arXiv subjects

Michael McGuigan

Publications and source records attributed to Michael McGuigan.

At least 37 records · Page 2Linked to original sources

arXiv2019

Thermo field dynamics on a quantum computer

In this paper we develop a quantum algorithm to realize finite temperature simulation on a quantum computer. As quantum computers use real-time evolution we did not use the imaginary time methods popular on classical algorithms. Instead, we implemented a real-time thermo field dynamics formalism, which has the added benefit of being able to compute quantities that are both time- and temperature-dependent. To implement thermo field dynamics we apply a unitary transformation to discrete quantum mechanical operators to make new Hamiltonians with encoded temperature dependence. The method works normally for fermions, which have a finite representation, but needs some modification to work with bosons. These Hamiltonians are then processed into a Pauli matrix representation in order to be used as input for IBM's Qiskit package. We then use IBM's quantum simulator to calculate an approximation to the Hamiltonaian's ground state energy via the variational quantum eigensolver (VQE) algorithm. This approximation is then compared to a classically calculated value for the exact energy. The thermo field dynamics quantum algorithm has general applications to material science, high-energy physics and nuclear physics, particularly in those situations involving real-time evolution at high temperature.

quant-ph↗

arXiv2019

Opportunities for Nuclear Physics & Quantum Information Science

This whitepaper is an outcome of the workshop Intersections between Nuclear Physics and Quantum Information held at Argonne National Laboratory on 28-30 March 2018 [www.phy.anl.gov/npqi2018/]. The workshop brought together 116 national and international experts in nuclear physics and quantum information science to explore opportunities for the two fields to collaborate on topics of interest to the U.S. Department of Energy (DOE) Office of Science, Office of Nuclear Physics, and more broadly to U.S. society and industry. The workshop consisted of 22 invited and 10 contributed talks, as well as three panel discussion sessions. Topics discussed included quantum computation, quantum simulation, quantum sensing, nuclear physics detectors, nuclear many-body problem, entanglement at collider energies, and lattice gauge theories.

nucl-th↗

arXiv2019

Dark Horse, Dark Matter: Revisiting the SO(16)x SO(16)' Nonsupersymmetric Model in the LHC and Dark Energy Era

We revisit the nonsupersymmetric SO(16)x SO(16)' model in light of LHC and Dark Energy data. Recently nonsupersymmetric models have become of great interest because the LHC has not found evidence of supersymmetry. In addition nonsupersymmetric models with a single Higgs-like field and small one loop vacuum energy have been constructed. Also models of dark energy with a dilaton-radion potential have also been recently examined in the light of dark energy data and the swampland conjecture. In this paper some of the features of the nonsupersymmetric SO(16)x SO(16)' model with regards to high energy physics and cosmology such as dark energy, vacuum stablilization, dark matter candidates, dark matter portals, gauge-Higgs unification, and quantum cosmology are examined in the context of the LHC and dark energy era.

hep-th↗

arXiv2018

Simulating 0+1 Dimensional Quantum Gravity on Quantum Computers: Mini-Superspace Quantum Cosmology and the World Line Approach in Quantum Field Theory

Quantum computers are a promising candidate to radically expand computational science through increased computing power and more effective algorithms. In particular quantum computing could have a tremendous impact in the field of quantum cosmology. The goal of quantum cosmology is to describe the evolution of the Universe through the Wheeler-DeWitt equation or path integral methods without having to first formulate a full theory of quantum gravity. The quantum computer provides an advantage in this endeavor because it can perform path integrals in Lorentzian space and does not require constructing contour integrations in Euclidean gravity. Also quantum computers can provide advantages in systems with fermions which are difficult to analyze on classical computers. In this study, we first employed classical computational methods to analyze a Friedmann-Robertson-Walker mini-superspace with a scalar field and visualize the calculated wave function of the Universe for a variety of different values of the spatial curvature and cosmological constant. We them used IBM's Quantum Information Science Kit Python library and the variational quantum eigensolver to study the same systems on a quantum computer. The framework can also be extended to the world line approach to quantum field theory.

quant-ph↗

arXiv2018

Quantum Computation and Visualization of Hamiltonians using Discrete Quantum Mechanics and IBM QISKit

Quantum computers have the potential to transform the ways in which we tackle some important problems. The efforts by companies like Google, IBM and Microsoft to construct quantum computers have been making headlines for years. Equally important is the challenge of translating problems into a state that can be fed to these machines. Because quantum computers are in essence controllable quantum systems, the problems that most naturally map to them are those of quantum mechanics. Quantum chemistry has seen particular success in the form of the variational quantum eigensolver (VQE) algorithm, which is used to determine the ground state energy of molecular systems. The goal of our work has been to use the matrix formulation of quantum mechanics to translate other systems so that they can be run through this same algorithm. We describe two ways of accomplishing this using a position basis approach and a Gaussian basis approach. We also visualize the wave functions from the eigensolver and make comparisons to theoretical results obtained with continuous operators.

quant-ph↗

arXiv2013

A First-Principles Study of Thiol Ligated CdSe Nanoclusters

A first-principles study of small CdnSen Quantum Dots (QD) ('n' =6, 12, 13, and 33) has been performed for application to QD solar cell development. We separately assess the effects of the particle size and the passivating ligands upon the optimized structure and the energy gap (from a density functional theory (DFT) calculation) and the corresponding absorption spectrum (from a time-dependent density functional theory (TDDFT) calculation). The structures of four thiol ligands, namely - cysteine (Cys), mercaptopropionic acid (MPA), and their reduced-chain analogues, are investigated. We have documented significant passivation effects of the surfactants upon the structure and the optical absorption properties of the CdSe quantum dots: The surface Cd-Se bonds are weakened, whereas the core bonds are strengthened. A blue shift of the absorption spectrum by ~0.2 eV is observed. Also, the optical absorption intensity is enhanced by the passivation. By contrast, we have observed that varying the length of ligands yields only a minor effect upon the absorption properties: a shorter alkane chain might induce a slightly stronger interaction between the -NH2 group and the nearest surface Se atom, which is observed as a stronger ligand binding energy. For Cd12Se12, which is regarded as the 'non-magic' size QD, neither the self-relaxation nor the ligand passivation could fully stabilize the structure or improve the poor electronic properties. We also observe that the category of thiol ligands possesses a better ability to open the band gap of CdSe QD than either phosphine oxide or amine ligands. Our estimation of the absorption peak of the Cys-capped QDs ranges from 413 nm to 460 nm, which is consistent to the experimental peak as 422 nm.

cond-mat.mes-hall↗

arXiv2013

A First-Principles Study of CdSe Nanoclusters Capped by Thiol Ligands

A first-principles study of small CdnSen quantum dots (QDs) (n = 6, 13, and 33) has been performed for the study of QD-sensitized solar cells. We assessed the effects of the passivating thiol-radical ligands on the optimized structure, the energy gap, and on the absorption spectrum. The simplest thiol, methanethiol, and four other thiol type ligands, namely - cysteine (Cys), mercaptopropionic acid (MPA), and their reduced-chain analogues, were investigated. We have come to the following conclusions. (a) Thiol-radical ligands possessed greater effects on the structure and electronic properties of the CdSe QDs than thiol ligands alone. (b) The sulfur 3p orbitals were localized as the midgap states for the thiol-radical-ligated complex, which altered the absorption spectrum of bare Cd6Se6 by inducing a new lower energy absorption peak at 2.37 eV. (c) The thiol-radical-ligated complex was also found to be sensitive to the position and number of ligands. (d) Both the amine group on Cys and the carboxyl group on Cys and MPA showed a strong tendency to bond with the neighboring Cd atom, especially when the length of the ligand was reduced. This formation of Cd-N and Cd-O bonds resulted in smaller HOMO-LUMO gaps and a stronger binding between the ligands and the surface atoms of CdSe nanoclusters.

cond-mat.mtrl-sci↗

arXiv2009

Computational Exploration of the Nanogold Energy Landscape

We use density functional theory to quantify finite size and shape effects for gold nanoclusters. We concentrate on the computation of binding energy as a function of bond length for icosahedral and cuboctohedral clusters. We find that the cuboctoheral gold clusters have lower energy for 13 atoms. For 55 atoms we find that the icosahedral gold clusters have lower binding energy. We also introduce a one parameter family of geometries that interpolate between the icosahedral and cuboctohedral clusters that is parametrized by an angle variable. We determine the binding energy dependence on shape as a function of the angle variable for 13 and 55 atom clusters with a minimum at the cuboctohedral point and icosahedral point respectively. We also compute the binding energy for the 147 atom gold nanocluster and show that the binding energy of the icosahedral cluster is lower than the 147 atom cuboctohedral gold cluster. We also compute the binding energy of the $Au_{55}O_2$ molecule with possible applications to catalysis.

cond-mat.mes-hall↗

arXiv2009

The Tiger and the Sun: Solar Power Plants and Wildlife Sanctuaries

We discuss separate and integrated approaches to building scalable solar power plants and wildlife sanctuaries. Both solar power plants and wildlife sanctuaries need a lot of land. We quantify some of the requirements using various estimates of the rate of solar power production as well as the rate of adding wildlife to a sanctuary over the time range 2010-2050. We use population dynamics equations to study the evolution of solar energy and tiger populations up to and beyond 2050.

q-bio.PE↗

arXiv2008

QCD Cosmology from the Lattice Equation of State

We numerically determine the time dependence of the scale factor from the lattice QCD equation of state, which can be used to define a QCD driven cosmology. We compare a lattice approach to QCD cosmology at late times with other models of the low temperature equation of state including the hadronic resonance gas model, Hagedorn model and AdS/CFT.

hep-th↗

arXiv2008

Linear Augmented Slater-Type Orbital Method for Free Standing Clusters

We have developed a Scalable Linear Augmented Slater-Type Orbital (LASTO) method for electronic-structure calculations on free-standing atomic clusters. As with other linear methods we solve the Schrödinger equation using a mixed basis set consisting of numerical functions inside atom-centered spheres and matched onto tail functions outside. The tail functions are Slater-type orbitals, which are localized, exponentially decaying functions. To solve the Poisson equation between spheres, we use a finite difference method replacing the rapidly varying charge density inside the spheres with a smoothed density with the same multipole moments. We use multigrid techniques on the mesh, which yield the Coulomb potential on the spheres and in turn defines the potential inside via a Dirichlet problem. To solve the linear eigen-problem, we use ScaLAPACK, a well-developed package to solve large eigensystems with dense matrices. We have tested the method on small clusters of palladium.

cond-mat.mtrl-sci↗

arXiv2008

Riemann Hypothesis and Master Matrix for FZZT Brane Partition Functions

We continue to investigate the physical interpretation of the Riemann zeta function as a FZZT brane partition function associated with a matrix/gravity correspondence begun in arxiv:0708.0645. We derive the master matrix of the $(2,1)$ minimal and $(3,1)$ minimal matrix model. We use it's characteristic polynomial to understand why the zeros of the FZZT partition function, which is the Airy function, lie on the real axis. We also introduce an iterative procedure that can describe the Riemann $Ξ$ function as a deformed minimal model whose deformation parameters are related to a Konsevich integrand. Finally we discuss the relation of our work to other approaches to the Riemann $Ξ$ function including expansion in terms of Meixner-Pollaczek polynomials and Riemann-Hilbert problems.

math-ph↗

arXiv2008

Toward the Graphics Turing Scale on a Blue Gene Supercomputer

We investigate raytracing performance that can be achieved on a class of Blue Gene supercomputers. We measure a 822 times speedup over a Pentium IV on a 6144 processor Blue Gene/L. We measure the computational performance as a function of number of processors and problem size to determine the scaling performance of the raytracing calculation on the Blue Gene. We find nontrivial scaling behavior at large number of processors. We discuss applications of this technology to scientific visualization with advanced lighting and high resolution. We utilize three racks of a Blue Gene/L in our calculations which is less than three percent of the the capacity of the worlds largest Blue Gene computer.

cs.GR↗

arXiv2007

Riemann Hypothesis, Matrix/Gravity Correspondence and FZZT Brane Partition Functions

We investigate the physical interpretation of the Riemann zeta function as a FZZT brane partition function associated with a matrix/gravity correspondence. The Hilbert-Polya operator in this interpretation is the master matrix of the large N matrix model. Using a related function $Ξ(z)$ we develop an analogy between this function and the Airy function Ai(z) of the Gaussian matrix model. The analogy gives an intuitive physical reason why the zeros lie on a critical line. Using a Fourier transform of the $Ξ(z)$ function we identify a Kontsevich integrand. Generalizing this integrand to $n \times n$ matrices we develop a Kontsevich matrix model which describes n FZZT branes. The Kontsevich model associated with the $Ξ(z)$ function is given by a superposition of Liouville type matrix models that have been used to describe matrix model instantons.

math-ph↗

arXiv2007

Universe Decay, Inflation and the Large Eigenvalue of the Cosmological Constant Seesaw

We discuss implications of the large eigenvalue of the cosmological constant seesaw mechanism extending hep-th/0602112 and hep-th/0604108. While the previous papers focused on the small eigenvalue as a cosmological constant associated with the accelerating Universe, here we draw attention to the physical implications of the large eigenvalue. In particular we find that the large eigenvalue can give rise to a period of inflation terminated by Universe decay. The mechanism involves quantum tunneling and mixing and introduces parameters $Γ$, the decay constant, and $θ$, the mixing angle. We discuss the cosmological constant seesaw mechanism in the context of various models of current interest including chain inflation, inflatonless inflation, string theory, Universe entanglement and different approaches to the hierarchy problem.

hep-th↗

arXiv2007

Computational approach to finite size and shape effects in iron nanomagnets

We develop and validate a computational approach to nanomagnets. It is built on the spin wave approximation to a Heisenberg ferromagnet whose parameters can be calculated from a first principles theory (e.g. density functional theory). The method can be used for high throughput analysis of a variety of nanomagnetic materials. We compute the dependence of the magnetization of an iron nanomagnet on temperature, size and shape. The approach is applied to nanomagnets in the range of 432 atoms to 59 million atoms, a size which is several orders of magnitude beyond the scalability of density functional theory.

cond-mat.mtrl-sci↗

arXiv2006

Cosmological Constant Seesaw in String/M-Theory

In this paper we extend the Cosmological Constant Seesaw treatment of hep-th/0602112 to String/M-Theory where the cosmological constant is finite. We discuss how transitions between different $λ$, one of Planckian vacuum energy, can give rise to a large $M_{Pl}^4$ denominator in the Cosmological Constant Seesaw relation discussed by Banks, Motl and Carroll. We apply these ideas to 2d/3d String/M-Theory and show how the existence of a large N dual fermionic theory makes the demonstration of a transition between different $λ$ relatively straight forward. We also consider 2d/3d Heterotic String/M-Theory cosmology, a theory for which the large N dual is unknown. The minisuperspace associated to these models is 26/27 dimensional for the SO(24) theory and 10/11 dimensional for the $SO(8) \times E_8$ theory and consists of the $T$ fields as well as the dilaton and metric. 2d Heterotic String Quantum Cosmology is similar to critical string dynamics except for the inclusion of the 2d gauge fields. These 2d gauge fields have an important effect on the vacuum energy and on transitions between different $λ$ through the effects of Wilson lines. Finally we discuss the extension to existing higher dimensional string cosmologies possessing large N duals.

hep-th↗

arXiv2006

Graphics Turing Test

We define a Graphics Turing Test to measure graphics performance in a similar manner to the definition of the traditional Turing Test. To pass the test one needs to reach a computational scale, the Graphics Turing Scale, for which Computer Generated Imagery becomes comparatively indistinguishable from real images while also being interactive. We derive an estimate for this computational scale which, although large, is within reach of todays supercomputers. We consider advantages and disadvantages of various computer systems designed to pass the Graphics Turing Test. Finally we discuss commercial applications from the creation of such a system, in particular Interactive Cinema.

cs.GR↗