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Evidence of gate-tunable mott insulator in trilayer graphene-boron nitride moiré superlattice

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arXiv 2018年

作者： Chen, Guorui Jiang, Lili Wu, Shuang Lv, Bosai Li, Hongyuan Chittari, Bheema Lingam Watanabe, Kenji Takashi Taniguchi Shi, Zhiwen Jung, Jeil Zhang, Yuanbo Wang, Feng Department of Physics University of California at Berkeley BerkeleyCA United States State Key Laboratory of Surface Physics Department of Physics Fudan University Shanghai200433 China Materials Science Division Lawrence Berkeley National Laboratory BerkeleyCA United States Key Laboratory of Artificial Structures and Quantum Control Ministry of Education School of Physics and Astronomy Shanghai Jiao Tong University Shanghai China Department of Electrical Engineering and Computer Sciences University of California BerkeleyCA94720 United States Collaborative Innovation Center of Advanced Microstructures Nanjing China National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan Department of Physics University of Seoul Seoul02504 Korea Republic of Institute for Nanoelectronic Devices and Quantum Computing Fudan University Shanghai200433 China Kavli Energy NanoSciences Institute University of California Berkeley Lawrence Berkeley National Laboratory BerkeleyCA United States

Mott insulator plays a central role in strongly correlated physics, where the repulsive Coulomb interaction dominates over the electron kinetic energy and leads to insulating states with one electron occupying each unit cell.1,2 Doped Mott insulator is often described by the Hubbard model3, which can give rise to other correlated phenomena such as unusual magnetism and even high temperature superconductivity2,4. A tunable Mott insulator, where the competition between the Coulomb interaction and the kinetic energy can be varied in situ, can provide an invaluable model system for the study of Mott physics. Here we report the realization of such a tunable Mott insulator in the ABC trilayer graphene (TLG) and hexagonal boron nitride (hBN) heterostructure with a moiré superlattice. Unlike massless Dirac electrons in monolayer graphene5,6, electrons in pristine ABC TLG are characterized by quartic energy dispersion and large effective mass7-11 that are conducive for strongly correlated phenomena. The moiré superlattice12-18 in TLG/hBN heterostructures leads to narrow electronic minibands that are gatetunable. Each filled miniband contains 4 electrons in one moiré lattice site due to the spin and valley degeneracy of graphene. The Mott insulator states emerge at 1/4 and 1/2 fillings, corresponding to one electron and two electrons per site, respectively. Moreover, the Mott states in the ABC TLG/hBN heterostructure exhibit unprecedented tunability: The Mott gap can be modulated in situ by a vertical electrical field, and at the mean time the electron doping can be gate-tuned to fill the band from one Mott insulating state to another. Our observation of a tunable Mott insulator opens up exciting opportunities to explore novel strongly correlated phenomena in two-dimensional moiré superlattice heterostructures. Copyright © 2018, The Authors. All rights reserved.

关键词： Mott insulators

Accelerated quantum walk, two-particle entanglement generation and localization

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arXiv 2018年

作者： Singh, Shivani Balu, Radhakrishnan Laflamme, Raymond Chandrashekar, C.M. Institute of Mathematical Sciences C. I. T. Campus Taramani Chennai600113 India Homi Bhabha National Institute Training School Complex Anushakti Nagar Mumbai400094 India U.S. Army Research Laboratory Computational and Information Sciences Directorate AdelphiMD20783 United States Computer Science and Electrical Engineering University of Maryland Baltimore County 1000 Hilltop Circle BaltimoreMD21250 United States Institute for Quantum Computing Department of Physics and Astronomy University of Waterloo WaterlooONN2L 3G1 Canada Perimeter Institute for Theoretical Physics WaterlooONN2L 2Y5 Canada

We present a scheme to describe the dynamics of accelerating discrete-time quantum walk for one- and two-particle in position space. We show the effect of acceleration in enhancing the entanglement between the particle and position space in one-particle quantum walk and in generation of entanglement between the two unentangled particle in two-particle quantum walk. By introducing the disorder in the form of phase operator we study the transition from localization to delocalization as a function of acceleration. These inter-winding connection between acceleration, entanglement generation and localization along with well established connection of quantum walks with Dirac equation can be used to probe further in the direction of understanding the connection between acceleration, mass and entanglement in relativistic quantum mechanics and quantum field theory. Expansion of operational tools for quantum simulations and for modelling quantum dynamics of accelerated particle using quantum walks is an other direction where these results can play an important role. Copyright © 2018, The Authors. All rights reserved.

关键词： quantum chemistry

Causal limit on quantum communication

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arXiv 2018年

作者： Pisarczyk, Robert Zhao, Zhikuan Ouyang, Yingkai Vedral, Vlatko Fitzsimons, Joseph F. Mathematical Institute University of Oxford Woodstock Road OxfordOX2 6GG United Kingdom Centre for Quantum Technologies National University of Singapore 3 Science Drive 2 117543 Singapore Department of Computer Science ETH Zürich Universitätstrasse 6 Zürich8092 Switzerland Singapore University of Technology and Design 8 Somapah Road 487372 Singapore University of Sheffield Department of Physics and Astronomy 226 Hounsfield Rd SheffieldS3 7RH United Kingdom Clarendon Laboratory Department of Physics University of Oxford Parks Road OxfordOX1 3PU United Kingdom Department of Physics National University of Singapore 2 Science Drive 3 117542 Singapore Horizon Quantum Computing 79 Ayer Rajah Crescent Singapore139955 Singapore

The capacity of a channel is known to be equivalent to the highest rate at which it can generate entanglement. Analogous to entanglement, the notion of a causality measure characterises the temporal aspect of quantum correlations. Despite holding an equally fundamental role in physics, temporal quantum correlations have yet to find their operational significance in quantum communication. Here we uncover a connection between quantum causality and channel capacity. We show the amount of temporal correlations between two ends of the noisy quantum channel, as quantified by a causality measure, implies a general upper bound on its channel capacity. The expression of this new bound is simpler to evaluate than most previously known bounds. We demonstrate the utility of this bound by applying it to a class of shifted depolarizing channels, which results in improvement over previously calculated bounds for this class of channels. Copyright © 2018, The Authors. All rights reserved.

关键词： Channel capacity

The Future of the Correlated Electron Problem

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arXiv 2020年

作者： Alexandradinata, A. Armitage, N.P. Baydin, Andrey Bi, Wenli Cao, Yue Changlani, Hitesh J. Chertkov, Eli da Silva Neto, Eduardo H. Delacretaz, Luca Baggari, Ismail El Ferguson, G.M. Gannon, William J. Akbar Ghorashi, Sayed Ali Goodge, Berit H. Goulko, Olga Grissonnanche, Gaël Hallas, Alannah Hayes, Ian M. He, Yu Huang, Edwin W. Kogar, Anshul Kumah, Divine Lee, Jong Yeon Legros, Anaëlle Mahmood, Fahad Maximenko, Yulia Pellatz, Nick Polshyn, Hryhoriy Sarkar, Tarapada Scheie, Allen Seyler, Kyle L. Shi, Zhenzhong Skinner, Brian Steinke, Lucia Thirunavukkuarasu, Komalavalli Trevisan, Thaís Victa Vogl, Michael Volkov, Pavel A. Wang, Yao Wang, Yishu Wei, Di Wei, Kaya Yang, Shuolong Zhang, Xian Zhang, Ya-Hui Zhao, Liuyan Zong, Alfred Institute of Condensed Matter Theory University of Illinois at Urbana-Champaign Urbana61801 IL United States Department of Physics University of Illinois at Urbana-Champaign Urbana61801 IL United States The Institute for Quantum Matter the Department of Physics and Astronomy The Johns Hopkins University BaltimoreMD21218 United States Department of Electrical and Computer Engineering Rice University HoustonTX70005 United States Department of Physics University of Alabama at Birmingham BirminghamAL35294 United States Materials Science Division Argonne National Laboratory LemontIL60439 United States Department of Physics Florida State University TallahasseeFL32306 United States National High Magnetic Field Laboratory TallahasseeFL32304 United States Department of Physics University of California DavisCA95616 United States Department of Physics Yale University New HavenCT06511 United States Kadanoff Center for Theoretical Physics University of Chicago ChicagoIL60637 United States Department of Physics Cornell University IthacaNY14853 United States Department of Physics and Astronomy University of Kentucky LexingtonKY40506 United States Department of Physics William & Mary WilliamsburgVA23187 United States School of Applied and Engineering Physics Cornell University IthacaNY14853 United States Boise State University Department of Physics BoiseID83725 United States Department of Physics University of Massachusetts Boston BostonMA02125 United States Laboratory of Atomic and Solid State Physics Cornell University IthacaNY14853 United States Department of Physics and Astronomy Quantum Matter Institute University of British Columbia VancouverBCV6T 1Z1 Canada Department of Physics Maryland Quantum Materials Center University of Maryland College ParkMD20742 United States Department of Physics University of California at Berkeley BerkeleyCA94720 United States Department of Applied Physics Yale University New HavenCT065

A central problem in modern condensed matter physics is the understanding of materials with strong electron correlations. Despite extensive work, the essential physics of many of these systems is not understood and there is very little ability to make predictions in this class of materials. In this manuscript we share our personal views on the major open problems in the field of correlated electron systems. We discuss some possible routes to make progress in this rich and fascinating field. This manuscript is the result of the vigorous discussions and deliberations that took place at Johns Hopkins University during a three-day workshop January 27, 28, and 29, 2020 that brought together six senior scientists and 46 more junior scientists. Our hope, is that the topics we have presented will provide inspiration for others working in this field and motivation for the idea that significant progress can be made on very hard problems if we focus our collective energies. Copyright © 2020, The Authors. All rights reserved.

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Experimental design for non-parametric correction of misspecified dynamical models

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arXiv 2017年

作者： Shulkind, Gal Horesh, Lior Avron, Haim Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology CambridgeMA United States Quantum Computing IBM TJ Watson Research Center Yorktown HeightsNY United States Department of Applied Mathematics Tel Aviv University Israel

We consider a class of misspecified dynamical models where the governing term is only approximately known. Under the assumption that observations of the system’s evolution are accessible for various initial conditions, our goal is to infer a non-parametric correction to the misspecified driving term such as to faithfully represent the system dynamics and devise system evolution predictions for unobserved initial conditions. We model the unknown correction term as a Gaussian Process and analyze the problem of efficient experimental design to find an optimal correction term under constraints such as a limited experimental budget. We suggest a novel formulation for experimental design for this Gaussian Process and show that approximately optimal (up to a constant factor) designs may be efficiently derived by utilizing results from the literature on submodular optimization. Our numerical experiments exemplify the effectiveness of these techniques.62K05, 37M05, 62G08, 68T05 Copyright © 2017, The Authors. All rights reserved.

关键词： Dynamical systems

Complete extension: the non-signalling analog of quantum purification

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arXiv 2018年

作者： Winczewski, Marek Das, Tamoghna Selby, John H. Horodecki, Karol Horodecki, Pawel Pankowski, Lukasz Piani, Marco Ramanathan, Ravishankar International Centre for Theory of Quantum Technologies University of Gdańsk Wita Stwosza 63 Gdańsk 80-308 Poland Institute of Theoretical Physics and Astrophysics National Quantum Information Centre in Gdańsk University of Gdańsk Gdańsk 80–952 Poland Department of Physics Indian Institute of Technology Kharagpur Kharagpur721302 India Institute of Informatics and National Quantum Information Centre in Gdańsk Faculty of Mathematics Physics and Informatics University of Gdańsk Gdańsk 80–952 Poland Faculty of Applied Physics and Mathematics Gdańsk University of Technology Gdańsk 80–233 Poland National Quantum Information Centre University of Gdańsk ul. Jana Bazy ńskiego 8 Gdańsk 80-309 Poland VOICELAB.AI Al. Grunwaldzka 135A Gdańsk 80-264 Poland evolutionQ Inc. WaterlooONN2L 3L3 Canada SUPA Department of Physics University of Strathclyde GlasgowG4 0NG United Kingdom Department of Computer Science The University of Hong Kong Pokfulam Road Hong Kong

Deriving quantum mechanics from information-theoretic postulates is a recent research direction taken, in part, with the view of finding a beyond-quantum theory;once the postulates are clear, we can consider modifications to them. A key postulate is the purification postulate, which we propose to replace by a more generally applicable postulate that we call the complete extension postulate (CEP), i.e., the existence of an extension of a physical system from which one can generate any other extension. This new concept leads to a plethora of open questions and research directions in the study of general theories satisfying the CEP (which may include a theory that hyper-decoheres to quantum theory). For example, we show that the CEP implies the impossibility of bit-commitment. This is exemplified by a case study of the theory of non-signalling behaviors which we show satisfies the CEP. We moreover show that in certain cases the complete extension will not be pure, highlighting the key divergence from the purification postulate. © 2018, CC BY.

关键词： Purification

Sufficient condition for nonexistence of symmetric extension of qudits using Bell inequalities

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Physical Review A 2017年第1期96卷 012128-012128页

作者： Meenu Kumari Shohini Ghose Robert B. Mann Institute for Quantum Computing University of Waterloo Canada N2L 3G1 Department of Physics and Astronomy University of Waterloo Canada N2L 3G1 Department of Physics and Computer Science Wilfrid Laurier University Waterloo Canada N2L 3C5

We analyze the connection between Bell inequality violations and symmetric extendibility of quantum states. We prove that 2-qubit reduced states of multiqubit symmetric pure states do not violate the Bell Clauser-Horne-Shimony-Holt (CHSH) inequality. We then prove the more general converse that any 2-qubit state that violates the CHSH inequality cannot have a symmetric extension. We extend our analysis to qudits and provide a test for symmetric extendibility of 2-qudit states. We show that if a 2-qudit Bell inequality is monogamous, then any 2-qudit state that violates this inequality does not have a symmetric extension. For the specific case of 2-qutrit states, we use numerical evidence to conjecture that the Collins-Gisin-Linden-Massar-Popescu (CGLMP) inequality is monogamous. Hence, the violation of the CGLMP inequality by any 2-qutrit state could be a sufficient condition for the nonexistence of its symmetric extension.

关键词： quantum computation quantum entanglement quantum information processing

Validating quantum-classical programming models with tensor network simulations

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arXiv 2018年

作者： McCaskey, Alexander Dumitrescu, Eugene Chen, Mengsu Lyakh, Dmitry Humble, Travis S. Quantum Computing Institute Oak Ridge National Laboratory Oak RidgeTN37831 United States Computer Science and Mathematics Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Computational Sciences and Engineering Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Department of Physics Virginia Tech BlacksburgVA24060 United States National Center for Computational Sciences Oak Ridge National Laboratory Oak RidgeTN37831 United States Bredesen Center for Interdisciplinary Research University of Tennessee KnoxvilleTN37996 United States

The exploration of hybrid quantum-classical algorithms and programming models on noisy near-term quantum hardware has begun. As hybrid programs scale towards classical intractability, validation and benchmarking are critical to understanding the utility of the hybrid computational model. In this paper, we demonstrate a newly developed quantum circuit simulator based on tensor network theory that enables intermediate-scale verification and validation of hybrid quantum-classical computing frameworks and programming models. We present our tensor-network quantum virtual machine (TNQVM) simulator which stores a multi-qubit wavefunction in a compressed (factorized) form as a matrix product state, thus enabling single-node simulations of larger qubit registers, as compared to brute-force state-vector simulators. Our simulator is designed to be extensible in both the tensor network form and the classical hardware used to run the simulation (multicore, GPU, distributed). The extensibility of the TNQVM simulator with respect to the simulation hardware type is achieved via a pluggable interface for different numerical backends (e.g., ITensor and ExaTENSOR numerical libraries). We demonstrate the utility of our TNQVM quantum circuit simulator through the verification of randomized quantum circuits and the variational quantum eigensolver algorithm, both expressed within the eXtreme-scale ACCelerator (XACC) programming model. Copyright © 2018, The Authors. All rights reserved.

关键词： Tensors

On the polynomial parity argument complexity of the Combinatorial Nullstellensatz

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arXiv 2017年

作者： Belovs, Aleksandrs Ivanyos, Gábor Qiao, Youming Santha, Miklos Yang, Siyi Faculty of Computing University of Latvia Institute for Computer Science and Control Hungarian Academy of Sciences Budapest Hungary Centre for Quantum Computation and Intelligent Systems University of Technology Sydney Australia IRIF Université Paris Diderot CNRS Paris75205 France Centre for Quantum Technologies National University of Singapore MajuLab CNRS Singapore117543 Singapore Centre for Quantum Technologies National University of Singapore Singapore117543 Singapore

The complexity class PPA consists of NP-search problems which are reducible to the parity principle in undirected graphs. It contains a wide variety of interesting problems from graph theory, combinatorics, algebra and number theory, but only a few of these are known to be complete in the class. Before this work, the known complete problems were all discretizations or combinatorial analogues of topological fixed point theorems. Here we prove the PPA-completeness of two problems of radically different style. They are PPA-Circuit CNSS and PPA-Circuit Chevalley, related respectively to the Combinatorial Nullstellensatz and to the Chevalley-Warning Theorem over the two elements field F2. The input of these problems contain PPA-circuits which are arithmetic circuits with special symmetric properties that assure that the polynomials computed by them have always an even number of zeros. In the proof of the result we relate the multilinear degree of the polynomials to the parity of the maximal parse subcircuits that compute monomials with maximal multilinear degree, and we show that the maximal parse subcircuits of a PPA-circuit can be paired in polynomial time. Copyright © 2017, The Authors. All rights reserved.

关键词： Polynomial approximation