Browsing by Author "Scarola, Vito W."

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    The ALPS project release 2.0: open source software for strongly correlated systems
    Bauer, B.; Carr, L. D.; Evertz, H. G.; Feiguin, A.; Freire, J.; Fuchs, S.; Gamper, L.; Gukelberger, J.; Gull, E.; Guertler, S.; Hehn, A.; Igarashi, R.; Isakov, S. V.; Koop, D.; Ma, P. N.; Mates, P.; Matsuo, H.; Parcollet, O.; Pawlowski, G.; Picon, J. D.; Pollet, L.; Santos, Eunice E.; Scarola, Vito W.; Schollwoeck, U.; Silva, C.; Surer, B.; Todo, S.; Trebst, S.; Troyer, M.; Wall, M. L.; Werner, P.; Wessel, S. (IOP, 2011-05-01)
    We present release 2.0 of the ALPS (Algorithms and Libraries for Physics Simulations) project, an open source software project to develop libraries and application programs for the simulation of strongly correlated quantum lattice models such as quantum magnets, lattice bosons, and strongly correlated fermion systems. The code development is centered on common XML and HDF5 data formats, libraries to simplify and speed up code development, common evaluation and plotting tools, and simulation programs. The programs enable non-experts to start carrying out serial or parallel numerical simulations by providing basic implementations of the important algorithms for quantum lattice models: classical and quantum Monte Carlo (QMC) using non-local updates, extended ensemble simulations, exact and full diagonalization (ED), the density matrix renormalization group (DMRG) both in a static version and a dynamic time-evolving block decimation (TEBD) code, and quantum Monte Carlo solvers for dynamical mean field theory (DMFT). The ALPS libraries provide a powerful framework for programers to develop their own applications, which, for instance, greatly simplify the steps of porting a serial code onto a parallel, distributed memory machine. Major changes in release 2.0 include the use of HDF5 for binary data, evaluation tools in Python, support for the Windows operating system, the use of CMake as build system and binary installation packages for Mac OS X and Windows, and integration with the VisTrails work ow provenance tool. The software is available from our web server at http://alps.comp-phys.org/.
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    Benchmarking measurement-based quantum computation on graph states
    Qin, Zhangjie (Virginia Tech, 2024-08-26)
    Measurement-based quantum computation is a form of quantum computing that operates on a prepared entangled graph state, typically a cluster state. In this dissertation, we will detail the creation of graph states across various physical platforms using different entangling gates. We will then benchmark the quality of graph states created with error-prone interactions through quantum wire teleportation experiments. By leveraging underlying symmetry, we will design graph states as measurement-based quantum error correction codes to protect against perturbations, such as ZZ crosstalk in quantum wire teleportation. Additionally, we will explore other measurement-based algorithms used for the quantum simulation of time evolution in fermionic systems, using the Kitaev model and the Hubbard model as examples.
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    Boson core compressibility
    Khorramzadeh, Y.; Lin, F.; Scarola, Vito W. (American Physical Society, 2012-04-16)
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    Boson core compressibility
    Khorramzadeh, Y.; Lin, Fei; Scarola, Vito W. (American Physical Society, 2012-04-16)
    Strongly interacting atoms trapped in optical lattices can be used to explore phase diagrams of Hubbard models. Spatial inhomogeneity due to trapping typically obscures distinguishing observables. We propose that measures using boson double occupancy avoid trapping effects to reveal two key correlation functions. We define a boson core compressibility and core superfluid stiffness in terms of double occupancy. We use quantum Monte Carlo on the Bose-Hubbard model to empirically show that these quantities intrinsically eliminate edge effects to reveal correlations near the trap center. The boson core compressibility offers a generally applicable tool that can be used to experimentally map out phase transitions between compressible and incompressible states.
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    Cooper instability of composite fermions
    Scarola, Vito W.; Park, K.; Jain, J. K. (2000-08-24)
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    Discerning Incompressible and Compressible Phases of Cold Atoms in Optical Lattices
    Scarola, Vito W.; Pollet, L.; Oitmaa, J.; Troyer, M. (2009-04-03)
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    Disordered Supersolids in the Extended Bose-Hubbard Model
    Lin, Fei; Maier, T. A.; Scarola, Vito W. (Nature, 2017-10-06)
    The extended Bose-Hubbard model captures the essential properties of a wide variety of physical systems including ultracold atoms and molecules in optical lattices, Josephson junction arrays, and certain narrow band superconductors. It exhibits a rich phase diagram including a supersolid phase where a lattice solid coexists with a superfluid. We use quantum Monte Carlo to study the supersolid part of the phase diagram of the extended Bose-Hubbard model on the simple cubic lattice. We add disorder to the extended Bose-Hubbard model and find that the maximum critical temperature for the supersolid phase tends to be suppressed by disorder. But we also find a narrow parameter window in which the supersolid critical temperature is enhanced by disorder. Our results show that supersolids survive a moderate amount of spatial disorder and thermal fluctuations in the simple cubic lattice.
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    Distinguishing phases with ansatz wave functions
    Bauer, B.; Troyer, M.; Scarola, Vito W.; Whaley, K. B. (2010-02)
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    Dynamics of Hubbard-band quasiparticles in disordered optical lattices
    Scarola, Vito W.; De Marco, B. (American Physical Society, 2015-11-30)
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    Dzyaloshinskii-Moriya Interaction and Spiral Order in Spin-orbit Coupled Optical Lattices
    Gong, M.; Qian, Y.; Yan, M.; Scarola, Vito W.; Zhang, C. (Nature Publishing Group, 2015-05-27)
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    Edge transport in 2D cold atom optical lattices
    Scarola, Vito W.; Das Sarma, S. (2007-05-25)
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    Effects of Electron-Vibron Coupling in Single-Molecule Magnet Transport Junctions Using a Hybrid Density Functional Theory and Model Hamiltonian Approach
    Mccaskey, Alexander Joseph (Virginia Tech, 2014-05-14)
    Recent experiments have shown that junctions consisting of individual single-molecule magnets (SMMs) bridged between two electrodes can be fabricated in three-terminal devices, and that the characteristic magnetic anisotropy of the SMMs can be affected by electrons tunneling through the molecule. Vibrational modes of the SMM can couple to electronic charge and spin degrees of freedom, and this coupling also influences the magnetic and transport properties of the SMM. The effect of electron-vibron coupling on transport has been extensively studied in small molecules, but not yet for junctions of SMMs. The goals of this thesis will be two-fold: to present a novel approach for studying the effects of this electron-vibron coupling on transport through SMMs that utilizes both density functional theory calculations and model Hamiltonian construction and analysis, and to present a software framework based on this hybrid approach for the simulation of transport across user-defined SMMs. The results of these simulations will indicate a characteristic suppression of the current at low energies that is strongly dependent on the overall electron-vibron coupling strength and number of molecular vibrational modes considered.
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    Electron Transport via Single Molecule Magnets with Magnetic Anisotropy
    Luo, Guangpu (Virginia Tech, 2019-02-07)
    Single molecule magnets (SMMs) are molecules of mesoscopic scale which exhibit quantum properties such as quantum tunneling of magnetization, quantum interference, spin filtering effects, strong spin-phonon coupling and strong hyperfine Stark effects. These effects allow applications of SMMs to high-density information storage, molecular spintronics, and quantum information science. Therefore, SMMs are of interest to physicists, chemists, and engineers. Recently, experimental fabrication of individual SMMs within transistor set-ups have been achieved, offering a new method to examine magnetic properties of individual SMMs. In this thesis, two types of SMMs, specifically Eu2(C8H8)3 and Ni9Te6(PEt3)8, are theoretically investigated by simulating their electron transport properties within three-terminal transistor set-ups. An extended metal atom chain (EMAC) consists of a string of metallic atoms with organic ligands surrounding the string. EMACs are an important research field for nanoelectronics. Homometallic iron-based EMACs are especially attractive due to the high spin and large magnetic anisotropy of iron(II). We explore the exchange coupling of iron atoms in two EMACs: [Fe2(mes)2(dpa)2] and [Fe4(tpda)3Cl2]. Chapter 1 provides an introduction to SMMs, electron transport experiments via SMMs and an introduction to density functional theory (DFT). Chapter 2 presents a theoretical study of electron transport via Eu2(C8H8)3. This type of molecule is interesting since its magnetic anisotropy type changes with oxidation state. The unique magnetic properties lead to spin blockade effects at zero and low bias. In other words, the current through this molecule is completely suppressed until the bias voltage exceeds a certain value. Chapter 3 discusses a theoretical study of electron transport via Ni9Te6(PEt3)8. The magnetic anisotropy of this magnetic cluster has cubic symmetry, which is higher than most SMMs. With appropriate magnetic anisotropy parameters, in the presence of an external magnetic field, uncommon phenomena such as low-bias blockade effects, negative conductance and discontinuous conductance lines, are observed. In Chapter 2 and 3 DFT-calculated magnetic anisotropy parameters are used and electron transport properties are calculated by solving master equations at low temperature. Chapter 4 examines the exchange coupling between iron ions in EMACs [Fe2(mes)2(dpa)2] and [Fe4(tpda)3Cl2]. The exchange coupling constants are calculated by using the least-squares fitting method, based on the DFT-calculated energies from different spin configurations.
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    Emergent Kinetics and Fractionalized Charge in 1D Spin-Orbit Coupled Flatband Optical Lattices
    Lin, F.; Zhang, C.; Scarola, Vito W. (American Physical Society, 2014-03-18)
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    Emulating non-Abelian topological matter in cold-atom optical lattices
    Scarola, Vito W.; Das Sarma, S. (2008-02)
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    Enhancing the Thermal Stability of Majorana Fermions with Redundancy Using Dipoles in Optical Lattices
    Lin, F.; Scarola, Vito W. (American Physical Society, 2013-11-25)
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    Equilibration Dynamics of Strongly Interacting Bosons in 2D Lattices with Disorder
    Yan, M.; Hui, H.-Y.; Rigol, M.; Scarola, Vito W. (2016)
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    Exact Diagonalization Studies of Strongly Correlated Systems
    Raum, Peter Thomas (Virginia Tech, 2020-01-14)
    In this dissertation, we use exact diagonalization to study a few strongly correlated systems, ranging from the Fermi-Hubbard model to the fractional quantum Hall effect (FQHE). The discussion starts with an overview of strongly correlated systems and what is meant by strongly correlated. Then, we extend cluster perturbation theory (CPT), an economic method for computing the momentum and energy resolved Green's function for Hubbard models to higher order correlation functions, specifically the spin susceptibility. We benchmark our results for the one-dimensional Fermi-Hubbard model at half-filling. In addition we study the FQHE at fillings $nu = 5/2$ for fermions and $nu = 1/2$ for bosons. For the $nu = 5/2$ system we investigate a two-body model that effectively captures the three-body model that generates the Moore-Read Pfaffian state. The Moore-Read Pfaffian wave function pairs composite fermions and is believed to cause the FQHE at $nu = 5/2$. For the $nu = 1/2$ system we estimate the entropy needed to observe Laughlin correlations with cold atoms via an ansatz partition function. We find entropies achieved with conventional cooling techniques are adequate.
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    Exact diagonalization study of strongly correlated topological quantum states
    Chen, Mengsu (Virginia Tech, 2019-02-04)
    A rich variety of phases can exist in quantum systems. For example, the fractional quantum Hall states have persistent topological characteristics that derive from strong interaction. This thesis uses the exact diagonalization method to investigate quantum lattice models with strong interaction. Our research topics revolve around quantum phase transitions between novel phases. The goal is to find the best schemes for realizing these novel phases in experiments. We studied the fractional Chern insulator and its transition to uni-directional stripes of particles. In addition, we studied topological Mott insulators with spontaneous time-reversal symmetry breaking induced by interaction. We also studied emergent kinetics in one-dimensional lattices with spin-orbital coupling. The exact diagonalization method and its implementation for studying these systems can easily be applied to study other strongly correlated systems.
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    A General Study of the Complex Ginzburg-Landau Equation
    Liu, Weigang (Virginia Tech, 2019-07-02)
    In this dissertation, I study a nonlinear partial differential equation, the complex Ginzburg-Landau (CGL) equation. I first employed the perturbative field-theoretic renormalization group method to investigate the critical dynamics near the continuous non-equilibrium transition limit in this equation with additive noise. Due to the fact that time translation invariance is broken following a critical quench from a random initial configuration, an independent ``initial-slip'' exponent emerges to describe the crossover temporal window between microscopic time scales and the asymptotic long-time regime. My analytic work shows that to first order in a dimensional expansion with respect to the upper critical dimension, the extracted initial-slip exponent in the complex Ginzburg-Landau equation is identical to that of the equilibrium model A. Subsequently, I studied transient behavior in the CGL through numerical calculations. I developed my own code to numerically solve this partial differential equation on a two-dimensional square lattice with periodic boundary conditions, subject to random initial configurations. Aging phenomena are demonstrated in systems with either focusing and defocusing spiral waves, and the related aging exponents, as well as the auto-correlation exponents, are numerically determined. I also investigated nucleation processes when the system is transiting from a turbulent state to the ``frozen'' state. An extracted finite dimensionless barrier in the deep-quenched case and the exponentially decaying distribution of the nucleation times in the near-transition limit are both suggestive that the dynamical transition observed here is discontinuous. This research is supported by the U. S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering under Award DE-FG02-SC0002308