theoretische Physik Goethe-Universität Frankfurt Max-von-Laue-Strasse 1 Frankfurt am Main60438 Germany Department of Physics Center for Functional Materials Wake Forest University Winston-SalemNC27109 United States Department of Physics Beijing Key Laboratory of Opto-electronic Functional Materials & Micro-nano Devices Renmin University of China Beijing100872 China Department of Physics Cornell University IthacaNY United States School of Physics and Astronomy Shanghai Jiao Tong University Shanghai China Applied Physics Program University of Michigan Ann ArborMI48109 United States Department of Chemistry University of Waterloo WaterlooONN2L 3G1 Canada

The Kitaev model is a celebrated spin-½ model on the two-dimensional (2D) honeycomb lattice with bond-dependent Ising interactions1, which features a highly entangled quantum spin liquid (QSL) ground state, fractionalized Majorana excitations, and a series of magnetic-field-induced quantum phase transitions1-7. The search for materials realizing the Kitaev model has been an ongoing challenge for over a decade and may potentially lead to applications in fault-tolerant topological quantum computing8. Yet, the unavoidable presence of non-Kitaev interactions (Heisenberg, off-diagonal, next-nearest neighbor, etc.) almost always drives the ground state away from the QSL phase, and a careful tuning of the exchange parameters is needed9-12. α-RuCl3 is a layered van der Waals material that is a particularly promising candidate to realize Kitaev physics13-15. Although the ground state is zigzag (ZZ) antiferromagnetic (AFM), this ordering can be suppressed with the application of an ~ 6-8T in-plane magnetic field. The presence of a half-integer thermal quantum Hall effect has been reported in this intermediate phase at low temperature16,17, while an unusual continuum of magnetic excitations can be seen even without magnetic field that persists far above the Néel temperature (TN ~ 7-8K)18,19. Both observations hint at α-RuCl3 being in proximity to a QSL, making it a current subject of intense scrutiny. Yet from a theoretical point of view, a QSL induced by in-plane field generally cannot be accounted for, as most calculations for α-RuCl3 show Kitaev phases more broadly emerging from an out-of-plane field6,20-23. Due to the strong "easy-plane" magnetic anisotropy of bulk crystals, however, prohibitively high fields above 30T are required to access such states24-26. The strong coupling between the spin, charge, and lattice degrees of freedom in α-RuCl3 presents an exciting opportunity to tune its magnetic interactions via external perturbations. Although pressure27-29, strain30,

关键词： Ground state

Resource theories of communication

学校读者我要写书评

暂无评论

arXiv 2019年

作者： Kristjánsson, Hlér Chiribella, Giulio Salek, Sina Ebler, Daniel Wilson, Matthew Department of Computer Science University of Oxford Wolfson Building Parks Road Oxford United Kingdom HKU-Oxford Joint Laboratory for Quantum Information and Computation Department of Computer Science The University of Hong Kong Pokfulam Road Hong Kong Hong Kong Perimeter Institute for Theoretical Physics 31 Caroline Street North WaterlooON Canada HKU Shenzhen Institute of Research and Innovation Kejizhong 2nd Road Shenzhen China Center for Quantum Computing Peng Cheng Laboratory No. 2 Xingke 1st Street Nanshan Shenzhen China Shenzhen China Wolfson College University of Oxford Linton Road Oxford United Kingdom

A series of recent works has shown that placing communication channels in a coherent superposition of alternative configurations can boost their ability to transmit information. Instances of this phenomenon are the advantages arising from the use of communication devices in a superposition of alternative causal orders, and those arising from the transmission of information along a superposition of alternative trajectories. The relation among these advantages has been the subject of recent debate, with some authors claiming that the advantages of the superposition of orders could be reproduced, and even surpassed, by other forms of superpositions. To shed light on this debate, we develop a general framework of resource theories of communication. In this framework, the resources are communication devices, and the allowed operations are (a) the placement of communication devices between the communicating parties, and (b) the connection of communication devices with local devices in the parties’ laboratories. The allowed operations are required to satisfy the minimal condition that they do not enable communication independently of the devices representing the initial resources. The resource-theoretic analysis reveals that the aforementioned criticisms on the superposition of causal orders were based on an uneven comparison between different types of quantum superpositions, exhibiting different operational features. Copyright © 2019, The Authors. All rights reserved.

关键词： quantum theory

Learning to learn with quantum neural networks via classical neural networks

学校读者我要写书评

暂无评论

arXiv 2019年

作者： Verdon, Guillaume Broughton, Michael McClean, Jarrod R. Sung, Kevin J. Babbush, Ryan Jiang, Zhang Neven, Hartmut Mohseni, Masoud Google LLC VeniceCA90291 United States Department of Applied Mathematics University of Waterloo WaterlooONN2L3G1 Canada Department of Computer Science University of Waterloo WaterlooONN2L3G1 Canada Institute for Quantum Computing University of Waterloo WaterlooONN2L3G1 Canada Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109 United States

quantum Neural Networks (QNNs) are a promising variational learning paradigm with applications to near-term quantum processors, however they still face some significant challenges. One such challenge is finding good parameter initialization heuristics that ensure rapid and consistent convergence to local minima of the parameterized quantum circuit landscape. In this work, we train classical neural networks to assist in the quantum learning process, also know as meta-learning, to rapidly find approximate optima in the parameter landscape for several classes of quantum variational algorithms. Specifically, we train classical recurrent neural networks to find approximately optimal parameters within a small number of queries of the cost function for the quantum Approximate Optimization Algorithm (QAOA) for MaxCut, QAOA for Sherrington-Kirkpatrick Ising model, and for a Variational quantum Eigensolver for the Hubbard model. By initializing other optimizers at parameter values suggested by the classical neural network, we demonstrate a signifi-cant improvement in the total number of optimization iterations required to reach a given accuracy. We further demonstrate that the optimization strategies learned by the neural network generalize well across a range of problem instance sizes. This opens up the possibility of training on small, classically simulatable problem instances, in order to initialize larger, classically intractably simulatable problem instances on quantum devices, thereby significantly reducing the number of required quantum-classical optimization iterations. Copyright © 2019, The Authors. All rights reserved.

关键词： Optimization

Upperbounds on the probability of finding marked connected components using quantum walks

学校读者我要写书评

暂无评论

arXiv 2019年

作者： Glos, Adam Nahimovs, Nikolajs Balakirev, Konstantin Khadiev, Kamil Institute of Theoretical and Applied Informatics Polish Academy of Sciences Baltycka 5 Gliwice44-100 Poland Institute of Informatics Silesian University of Technology Akademicka 16 Gliwice44-100 Poland Center for Quantum Computer Science Faculty of Computing University of Latvia Raina bulv. 19 RigaLV-1586 Latvia Higher School of Economics Kochnovskiy passage 3 Moscow Russia Kazan Federal University Kremlevskaya 18 Kazan Russia Smart Quantum Technologies Ltd. K. Marksa 5 Kazan Russia

Finding a marked vertex in a graph can be a complicated task when using quantum walks. Recent results show that for two or more adjacent marked vertices search by quantum walk with Grover's coin may have no speed-up over classical exhaustive search. In this paper, we analyze the probability of finding a marked vertex and prove several upper bounds for various sets of marked vertices. All upper bounds are given in explicit form. Copyright © 2019, The Authors. All rights reserved.

关键词：

An approach for security evaluation and certification of a complete quantum communication system

学校读者我要写书评

暂无评论

arXiv 2019年

作者： Sajeed, Shihan Chaiwongkhot, Poompong Huang, Anqi Qin, Hao Egorov, Vladimir Kozubov, Anton Gaidash, Andrei Chistiakov, Vladimir Vasiliev, Artur Gleim, Artur Makarov, Vadim Institute for Quantum Computing University of Waterloo WaterlooONN2L 3G1 Canada Department of Physics and Astronomy University of Waterloo WaterlooONN2L 3G1 Canada Department of Electrical and Computer Engineering University of Waterloo WaterlooONN2L 3G1 Canada Department of Electrical and Computer Engineering University of Toronto M5S 3G4 Canada Institute for Quantum Information State Key Laboratory of High Performance Computing College of Computer National University of Defense Technology Changsha410073 China CAS Quantum Network Co. Ltd. 99 Xiupu road Shanghai201315 China Faculty of Photonics and Optical Information ITMO University Kadetskaya line 3/2 St. Petersburg199034 Russia Shanghai Branch National Laboratory for Physical Sciences at Microscale CAS Center for Excellence in Quantum Information University of Science and Technology of China Shanghai201315 China

Although quantum communication systems are being deployed on a global scale, their realistic security certification is not yet available. Here we present a security evaluation and improvement protocol for complete quantum communication systems. The protocol subdivides a system by defining seven system implementation sub-layers based on a hierarchical order of information flow;then it categorises the known system implementation imperfections by hardness of protection and practical risk. Next, an initial analysis report lists all potential loopholes in its quantum-optical part. It is followed by interactions with the system manufacturer, testing and patching most loopholes, and re-assessing their status. Our protocol has been applied on multiple commercial quantum key distribution systems to improve their security. A detailed description of our methodology is presented with the example of a subcarrier-wave system. Our protocol is a step towards future security evaluation and security certification standards. Copyright © 2019, The Authors. All rights reserved.

关键词： quantum communication

VECTOR REPRESENTATIONS OF GRAPHS AND DISTINGUISHING quantum PRODUCT STATES WITH ONE-WAY LOCC

学校读者我要写书评

暂无评论

arXiv 2019年

作者： Kribs, David W. Mintah, Comfort Nathanson, Michael Pereira, Rajesh Department of Mathematics & Statistics University of Guelph GuelphONN1G 2W1 Canada Institute for Quantum Computing Department of Physics & Astronomy University of Waterloo WaterlooONN2L 3G1 Canada Department of Mathematics and Computer Science Saint Mary’s College of California MoragaCA94556 United States

Distinguishing sets of quantum states shared by two parties using only local operations and classical communication measurements is a fundamental topic in quantum communication and quantum information theory. We introduce a graph-theoretic approach, based on the theory of vector representations of graphs, to the core problem of distinguishing product states with one-way LOCC. We establish a number of results that show how distinguishing such states can be framed in terms of properties of the underlying graphs associated with a set of vector product states. We also present a number of illustrative examples. © 2019, CC BY.

关键词： quantum communication

computing endomorphism rings of supersingular elliptic curves and connections to pathfinding in isogeny graphs

学校读者我要写书评

暂无评论

arXiv 2020年

作者： Eisentrager, Kirsten Hallgren, Sean Leonardi, Chris Morrison, Travis Park, Jennifer Department of Mathematics Pennsylvania State Univer-sity 109 McAllister Building University ParkPA16802 United States Department of Computer Science and Engineering Pennsylvania State University 350W Westgate Building University ParkPA16802 United States University of Waterloo 200 University Ave W WaterlooONN2L 3G1 Canada Institute for Quantum Computing University of Waterloo 200 University Ave W WaterlooONN2L 3G1 Canada Ohio State University 231 W. 18th Ave ColumbusOH43210 United States

Abstract. computing endomorphism rings of supersingular elliptic curves is an important problem in computational number theory, and it is also closely connected to the security of some of the recently proposed isogeny-based cryptosystems. In this paper we give a new algorithm for computing the endomorphism ring of a supersingular elliptic curve E that runs, under certain heuristics, in time O((log p)2p1/2). The algorithm works by first finding two cycles of a certain form in the supersingular -isogeny graph G(p, ), generating an order End(E). Then all maximal orders containing are computed, extending work of Voight [28]. The final step is to determine which of these maximal orders is the endomorphism ring. As part of the cycle finding algorithm, we give a lower bound on the set of all j-invariants j that are adjacent to jp in G(p, ), answering a question in [1]. We also give a new polynomial-Time reduction from computing End(E) to pathfinding in the -isogeny graph which is simpler in several ways than previous ones. We show that this reduction leads to another algorithm for computing endomorphism rings which runs in time O(p1/2). This allows us to break the second preimage resistance of a hash function in the family constructed in [8].MSC Codes 14H52, 14K02, 11G20 Copyright © 2020, The Authors. All rights reserved.

关键词： Hash functions

Resilience of scrambling measurements

学校读者我要写书评

暂无评论

Physical Review A 2018年第6期97卷 062113-062113页

作者： Brian Swingle Nicole Yunger Halpern Condensed Matter Theory Center Maryland Center for Fundamental Physics Joint Center for Quantum Information and Computer Science and Department of Physics University of Maryland College Park Maryland 20742 USA Kavli Institute for Theoretical Physics University of California Santa Barbara Santa Barbara California 93106 USA Institute for Quantum Information and Matter Caltech Pasadena California 91125 USA

Most experimental protocols for measuring scrambling require time evolution with a Hamiltonian and with the Hamiltonian's negative counterpart (backward time evolution). Engineering controllable quantum many-body systems for which such forward and backward evolution is possible is a significant experimental challenge. Furthermore, if the system of interest is quantum chaotic, one might worry that any small errors in the time reversal will be rapidly amplified, obscuring the physics of scrambling. This paper undermines this expectation: We exhibit a renormalization protocol that extracts nearly ideal out-of-time-ordered-correlator measurements from imperfect experimental measurements. We analytically and numerically demonstrate the protocol's effectiveness, up to the scrambling time, in a variety of models and for sizable imperfections. The scheme extends to errors from decoherence by an environment.

关键词： Atomic & molecular processes in external fields Nonlocality quantum correlations in quantum information quantum entanglement

Untangling entanglement and chaos

学校读者我要写书评

暂无评论

Physical Review A 2019年第4期99卷 042311-042311页

作者： Meenu Kumari Shohini Ghose Institute for Quantum Computing University of Waterloo Waterloo Ontario Canada N2L 3G1 Department of Physics and Astronomy University of Waterloo Waterloo Ontario Canada N2L 3G1 Department of Physics and Computer Science Wilfrid Laurier University Waterloo Ontario Canada N2L 3C5 Perimeter Institute for Theoretical Physics 31 Caroline St N Waterloo Ontario Canada N2L 2Y5

We present a method to calculate an upper bound on the generation of entanglement in any spin system using the Fannes-Audenaert inequality for the von Neumann entropy. Our method not only is useful for efficiently estimating entanglement, but also shows that entanglement generation depends on the distance of the quantum states of the system from corresponding minimum-uncertainty spin-coherent states (SCSs). We illustrate our method using a quantum kicked top model and show that our upper bound is a very good estimator for entanglement generated in both regular and chaotic regions. In a deep quantum regime, the upper bound on entanglement can be high in both regular and chaotic regions, while in the semiclassical regime, the bound is higher in chaotic regions where the quantum states diverge from the corresponding SCSs. Our analysis thus explains previous studies and clarifies the relationship between chaos and entanglement.

关键词： quantum chaos quantum control quantum entanglement