Recursos de colección

DSpace at MIT (104.280 recursos)

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Physics - Ph.D. / Sc.D.

Mostrando recursos 1 - 20 de 1.134

  1. Measurement of helium isotopic composition in cosmic rays with AMS-02

    Behlmann, Matthew Daniel
    The isotopic composition of helium in cosmic ray fluxes provides valuable information about cosmic ray propagation through the Galaxy, which is of particular interest to indirect dark matter searches. Helium-3, mainly a secondary cosmic ray species, is primarily produced by spallation of heavier cosmic rays, such as primary helium-4, with interstellar matter. In six years of data taking, AMS has collected the largest available data set on fluxes of cosmic-ray helium. Events are selected to form a clean sample of galactic helium nuclei, for which velocity and rigidity give a measurement of particle mass that allows the measurement of relative...

  2. Controlling ultracold fermions under a quantum gas microscope

    Okan, Melih
    This thesis presents the experimental work on building a quantum gas microscope, employing fermionic 40K atoms in an optical lattice, and precision control of the atoms under the microscope. This system works as a natural simulator of the 2D Hubbard model, which describes materials with strongly correlated electrons. After preparing ultracold 40K atoms in an optical lattice and performing Raman sideband cooling, single lattice site resolution was obtained. Metallic, Mott insulating, and band insulating states were observed in situ and local moment was directly accessed as a local observable with the site-resolved imaging. Performing spin-selective imaging also gave access to...

  3. Quantum electronic transport in atomically layered topological insulators

    Fatemi, Valla
    The merger of topology and symmetry established a new foundation for understanding the physics of condensed matter, beginning with the notion of topological insulators (TIs) for electronic systems. For the time-reversal invariant TIs, a key aspect is the "helical" mode at the boundary of the system - that is, the ID edge of a 2D topological insulator or the 2D surface of a 3D topological insulator. These helical modes represent the extreme limit of spin-orbit coupling in that the spin-degenercy has been completely lifted while preserving time-reversal symmetry. This property is crucial for proposals realizing exotic excitations like the Majorana...

  4. Practical fault-tolerant quantum computation

    Yoder, Theodore J
    For the past two and a half decades, a subset of the physics community has been focused on building a new type of computer, one that exploits the superposition, interference, and entanglement of quantum states to compute faster than a classical computer on select tasks. Manipulating quantum systems requires great care, however, as they are quite sensitive to many sources of noise. Surpassing the limits of hardware fabrication and control, quantum error-correcting codes can reduce error-rates to arbitrarily low levels, albeit with some overhead. This thesis takes another look at several aspects of stabilizer code quantum error-correction to discover solutions...

  5. A combined phase contrast imaging and heterodyne interferometer system for multiscale fluctuation measurements on DIII-D

    Davis, Evan Michael
    A novel combined diagnostic capable of measuring multiscale density fluctuations that extend from magnetohydrodynamic (MHD) scales to the lower bound of the electron temperature gradient (ETG) mode has been designed, installed, and operated at the DIII-D tokamak. The combined diagnostic was constructed by adding a heterodyne interferometer to the pre-existing phase contrast imaging (PCI) system, both of which measure line-integrated electron-density fluctuations. The port-space footprint is minimized by using a single 10.6 pm CO2 laser and a single beampath. With temporal bandwidths in excess of 1 MHz, the PCI measures high-k (1.5 cm-1 < k +/

  6. Population oscillations, synchronization, and range expansion in a bacterial cross-protection mutualism

    Conwill, Arolyn.
    Cooperation between microbes can enable microbial communities to survive in harsh environments. Enzymatic deactivation of antibiotics is a cooperative behavior that can allow resistant cells to protect sensitive cells from antibiotics. The prevalence of this mechanism of antibiotic resistance in clinical isolates and in soil bacteria makes it important both clinically and ecologically. Here, we show that two Escherichia coli strains can form a cross-protection mutualism, protecting each other in the presence of two antibiotics (ampicillin and chloramphenicol) so that the coculture can survive in antibiotic concentrations that inhibit growth of either strain alone. Moreover, we find that daily dilutions...

  7. Strongly interacting photons via Rydberg-Rydberg interactions

    Liang, Qiyu, Ph. D. Massachusetts Institute of Technology
    A quantum nonlinear optical medium, i.e. a medium where the light propagation depends on photon number, has been a long-standing goal due to its applications in quantum information, communication and metrology. When the medium is nonlinear at single photon level, it can be viewed as strong interactions between individual photons mediated by the medium. Here, we achieve such strong interactions by coupling the photons to highly polarizable Rydberg states with a phenomena called electromagnetically induced transparency (EIT). The strong van der Waals or dipole-dipole interactions between Rydberg excitations map to the photons under EIT conditions. The photons are incident on...

  8. Top mass determination using Effective Field Theories

    Pathak, Aditya, Ph. D. Massachusetts Institute of Technology
    The top quark mass is one of the most important Standard Model parameters and its mass has been measured at sub-percent precision by the Tevatron and LHC using Monte Carlo (MC) based methods. The resulting MC top mass parameter suffers from 0(1 GeV) uncertainty due to lack of specification of a precise field theoretic definition. Here a kinematic extraction method for obtaining a precisely defined short distance top mass at the LHC is proposed. A formula for factorized top jet mass cross section in the peak region is derived using methods of Effective Field Theory (EFT). It can then be...

  9. Quantum signal processing by single-qubit dynamics

    Low, Guang Hao
    Quantum computation is the most powerful realizable model of computation, and is uniquely positioned to solve specialized problems intractable to classical computers. This quantum advantage arises from directly exploiting the strangeness of quantum mechanics that is fundamental to reality. As such, one expects our understanding of quantum processes in physical systems to be indispensable to the design and execution of quantum algorithms. We present quantum signal processing, which exploits the dynamics of simple quantum systems to perform non-trivial computations. Such systems applied as computational modules in larger quantum algorithms, offer a natural physical alternative to standard tasks such as the...

  10. Detectability of dynamical tidal effects and the detection of gravitational-wave transients with LIGO

    Essick, Reed Clasey
    Dynamical tidal effects impact the orbital motion of extended bodies, imprinting themselves in several measurable ways. This thesis explores the saturation of weakly nonlinear dynamical tidal interactions within two very different systems: hot Jupiters orbiting main-sequence hosts with radiative cores and compact stellar remnants inspiraling due to gravitational radiation. In addition, it discusses general aspects of detecting Gravitational Waves with ground-based laser interferometers. Data quality and noise reduction along with source parameter estimation, with particular emphasis on localization, are discussed in great detail. Conclusions drawn from statistical ensembles of simulated signals are applied to the first three confirmed detections of...

  11. Accretion flows and neutron star heating in low-mass X-ray binaries

    Allen, Jessamyn Leigh
    X-ray binaries are excellent test beds for studies of high-energy accretion flows and the properties of compact objects. Neutron star (NS) low-mass X-ray binaries (LMXBs) vary in brightness by almost 8 orders of magnitude and are hosts to diverse accretion flows, transporting varying amounts of energy and mass toward the central NS, as well as expelling significant mass from the binary. This thesis aims to shed light on the accretion flow properties across the mass and luminosity scale, with particular emphasis on constraining the matter accreted on the neutron star surface and the resulting heating, which has important implications for...

  12. Chasing ancient demons : tools for measuring 21 cm fluctuations before reionization

    Ewall-Wice, Aaron
    In this thesis, we take the first steps towards measuring the fluctuations in HI emission before reionization which carry information on the first X-ray emitting compact objects and hot interstellar gas heated by the deaths of the first stars (ancient demons). First, we show that existing and planned interferometers are sensitive enough to place interesting constraints on the astrophysics of X-ray heating. Second, we obtain first upper limits on the pre-reionization fluctuations with the Murchison Widefield Array. We also use these measurements to explore the impact of low-frequency systematics, such as increased foreground brightness and the ionosphere. We discover that...

  13. Light-induced many-body correlations in ultracold gases

    Hu, Jiazhong, Ph. D. Massachusetts Institute of Technology
    In this thesis, we investigate several methods to generate and probe the quantum correlations in ultracold gases using light. A high-finesse optical cavity is used to enhance the atom-light interaction and we can produce a variety of entangled states which can overcome the standard quantum limit. The quantum correlations are generated by sending very weak light into the cavity which contains many neutral atoms. We control the properties of the incoming photon, such as the polarization and/or the frequency spectrum, to obtain the final atomic states as desired. The photon transmitted through the cavity interacts with the atomic ensemble and...

  14. Towards spin squeezed ¹⁷¹Yb atomic clock beyond the standard quantum limit

    Kawasaki, Akio, Ph. D. Massachusetts Institute of Technology
    State-of-the-art atomic clocks have fractional frequency instability of 6 x 10-17 at 1 s averaging time, and are aiming for even higher stability. One of the main factors limiting this stability is the standard quantum limit (SQL) of quantum projection noise, which can be overcome by spin squeezing. We constructed an apparatus to perform spin squeezing on an ytterbium optical lattice clock to demonstrate the enhancement of clock stability by spin squeezing. Using the spin 1/2 system of the ground state Zeeman sublevels of 171Yb, two different methods are utilized to perform a spin squeezing via coupling to 6s6p3P1 excited...

  15. Measurement of cosmic antiprotons with the alpha magnetic spectrometer aboard the International Space Station

    Chen, Andrew Ian
    A precision measurement of the cosmic antiproton ( -p) flux and the antiproton-to-proton flux ratio ( -p/p) made with the Alpha Magnetic Spectrometer aboard the International Space Station is presented. The measurement covers the absolute rigidity range from 1 to 450 GV, and is based on 3.49x105 -p events and 2.42x109 proton (p) events. This completes the measurements of the fluxes and flux ratios for the charged elementary particles in cosmic rays by AMS. In the absolute rigidity range 60 to 500 GV, the -p , p, and positron (e+) fluxes are found to have nearly identical rigidity dependence. This...

  16. A spatially resolved study of the KATRIN main spectrometer using a novel fast multipole method

    Barrett, John Patrick, Ph. D. Massachusetts Institute of Technology
    The Karlsruhe Tritium Neutrino (KATRIN) experiment is intended to make a sensitive (~ 200 meV) model-independent measurement of the neutrino mass through high precision electrostatic spectroscopy of the tritium /-decay spectrum. One of the principle components in this experiment is the main spectrometer which serves as an integrating MAC-E filter with 0(1) eV resolution. Thorough understanding of the transmission properties of the main spectrometer system is an inextricable challenge associated with this effort, and requires a very accurate and fast method for calculating the electrostatic fields created within its volume. To this end, the work described in this thesis documents...

  17. Study of the electron component of the solar wind and magnetospheric plasma

    Sittler, Edward Charles
    by Edward Charles Sittler, Jr.

  18. Forced oscillations of electromagnetic cavity resonators

    Clogston, Albert McCavour
    by Albert McCavour Clogston.

  19. Pion production in pion-nucleon collisions in the Chew-Low-Wick formalism

    Rodberg, Leonard Sidney
    by Leonard Sidney Rodberg.

  20. Observations of several discrete radio sources at 3.64 and 1.94 centimeters

    Allen, Ronald J
    by Ronald John Allen.

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