Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 20 for “"sign problem"”.
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Strong coupling methods for lattice QCD
… suffers from the numerical finite density sign problem. Strong coupling methods, expanding in the inverse gauge coupling, give rise to alternative representations of the partition function that can make the sign problem milder. This Habilitation discusses the strong coupling methods …
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Solving sign problems with meron cluster algorithms : simulating field theories at non-zero chemical potential
Numerical simulation of quantum systems develop sign problems upon the introduction of a chemical potential. The sign problem thus makes many interesting physical systems very difficult to study numerically. In this thesis, two related systems which develop sign problems in this way are considered: …
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Dissipative Matsubara Dynamics
… to be a useful method because of a severe sign problem, which limited the number of Matsubara modes in a calculation to around 10 or less. Therefore, Matsubara dynamics has never been directly compared to exact quantum results with the exception of the harmonic oscillator and a linear …
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Semiclassical Approaches to Complex Chemical Simulation in Real Time
… of highly oscillatory functions (i.e. the SC ``sign problem"), generally renders SC theory impractical for all but very simple, low-dimensional systems. In this dissertation we derive a variety of mixed quantum-classical (MQC) representations of the real-time correlation function within the SC …
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Path integral Monte Carlo and the electron gas
… exact simulation of Fermi systems, the sign problem. Afterwards, we introduce a way to circumvent the sign problem in PIMC simulations through a fixed-node constraint. We then apply this method to the homogeneous electron gas at a large swatch of densities and temperatures in order to …
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Fourier-accelerated Langevin simulation of the frustrated XY model and simulation of the spinless and spin one-half Hubbard model
… and the autocorrelation of the spin showed significant speedup. The frustrated case has Isinglike domains. It was found that Fourier acceleration speeds the evolution of spinwaves but has negligible effect on the Ising-like domains. In the Hubbard model, the fermion determinant weight factor …
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Mocking quantum mechanics: Semiclassical and machine-learning approaches to frustrated magnetism
… neural networks in a range of machine-learning problems makes them a natural candidate for representing highly entangled quantum states, allowing in principle an accurate simulation of large, challenging quantum systems with modest computational resources. However, most current approaches using …
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Topics in Supersymmetry: Implications for Cosmology and Non-Perturbative Studies on a Spacetime Lattice
… theory is explored. An analysis of the fermionic sign problem is presented and it is shown to be absent in the studied formulation. A first study of the phase structure of supersymmetric N = 4 supersymmetric gauge theory is also presented.</p>
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Nuclear and Chiral transition using the strong coupling expansion of Lattice QCD
… conventional lattice QCD methods encounter the sign problem. To address this, we utilize the dual representation of lattice QCD obtained via the strong coupling expansion. The nuclear transition is studied in the strong coupling limit for large quark masses, and the necessary algorithmic …
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Magnetic-field-induced antiferromagnetism in the Kondo lattice
… fermionic degrees of freedom. The formulation is sign-problem-free for all values of the Kondo coupling and magnetic field strength. The matrix operations are specially organized to maintain numerical stability down to arbitrarily low temperatures. Spectral data is extracted from the …
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Lattice gauge theories on Lefschetz thimbles
… finite chemical potential. These suffer from a sign problem, which prohibits their simulation with traditional MCMC techniques. We alleviate this problem caused by complex actions using a generalization of Picard-Lefschetz theory for complex Morse functions with degenerate critical points i.e. …
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Quantum computing for biophysical and optimization problems
… technologies over recent years has driven significant efforts toward developing algorithms with applications to a wide range of research fields. Beyond fully quantum algorithms — whose efficacy remains constrained by technological limitations — hybrid quantum-classical algorithms and …
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Conductance of single-electron devices from imaginary-time path integrals
… response <br>theory. To circumvent the dynamical sign problem in the numerical <br>determination of real-time correlation functions, we calculated <br>the current autocorrelator for imaginary times and employed a <br>scheme for the analytical continuation of the numerical data. <br> <br>For the …
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Quasicentroid Molecular Dynamics
… includes a complex phase, which gives rise to a sign problem. Unlike in the original, restricting the shapes of the smooth paths (limiting the number of Matsubara modes) only changes the accuracy of the dynamics, while the mean-field thermal distribution remains exact. This improves convergence …
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Field Theoretical Approach to the Phases of QCD
… in theoretical physics and represents a significant step towards understanding the collective behavior of the strong force. The non-perturbative region of QCD, where atomic matter dissolves into a Quark-Gluon-Plasma state, can only be studied from first principles by numerical lattice …
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Quantum Monte Carlo simulations of electrons and holes
… Restricted paths are used to handle the Fermion sign problem. With an appropriate choice of paired nodes for the restricted path approximation we find an excitonic Bose condensate. The energy of the low temperature, low density exciton gas determined from PIMC agrees well with the theory of …
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Thermal QCD on the lattice – from finite density to non-uniform magnetic fields
… of QCD via Taylor expansion to circumvent the sign problem. We determined the $T$ and $B$ dependence of the Leading Order (LO) contribution to the EoS in the presence of strangeness-neutrality and isospin-asymmetry constraints, which are relevant in phenomenological studies of HICs. In part …
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Study of the properties of dilute Fermi gases in the strongly interacting regime
… wave function in order to deal with the fermion sign problem. We consider the possibility of Cooper pairing between fermions of different species. The strength of the interaction is varied to study different pairing regimes which are characterized by the product of the s-wave scattering length a …
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Thermodynamic and hydrodynamic behaviour of interacting Fermi gases
… of particles in the two components) due to a sign problem. I will show how to apply reweighting techniques to generalise the algorithm to the imbalanced case, and present results for the critical temperature and other thermodynamic observables at the critical point, namely the chemical …
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Theoretical methods for the study of quantum dynamics
… of stationary action applicable to initial-value problems. This has resulted in the first reported synthetic computation of non-stationary quantum trajectories for a fully anharmonic oscillator. Success in one dimension has laid the groundwork for future extension to a rigorous quantum-classical …