Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2006. / Includes bibliographical references (leaves 115-121). / This thesis describes the design and construction of two laser systems to probe the 674nm transition of ⁸⁸Sr⁺ ions in a linear Paul trap. The first laser system made use of a molecular transition in Iodine to stabilize the length of a Fabry-Perot cavity for laser locking. After constructing this laser, we measured an unsuitable experimental stability of 10 MHz over 5 minutes. A completely new monolithic laser system was built, providing better environmental isolation and a frequency stability of at least 1 MHz over 5 minutes. Using this laser, we were able to observe depletion and quantum jump effects in our ion trap system. Additionally, by scanning the red laser frequency, we were able to see the blue-laser broadened spectrum of the 674nm transition. Fitting the spectrum to a Voigt function yielded an ion temperature of 35 mK. To avoid blue-broadening, we set up blue and red laser pulse sequences. This allowed us to observe a red spectrum with secular sidebands and calculate an ion temperature of 6.8 +4.4 / -2.2 mK. / by Philip J. Richerme / S.B.

Massachusetts Institute of Technology. Dept. of Physics. Thesis. 1967. Ph.D. / Bibliography: leaves 156-160. / by Ronald John Allen. / Ph.D.

Massachusetts Institute of Technology. Dept. of Physics. Thesis. 1968. Ph.D. / Vita. / Bibliography: leaves 241-242. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 119-128). / In this thesis, we use the methods of statistical physics to provide quantitative insights into the behavior of biological systems. In the first half of the thesis, we use equilibrium statistical physics to develop a phenomenological model of how the hydrophobic effect impacts the structure of proteins, and in the second half, we study the phenomenon of adaptation and Darwinian selection from the standpoint of nonequilibrium statistical physics. It has been known for a long time that the hydrophobic effect plays a major role in driving protein folding. However, it has been challenging to translate this understanding into a predictive, quantitative theory of how the full pattern of sequence hydrophobicity in a protein helps to determine its structure. Here, we develop and apply a phenomenological theory of the sequence-structure relationship in globular protein domains. In an effort to optimize parameters for the model, we first analyze the patterns of backbone burial found in single-domain crystal structures and discover that classic hydrophobicity scales derived from bulk physicochemical properties of amino acids are already nearly optimal for prediction of burial using the model. Subsequently, we apply the model to studying structural fluctuations in proteins and establish a means of identifying ligand-binding and protein-protein interaction sites using this approach. In the second half of the thesis, we undertake to address the question of adaptation from the standpoint of physics. Building on past fundamental results in nonequilibrium statistical mechanics, we demonstrate a generalization of the Helmholtz free energy for the finite-time stochastic evolution of driven Newtonian matter. By analyzing this expression, we show a general tendency in a broad class of driven many-particle systems toward self-organization into states formed through reliable absorption and dissipation of work energy from the surrounding environment. We demonstrate how this tendency plays out in the familiar example of Darwinian competition between two exponentially growing self-replicators. Subsequently, we illustrate the more general mechanism by which extra dissipation drives adaptation by analyzing the process of random hopping in driven energy landscapes. / by Nikolay Perunov. / Ph. D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Physics, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 35). / Inflation is a substantial modification to the big bang theory, and supernatural inflation is a hybrid inflation motivated from supersymmetry. In this thesis we carry out a one dimensional numerical simulation to verify the untested analytic approximation of Radall et al. The results show a good agreement for a wide range of parameters. We also propose a new method for calculating density perturbations in hybrid inflation, which shows an excellent agreement with the simulation in one dimension. / by Nguyen Thanh Son. / S.M.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1999. / Includes bibliographical references (p. 267-274). / by Jefferson Michael Kommers. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2003. / Includes bibliographical references. / This thesis comprises the results of two distinct areas of research, namely, X-ray studies of Galactic globular clusters and X-ray studies of recent core collapse supernovae. My analyses of the Chandra X-ray Observatory observations of the globular clusters NGC 6752 and NGC 6440 revealed as many low-luminosity X-ray sources as was in the entire census of globular cluster sources with the previous best X-ray imaging instrument, Rontgensatellit. In the observation of NGC 6752, I detect 6 X-ray sources within the 10':5 core radius and 13 more within the 115" half-mass radius down to a limiting luminosity of Lx = 1030 ergs s-l for cluster sources. Based on a reanalysis of archival data from the Hubble Space Telescope and the Australia Telescope Compact Array, I make 12 optical identifications and one radio identification. Based on X-ray and optical properties of the identifications, I find 10 likely cataclysmic variables (CVs), 1-3 likely RS CVn or BY Dra systems, and 1 or 2 possible background objects. Of the 7 sources for which no optical identifications were made, one was detected in the archival radio data, and another was found to be a millisecond pulsar. Of the remaining sources, I expect that 2-4 are background objects and that the rest are either CVs or millisecond pulsars whose radio emission has not been detected. These and other Chandra results on globular clusters indicate that the dozens of CVs per cluster expected by theoretical arguments are being found. The findings to date also suggest that the ratio of CVs to other types of X-ray sources is remarkably similar in clusters of very different structural parameters. / (cont.) In the observation of NGC 6440, I detect 24 sources to a limiting luminosity of 2 x 1031 ergs s-1 (0.5-2.5 keV) inside the cluster's half-mass radius, all of which lie within 2 core radii of the cluster center. I also find excess emission in and around the core which could be due to unresolved point sources. Based upon X-ray luminosities and colors, I conclude that there are 4-5 likely quiescent low-mass X-ray binaries and that most of the other sources are cataclysmic variables. I compare these results to Chandra results from other globular clusters and find the X-ray luminosity functions differ among the clusters. Observations of the Type II-P (plateau) Supernova (SN) 1999em and Type IIn (narrow emission line) SN 1998S have enabled estimation of the profile of the SN ejecta, the structure of the circumstellar medium (CSM) established by the pre-SN stellar wind, and the nature of the shock interaction. SN 1999em is the first Type II-P detected at both X-ray and radio wavelengths. It is the least radio luminous and one of the least X-ray luminous SNe ever detected (except for the unusual and very close SN 1987A). My analysis of the Chandra X-ray data indicate non-radiative interaction of SN ejecta with a power-law density profile ... for a pre-SN wind with a low mass-loss rate of ... for a wind velocity of 10 km s-1, in agreement with radio mass-loss rate estimates. The Chandra data show an unexpected, temporary rise in the 0.4-2.0 keV X-ray flux at 100 days after explosion. My analysis of SN 1998S yielded the first X-ray spectrum of a supernova in which numerous heavy element emission features (Ne, Al, Si, S, Ar, Fe) were present ... / by David Aaron Pooley. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 105-112). / In this thesis, we will theoretically explore three nanophotonics phenomena which enable strong light-matter interaction. The first phenomenon is plasmonic resonance, where the surface plasmon mode at metal and dielectric boundaries significantly enhances the optical response of nanoparticles. We propose an optimization-based theoretical approach to tailor the optical response of silver/silica multilayer nanospheres over the visible spectrum. We show that the structure that provides the largest cross-section per volume/mass, averaged over a wide frequency range, is the silver coated silica sphere. We also show how properly chosen mixture of several species of different nanospheres can have an even larger minimal cross-section per volume/mass over the entire visible spectrum. The second phenomenon is photonic chiral edge state, where the breaking of time-reversal symmetry forces light to travel in only one direction. Based on the directional coupling between one-way waveguide and conventional two-waveguide, we propose a new type of optical circulators, which has the potential for simultaneous broadband operation and small device footprint. The third phenomenon is Stimulated Brillouin Scattering (SBS), where photon and phonon are coupled through optical forces such as electrostriction force and radiation pressure. We develop a general method of calculating SBS gain via the overlap integral between optical and elastic modes. Applying this method to a rectangular waveguide, we demonstrate that the distribution of optical force and elastic modal profile jointly determine the magnitude and scaling of SBS gains. Applying this method to a periodic waveguide, we demonstrate that SBS gain can be further enhanced in the slow light regime. Based on this framework, we theoretically characterize a novel class of hybrid photon-phonon waveguides. Our analysis reveals that photon-phonon coupling via SBS can be directed and tailored over an exceptionally wide frequency range, enabling a host of chip-scale filtering, delay, and signal processing schemes. / by Wenjun Qiu. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references. / In this thesis we are primarily interested in studying how to suppress errors, perform simulation, and implement logic gates in quantum computation within the context of using Hamiltonian controls. We also study the complexity class QMA-complete. We first investigate a method (introduced by Jordan, Farhi, and Shor) for suppressing environmentally induced errors in Hamiltonian-based quantum computation, involving encoding the system with a quantum error-detecting code and enforcing energy penalties against leaving the codespace. We prove that this method does work in principle: in the limit of infinitely large penalties, local errors are completely suppressed. We further derive bounds for the finite-penalty case and present numerical simulations suggesting that the method achieves even greater protection than these bounds indicate. We next consider the task of Hamiltonian simulation, i.e. effectively changing a system Hamiltonian to some other desired Hamiltonian by applying external time-dependent controls. We propose protocols for this task that rely solely on realistic bounded-strength control Hamiltonians. For systems coupled to an uncontrollable environment, our approach may be used to perform simulation while simultaneously suppressing unwanted decoherence. We also consider the scenario of removing unwanted couplings in many-body quantum systems obeying local system Hamiltonians and local environmental interactions. We present protocols for efficiently switching off the Hamiltonian of a system, i.e. simulating the zero Hamiltonian, using bounded-strength controls. To this end, we introduce the combinatorial concept of balanced-cycle orthogonal arrays, show how to construct them from classical error-correcting codes, and show how to use them to decouple n-qudit l-local Hamiltonians using protocols of length at most O(l-1 log n). We then present a scheme for implementing high-fidelity quantum gates using a few interacting bosons obeying a Bose-Hubbard Hamiltonian on a line. We find high-fidelity logic operations for a gate set (including the CNOT gate) that is universal for quantum information processing. Lastly, we discuss the quantum complexity class QMA-complete, surveying all known such problems, and we introduce the "quantum non-expander" problem, proving that it is QMA-complete. A quantum expander is a type of rapidly-mixing quantum channel; we show that estimating its mixing time is a co-QMA-complete problem. / by Adam Darryl Bookatz. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2004. / Includes bibliographical references (p. 159-170). / The massive stellar progenitor of a hypernova explosion and an associated gamma-ray burst must satisfy two primary constraints: (1) the outer layers of the stellar core must possess sufficient angular momentum to form a centrifugally supported torus about the collapsed central object (a Kerr black hole); and, (2) the envelope of the star must not be excessively massive or distended, so that the energetic, ultrarelativistic outflow generated by the central engine in the core of the star does not risk being smothered before it can escape from the star and expand outward to produce a gamma-ray burst. Physical processes which occur during the evolution of an isolated massive star will tend to diminish its initial angular momentum content, rendering it difficult for such a star to become a hypernova progenitor since its core will likely no longer spin rapidly enough to support a torus about its collapsed core. However, a substantial fraction of massive stars are members of binary systems. Tidal locking, mass transfer, or stellar merger in an evolved massive binary system could possibly lead to the transfer of orbital angular momentum to the core of one of the stars (or to the core of a merged star, if a common envelope develops), of sufficient magnitude to produce the core of a successful hypernova progenitor (constraint 1). Further interaction between the stars or their compact remnants could lead to the loss of the hydrogen and possibly helium envelopes of one of the stars (constraint 2). We have developed a new one-dimensional stellar evolution code that includes the effects of rotation on equilibrium stellar structure, and calculates the transport of angular momentum through the stellar interior due to convection, dynamical and secular shear instabilities, and gravity (buoyancy) waves. / (cont.) We have used this code to calculate a variety of evolutionary sequences involving the transfer of mass from one component of the binary system to the other. We have also calculated an evolutionary sequence ending in the merger of one component of the system with the core of the other, induced by a prior common-envelope phase. We find that over a wide range of initial binary system parameters, the initially less massive component of the system can accrete a substantial amount of mass and angular momentum from the initially more massive component. The accreted angular momentum is efficiently transported inward from the surface of the accreting star toward its core by a combination of convection and dynamical and secular shear instabilities. If accretion commences while the accretor is still on the main sequence, we find that the inward-progressing wave of angular momentum can penetrate the core of the mass-gaining star, contributing to its store of rotational angular momentum without the need for gravity wave transport of angular momentum across the core- envelope interface. These stars end their evolution (just prior to core carbon ignition) as red supergiants, with cores endowed with sufficient angular momentum to give rise to a hypernova explosion. We also find that a subsequent common-envelope phase with the compact remnant of the primary might result in the ejection of the accretor's red-giant envelope, leaving either a bare helium or carbon-oxygen star. Such a star would be expected to explode in a Type lb or Ic supernova/hypernova. / by John Alex Becker. / Ph.D.