Degree Date: December, 2013

Kurtis Geerlings
Michel Devoret

Improving Coherence of Superconducting Qubits and Resonators

Superconducting qubits and resonators with quality factors exceeding 10^7 are of great interest for quantum information processing applications. The improvement of present devices necessarily involves the consideration of participation ratios, which budget the influence of each physical component in the total energy decay rate. Experiments on compact resonators in which participation ratios were varied has demonstrated the validity of this method, yielding a two-fold improvement in quality... more

Aaron Mertz
Eric Dufresne

Collective Mechanics of Epithelial Cells

Cell–cell and cell–matrix adhesions play essential roles in the function of tissues, yet little is known about how crosstalk between these two adhesion types regulate cells' material properties and active processes. This dissertation combines experiment and theory to reveal how colonies of cells apply forces to the extracellular matrix. Using traction force microscopy, we measure forces transmitted to the substrate by colonies of epithelial cells with strong and weak cadherin-... more

Konstantin Nesterov
Yoram Alhassid

Mesoscopic Effects in Chaotic Metallic Nanoparticles

We study electron interactions in a nanosized chaotic metallic grain with a large Thouless conductance. We use the so-called universal Hamiltonian, which describes the low-energy physics of such a grain. The noninteracting part of this model fluctuates and is described by random-matrix theory, while its interaction terms are universal and do not fluctuate. Of particular interest are grains in the fluctuation-dominated regime of pairing correlations, where the grain is so small that its single-... more

Alice Ohlson
John Harris

Investigating Parton Energy Loss with Jet-hadron Correlations and Jet vn at STAR

A strongly-coupled, deconfined state of quarks and gluons, known as the Quark-Gluon Plasma (QGP), is created in high-energy collisions of heavy nuclei. The QGP can be probed by high-momentum quarks and gluons (collectively known as partons) that are produced in hard scatterings early in the collision. The partons traverse the QGP and fragment into collimated "jets" of hadrons. Studies of parton energy loss within the QGP, or medium-induced jet quenching, can lead to insights into the... more

Kinga Partyka
Bonnie Fleming

Exclusive Muon-Neutrino Charged Current mu+Np topologies in ArgoNeuT

Neutrinos remain among the least understood fundamental particles even after decades of study. As we enter the precision era of neutrino measurements bigger and more sophisticated detectors have emerged. The leading candidate among them is a Liquid Argon Time Projection Chamber (LArTPC) detector technology due to its bubble-like chamber imaging, superb background rejection and scalability. It is a perfect candidate that will aim to answer the remaining questions of the nature of neutrino and... more

William Pontius
Thierry Emonet

The Molecular Origins and Functional Role of Noise in a Simple Sensory Network

Biological pathways perform calculations with often-small numbers of constituent molecules, leading to potentially significant variability in their output. In this thesis, I use the chemotaxis pathway of the bacterium Escherichia coli as a model to investigate the molecular origins of large temporal fluctuations and their consequences for cellular behavior. The bacterial chemotaxis pathway is a simple sensory network that performs temporal comparisons of external chemical stimuli, enabling the... more

Matthew Reed
Robert Schoelkopf

Entanglement and Quantum Error Correction with Superconducting Qubits

A quantum computer will use the properties of quantum physics to solve certain computational problems much faster than otherwise possible. One promising potential implementation is to use superconducting quantum bits in the circuit quantum electrodynamics (cQED) architecture. There, the low energy states of a nonlinear electronic oscillator are isolated and addressed as a qubit. These qubits are capacitively coupled to the modes of a microwave-frequency transmission line resonator which serves... more

Charles Riley
Jack Sandweiss

Searching for Local Parity Violation in Heavy Ion Collisions

Parity violation of the strong interaction is prohibited globally, however, it may be possible for parity to be violated locally in hot, dense, and deconfined QCD matter created in heavy ion collisions. Microscopic parity-odd domains in QCD are the consequence of topologically non-trivial configurations of gauge fields, and may be observable in heavy ion collisions due to the so called Chiral Magnetic Effect (CME). The CME predicts that provided a strong magnetic field (produced in a non-... more

Flavius Schackert
Michel Devoret

A Practical Quantum-Limited Parametric Amplifier Based on the Josephson Ring Modulator

This dissertation has addressed the problem of developing the Josephson Parametric Converter (JPC) as a practical phase-preserving microwave parametric amplifier operating at the quantum limit of added noise. The device consists of two superconducting resonators coupled through the Josephson Ring Modulator (JRM), which in essence consists of a loop of four identical Josephson tunnel junctions, threaded by an applied magnetic flux. The nonlinearity of the JRM is of the tri-linear form XYZ... more

Adam Sears
Robert Schoelkopf

Extending Coherence of Superconducting Qubits: from microseconds to milliseconds

Circuit quantum electrodynamics (Circuit QED) is the extremely successful framework for studying quantum devices developed along with the transmon, a superconducting charge qubit with an insensitivity to several types of dephasing. It involves the description of superconducting qubits and harmonic oscillators as quantized circuits. This thesis describes the implementation of two experiments that reduce circuit QED to its simplest components. Both experiments utilize elements that are known to... more
Degree Date: May, 2013

Sourpouhi Bedikian
Sarah Demers

A Search for the Charged Higgs: Using Tau Polarimetry with Proton-Proton Collisions at the ATLAS Detector

A search for a 130 GeV charged Higgs boson in ttbar events containing a tau lepton is presented. Tau polarimetry is used in order to distinguish the signal, t → H±b → τνb, from the dominant Standard Model background, t → W±b → τνb. The signal extraction is performed by a log-likelihood template fit. The dataset corresponds to an integrated luminosity of 4.6 fb^−1 of sqrt(s)=7 TeV proton-proton collisions collected with the ATLAS detector in... more

Christopher Gilbreth
Yoram Alhassid

Ultracold Fermi Gases: Effective Interactions and Superfluidity

Cold atomic Fermi gases are clean, highly experimentally tunable systems with connections to many different fields of physics. However, in the strongly-interacting regime they are nonperturbative and difficult to study theoretically. One challenge is to calculate the energy spectra of few-body cold atom systems along the crossover from a gas described by a Bose-Einstein condensate (BEC) to a gas described by Bardeen-Cooper-Schrieffer (BCS) theory. The configuration-interaction (CI) method is... more

Archana Kamal
Michel Devoret

Nonreciprocity in active Josephson junction circuits

I will present different flavors of nonreciprocal photon dynamics realized using active parametric circuits based on Josephson junctions. The motivation stems from developing non-magnetic alternatives to existing nonreciprocal devices, invariably employing magnetic materials and fields and hence limited in their application potential for use with on-chip microwave superconducting circuits. The main idea rests on the fact the “pump” wave (or the carrier) in an active nonlinear system... more

Zuhair Khandker
Walter Goldberger

Embedding Methods for Conformal Field Theor

Conformal field theories (CFTs) are highly constrained by symmetry. For instance, based on symmetry considerations alone one can derive constraints on the form of correlators and on the scaling dimensions of certain operators. However, the full implications of symmetry are still far from understood, i.e. we still do not know the extent to which conformal symmetry constrains the space of all possible CFTs. In the non-supersymmetric setting, the embedding-space formalism for CFTs has proven to be... more

Nicholas Masluk
Michel Devoret

Purifying the environment of the fluxonium artificial atom

Fluxonium is a highly anharmonic artificial atom, which makes use of an array of large Josephson junctions to shunt the junction of a Cooper-pair box for protection from charge noise. At microwave frequencies the array forms a "superinductance", a superconducting inductance whose impedance exceeds the resistance quantum h/(2e)^2 = 6.5 kOhm. The first excited state transition frequency is widely tunable with flux, covering more than five octaves, yet the second excited state remains... more