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Online 1. Developing angular intensity correlations of Xray photons as a tool for studying structures of proteins in noncrystalline solutions [2019]
 Qiao, Shenglan, author.
 [Stanford, California] : [Stanford University], 2019.
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 Book — 1 online resource.
 Summary

This dissertation offers lessons learned and tools developed as we attempt to apply correlated Xray scattering (CXS) to noncrystalline proteins in solution. It builds on our previous work of extracting correlation signals from scattering intensities of ensembles of mental nanoparticles, which has led to threedimensional (3D) structural insights not reflected in azimuthally averaged measurements. In his 1977 paper, Zvi Kam proposed the idea of correlating Xray photons scattered by an ensemble of randomly oriented particles suspended in solution. He found that if the exposure time is much shorter than the diffusion timescale of Brownian motion, correlations between photons scattered into different angles encode 3D structural information of the particles not accessible via conventional small or wideangle Xray scattering. The advent of the Xray free electron laser (XFEL) renders Kam's idea feasible for noncrystalline solutions of proteins. With femtosecond pulses and extremely high fluences, the XFEL is not only capable of probing ensembles of molecules essentially frozen in time but also delivering a large number of photons per pulse, a capability critical for enhancing angular intensity correlation signals. Meanwhile, probing proteins in solution removes the need for crystallization, allows measurements of mixtures of conformational states under physiological conditions, and broadens opportunities for timeresolved experiments. The body of work in this dissertation draws from scattering data collected with samples containing the Gprotein Gi alpha subunit during two separate beam times conducted at the Linac Coherent Light Source. The Gi alpha subunit was chosen for these proofofprinciple experiments because of its important role in the Gprotein coupled receptor signaling pathway. This dissertation has taken the first steps in developing and validating CXS as a tool for probing ensembles of biomolecules in solution. These first steps as well as ideas described in this dissertation to improve CXS towards a mature pipeline that yields reliable and detailed structural insights aim to inspire others in the solution scattering community to engage with the unique challenges and rewards of this technique.
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Online 2. From timeresolved to frequencyresolved xray scattering [2019]
 Ware, Matthew Robert, author.
 [Stanford, California] : [Stanford University], 2019.
 Description
 Book — 1 online resource.
 Summary

Gasphase timeresolved xray scattering (TRXS) measures internuclear separations in a molecule following laserinduced photoexcitation. TRXS constitutes an indirect measurement of the molecular motion because it captures information in reciprocalspace and realtime, which then must be inverted to recover the charge density as it changes in time. The spatial resolution of the recovered charge density is fundamentally restricted by the xray wavelength used in the experiment. There is no corresponding technical restriction on the ability to scan the delay between the pumplaser pulse and the xrayprobe pulses, and thus no lower limit on the ability to resolve beat frequencies from TRXS measurements. This observation motivates transforming the measured TRXS in reciprocalspace and realtime into its reciprocalspace and reciprocaltime representation through a temporal Fourier transform. This representation is called frequencyresolved xray scattering (FRXS). The novel aspect of this approach is that an interpretable and compact representation of the experimental measurement may be obtained in reciprocalspace and reciprocaltime without the difficulty of inverting the measurement to the traditional realspace and time representation, and thus FRXS presents an alternative to traditional analyses of TRXS. The traditional approach based on pair correlation functions is limited by the range of momentum transfer, Q, that is accessible at xray free electron lasers (FELs). FRXS does not suffer this limitation, and in fact, FRXS leverages the strengths of FELs, namely fine time resolution and (relatively) fast data accumulation. This enables a long range of pumpprobe delays to be measured in an experiment, thus improving the frequency resolution of an experiment, while maintaining sufficient temporal resolution to measure high beat frequencies. These advantages have been used to obtain compact representations of bound states and dissociations along lines in reciprocalspace and reciprocaltime, demonstrating an alternative to traditional analyses of timeresolved xray scattering for gasphase photochemistry.
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 Chen, Ruizhu, author.
 [Stanford, California] : [Stanford University], 2019.
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 Book — 1 online resource.
 Summary

In this thesis, we use helioseismic methods to study two separate topics, the Sun's meridional circulation and sunquake events. The Sun's meridional circulation is a key component of solar dynamo and interior dynamics, playing an important role in transporting magnetic flux and redistributing angular momentum. A profile of the meridional circulation has long been sought, but results from previous studies were not fully consistent, due to a systematic center tolimb (CtoL) effect in helioseismic measurements that complicates the inference of meridional circulation in the deep interior. In the first part of this thesis, we measure the Sun's meridional circulation and its temporal evolution using 8 years of SDO/HMI Dopplervelocity observations, with a new CtoLeffectremoval method that we have developed in timedistance helioseismology. The longtimeaveraged meridional circulation profile is found to have a threelayer flow structure: an equatorward flow is sandwiched between two poleward flow zones above and beneath it, indicating a doublecell circulation in each hemisphere. Moreover, the 3layer flow pattern is more significant when the Sun's magnetic activity level is low, while significant changes are found in the flow structure during the active phase of the solar cycle. Besides, we also study the observational properties of the CtoL effect in the measured travel time of helioseismic waves. The CtoL effect is found isotropic relative to the azimuthal angle around the solar disk center. It also exhibits a significant frequency dependence  it reverses sign at a frequency around 5.4 mHz, and is strongest at around 4.0 mHz. The tendency of frequency dependence varies with diskcentric distance but not with the waves' travel distance. In the second part this thesis, we focus on sunquakes. Sunquakes are helioseismic power enhancements initiated by solar flares, but not all flares generate sunquakes. It is curious why some flares cause sunquakes while others do not. Here we propose a hypothesis to explain the disproportionate occurrence of sunquakes: during a flare's impulsive phase when the flare's impact acts upon the photosphere, a sunquake tends to occur if the background oscillation at the flare's footpoint happens to oscillate downward, in the same direction with the impulse from above. To verify this hypothesis, we survey 60 strong flares in Solar Cycle 24 to search for sunquakes, by reconstructing the oscillatory velocity in the flare sites using a helioseismic holography method. A total of 24 flares are found to be sunquake active, giving a total of 41 sunquakes. It is found that in 3 − 5 mHz frequency band, 25 out of 31 (81%) sun quakes show net downward oscillatory velocities during the flares' impulsive phases, and in 5 − 7 mHz frequency band, 33 out of 38 (87%) sunquakes show net downward velocities. These results support our hypothesis that a sunquake more likely occurs when a flare impacts a photospheric area that happens to have a downward background oscillation.
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Online 4. Impurity quantum phase transitions in quantum dot nanostructures [2019]
 Peeters, Lucas Bernd Marie, author.
 [Stanford, California] : [Stanford University], 2019.
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 Book — 1 online resource.
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Electronic systems subject to competing interactions can end up in different phases as the balance between these interactions shifts. When a quantum critical point separates these phases, exotic electronic behavior often marks the vicinity of the transition. In this work, we construct nanopatterned devices to probe such critical phenomena. The basic element of our devices is the GaAs/AlGaAs quantum dot, an isolated region of electronic charge which is coupled to a twodimensional gas of weakly interacting electrons. We use different designs of quantum dots to realize different models. The first device studied in this work realizes the spin twochannel Kondo ('spin 2CK') model. In this model, a single impurity (i.e. a single spindegenerate dot) is coupled to two separate reservoirs. When the couplings to both reservoirs are unequal, the more strongly coupled reservoir screens the impurity spin degeneracy and forms a manybody singlet; this is known as the Kondo effect. When both reservoirs are coupled equally strongly, a nonFermi liquid ground state arises as a result of the overscreening by both reservoirs. We probe the anomalous scaling properties of this state, and show how it transitions into a more conventional Fermi liquid under the influence of various perturbations. The second device is first operated as a single metallic quantum dot in the quantum Hall regime. Spin degeneracy is broken, but the device can be tuned such that there is now a charge degeneracy which can then be screened by coupling to a reservoir. We tune to and away from equal couplings to see the effect of the twochannel Kondo state. Finally, we operate the second device in its full form as a doubledot device, to explore the competition between dotlead and interdot interactions.
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Online 5. The LZ dark matter search and development of a new gas phase technique to characterize low level electron emission from electrode grids [2019]
 Ji, Wei, 1990 author.
 [Stanford, California] : [Stanford University], 2019.
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 Summary

Dark Matter is needed to explain many cosmological observations and therefore has been proposed for many decades, but it awaits direct detection. One of the most popular classes of dark matter candidates is Weakly Interacting Massive Particles (WIMPs), which have masses in the order of 100 GeV and couple to ordinary matter at weak scale. In WIMP direct detection experiments, we look for WIMPs being scattered by nuclei, a process which produces low energy (smaller than 100 keV) recoiling nuclei that can be observed. We are building LZ, a detector looking for WIMPs using liquid xenon in a dualphase time projection chamber (TPC), at 4850 feet underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. LZ aims to achieve the world's highest sensitivity to find WIMPs via WIMPnucleon interactions. After a brief discussion of dark matter and the LZ experiment, this dissertation presents the details of my study to solve the electron emission problem. The LZ TPC will consist of electrode grids and other metallic surfaces that can emit electrons when operated under voltage. Because the charge measurement in the LZ detector is sensitive to single electrons, electrons from the grids can be both a significant nuisance for data collection and a source of background at lowenergies, limiting the sensitivity of the experiment for lowmass WIMPs. This has motivated us to develop a test detector to study how to reduce this background. The test detector consists of a pair of grids biased to high voltage and operated in xenon gas. The electric field between the grid causes the electrons to produce electroluminescence scintillation light that is measured by PMTs. This new technique is sensitive to single electrons emitted by the grids, allowing a measurement of emission currents as low as attoamperes. We used this detector to study the properties of different grids and to determine what treatments can be done to reduce their electron emission. We found that passivation with citric acid reduces electron emission from stainless steel surfaces. This work was supervised by Professor Thomas Shutt and was completed in collaboration with members of the LZ collaboration and the SLAC LZ group.
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Online 6. Measurement and control of nonadiabatic dynamics a study in the acetylene dication [2019]
 LiekhusSchmaltz, Chelsea Elizabeth, author.
 [Stanford, California] : [Stanford University], 2019.
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 Summary

Nonadiabatic structural dynamics occur in lighter molecules and are often described using Conical Intersections (CI) in molecules with at least three atoms. Light that is resonant near regions of strong nonadiabatic coupling can play an important role in controlling and understanding these dynamics. This thesis presents both simple model simulations and experimental data in the acetylene dication to analyze how light interacts with nonadiabatic dynamics. A key parameter that relates how the nuclear energy changes in time compared to the relative electronic energy is used to explain and predict the role that dipole coupling has in controlling nonadiabatic dynamics.
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Online 7. Measurements with optically levitated microspheres [2019]
 Rider, Alexander David, author.
 [Stanford, California] : [Stanford University], 2019.
 Description
 Book — 1 online resource.
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I discuss the development of optically levitated microspheres as a tool for precision measurements and tests of fundamental physics. Micronscale dielectric spheres are trapped by the radiation pressure at the focus of a Gaussian laser beam, where the optical suspension enables thermal, electrical, and mechanical isolation from the surrounding environment at high vacuum. Forces and torques can be measured from changes in the angle and polarization of light both transmitted through and reflected by the trapped particle. Additionally, the charge of the particle can be controlled with single electron precision. We have used these methods for the following three purposes: to search for fractionally charged particles and dark energy, to develop measurement techniques for surface potentials, and to construct an electrically driven microgyroscope.
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Online 8. Search of the Higgs boson produced through vector boson fusion decaying to a pair of bb with the ATLAS detector [2019]
 Jiang, Zihao, author.
 [Stanford, California] : [Stanford University], 2019.
 Description
 Book — 1 online resource.
 Summary

This thesis presents the search of the Higgs boson produced by Vector Boson Fusion (VBF) and decaying to bottom quarks. A search using the ATLAS detector was performed with 2016 protonproton collision data. The multivariate analysis measured the signal strengths of both the inclusive Higgs production and the vectorboson fusion production relative to the Standard Model prediction. This analysis led to the observation of Higgs coupling to bquarks in the summer of 2018. Furthermore, potential improvements of the analysis techniques using complex neural networks are investigated. In order to understand better the Quantum Chromodynamics (QCD) backgrounds of the Higgs search, the characteristic variables of the gluon splitting vertex are measured.
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Online 9. Angular momentum conservation law in lightfront quantum field theory and extended conformal symmetry of Abelian gauge theory in D ≠ 4 [2018]
 Chiu, YuJu, author.
 [Stanford, California] : [Stanford University], 2018.
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This thesis investigates two independent aspects of spacetime symmetries. The first part of my thesis is about the angular momentum conservation law in lightfront quantum field theory. We prove the lightfront Poincare invariance of the angular momentum conservation law and the helicity sum rule for relativistic composite systems. We show that the lightfront wavefunction (LFWF), which describes the internal structure of a bound state, is in fact frame independent, in contrast to instant form wavefunctions. In particular, we demonstrate that j3, the intrinsic angular momentum projected onto the lightfront direction, is independent of the bound state's 4momentum and the observer's Lorentz frame. The frame independence of j3 is a feature unique to the front form. The angular momentum conservation law leads directly to a nonperturbative proof of the constraint A(0)=1 and the vanishing of the anomalous gravitomagetic moment B(0)=0. Based on the conservation of angular momentum, we derive a selection rule for orbital angular momentum which can be used to eliminate certain interaction vertices in QED and QCD. We also generalize the selection rule to any renormalizable theory and show that there exists an upper bound on the change of orbital angular momentum in scattering processes at any fixed order in perturbation theory. The second part of my thesis investigates an extended conformal symmetry for Abelian gauge theory in general dimensions. Maxwell theory in d \neq 4 spacetime dimensions is an example of a scaleinvariant theory which does not possess conformal symmetry  the special conformal transformation (SCT) explicitly breaks the gauge invariance of the theory. We construct a nonlocal gaugeinvariant extension of the SCT, which is compatible with the BRST formalism and defines a new symmetry of the physical Hilbert space of the Maxwell theory for any dimension d \geqslant 3. We prove the invariance of Maxwell theory in d \geqslant 3 by explicitly showing that the gaugeinvariant twopoint correlation functions, the action, and the classical equation of motion are unchanged under such a transformation.
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3781 2018 C  Unavailable In process 
 Benjamin, Nathan, author.
 [Stanford, California] : [Stanford University], 2018.
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 Book — 1 online resource.
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In this thesis, we study aspects of threedimensional gravity in Anti de Sitter (AdS) space by studying the holographically dual twodimensional conformal field theory (CFT). We begin by describing general constraints on the elliptic genus of a twodimensional supersymmetric conformal field theory which has a gravity dual with large radius in Planck units. We discuss the distinction between theories with supergravity duals and those whose duals have strings at the scale set by the AdS curvature, using symmetric orbifolds as a case study. We then move on to study extremal theories, conjectured to be dual to "pure" threedimensional gravity. We first provide an example of an extremal chiral N=2 superconformal field theory at c=24. We then consider extremal CFTs at large central charge, and consider the quantum corrections to the classical spectrum. Our conjecture passes various consistency checks, especially when generalized to include theories with supersymmetry. Finally, we examine a specific topdown construction of AdS3/CFT2 from string theory, called the D1/D5 system. We examine the lowlying quarter BPS spectrum of the K3 symmetric orbifold CFT at various points in moduli space, and look at a more refined count than the ordinary elliptic genus. We do a decomposition of the spectra into N=4 characters, and show that at large N the character decomposition satisfies an unusual property, in which the degeneracy only depends on a certain linear combination of left and rightmoving quantum numbers, suggesting deeper symmetry structure.
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Online 11. Complexity and black hole geometry [2018]
 Zhao, Ying, author.
 [Stanford, California] : [Stanford University], 2018.
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This thesis discusses various aspects of black hole interior. We explore the connection between black hole geometry and quantum complexity. We look for quantum circuit protocols corresponding to traversable wormhole. We also point out various puzzles we encountered.
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Online 12. Exploring dark matter with improved numerical techniques [2018]
 Powell, Devon, author.
 [Stanford, California] : [Stanford University], 2018.
 Description
 Book — 1 online resource.
 Summary

In this thesis, I discuss several computational physics developments. The context is the study of potential dark matter observables calculated from traditional cosmological Nbody simulations. These particlebased simulation techniques often suffer from shot noise when sampling of the density field. Building on the phase space sheet (PSS) interpretation of Abel, Hahn and Kaehler (2012) of cold collisionless fluid, I develop a method for geometrically exact and robust volume and pointsampling algorithms. These operate on a simplicial tessellation of a 3manifold embedded in the 6D phase space, such that the mass is interpolated between particles, which are interpreted as Langrangian flow tracers. This results in a smooth continuous and noise free density field that aids accurate interpretations of cosmological dark matter simulations. I discuss the application of these algorithmic developments to the indirect detection of dark matter (via decay and annihilation), studies of cosmic voids, the cosmic neutrino background, and simulations. I also present recent work on extending these concepts to radiation transport with "adaptive beam tracing." This method extends raytracing, which follows 1dimensional rays along their trajectories, to beam tracing, which instead volumesamples 3D photon packets called "beams".
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Online 13. Highenergy gammaray observations of solar flares with the Fermi large area telescope [2018]
 Allafort, Alice Julia, author.
 [Stanford, California] : [Stanford University], 2018.
 Description
 Book — 1 online resource.
 Summary

Solar flares are the most energetic events in our Solar System. They consist of sudden energy release from reconfiguration of magnetic fields, leading to acceleration of particles to relativistic energies. The Fermi Large Area Telescope (LAT) gammaray observations of the Sun present a unique opportunity to explore the mechanisms of highenergy emission as well as particle acceleration and transport in solar flares. I will present the results of the first 9 years of observations of the active Sun by the FermiLAT, which represents the largest sample to date of detected solar flares with emission greater than 30 MeV. Some of the new detections confirm the standard models for solar flares based on observations from past missions in the 1980s and 90s, but new behaviors have also been identified: detections of delayed gammaray emission lasting up to 20 hours and the first detection of gammaray emission above 100 MeV from three solar flares originating from behind the visible part of the Sun. Considering all of the 46 flares detected by the FermiLAT, I will describe the characteristics of the first gammaray solar flare catalog covering Solar Cycle 24, exploring trends and correlations with the most relevant solar events: Xray emission, coronal mass ejections, and direct detection of solar energetic particles.
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Online 14. Improved discrimination for neutrinoless double beta decay searches with EXO200 and nEXO [electronic resource] [2018]
 Fudenberg, Daniel.
 2018.
 Description
 Book — 1 online resource.
 Summary

Neutrinos have been shown to have nonzero mass, however how they generate their minuscule masses is an open question. One well motivated possibility is that neutrinos have Majorana masses, for which the most sensitive test is the observation of neutrinoless doublebeta decay. The halflife of this neutrinoless mode is much slower than that of the observed twoneutrino mode of doublebeta decay, which is many orders longer than the age of the universe, thus searches are heavily background dominated. In this work discusses two, completely distinct, methods to improve discrimination of neutrinoless doublebeta decay, of xenon136, from backgrounds. The first method is through training new discriminators to more fully exploit the observed topological information in EXO200 to distinguish neutrinoless doublebeta decay from the most common backgrounds. The second method is to enable the observation of barium136 resulting from doublebeta decay for a future generation detector via a hardwarecentric approach. One path requires extraction from high pressure gas to vacuum of heavy ions from similarly heavy medium with high efficiency. Work on a prototype extraction apparatus for the nEXO collaboration and lessons learned are presented here.
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Online 15. Improving dark energy measurements by controlling systematics in the point spread function and redshift distribution [2018]
 Davis, Christopher Paul, author.
 [Stanford, California] : [Stanford University], 2018.
 Description
 Book — 1 online resource.
 Summary

Most of the universe is made up of dark energy, but we are unsure of its fundamental nature. Large, widefield optical galaxy surveys such as the Dark Energy Survey (DES) seek to measure any time variation in dark energy through its impact on the growth of large scale structure. Among the many features that must be controlled in order to achieve this measurement are the point spread function (PSF) and redshift distribution. In the first half of my thesis I will present a physically motivated model for the optical and atmospheric portions of the PSF and apply them to DES data. In the second half of my thesis I will turn to the measurement and calibration of redshift distributions. First, I present `clustering redshifts, ' a novel method of calibrating the redshift distributions of an ensemble of galaxies using their correlations with quasispectroscopic tracers of large scale structure, such as galaxy clusters. Then, I present a calibration of the DES Year 1 source redshift distributions using these clustering redshifts. Finally, I present a scheme for calibrating redshift distributions using selforganizing maps and overlapping infrared data. Both threads of this thesis will be useful for future cosmological galaxy surveys like the Large Synoptic Survey Telescope, Euclid, and the Wide Field Infrared Survey Telescope.
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 Kurinsky, Noah, author.
 [Stanford, California] : [Stanford University], 2018.
 Description
 Book — 1 online resource.
 Summary

The SuperCDMS SNOLAB experiment will be a 20kg scale Si and Ge direct dark matter detection experiment designed to probe down to 300 MeV in dark matter (DM) mass through DMnucleus scattering and 500 keV in DM electron scattering. In order to reach these low masses with appreciable sensitivity to dark matter, it needs to achieve very low energy resolution (≤ 10 ev) for nuclear recoils in both detector materials, which will be achieved using a new detector design and operating mode, CDMS HV. This detector is designed to operate at a bias of 100V to convert charges liberated in our detector targets to into phonon energy in order to resolve individual electronhole pairs. This has never before been achieved in a kgscale detector. In this thesis, I cover three elements of the design of the CDMS HV detectors. I discuss the detector physics controlling how charges and phonons are generated in our detector crystals, com paring theory to results of recent experiments carried out at Stanford. I move on to describe the operating principles of our phononmediated charge readout, as well as the design of the CDMS HV detector. I then describe the performance tests of early CDMS HV prototypes in conjunction with the SuperCDMS SNOLAB electronics, and discuss the path towards achieving single electronhole pair resolving detectors at the kgscale given the performance obtained thus far. As a result of these tests, we were able to refine our noise and sensor dynamics models, and develop new metrics for diagnosing nonideal sources of noise to aid in reducing coupling of the external environment to our detectors. In order to study the microphysics of phonon and charge production in our target crystals, we fabricated a number of gramscale devices with various sensor designs in order to separate sensor and environmental effects from intrinsic crystal properties. These devices provided the first successful demonstrating of using voltage to amplify charge energy by production of phonons (the NeganovTrofimovLuke effect) in order to resolve electronhole pairs, and opened up a new regime of dark matter and photon science at the gramscale that we are just beginning to explore. A first dark matter search was carried out with one of these gramscale devices, producing worldleading limits on electronrecoiling dark matter between 0.5 and 5 MeV in dark matter mass for multiple form factors. This device achieved a phonon resolution of 10 eV, allowing a single gramday of exposure to rival kgdays of exposure in the competing liquidnoble based electronrecoil search.
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Online 17. Novel methods and applications for kinetic plasma simulation [2018]
 Totorica, Samuel Richard, author.
 [Stanford, California] : [Stanford University], 2018.
 Description
 Book — 1 online resource.
 Summary

Understanding the behavior of plasma is important for a broad range of applications, such as understanding the production of energetic particles in astrophysics, developing predictive models for space weather, and harnessing the potential of nuclear fusion power. Due to limitations such as noise from numerical collisions and the large number of simulation particles required to capture the development of nonthermal tails in the particle distribution, multiscale plasma simulations are extremely challenging. In this thesis the simplexincell algorithm is presented, which holds promise for overcoming these difficulties by interpreting the simulation particles as the vertices of a mesh that traces the evolution of the distribution function in phase space. This enables a discretization using deformable phase space volume elements rather than fixedshape clouds of charge. Using test problems including Landau damping and the Weibel instability it is shown how this new view retains finescale structure in the distribution function and can drastically reduce the number of simulation particles required to reach a given noise level. Magnetic reconnection is a promising candidate mechanism for accelerating the nonthermal particles associated with explosive phenomena in astrophysics. Laboratory experiments with highpower lasers can play an important role in the study of the detailed microphysics of reconnection and the dominant particle acceleration mechanisms. In this thesis the results of particleincell simulations used to explore particle acceleration in conditions relevant for current and future laserdriven reconnection experiments are presented. These simulations indicate that laserdriven plasmas offer a promising platform for studying particle acceleration from reconnection, with the potential to reach multiplasmoid regimes of strong astrophysical interest. These results provide new insight into the physics of reconnection and particle acceleration and are now helping to guide experimental campaigns.
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 Yang, Qi, author.
 [Stanford, California] : [Stanford University], 2018.
 Description
 Book — 1 online resource.
 Summary

To investigate the effects due to proximity between a threedimensional topological insulator (TI) and an insulating ferromagnet (IF), TIIF thin film bilayers were fabricated with pulsed laser deposition. Either bismuth(III) selenide (Bi2Se3) or bismuthantimony(III) telluride (BST) was used for the TI layer, whereas the IF layer was formed by the Heisenberg ferromagnet EuS. While a positive magnetoresistance was observed above the Curie temperature of EuS, as ubiquitously observed in highquality TI thin films, an unusual negative magnetoresistance was observed below the Curie temperature in the variablerange hopping regime. The angular dependence of such negative magnetoresistance indicates an orbit origin. Specific to BSTEuS bilayers, when the bulk conduction is minimized, magnetic anomalies in AC susceptibility were observed concurrently with resistive anomalies at the same temperatures, suggesting an interface magnetic order. These phenomena together suggest twostage proximity effects between the topological insulators and the insulating ferromagnet, and provide first steps to realize the halfinteger quantum anomalous Hall effect.
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Online 19. Quantum error correction and spacetime [2018]
 Salton, Grant, author.
 [Stanford, California] : [Stanford University], 2018.
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Quantum error correction (QEC) is a branch of quantum information theory, originally invented to protect hypothetical quantum computers against realistic sources of noise. QEC has enjoyed significant success within the paradigm of computation, but the ideas and techniques of quantum error correction have also been effective in tools many fields of physics. In this thesis, we will shed light on the way in which QEC manifests outside of the usual computational paradigm and informs other areas of physics. We'll focus on the role of QEC in quantum gravity, spacetime, and high energy theoretical physics. We start with the general problem of quantum information replication in spacetime, and we show that information replication is possible if and only if transmission of the quantum information does not result in cloning of quantum information or fasterthanlight communication. We then study the role of quantum error correction in quantum gravity, specifically within a gaugegravity duality known as AdS/CFT. We establish a new formula for mapping observables on either side of the duality, showing that the socalled bulktoboundary map defines an approximate quantum error correcting code. Motivated by the study of entangled states dual to multiboundary wormholes in AdS/CFT, we then turn our attention to characterizing the states that can arise from the euclidean path integral in threedimensional ChernSimons theories. We study U(1) level k and SO(3) level k ChernSimons theories on euclidean 3manifolds with torus boundaries. For the abelian U(1) theory, we find that the set of states that can be prepared exactly coincides with the set of stabilizer states, which are characterized by quantum error correcting codes. For the nonabelian SO(3) theory, we find that any state can be prepared to arbitrary precision, giving rise to a notion of state universality. We conclude with some final observations to support the idea that entanglement gives rise to the connectedness of spacetime. We study the partial transpose of the thermofield double (TFD) state geometrically, and we demonstrate that local time reversal (which is unitarily equivalent to partial transpose) leads to inconsistencies in the connected spacetime dual to the TFD state.
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Online 20. Searching materials for novel physics from theory and from data [electronic resource] [2018]
 Zhou, Quan.
 2018.
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Materials search and discovery is crucially important in condensed matter physics. Besides experimental trialanderrors, there exist two types of methods to guide materials explorations: "from theory" that starts from theoretic analysis and numerical simulations, and "from data" that leverages massive materials data via statistical machine learning. I will present one work for each of both methods of materials discovery in this dissertation. Firstly, I will discuss the theoretic proposal and materials realization of antiferromagnetic Dirac semimetal. I will specifically show how a nonsymmorphic crystal symmetry stabilizes a fourfold degenerate point in the electronic band structure of an antiferromagnetic system that is invariant under the combination of timereversal and inversion symmetry, thus realizing massless Dirac fermions as low energy excitations. Secondly, I will talk about how to learn atoms' properties from extensive materials data, inspired by ideas from computational linguistics. I will present analysis of the constructed atom vectors, as well as their applications in databased materials prediction using machine learning.
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