Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2007. / Includes bibliographical references (p. 65-67). / Introduction: Water entry of projectiles has long been a topics of interest in both sciences and engineering. It began with Worthington, who in the late XIX century found experimentally that a cavity is being formed when a steel sphere enters water (Worthington and Cole (1895-1896)). As we know today, water entry of a sphere is a complex process which nonetheless can be enormously simplified, making it a particularly rewarding area of research. / by Jakub K. Kominiarczuk. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 217-228). / Quantum simulation offers the possibility of using a controllable quantum-mechanical system to implement the dynamics of another quantum system, performing calculations that are intractable on classical computers for all but the smallest systems. This great possibility carries with it great challenges, two of which motivate the experiments with nuclear spins and trapped ions presented in this thesis. The first challenge is determining the bounds on the precision of quantities that are calculated using a digital quantum simulator. As a specific example, we use a three-qubit nuclear spin system to calculate the low-lying spectrum of a pairing Hamiltonian. We find that the simulation time scales poorly with the precision, and increases further if error correction is employed. In addition, control errors lead to yet more stringent limits on the precision. These results indicate that quantum simulation is more efficient than classical computation only when a limited precision is acceptable and when no efficient classical approximation is known. The second challenge is the scaling-up of small quantum simulators to incorporate tens or hundreds of qubits. With a specific goal of analog quantum simulation of spin models in two dimensions, we present novel ion trap designs, a lattice ion trap and a surface-electrode elliptical ion trap. We experimentally confirm a theoretical model of each trap, and evaluate the suitability of each design for quantum simulation. We find that the relevant interaction rates are much higher in the elliptical trap, at the cost of additional systematic control errors. / (cont.) We also explore the interaction of ions over a wire, a potentially more scalable system than the elliptical trap. We calculate the expected coupling rate and decoherence rates, and find that an extremely low capacitance (O(fF)) between the coupling wire and ground is required, as well as ion-wire distances of O(50 [mu]m) to realize a motional coupling of 0(1 kHz). In pursuit of this situation, we measure the effect on a single ion of a floating wire's static and induced ac voltages as a function of the ion-wire distance. / by Robert J. Clark. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, June 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 69-70). / We perform extensive analysis on the physics of L-mode tokamak fusion reactors to identify (1) a favorable parameter space for a large scale steady-state reactor and (2) an operating point for a minimum scale steady-state reactor. The identification of the large scale parameter space is part of the 2008 MIT Nuclear Systems Design Project, which also includes sustainability and economic optimizations to identify a plausible operating point for a large scale (a 14 m major radius) hydrogen production reactor dubbed HYPERION. Due to the potentially prohibitive capital cost (a $50 billion) and exorbitant thermal power (a 35 GWth) of HYPERION, we identify a conservative estimate for the minimum scale of a similar steady-state L-mode reactor of approximately 7.5 meters, half the size of HYPERION and only 20% larger than ITER. This minimum scale reactor would require an on-coil magnetic field of a 16 T and a blanket power density of ~ 5 MW/m 2 . It would produce 7 GWth of power with a power gain of 30, and it would operate far from all stability and confinement limits. To confirm the viability of this operating point, we perform various 1-D calculations. The crucial advantage of a steady-state (or fully non-inductive) reactor is that it is not limited by flux swing and can operate continuously, recharging its solenoid during operation. The crucial advantages of L-mode are that it avoids instabilities associated with edge localized modes (ELMs) and that it allows volumetric heating in the mantle due to the absence of a pedestal. Steady-state L-mode tokamak reactors could be the future of controlled fusion research and even play an important role in meeting the world's clean energy needs. / by Mark Reed. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 45-47). / Energy levels of the valence electron of a single trapped ⁸⁸Sr+ ion can be harnessed as an effective qubit for quantum information processing. The qubit transition to a metastable energy state can be stimulated by a laser at a frequency of 444.779044 THz. A laser beam with higher intensity causes more rapid transitions between quantum states, and thus allows more computational operations within the coherence time of the system. The focus of this thesis is the design and construction of a more powerful laser to stimulate the qubit transition of the 88Sr+ ion, using injection-locking to stabilize the frequency of the new laser. Injection-locking is a technique for using an existing, stable laser to control the frequency of a second laser diode. A small amount of input power is enough to produce a much more powerful output beam at the same frequency, so the system acts as an amplifier. We found that a AlGaInP laser diode required 9 +/- 2 pW of injected input power to lock to the input frequency, producing an output power of 11.56 +/- 0.31 mW. The ratio of input to output power was (7.8 +/- 1.7) x10-⁴. The injection-locking frequency range was 18.4 +/- 1.6 MHz. / by Rena J. Katz. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Includes bibliographical references. / by Una Hwang. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2004. / Includes bibliographical references (leaves 69-73). / We develop a technique for measuring cosmological parameters ([omega]M and w) using gravitational lens geometry, source and lens redshifts, and the velocity dispersion of the lensing galaxy. This technique makes use of the relation [theta][sub]E = 4[pi]... where the critical radius [theta][sub]E and the one-dimensional velocity dispersion of the lensing galaxy [sigma]v are observable and the angular diameter distance ratio D[sub]LS/D[sub]S is related to the source and lens redshifts Z[source] and Z[lens] through the cosmological model. We assess the feasibility of this technique by examining the dependence of that ratio on cosmological parameters, doing a Monte Carlo simulation with a singular isothermal sphere lens galaxy, and estimating the error due to the asymmetry of real lenses. We conclude that the method is feasible with a large lens sample and a nearly circular projected mass distribution. We expect errors of less than 0.1 in [omega]M for a flat universe with a cosmological constant and a lens sample selected so that the axial ratio f > 0.8 for each lens. / by Susan E. Dorsher. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 213-223). / In this thesis we study the event shapes variable thrust. Event shape variables are observables that characterize the shape of the distribution of the final state particles of a reaction. We take advantage of the formalism of Soft Collinear Effective Theory (SCET), an effective theory of the strong interactions appropriate for describing energetic jets. We give a factorization theorem for the process e+e- to hadrons, valid in the whole range of thrust values. This factorization theorem resums large logarithms at the N3LL accuracy and contains the full O(a) result for the fixed order cross section. In order to be able to describe the whole range of thrust values, we define the profile functions, which are thrust-dependent factorization scales which smoothly interpolate between regions where resummation of large logarithms is important and where it is not. To determine non perturbative effects, we fit renormalon-free nonperturbative matrix elements of operators defined in field theory, Q1. We perform a global analysis to all available thrust data in the tail region, where a two parameter fit to a,(mz) and the first power correction Q1 suffices. We find cr(mz) = 0.1135 i (0.0002)expt ± (0.0005)hadr ± (0.0009)pert, with X2 /dof(= 485) = 0.91, where the displayed 1-sigma errors are the total experimental error, the hadronization uncertainty, and the perturbative theory uncertainty, respectively. Furthermore, we perform a global analysis to all available data on the first moment of the thrust distribution. This analysis is a partially independent check of the tail fit, in fact it probes different regions of the thrust distribution and the analysis of experimental systematic uncertainties was conducted independently with respect to the data for the distribution. We find a,(mz) = 0.1141 i (0.0004)exp ± (0.0014)hadr ± (0.0007)pert with X2/dof(= 45) = 1.33. We also consider pp collisions, in particular the Drell-Yan process. Here we calculate analytically the beam thrust logarithms of the relevant beam functions and of the coefficient function at O(a2). This is a necessary ingredient for the calculation of the nonsingular terms in resummed predictions. / by Riccardo Abbate. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2018. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged student-submitted from PDF version of thesis. / Includes bibliographical references (pages 121-131). / In this thesis, I present my experimental work on twisted bilayer graphene, a van der Waals heterostructure consisting of two graphene sheets stack on top of each other. In particular, the twist angle is a new degree of freedom in this system, and has an important effect in the determination of its transport properties. The work presented will explore the twist-dependent physics in two regimes: the large twist angle and small twist angle regimes. In the large-twist angle limit, the two sheets have little interlayer interactions and are strongly decoupled, allowing us to put independent quantum Hall edge modes in both layers. We study the edge state interactions in this system, culminating in the formation of a quantum spin Hall state in twisted bilayer graphene. In the small twist angle limit, interlayer interactions are strong and the layers are strongly hybridized. Additionally, a new long-range moiré phenomenon emerges, and we study the effects of the interplay between moiré physics and interlayer interactions on its transport properties. / by Yuanhong Luo. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2003. / Includes bibliographical references (leaves 109-113). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Despite the study of shock wave compression of condensed matter for over 100 years, scant progress has been made in understanding the microscopic details. This thesis explores microscopic phenomena in shock compression of condensed matter including electronic excitations at the shock front, a new dynamical formulation of shock waves that links the microscopic scale to the macroscopic scale, and basic questions regarding the role of crystallinity in the propagation of electromagnetic radiation in a shocked material. In Chapter 2, the nature of electronic excitations in crystalline solid nitromethane are examined under conditions of shock compression. Density functional theory calculations are used to determine the crystal bandgap under hydrostatic stress, uniaxial strain, and shear strain for pure and defective materials. In all cases, the bandgap is not lowered enough to produce a significant population of excited states. In Chapter 3, a new multi-scale simulation method is formulated for the study of shocked materials. The method allows the molecular dynamics simulation of the system under dynamical shock conditions for orders of magnitude longer time periods than is possible using the popular non-equilibrium molecular dynamics (NEMD) approach. An example calculation is given for a model potential for silicon in which a computational speedup of 10⁵ is demonstrated. Results of these simulations are consistent with some recent experimental observations. Chapters 4 and 5 present unexpected new physical phenomena that result when light interacts with a shock wave propagating through a photonic crystal. / (cont.) These new phenomena include the capture of light at the shock wave front and re-emission at a tunable pulse rate and carrier frequency across the bandgap, and bandwidth narrowing of an arbitrary signal as opposed to the ubiquitous bandwidth broadening. Reversed and anomalous Doppler shifts are also predicted in light reflected from the shock front. / by Evan J. Reed. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 167-177). / Motivated by the AdS/CFT correspondence for relativistic CFTs, it seems natural to generalize it to non-relativistic CFTs. Such a dual description could provide insight into strong coupling phenomena observed in condensed matter systems. Scale invariance can be realized in non-relativistic theories in many ways. One freedom is the relative scale dimension of time and space, called the dynamical exponent z. In this thesis, we will mainly focus on the case where z = 2, however gravity duals for other values of z have also been found. In the first part of the thesis, we study NRCFTs that are Galilean invariant. Discrete light cone quantization (DLCQ) of V= 4 super Yang-Mills theory is an example of such a system with z = 2 scaling symmetry. A more realistic example of a system with the same set of symmetries is a system of cold fermions at unitarity. These non-relativistic systems respect a symmetry algebra known as the Schrödinger algebra. We propose a gravity dual that realizes the symmetries of the Schrödinger algebra as isometries. An unusual feature of this duality is that the bulk geometry has two extra dimensions than the CFT, instead of the usual one. The additional direction is a compact direction and shift symmetry along this direction corresponds to the particle number transformation. This solution can be embedded into string theory by performing a set of operations (known as the Null-Melvin twist) on AdS5 x S' solution of type IIB supergravity. This method also provides a way of finding a black hole solution which has asymptotic Schrödinger symmetries. The field theory dual of these gravity solutions happens to be a modified version of DLCQ V = 4 super Yang-Mills theory. The thermodynamics of these theories is very different from that of cold atoms. This happens to be a consequence of realizing the entire Schrödinger group as isometries of the spacetime. We give an example of a holographic realization in which the particle number symmetry is realized as a bulk gauge symmetry. In this proposal, the Schrödinger algebra is realized in the bulk without the introduction of an additional compact direction. Using this proposal, we find a confining solution that describes a non-relativistic system at finite density. We use the holographic dictionary to compute the conductivity of this system and it is found to exhibit somewhat unusual behavior. In the second part of the thesis we study gravity duals of Lifshitz theories. These are non-relativistic scale invariant theories that are not boost invariant. These theories do not have a particle number symmetry unlike the boost invariant NRCFTs. We present solutions of 1OD and 111D supergravity theories that are dual to Lifshitz theories. We present a black hole solution that is dual to a strongly interacting Lifshitz theory at finite temperature. We show that the finite temperature correlators in the interacting theories do not exhibit ultra-local behavior which was observed in free Lifshitz theories. / by Koushik Balasubramanian. / Ph.D.