The 12th Annual Pappalardo Fellowships
in Physics Symposium

Prof. Janet Conrad, Chair, 2013-14 Pappalardo Fellowships Executive Committee

Meng Su,
2012-15 Fellow,
Theoretical Astrophysics

"Surprises When You Look Up at the Sky with Gamma-ray Goggles"

Astronomers have been studying our home galaxy, the Milky Way, for centuries, yet we still find it full of surprises. In this talk, I will describe a mysterious phenomenon we recently discovered using NASA's Fermi Gamma-ray Space Telescope: a pair of gigantic gamma-ray emitting bubbles—dubbed the Fermi bubbles. This double-bubble structure spans more than half of the visible sky and may be only a few million years old. It was most likely created as the remnant of a gigantic eruption of the super-massive black hole that sits in the Galactic center, and with a mass four million times that of our Sun.

In addition to the huge gamma-ray bubbles, recent study unveils an excess of gamma rays towards the Galactic center at a particular energy. If confirmed, this may be one of the first direct signs of dark matter particles.

Hugh Churchill,
2012-15 Fellow,
Experimental Condensed Matter

"Nanoelectronics with Atomically Layered Materials"

The isolation of graphene—a one-atom thick sheet of carbon atoms—from its parent material graphite, inspired unprecedented interest among condensed matter physicists in the extraordinary properties of graphene. Since then, the same techniques developed to isolate graphene have been extended to other layered materials, so it is now possible to study atomically thin, two-dimensional materials with widely-ranging properties—including metals, insulators, and, most recently, semiconductors.

In this talk, I will describe our plans to create an architecture for nanoelectronic devices based on combinations of these atomically layered materials. I will also discuss some of the experiments we are initiating to explore some of the unique physical properties of the newest addition to the toolbox of atomically layered materials: the semiconducting transition metal dichalcogenides.

"Quantum Walks with Integrated Photonics"

Quantum information processing using photons is a fast-developing branch of quantum information science. Photons are ideal information carriers, as individual photons can be easily generated and manipulated, and information can be easily encoded by them. In recent years the field has been undergoing a revolution, as new ways to implement quantum photonic circuits on integrated chips enable the implementation of existing schemes and new components on a much smaller, more efficient and more robust platform.

I will describe my research in this direction, focused on the theoretical and experimental study of Quantum Walks—the quantum mechanical analogue of the classical random walk—and how they can be used to simulate condensed matter systems and implement new quantum information schemes.

Duff Neill,
2012-15 Fellow,
Quantum Field Theory

"Dynamics at the Large Hadron Collider (LHC) with Effective Field Theories"

Many processes in nature exhibit a large hierarchy of scales. For example, when tossing a ball, one only bothers about its center of mass motion. Solving for the wave functions of the billions of atoms in the ball at a microscopic scale, while being a "true" description, is irrelevant to actually discussing the ball's motion. Effective field theories systematize this intuitive notion that there are important degrees of freedom at a given length/energy scale, and at smaller lengths, or higher energies, the more numerous degrees of freedom act only to determine the bulk properties of the system. I will show how using effective field theory can simplify the dynamics of hadronic collisions, and lead to precise predictions for processes at the LHC needed to measure the fundamental parameters of the Standard Model.

"Fractal Butterflies in Moiré Superlattices"

The problem of a quantum mechanical electron moving under the simultaneous influence of a periodic potential and a magnetic field is simple to state but has an unexpectedly intricate energy spectrum. This spectrum, known as the Hofstadter butterfly, is one of the first examples of a fractal in physics. Indeed, it was discovered slightly before the word "fractal" appeared in the English language.

Since its first theoretical description, realizing the Hofstadter butterfly in an experimental system has been an outstanding challenge in condensed matter physics. The effects of the interplay between magnetic field and crystal lattice are most dramatic when the cyclotron motion of particles happens on a comparable length scale to the lattice spacing. Unfortunately for experimentalists, in a real crystal in which the atoms are but a few angstroms apart this requires magnetic fields hundreds of times larger than exist anywhere on earth. In this talk, I’ll describe how we can bring the necessary magnetic field within the range of experiments by studying electrons moving in an artificially enlarged "moiré superlattice," which is generated by the interplay of two slightly misaligned crystals.