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Field‐Effect Transistors: Low‐Symmetry PdSe2 for High Performance Thermoelectric Applications (Adv. Funct. Mater. 52/2020)

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Advanced Functional Materials 2020年第52期30卷 2070347-2070347页

作者： Yunshan Zhao Peng Yu Gang Zhang Minglei Sun Dongzhi Chi Kedar Hippalgaonkar John T. L. Thong Jing Wu NNU‐SULI Thermal Energy Research Center (NSTER) & Center for Quantum Transport and Thermal Energy Science (CQTES) School of Physics and Technology Nanjing Normal University Nanjing 210023 China Institute of Materials Research and Engineering A*STAR (Agency for Science Technology and Research) 2 Fusionopolis Way Innovis #08‐03 Singapore 138634 Singapore Department of Electrical and Computer Engineering National University of Singapore Singapore 117583 Singapore School of Materials Science and Engineering State Key Laboratory of Optoelectronic Materials and Technologies Sun Yat‐Sen University Guangzhou 510275 P. R. China Institute of High Performance Computing Singapore 138632 Singapore Department of Materials Science and Engineering Nanyang Technological University 50 Nanyang Avenue Singapore 639798 Singapore

In article number 2004896, John T. L. Thong, Jing Wu, and co‐workers investigate thermoelectric transport in novel 2D palladium diselenide (PdSe2) with a low‐symmetry pentagonal lattice. Due to its sensitive dependence on the interlayer coupling originating from the special lattice structure, the thermoelectric performance can be largely enhanced. The high band convergence and quantum confinement through thickness engineering advance and broaden the applications of thermoelectric such as in soft robotics, health monitoring, and human‐machine interfaces.

关键词： 2D field‐effect transistors palladium diselenide pentagonal crystals thermoelectric devices

Generalized Entanglement Entropies of quantum Designs

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Physical Review Letters 2018年第13期120卷 130502-130502页

作者： Zi-Wen Liu Seth Lloyd Elton Yechao Zhu Huangjun Zhu Center for Theoretical Physics Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Department of Physics Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Department of Mechanical Engineering Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Institute for Theoretical Physics University of Cologne 50937 Cologne Germany Department of Physics and Center for Field Theory and Particle Physics Fudan University Shanghai 200433 China Institute for Nanoelectronic Devices and Quantum Computing Fudan University Shanghai 200433 China State Key Laboratory of Surface Physics Fudan University Shanghai 200433 China Collaborative Innovation Center of Advanced Microstructures Nanjing 210093 China

The entanglement properties of random quantum states or dynamics are important to the study of a broad spectrum of disciplines of physics, ranging from quantum information to high energy and many-body physics. This Letter investigates the interplay between the degrees of entanglement and randomness in pure states and unitary channels. We reveal strong connections between designs (distributions of states or unitaries that match certain moments of the uniform Haar measure) and generalized entropies (entropic functions that depend on certain powers of the density operator), by showing that Rényi entanglement entropies averaged over designs of the same order are almost maximal. This strengthens the celebrated Page’s theorem. Moreover, we find that designs of an order that is logarithmic in the dimension maximize all Rényi entanglement entropies and so are completely random in terms of the entanglement spectrum. Our results relate the behaviors of Rényi entanglement entropies to the complexity of scrambling and quantum chaos in terms of the degree of randomness, and suggest a generalization of the fast scrambling conjecture.

关键词： Many-body localization quantum cryptography quantum entanglement quantum gravity Random matrix theory

Erbium implanted silicon for solid-state quantum technologies

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arXiv 2020年

作者： Hughes, Mark A. Panjwani, Naitik A. Urdampilleta, Matias Wisby, Ilana Homewood, Kevin P. Murdin, Ben Lindström, Tobias Carey, J. David Joule Physics Laboratory School of Computing Science and Engineering University of Salford M5 4WT United Kingdom University College London London Centre for Nanotechnology Gower Place LondonWC1E 6BT United Kingdom Berlin Joint EPR Lab Fachbereich Physik Freie Universität Berlin BerlinD-14195 Germany Institut Néel-CNRS-UJF-INPG UPR2940 25 rue des Martyrs BP 166 Grenoble cedex 938042 France National Physical Laboratory Hampton Road TeddingtonTW11 0LW United Kingdom Royal Holloway University of London EghamTW20 0EX United Kingdom Oxford Quantum Circuits Ltd. King Charles House 2nd Floor Park End Street Oxford OxfordshireOX1 1JD United Kingdom Advanced Technology Institute Faculty of Engineering and Physical Sciences University of Surrey GuildfordGU2 7XH United Kingdom School of Materials Science and Engineering Hubei University Wuhan430062 China Department of Electrical and Electronic Engineering University of Surrey GuildfordGU2 7XH United Kingdom

quantum technology (QT) platforms with telecommunications and integrated circuit (IC) processing compatibility have important implications for the long-distance transfer of quantum information, and QT platforms based on ion implantation are inherently scalable. Here we establish the potential of Er implanted Si as a scalable QT platform with telecommunications and IC processing compatibility through coherence and superconducting resonator coupling measurements. The electron spin coherence time of Er implanted Si with an Er concentration of 3×1017 cm-3 is ~10 μs at 5 K. The spin echo decay profile displays strong modulation due to super-hyperfine interaction with 29Si nuclei beyond the first coordination sphere;this interaction could be utilised for the telecommunications wavelength addressing of 29Si qubits. The collective coupling strength between a superconducting NbN lumped-element microresonator and Er implanted Si with an Er concentration of 1017 cm-3 at 20 mK was ~ 1MHz. Copyright © 2020, The Authors. All rights reserved.

关键词： Magnetic moments

Visualization of correlations in hybrid quantum systems

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arXiv 2018年

作者： Rundle, R.P. Davies, B.I. Dwyer, V.M. Tilma, Todd Everitt, M.J. Quantum Systems Engineering Research Group Department of Physics Loughborough University LeicestershireLE11 3TU United Kingdom Wolfson School Loughborough University Department of Physics College of Science Tokyo Institute of Technology H-63 2-12-1 Ōokayama Meguro-ku Tokyo152-8550 Japan Quantum Computing Unit Institute of Innovative Research Tokyo Institute of Technology S1-16 4259 Nagatsuta-cho Midori-ku Yokohama226-8503 Japan

In this work we construct Wigner functions for hybrid continuous and discrete variable quantum systems. We demonstrate new capabilities in the visualization of the interactions and correlations within hybrid quantum systems. Specifically, we show how to clearly distinguish signatures that arise due to quantum and classical correlations in an entangled Bell-cat state. We further show how correlations are manifested in different types of interaction, leading to a deeper understanding of how quantum information is shared between two subsystems. Understanding the nature of the correlations between systems is central to harnessing quantum effects for information processing;the methods presented here reveal the nature of these correlations, allowing a clear visualization of the quantum information present in hybrid quantum systems. The methods presented here could be viewed as a form of quantum state spectroscopy. Copyright © 2018, The Authors. All rights reserved.

关键词： quantum optics

Joint product numerical range and geometry of reduced density matrices

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Science China(Physics,Mechanics & Astronomy) 2017年第2期60卷 9-17页

作者： Jianxin Chen Cheng Guo Zhengfeng Ji Yiu-Tung Poon Nengkun YU Bei Zeng Jie Zhou Joint Center for Quantum Information and Computer Science University of Maryland College Park 20740 USA Institute for Advanced Study Tsinghua University Beijing 100084 China Centre for Quantum Computation ＆ Intelligent Systems School of Software Faculty of Engineering and Information Technology University of Technology Sydney Sydney 2007 Australia State Key Laboratory of Computer Science.Institute of Software Chinese Academy of Sciences Beijing 100084 China Department of Mathematics Iowa State University Ames 50011-2140 USA Institute for Quantum Computing University of Waterloo Waterloo N2L 3G1 Canada Department of Mathematics ＆ Statistics University of Guelph Guelph N1G 2 W1 Canada Perimeter Institute for Theoretical Physics Waterloo N2L 2Y5 Canada

The reduced density matrices of a many-body quantum system form a convex set, whose three-dimensional projection is convex in R3. The boundary of may exhibit nontrivial geometry, in particular ruled surfaces. Two physical mechanisms are known for the origins of ruled surfaces： symmetry breaking and gapless. In this work, we study the emergence of ruled surfaces for systems with local Hamiltonians in infinite spatial dimension, where the reduced density matrices are known to be separable as a consequence of the quantum de Finetti＇s theorem. This allows us to identify the reduced density matrix geometry with joint product numerical range II of the Hamiltonian interaction terms. We focus on the case where the interaction terms have certain structures, such that a ruled surface emerges naturally when taking a convex hull of ∏. We show that, a ruled surface on sitting in ∏ has a gapless origin, otherwise it has a symmetry breaking origin. As an example, we demonstrate that a famous ruled surface, known as the oloid, is a possible shape of , with two boundary pieces of symmetry breaking origin separated by two gapless lines.

关键词： reduced density matrices quantum tomography numerical range quantum information oloid ruled surface

Physical origins of ruled surfaces on the reduced density matrices geometry

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Science China(Physics,Mechanics & Astronomy) 2017年第2期60卷 1-8页

作者： Ji-Yao Chen Zhengfeng Ji Zheng-Xin Liu Xiaofei Qi Nengkun Yu Bei Zeng Duanlu Zhou State Key Laboratory of Low Dimensional Quantum Physics Department of Physics Tsinghua University Beijing 100084 China Perimeter Institute for Theoretical Physics Waterloo N2L 2Y5 Canada Centre for Quantum Computation ＆ Intelligent Systems School of Software Faculty of Engineering and Information Technology University of Technology Sydney Sydney 2007 Australia State Key Laboratory of Computer Science Institute of Software Chinese Academy of Sciences Beijing 100190 China Department of Physics Renmin University of China Beijing 100872 China Department of Mathematics Shanxi University Taiyuan 030000 China Institute for Quantum Computing University of Waterloo Waterloo N2L 3G1 Canada Department of Mathematics ＆ Statistics University of Guelph Guelph N1G 2W1 Canada Institute of Physics Chinese Academy of Sciences Beijing 100190 China

The reduced density matrices （RDMs） of many-body quantum states form a convex set. The boundary of low dimensional projections of this convex set may exhibit nontrivial geometry such as ruled surfaces. In this paper, we study the physical origins of these ruled surfaces for bosonic systems. The emergence of ruled surfaces was recently proposed as signatures of symmetry- breaking phase. We show that, apart from being signatures of symmetry-brealdng, ruled surfaces can also be the consequence of gapless quantum systems by demonstrating an explicit example in terms of a two-mode Ising model. Our analysis was largely simplified by the quantum de Finetti＇s theorem--in the limit of large system size, these RDMs are the convex set of all the symmetric separable states. To distinguish ruled surfaces originated from gapless systems from those caused by symmetry- breaking, we propose to use the finite size scaling method for the corresponding geometry. This method is then applied to the two-mode XY model, successfully identifying a ruled surface as the consequence of gapless systems.

关键词： ruled surfaces reduced density matrices bosonic system geometry

quantum Neural Network States: A Brief Review of Methods and Applications

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arXiv 2018年

作者： Jia, Zhih-Ahn Yi, Biao Zhai, Rui Wu, Yu-Chun Guo, Guang-Can Guo, Guo-Ping Key Laboratory of Quantum Information Chinese Academy of Sciences School of Physics University of Science and Technology of China Hefei Anhui230026 China CAS Center For Excellence in Quantum Information and Quantum Physics University of Science and Technology of China Hefei Anhui230026 China Microsoft Station Q Department of Mathematics University of California Santa BarbaraCA93106-6105 United States Department of Mathematics Capital Normal University Beijing100048 China Institute of Technical Physics Department of Engineering Physics Tsinghua University Beijing10084 China Origin Quantum Computing Hefei230026 China

One of the main challenges of quantum many-body physics is the exponential growth in the dimensionality of the Hilbert space with system size. This growth makes solving the Schrödinger equation of the system extremely difficult. Nonetheless, many physical systems have a simplified internal structure that typically makes the parameters needed to characterize their ground states exponentially smaller. Many numerical methods then become available to capture the physics of the system. Among modern numerical techniques, neural networks, which show great power in approximating functions and extracting features of big data, are now attracting much interest. In this work, we briefly review the progress in using artificial neural networks to build quantum many-body states. We take the Boltzmann machine representation as a prototypical example to illustrate various aspects of the states of a neural network. We briefly review also the classical neural networks and illustrate how to use neural networks to represent quantum states and density operators. Some physical properties of the neural network states are discussed. For applications, we briefly review the progress in many-body calculations based on neural network states, the neural network state approach to tomography, and the classical simulation of quantum computing based on Boltzmann machine states. Copyright © 2018, The Authors. All rights reserved.

关键词： Neural networks

Exact entanglement cost of quantum states and channels under positive-partial-transpose-preserving operations

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arXiv 2018年

作者： Wang, Xin Wilde, Mark M. Institute for Quantum Computing Baidu Research Beijing100093 China Joint Center for Quantum Information and Computer Science University of Maryland College ParkMD20742 United States Hearne Institute for Theoretical Physics Department of Physics and Astronomy Center for Computation and Technology Louisiana State University Baton RougeLA70803 United States School of Electrical and Computer Engineering Cornell University IthacaNY14850 United States

This paper establishes single-letter formulas for the exact entanglement cost of simulating quantum channels under free quantum operations that completely preserve positivity of the partial transpose (PPT). First, we introduce the κ-entanglement measure for point-to-point quantum channels, based on the idea of the κ-entanglement of bipartite states, and we establish several fundamental properties for it, including amortization collapse, monotonicity under PPT superchannels, additivity, normalization, faithfulness, and non-convexity. Second, we introduce and solve the exact entanglement cost for simulating quantum channels in both the parallel and sequential settings, along with the assistance of free PPT-preserving operations. In particular, we establish that the entanglement cost in both cases is given by the same single-letter formula, the κ-entanglement measure of a quantum channel. We further show that this cost is equal to the largest κ-entanglement that can be shared or generated by the sender and receiver of the channel. This formula is calculable by a semidefinite program, thus allowing for an efficiently computable solution for general quantum channels. Noting that the sequential regime is more powerful than the parallel regime, another notable implication of our result is that both regimes have the same power for exact quantum channel simulation, when PPT superchannels are free. For several basic Gaussian quantum channels, we show that the exact entanglement cost is given by the Holevo-Werner formula [Holevo and Werner, Phys. Rev. A 63, 032312 (2001)], giving an operational meaning of the Holevo-Werner quantity for these channels. Copyright © 2018, The Authors. All rights reserved.

关键词： quantum entanglement

Gapped boundary theory of the twisted gauge theory model of three-dimensional topological orders

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arXiv 2018年

作者： Wang, Hongyu Li, Yingcheng Hu, Yuting Wan, Yidun State Key Laboratory of Surface Physics Fudan University Shanghai200433 China Department of Physics Center for Field Theory and Particle Physics Fudan University Shanghai200433 China Department of Physics and Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Institute for Nanoelectronic devices and Quantum computing Fudan University Shanghai200433 China Collaborative Innovation Center of Advanced Microstructures Nanjing210093 China

We extend the twisted gauge theory model of topological orders in three spatial dimensions to the case where the three spaces have two dimensional boundaries. We achieve this by systematically constructing the boundary Hamiltonians that are compatible with the bulk Hamoltonian. Given the bulk Hamiltonian defined by a gauge group G and a four-cocycle ω in the fourth cohomology group of G over U(1), a boundary Hamiltonian can be defined by a subgroup K of G and a three-cochain α in the third cochain group of K over U(1). The boundary Hamiltonian to be constructed must be gapped and invariant under the topological renormalization group flow (via Pachner moves), leading to a generalized Frobenius condition. Given K, a solution to the generalized Frobenius condition specifies a gapped boundary condition. We derive a closed-form formula of the ground state degeneracy of the model on a three-cylinder, which can be naturally generalized to three-spaces with more boundaries. We also derive the explicit ground-state wavefunction of the model on a three-ball. The ground state degeneracy and ground-state wavefunction are both presented solely in terms of the input data of the model, namely, {G, ω, K, α}. Copyright © 2018, The Authors. All rights reserved.

关键词： Hamiltonians