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Jun 29, 2018
06/18

by
Lei Wang

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Unsupervised learning is a discipline of machine learning which aims at discovering patterns in big data sets or classifying the data into several categories without being trained explicitly. We show that unsupervised learning techniques can be readily used to identify phases and phases transitions of many body systems. Starting with raw spin configurations of a prototypical Ising model, we use principal component analysis to extract relevant low dimensional representations the original data...

Topics: Machine Learning, Statistical Mechanics, Condensed Matter, Statistics

Source: http://arxiv.org/abs/1606.00318

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Jun 30, 2018
06/18

by
Lei Wang

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Boltzmann machines are physics informed generative models with wide applications in machine learning. They can learn the probability distribution from an input dataset and generate new samples accordingly. Applying them back to physics, the Boltzmann machines are ideal recommender systems to accelerate Monte Carlo simulation of physical systems due to their flexibility and effectiveness. More intriguingly, we show that the generative sampling of the Boltzmann Machines can even discover unknown...

Topics: Physics, Condensed Matter, Learning, Computing Research Repository, Machine Learning, Statistical...

Source: http://arxiv.org/abs/1702.08586

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Jun 30, 2018
06/18

by
Lei Wang; Matthias Troyer

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We present a new algorithm for calculating the Renyi entanglement entropy of interacting fermions using the continuous-time quantum Monte Carlo method. The algorithm only samples interaction correction of the entanglement entropy, which by design ensures efficient calculation of weakly interacting systems. Combined with Monte Carlo reweighting, the algorithm also performs well for systems with strong interactions. We demonstrate the potential of this method by studying the quantum entanglement...

Topics: Quantum Physics, Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1407.0707

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Jun 28, 2018
06/18

by
Lei Wang; Nianbei Li; Peter Hanggi

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The study of heat transport in low-dimensional oscillator lattices presents a formidable challenge. Theoretical efforts have been made trying to reveal the underlying mechanism of diversified heat transport behaviors. In lack of a unified rigorous treatment, approximate theories often may embody controversial predictions. It is therefore of ultimate importance that one can rely on numerical simulations in the investigation of heat transfer processes in low-dimensional lattices. The simulation...

Topics: Statistical Mechanics, Condensed Matter

Source: http://arxiv.org/abs/1512.07717

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Jun 29, 2018
06/18

by
Li Huang; Lei Wang

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Despite their exceptional flexibility and popularity, the Monte Carlo methods often suffer from slow mixing times for challenging statistical physics problems. We present a general strategy to overcome this difficulty by adopting ideas and techniques from the machine learning community. We fit the unnormalized probability of the physical model to a feedforward neural network and reinterpret the architecture as a restricted Boltzmann machine. Then, exploiting its feature detection ability, we...

Topics: Computational Physics, Strongly Correlated Electrons, Machine Learning, Condensed Matter, Physics,...

Source: http://arxiv.org/abs/1610.02746

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Jun 28, 2018
06/18

by
Ye-Hua Liu; Lei Wang

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Building on recent solutions of the fermion sign problem for specific models we present two continuous-time quantum Monte Carlo methods for efficient simulation of mass-imbalanced Hubbard models on bipartite lattices at half-filling. For both methods we present the solutions to the fermion sign problem and the algorithms to achieve efficient simulations. As applications, we calculate the dependence of the spin correlation on the mass imbalance in a one-dimensional lattice and study the thermal...

Topics: Statistical Mechanics, Quantum Gases, Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1510.00715

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Jun 29, 2018
06/18

by
Jakub Imriška; Lei Wang; Matthias Troyer

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We study the interplay of topological band structure and conventional magnetic long-range order in spinful Haldane model with onsite repulsive interaction. Using the dynamical cluster approximation with clusters of up to 24 sites we find evidence of a first order phase transition from a Chern insulator at weak coupling to a topologically trivial antiferromagnetic insulator at strong coupling. These results call into question a previously found intermediate state with coexisting topological...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1604.03553

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Jun 29, 2018
06/18

by
Lei Wang; Ye-Hua Liu; Matthias Troyer

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We present an algorithm for the efficient simulation of the half-filled spinless $t$-$V$ model on bipartite lattices, which combines the stochastic series expansion method with determinantal quantum Monte Carlo techniques widely used in fermionic simulations. The algorithm scales linearly in the inverse temperature, cubically with the system size and is free from the time-discretization error. We use it to map out the finite temperature phase diagram of the spinless $t$-$V$ model on the...

Topics: Condensed Matter, Quantum Gases, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1602.02095

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Jun 28, 2018
06/18

by
Lei Wang; Hiroshi Shinaoka; Matthias Troyer

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The Kondo effect is an ubiquitous phenomenon appearing at low temperature in quantum confined systems coupled to a continuous bath. Efforts in understanding and controlling it have triggered important developments across several disciplines of condensed matter physics. A recurring pattern in these studies is that the suppression of the Kondo effect often results in intriguing physical phenomena such as impurity quantum phase transitions or non-Fermi-liquid behavior. We show that the fidelity...

Topics: Statistical Mechanics, Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1507.06991

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Jun 30, 2018
06/18

by
Lei Wang; Philippe Corboz; Matthias Troyer

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Spinless fermions on a honeycomb lattice provide a minimal realization of lattice Dirac fermions. Repulsive interactions between nearest neighbors drive a quantum phase transition from a Dirac semimetal to a charge-density-wave state through a fermionic quantum critical point, where the coupling of Ising order parameter to the Dirac fermions at low energy drastically affects the quantum critical behavior. Encouraged by a recently discovery of absence of the fermion sign problem in this model,...

Topics: High Energy Physics - Lattice, Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1407.0029

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Jun 30, 2018
06/18

by
Lei Wang; Hsiang-Hsuan Hung; Matthias Troyer

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We study the interplay between topological and conventional long range order of attractive fermions in a time reversal symmetric Hofstadter lattice using quantum Monte Carlo simulations, focussing on the case of one-third flux quantum per plaquette. At half-filling, the system is unstable towards s-wave pairing and charge-density-wave order at infinitesimally small interactions. At one-third-filling, the noninteracting system is a topological insulator, and a nonzero critical interaction...

Topics: Quantum Gases, Superconductivity, Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1402.6704

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Jun 29, 2018
06/18

by
Lei Wang; Wei Cai; Xinzheng Zhang; Jingjun Xu; Yongsong Luo

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The highly unidirectional excitation of graphene plasmons (GPs) through near-field interference of orthogonally polarized dipoles is investigated. The preferred excitation direction of GPs by a single circularly polarized dipole can be simply understood with the angular momentum conservation law. Moreover, the propagation direction of GPs can be switched not only by changing the phase difference between dipoles, but also by placing the z-polarized dipole to its image position, whereas the...

Topics: Mesoscale and Nanoscale Physics, Condensed Matter

Source: http://arxiv.org/abs/1601.00437

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Jun 30, 2018
06/18

by
Lei Wang; Wei Cai; Xinzheng Zhang; Jingjun Xu

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The interaction between graphene plasmons and surface phonons of a semiconductor substrate is investigated, which can be efficiently controlled by the carrier injection of the substrate. The energy and lifetime of surface phonons in a substrate depend a lot on the carrier concentration, which provides a new machanism to tune plasmon-phonon coupled modes (PPCMs). More specifically, the dispersion and lifetime of PPCMs can be controlled by the carrier concentration change of the substrate. The...

Topics: Mesoscale and Nanoscale Physics, Condensed Matter

Source: http://arxiv.org/abs/1406.4274

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Jun 29, 2018
06/18

by
Li Huang; Yi-feng Yang; Lei Wang

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Recommender systems play an essential role in the modern business world. They recommend favorable items like books, movies, and search queries to users based on their past preferences. Applying similar ideas and techniques to Monte Carlo simulations of physical systems boosts their efficiency without sacrificing accuracy. Exploiting the quantum to classical mapping inherent in the continuous-time quantum Monte Carlo methods, we construct a classical molecular gas model to reproduce the quantum...

Topics: Computational Physics, Strongly Correlated Electrons, Machine Learning, Condensed Matter, Physics,...

Source: http://arxiv.org/abs/1612.01871

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Jun 28, 2018
06/18

by
Shuta Nakajima; Takafumi Tomita; Shintaro Taie; Tomohiro Ichinose; Hideki Ozawa; Lei Wang; Matthias Troyer; Yoshiro Takahashi

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A gas of electrons in a one-dimensional periodic potential can be transported even in the absence of a voltage bias if the potential is modulated slowly and periodically in time. Remarkably, the transferred charge per cycle is only sensitive to the topology of the path in parameter space. Although this so-called Thouless charge pump has first been proposed more than thirty years ago, it has not yet been realized. Here we report the first demonstration of topological Thouless pumping using...

Topics: Quantum Gases, Condensed Matter

Source: http://arxiv.org/abs/1507.02223

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Jun 29, 2018
06/18

by
Li Huang; Yilin Wang; Lei Wang; Philipp Werner

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A generalized version of the fidelity susceptibility of single-band and multi-orbital Hubbard models is systematically studied using single-site dynamical mean-field theory in combination with a hybridization expansion continuous-time quantum Monte Carlo impurity solver. We find that the fidelity susceptibility is extremely sensitive to changes in the state of the system. It can be used as a numerically inexpensive tool to detect and characterize a broad range of phase transitions and...

Topics: Physics, Condensed Matter, Computational Physics, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1607.03407

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Jun 30, 2018
06/18

by
Jing Chen; Song Cheng; Haidong Xie; Lei Wang; Tao Xiang

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Restricted Boltzmann machine (RBM) is one of the fundamental building blocks of deep learning. RBM finds wide applications in dimensional reduction, feature extraction, and recommender systems via modeling the probability distributions of a variety of input data including natural images, speech signals, and customer ratings, etc. We build a bridge between RBM and tensor network states (TNS) widely used in quantum many-body physics research. We devise efficient algorithms to translate an RBM...

Topics: Strongly Correlated Electrons, Machine Learning, Condensed Matter, Quantum Physics, Statistics

Source: http://arxiv.org/abs/1701.04831

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Jun 26, 2018
06/18

by
Bela Bauer; Lei Wang; Iztok Pižorn; Matthias Troyer

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We explore the role of entanglement in adiabatic quantum optimization by performing approximate simulations of the real-time evolution of a quantum system while limiting the amount of entanglement. To classically simulate the time evolution of the system with a limited amount of entanglement, we represent the quantum state using matrix-product states and projected entangled-pair states. We show that the probability of finding the ground state of an Ising spin glass on either a planar or...

Topics: Disordered Systems and Neural Networks, Quantum Physics, Condensed Matter

Source: http://arxiv.org/abs/1501.06914

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Jun 25, 2018
06/18

by
Lei Wang; Mauro Iazzi; Philippe Corboz; Matthias Troyer

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We present the ground state extension of the efficient quantum Monte Carlo algorithm for lattice fermions of arXiv:1411.0683. Based on continuous-time expansion of imaginary-time projection operator, the algorithm is free of systematic error and scales \emph{linearly} with projection time and interaction strength. Compared to the conventional quantum Monte Carlo methods for lattice fermions, this approach has greater flexibility and is easier to combine with powerful machinery such as histogram...

Topics: Strongly Correlated Electrons, Condensed Matter, High Energy Physics - Lattice, Computational...

Source: http://arxiv.org/abs/1501.00986

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3.0

Jun 28, 2018
06/18

by
Lei Wang; Ye-Hua Liu; Mauro Iazzi; Matthias Troyer; Gergely Harcos

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We present a guiding principle for designing fermionic Hamiltonians and quantum Monte Carlo (QMC) methods that are free from the infamous sign problem by exploiting the Lie groups and Lie algebras that appear naturally in the Monte Carlo weight of fermionic QMC simulations. Specifically, rigorous mathematical constraints on the determinants involving matrices that lie in the split orthogonal group provide a guideline for sign-free simulations of fermionic models on bipartite lattices. This...

Topics: Quantum Physics, Computational Physics, Strongly Correlated Electrons, Condensed Matter, Physics

Source: http://arxiv.org/abs/1506.05349

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Jun 28, 2018
06/18

by
Lei Wang; R. J. H. Wesselink; Yi Liu; Zhe Yuan; Ke Xia; Paul J. Kelly

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The spin Hall angle (SHA) is a measure of the efficiency with which a transverse spin current is generated from a charge current by the spin-orbit coupling and disorder in the spin Hall effect (SHE). In a study of the SHE for a Pt$|$Py (Py=Ni$_{80}$Fe$_{20}$) bilayer using a first-principles scattering approach, we find a SHA that increases monotonically with temperature and is proportional to the resistivity for bulk Pt. By decomposing the room temperature SHE and inverse SHE currents into...

Topics: Materials Science, Condensed Matter, Mesoscale and Nanoscale Physics

Source: http://arxiv.org/abs/1512.07418

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Jun 27, 2018
06/18

by
Lei Wang; Yuanda Gao; Bo Wen; Zheng Han; Takashi Taniguchi; Kenji Watanabe; Mikito Koshino; James Hone; Cory R. Dean

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The Hofstadter energy spectrum provides a uniquely tunable system to study emergent topological order in the regime of strong interactions. Previous experiments, however, have been limited to the trivial case of low Bloch band filling where only the Landau level index plays a significant role. Here we report measurement of high mobility graphene superlattices where the complete unit cell of the Hofstadter spectrum is accessible. We observe coexistence of conventional fractional quantum Hall...

Topics: Mesoscale and Nanoscale Physics, Condensed Matter

Source: http://arxiv.org/abs/1505.07180

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Jun 29, 2018
06/18

by
Qian-Qian Shi; Hong-Lei Wang; Sheng-Hao Li; Sam Young Cho; Murray T. Batchelor; Huan-Qiang Zhou

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Geometric entanglement(GE), as a measure of multipartite entanglement, has been investigated as a universal tool to detect phase transitions in quantum many-body lattice models. We outline a systematic method to compute GE for two-dimensional (2D) quantum many-body lattice models based on the translational invariant structure of infinite projected entangled pair state (iPEPS) representations. By employing this method, the $q$-state quantum Potts model on the square lattice with $q \in \{2, 3...

Topics: Quantum Physics, Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1604.07278

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Jun 26, 2018
06/18

by
Lei Wang; Ye-Hua Liu; Jakub Imriška; Ping Nang Ma; Matthias Troyer

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The fidelity susceptibility is a general purpose probe of phase transitions. With its origin in quantum information and in the differential geometry perspective of quantum states, the fidelity susceptibility can indicate the presence of a phase transition without prior knowledge of the local order parameter, as well as reveal the universal properties of a critical point. The wide applicability of the fidelity susceptibility to quantum many-body systems is, however, hindered by the limited...

Topics: Quantum Physics, Strongly Correlated Electrons, Condensed Matter, Statistical Mechanics, Physics,...

Source: http://arxiv.org/abs/1502.06969

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Jun 30, 2018
06/18

by
Patrick Maher; Lei Wang; Yuanda Gao; Carlos Forsythe; Takashi Taniguchi; Kenji Watanabe; Dmitry Abanin; Zlatko Papić; Paul Cadden-Zimansky; James Hone; Philip Kim; Cory R. Dean

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Symmetry breaking in a quantum system often leads to complex emergent behavior. In bilayer graphene (BLG), an electric field applied perpendicular to the basal plane breaks the inversion symmetry of the lattice, opening a band gap at the charge neutrality point. In a quantizing magnetic field electron interactions can cause spontaneous symmetry breaking within the spin and valley degrees of freedom, resulting in quantum Hall states (QHS) with complex order. Here we report fractional quantum...

Topics: Mesoscale and Nanoscale Physics, Condensed Matter

Source: http://arxiv.org/abs/1403.2112

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Jun 29, 2018
06/18

by
Lei Wang; Jin-Chuan Zhang; Zhi-Wei Jia; Yue Zhao; Chuan-Wei Liu; Ying-Hui Liu; Shen-Qiang Zhai; Ning Zhuo; Feng-Qi Liu; Xian-Gang Xu

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We show a phase-locked array of three quantum cascade lasers with an integrated Talbot cavity at one side of the laser array. The coupling scheme is called diffraction coupling. By controlling the length of Talbot to be a quarter of Talbot distance (Zt/4), in-phase mode operation can be selected. The in-phase operation shows great modal stability under different injection currents, from the threshold current to the full power current. The far-field radiation pattern of the in-phase operation...

Topics: Mesoscale and Nanoscale Physics, Optics, Condensed Matter, Physics

Source: http://arxiv.org/abs/1609.08790

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Jun 29, 2018
06/18

by
Shaowen Chen; Zheng Han; Mirza M. Elahi; K. M. Masum Habib; Lei Wang; Bo Wen; Yuanda Gao; Takashi Taniguchi; Kenji Watanabe; James Hone; Avik W. Ghosh; Cory R. Dean

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Electrons transmitted across a ballistic semiconductor junction undergo refraction, analogous to light rays across an optical boundary. A pn junction theoretically provides the equivalent of a negative index medium, enabling novel electron optics such as negative refraction and perfect (Veselago) lensing. In graphene, the linear dispersion and zero-gap bandstructure admit highly transparent pn junctions by simple electrostatic gating, which cannot be achieved in conventional semiconductors....

Topics: Mesoscale and Nanoscale Physics, Condensed Matter

Source: http://arxiv.org/abs/1602.08182