Current Search: Research Repository (x) » Department of Physics (x) » Quantum theory (x)
Search results
 Title
 Entangling Qubits by Heisenberg Spin Exchange and Anyon Braiding.
 Creator

Zeuch, Daniel, Bonesteel, N. E., Sussman, Mark, Hill, S. (Stephen Olof), Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
 Abstract/Description

As the discovery of quantum mechanics signified a revolution in the world of physics more than one century ago, the notion of a quantum computer in 1981 marked the beginning of a drastic change of our understanding of information and computability. In a quantum computer, information is stored using quantum bits, or qubits, which are described by a quantummechanical superposition of the quantum states 0 and 1. Computation then proceeds by acting with unitary operations on these qubits. These...
Show moreAs the discovery of quantum mechanics signified a revolution in the world of physics more than one century ago, the notion of a quantum computer in 1981 marked the beginning of a drastic change of our understanding of information and computability. In a quantum computer, information is stored using quantum bits, or qubits, which are described by a quantummechanical superposition of the quantum states 0 and 1. Computation then proceeds by acting with unitary operations on these qubits. These operations are referred to as quantum logic gates, in analogy to classical computation where bits are acted on by classical logic gates. In order to perform universal quantum computation it is, in principle, sufficient to carry out singlequbit gates and twoqubit gates, where the former act on individual qubits and the latter, acting on two qubits, are used to entangle qubits with each other. The present thesis is divided into two main parts. In the first, we are concerned with spinbased quantum computation. In a spinbased quantum computer, qubits are encoded into the Hilbert space spanned by spin½ particles, such as electron spins trapped in semiconductor quantum dots. For a suitable qubit encoding, turning onandoff, or "pulsing," the isotropic Heisenberg exchange Hamiltonian JSi · Sj allows for universal quantum computation and it is this scheme, known as exchangeonly quantum computation, which we focus on. In the second part of this thesis, we consider a topological quantum computer in which qubits are encoded using socalled Fibonacci anyons, exotic quasiparticle excitations that obey nonAbelian statistics, and which may emerge in certain twodimensional topological systems such as fractional quantumHall states. Quantum gates can then be carried out by moving these particles around one another, a process that can be viewed as braiding their 2+1 dimensional worldlines. The subject of the present thesis is the development and theoretical understanding of procedures used for entangling qubits. We begin by presenting analytical constructions of pulse sequences which can be used to carry out twoqubit gates that are locally equivalent to a controlledPHASE gate. The corresponding phase can be arbitrarily chosen, and for one particular choice this gate is equivalent to controlledNOT. While the constructions of these sequences are relatively lengthy and cumbersome, we further provide a straightforward and intuitive derivation of the shortest known twoqubit pulse sequence for carrying out a controlledNOT gate. This derivation is carried out completely analytically through a novel "elevation" of a simple threespin pulse sequence to a more complicated fivespin pulse sequence. In the case of topological quantum computation with Fibonacci anyons, we present a new method for constructing entangling twoqubit braids. Our construction is based on an iterative procedure, established by Reichardt, which can be used to systematically generate braids whose corresponding operations quickly converge towards an operation that has a diagonal matrix representation in a particular natural basis. After describing this iteration procedure we show how the resulting braids can be used in two explicit constructions for twoqubit braids. Compared to twoqubit braids that can be found using other methods, the braids generated here are among the most efficient and can be obtained straightforwardly without computational overhead.
Show less  Date Issued
 2016
 Identifier
 FSU_2016SU_Zeuch_fsu_0071E_13323
 Format
 Thesis
 Title
 Search for Supersymmetry at CMS in Events with Photons, Jets and Low Missing Transverse Energy.
 Creator

Adams, Jordon Rowe, Askew, Andrew, Chase, P. Bryant, Adams, Todd, Owens, Joseph F., Dobrosavljević, Vladimir, Florida State University, College of Arts and Science, Department...
Show moreAdams, Jordon Rowe, Askew, Andrew, Chase, P. Bryant, Adams, Todd, Owens, Joseph F., Dobrosavljević, Vladimir, Florida State University, College of Arts and Science, Department of Physics
Show less  Abstract/Description

The Standard Model (SM) of particle physics offers the most complete quantum description of the known universe to date, however is unable to address some still unanswered questions. Supersymmetry (SUSY) is a theory which proposes partner particles for all SM particles and offers explanations for many of these questions. Many SUSY searches performed rely on signatures of high missing transverse energy due to a heavy SUSY particle escaping the detector, however these searches have not yet...
Show moreThe Standard Model (SM) of particle physics offers the most complete quantum description of the known universe to date, however is unable to address some still unanswered questions. Supersymmetry (SUSY) is a theory which proposes partner particles for all SM particles and offers explanations for many of these questions. Many SUSY searches performed rely on signatures of high missing transverse energy due to a heavy SUSY particle escaping the detector, however these searches have not yet yielded positive results and therefore new search strategies must be employed. In this analysis, a search for new physics is performed at the CERN LHC which targets signatures of SUSY. Specifically, a search for Stealth SUSY is performed, based on a sample of protonproton collisions at √s = 8 TeV corresponding to 19.7 fb⁻¹ of integrated luminosity collected with the CMS detector in 2012. Stealth SUSY is a unique brand of SUSY which conserves RParity and naturally produces a low amount of missing transverse energy. The search strategy utilized is sen sitive to a wide variety of new physics models including compressed spectra and long decay chains. The Stealth SUSY final state topology considered in this analysis consists of two photons, many jets and low missing transverse energy. The results of this datadriven search for new physics are reported, and good agreement is observed with the background expectation. The data are thus used to determine limits on squark/gaugino masses in the Stealth SUSY framework.
Show less  Date Issued
 2015
 Identifier
 FSU_migr_etd9278
 Format
 Thesis
 Title
 Structural Stability and Emergent Phases in Oxygen Deficient Complex Transition Metal Oxides.
 Creator

Ghosh, Soham S., Manousakis, Efstratios, Shatruk, Mykhailo, Bonesteel, N. E., Roberts, Winston, Van Winkle, David, Flaherty, Francis A., Florida State University, College of...
Show moreGhosh, Soham S., Manousakis, Efstratios, Shatruk, Mykhailo, Bonesteel, N. E., Roberts, Winston, Van Winkle, David, Flaherty, Francis A., Florida State University, College of Arts and Sciences, Department of Physics
Show less  Abstract/Description

This dissertation is a theoretical and computational examination of structural, electronic and magnetic properties of complex transition metal oxide structures. Our work is motivated by experimental observations that transition metal oxides manifest novel properties at surfaces and interfaces that are absent in bulk, and that there exist competing ground states driven by offstoichiometry, oxygen vacancy and reduction of symmetry. We examine these properties using density functional theory ...
Show moreThis dissertation is a theoretical and computational examination of structural, electronic and magnetic properties of complex transition metal oxide structures. Our work is motivated by experimental observations that transition metal oxides manifest novel properties at surfaces and interfaces that are absent in bulk, and that there exist competing ground states driven by offstoichiometry, oxygen vacancy and reduction of symmetry. We examine these properties using density functional theory (DFT) within the spingeneralized gradient approximation (SpinGGA) along with the application of a Hubbard U (GGA + U). We present our detailed results for the following systems: oxygen deficient strontium titanate surface, strontium ruthenate interfaced with ruthenium metal inclusions, and ytterbium titanate with Yb "stuffing". In the course of our work, we cover materials with 3d, 4d and 4f band characters, each of which have different band masses, electronelectron correlations and spinorbit coupling (SOC) strength. We investigate the role of surface termination, oxygen vacancy doping and cation "stuffing" defects in these metaloxides and show the emergence of novel properties consistent with experimentally acquired information and possible applications. We conclude by presenting implications for further work.
Show less  Date Issued
 2017
 Identifier
 FSU_SUMMER2017_Ghosh_fsu_0071E_13962
 Format
 Thesis
 Title
 The Three Body Coulomb Problem: An Examination of Bound States and Stability as a Function of Individual Masses.
 Creator

Kondyukov, Grigoriy, Department of Physics
 Abstract/Description

In this work we study quantum nonrelativistic threebody systems interacting via Coulomb potential. The solution in this undertaking utilizes and expansion of wave functions using products of Laguerre polynomial, followed by variational adjustment of coordinate scaling parameters. The method used in this study was originally developed by C.L. Pekeris and its advantage stems from recursion relations available for Laguerre polynomial. We developed an implementation of modular C++ code for...
Show moreIn this work we study quantum nonrelativistic threebody systems interacting via Coulomb potential. The solution in this undertaking utilizes and expansion of wave functions using products of Laguerre polynomial, followed by variational adjustment of coordinate scaling parameters. The method used in this study was originally developed by C.L. Pekeris and its advantage stems from recursion relations available for Laguerre polynomial. We developed an implementation of modular C++ code for solving the threebody problem numerically with high precision, improving upon previous works. The stability of threebody systems as well as excitation energies of excited states and ionization energy in the parameter space of charges and masses is investigated.
Show less  Date Issued
 2015
 Identifier
 FSU_migr_uhm0502
 Format
 Thesis