Alumni

Degree Date: May, 2017

Saehanseul Oh
John Harris

Correlations in particle production in proton-lead and lead-lead collisions at the LHC


In high-energy heavy-ion collisions at the Large Hadron Collider (LHC), a hot and dense state of matter called the Quark-Gluon Plasma (QGP) is formed. The initial collision geometry and the subsequent expansion during the QGP stage result in the correlations of produced particles, through which the properties of the QGP can be investigated. Two analyses based on the geometrical correlations of produced particles, one in proton-lead (p–Pb) collisions and the other in lead-lead (Pb–Pb... more

Andrei Petrenko
Robert Schoelkopf

Enhancing the Lifetime of Quantum Information with Cat States in Superconducting Cavities


The field of quantum computation faces a central challenge that has thus far impeded the full-scale realization of quantum computing machines: decoherence.  Remarkably, however, protocols in Quantum Error Correction (QEC) exist to correct qubit errors and thus extend the lifetime of quantum information.  Reaching the "break-even" point of QEC, at which a qubit's lifetime exceeds the lifetime of the system's constituents, has thus far remained an outstanding goal.... more

Toshihiko Shimasaki
David DeMille

Continuous Production of 85Rb133Cs Molecules in the Rovibronic Ground State via Short-Range Photoassociation


We present our results on continuous production of ultracold ^{85}Rb^{133}Cs molecules in the rovibronic ground state via short-range photoassociation (PA). Starting with ultracold Rb and Cs atoms trapped in dual-species dark-SPOT MOT, we photoassociate a pair of Rb and Cs atoms into an excited molecular state, which decays into the electronic ground state by spontaneous emission. We apply depletion spectroscopy to the RbCs system and establish a rotationally-resolved, state-selective detection... more

Jukka Vayrynen
Leonid Glazman

Electron transport along the edge of a topological insulator


A two-dimensional topological insulator has a gap for bulk excitations, but conducts on its boundaries via gapless edge modes. Time-reversal symmetry prohibits elastic backscattering of electrons propagating within the edge, leading to quantized conductance at zero temperature. Inelastic backscattering, present at finite temperature, breaks the quantization and  increases the edge resistance; the resistance of a long edge acquires a linear dependence on its length. A phenomenological... more
Degree Date: December, 2016

Filip Kos
David Poland

Bootstrapping 3D CFTs


We use the method of conformal bootstrap to systematically study the space of allowed conformal field theories (CFT) in three spacetime dimensions. We consider the crossing symmetry equations coming from the correlators of several lowest dimension operators in a given CFT and show how to setup the semidefinite program to explore the constraints implied by the equations. Constraints lead to general bounds on dimensions and 3-point functions of the operators in CFT. Three classes of CFTs... more

Tomomi Sunayama
Nikhil Padamanabhan

Using galaxy surveys as a precision tool to measure dark energy


Future surveys will provide a deeper understanding of dark energy, dark matter, and early universe physics through the measurements of large scale structure. In particular, the baryon acoustic oscillation (BAO) method and the redshift-space distortion (RSD) method aim to achieve sub-percent precision on cosmological parameters. Understanding and reducing the systematics caused by the non-linear evolution of gravitational structures and galaxy formation and evolution is crucial for future galaxy... more

Mitchell Underwood
Jack Harris

Cryogenic Optomechanics with a Silicon Nitride Membrane


The field of optomechanics involves the study of the interaction between light and matter via the radiation pressure force. Though the radiation pressure force is quite weak compared with forces we normally experience in the macroscopic world, modern optical and microwave resonators are able to enhance the radiation pressure force so that it can be used to both measure and control the motion of macroscopic mechanical oscillators. Recently, optomechanical systems have reached a regime where the... more
Degree Date: May, 2016

Rostislav Boltyanskiy
Eric Dufresne

Mechanical Response of Single Cells to Stretch


A living cell is a complex soft matter system far from equilibrium. While it consists of components with definite mechanical properties such as stiffness, viscosity, and surface tension, the mechanics of a cell as a whole are more elusive. We explore cell mechanics by stretching single fibroblast cells and simultaneously measuring their traction stresses. Upon stretch there is a sudden, drastic increase in traction stresses, often followed by a relaxation over a time scale of ~1min. Upon... more

Diego Caballero Orduna
Corey O'Hern

Computational Studies of Protein Structure


Despite the abundance of crystallographic and structural data and many recent advances in computational methods for protein design, we still lack a quantitative and predictive understanding of the driving forces that control protein folding and stability.   For example,  we do not know the  relative  magnitudes  of the  side-chain entropy, van der Waals contact interactions, and other enthalpic contributions to the free energy of folded proteins. The... more

Jane Cummings
Sarah Demers

Tau Polarization at a Hadron Collider: W to tau,nu and Z to tau,tau decays at ATLAS


In this thesis, the first measurement of tau polarization at a hadron collider, and the first measurement of tau polarization in W boson decays to a tau and neutrino altogether, is presented.  The measurement of tau polarization is a test of the structure of the vector (V) and axial vector (A) couplings of the W boson to the third generation leptons.  Such a test is not possible with first and second generation leptons for which the helicity state is not accessible in a collider... more

Arvin Kakekhani
Sohrab Ismail-Beigi

Ferroelectrics to Tackle Fundamental Challenges in Catalysis


Surface catalysis based on transition metals and their alloys has been one of the most important research fields in theoretical and experimental catalysis and chemistry. Recently, the development of a microscopic theoretical framework combined with the computational capability and accuracy of first principles calculations has changed the nature of this field from a largely trial and error approach to a predictive and controlled design process. In addition to deepening our knowledge of catalysis... more

Nicole Larsen
Daniel McKinsey

An Effective Field Theory Analysis of The First LUX Dark Matter Search


A wealth of astrophysical research supports the existence of dark matter in the universe, yet the exact nature of this unknown particle remains elusive. The Large Underground Xenon (LUX) experiment is a 370-kg dual-phase xenon-based time projection chamber (TPC) that seeks to detect dark matter candidates such as Weakly Interacting Massive Particles (WIMPs) through the light and ionization signals generated by their collisions with xenon nuclei. The first part of this talk details the design of... more

Manuel Mai
Corey O'Hern

Outcome Prediction and Reconstruction for Systems of Ordinary Differential Equations


I will present two related analyses of systems of ordinary differential equations (ODEs). The first one investigates outcome prediction in several systems of ODEs for the immune response to infection. We show that patient-to-patient variability sets a fundamental limit on the outcome prediction accuracy. However, accuracy can be increased at the expense of delayed prognosis. In the second study, I develop a method to build, general nonlinear ODE models from time series data using machine... more

Eric Norrgard
David DeMille

Magneto-optical trapping of diatomic molecules


Laser cooling in a magneto-optical trap (MOT) is the workhorse technique for atomic physics in the ultracold regime, serving as the starting point in applications from optical clocks to quantum-degenerate gases. It was recently shown that optical cycling, and thus laser cooling, should be possible for a class of at least 40 molecular species, using just three (or fewer) lasers. In this work, we demonstrate the first laser slowing and first magneto-optical trapping of a molecule, strontium... more

Katrina Sliwa
Michel Devoret

Minimizing Effects Detrimental to the Heisenberg Back-Action of Qubit Measurements with Parametric Amplifiers


The quantum back-action of the measurement apparatus arising from the Heisenberg uncertainty principle is both a fascinating phenomenon and a powerful manipulation tool. Unfortunately, there are other effects which may overwhelm the Heisenberg back-action. This thesis focuses on two effects arising in the dispersive measurement of superconducting qubits made with two commonly used ultra-low-noise parametric amplifiers, the Josephson bifurcation amplifier (JBA) and the Josephson parametric... more