Physics

Seminars in Fall 2018

All seminars are held at 4:10 PM in Physics 123, unless otherwise noted.
Refreshments will be served at 4:00 PM.

Upcoming Seminar

November 14, 2018
Franklin Dollar, UC Irvine
Bringing Moore’s Law to Lawrence’s device: Miniaturizing the Particle Accelerator

Society has benefited tremendously from the rapid miniaturization of the transistor, to where describing modern nanoscale devices necessitates new physics models and theories. Through the use of high power, short pulse lasers (a technology which warranted the 2018 Nobel Prize in Physics), an analogous revolution is occurring in advanced accelerators where new capabilities and compact form factors are being developed. Intense laser interactions have been shown to generate beams of coherent x-rays with attosecond (10^-18 second) durations, multi-GeV electron beams with nanocoulomb charge, multi-MeV per nucleon beams of light ions with extremely low divergence, and mono-energetic beams of neutrons and positrons. An overview of some of the acceleration mechanisms, both experimentally and numerically, will be presented. 

Aug 29

Lucas Illing
Thesis Start-Up Talk

Sept 5

Patrick Bedard, Ely Eastman, Nate MacFadden, Trevor Schlack, Thomas Malthouse
Summer student presentations

Sept 12

Yunjia Bao, Beadle Beadle, Kees Benkendorfer, J.R. Cruise, Max Jennings
Summer student presentations

Sept 19

Jay Nadeau, Portland State University
Eppur si muove--designing a microscope to look for extraterrestrial microorganisms

The open ocean, even at the poles, is teeming with microscopic life. Emerging techniques using imaging (e.g. the Flow Cytobot) and DNA sequencing are revealing the richness of Earth ecosystems formerly thought to be almost lifeless.  Nevertheless, there is currently no instrument chosen for a NASA mission that could detect life in a cubic meter of seawater. Detecting bacterial-sized cells on another planet is challenging for a large number of reasons. Sequencing techniques are of no use, since we don't know if extraterrestrial organisms will encode using DNA, or even nucleic acids at all. Finding building blocks of life, such as amino acids and lipids, is necessary but insufficient, since these molecules can form abiotically. We do not have a reductionist definition of life--so the way life moves, behaves, and metabolizes is the only way to distinguish organic molecules from something actually alive. On Earth, microscopy with specific dyes or stains is the gold standard for bacterial enumeration, but this is difficult to implement on another planet. Microscopes are large and heavy and require operator input for sample preparation, placement, and focusing. Many elements of a typical high-resolution microscope, such as complex objective lenses, are unsuitable for the vibration and temperature extremes of space flight. Missions to the Jovian moons such as Europa are also subjected to intense ionizing radiation from Jupiter's magnetosphere. The goals of my research are to design volumetric microscopes based upon holographic and light-field techniques that have no moving parts, require no focusing, and are suitable for use in harsh environments. The instruments are ground-truthed in Earth's "extraterrestrial analog" environments, such as the Canadian High Arctic, Greenland, and Alaska. While we find life everywhere, there are complications in each environment that can lead to false negatives and false positives. Instrument designs, field and lab data, and lessons learned will all be presented in this talk, as well as challenges for the future both on Earth and in space.

Sept 26

Danielle McDermott, Pacific University
Separating Sand: Numerical Models of Granular Materials

What is sand? Remember building a sand castle – you poured sand from a bucket as if it was a liquid and compacted it into a solid structure. Sand is a granular material: a collection of many particles that can flow or solidify depending on its density, wetness, and interactions with its environment. We study granular materials for many reasons including discovering new material behaviors, states of matter, and practical applications like building better grain silos.

Using numerical models of frictionless granular disks, I study the dynamics of particle flows in a high friction environment. This simple model produces a surprisingly rich variety of behaviors including low density clogged phases, high density jammed phases, high flow lanes, and mixed phase systems comprised of clogged and liquid regions. All of these phases result from complex interactions between many particles as the system density and applied driving forces are modified. These results help us understand sand flows better, offer a beautiful perspective on how condensed matter systems undergo dynamical shifts, and offer insights in controlling pattern formation in granular systems.

Oct 3

Matthew McQuinn, University of Washington
The Thermal Odyssey of the Universe

The Universe started off hot, cooling until only neutral atoms of hydrogen and helium were left (plus a lot of photons and neutrinos), and then the hydrogen+helium gas continued to cool as the Universe expanded to temperatures of ~1 K.  Eventually, when the Universe was hundreds of millions of years old, the cosmic gas was heated up again by tens of thousands of degrees as ultraviolet photons from stars and black holes re-ionized the hydrogen and helium's bound electrons.  Exactly when and how this gas was re-ionized is one of the missing pieces in our understanding of the late-time history of the cosmos.  I will talk about the atomic physics that shapes the thermal history of gas after it became re-ionized and about recent observations of the temperature of intergalactic gas that largely confirm this standard picture for its heating, putting limits on other heating processes.

Oct 10

Rachel Pepper, University of Puget Sound
Dispersal of seeds from splash cup plants

Splash cup plants, many of which are native to the Pacific Northwest, disperse their seeds with the help of raindrops. The seeds sit in a small (mm-scale) conical cup and are ejected upon drop impact.  The seeds are ejected at velocities up to five times the impact speed of the raindrop, and are dispersed up to 1 m away from the parent plant, which is only a few cm high.  Previous work investigating the mechanism of this remarkable dispersal predicted an optimum cup opening angle of around 40 deg, which matched reasonably well with experiments performed with 3D-printed splash cup models.  Those experiments were done with drop impacts on initially empty cups with no seeds.  I discuss similar experiments for cups that are not initially empty, but rather contain seed mimics, water, or both seeds and water.  For some of these realistic initial states results are strikingly different from empty cups.  Connections to theory will also be discussed. 

Oct 24

Eliot Kapit ('05), Colorado School of Mines
Self-correcting quantum devices

Quantum computers promise revolutionary improvements in performance over classical machines, but digital quantum computing remains out of reach due in part to the serious challenge of random noise in the quantum bits themselves. This noise can be mitigated using quantum error correction, but the overhead costs, in both numbers of physical qubit devices and in control hardware, are severe. In this talk I present work on a new device, called the Very Small Logical Qubit, which is capable of correcting or suppressing all common single qubit error processes, potentially increasing coherence by an order of magnitude or more. The VSLQ's error correction process is fully autonomous, relying on dissipation in noisy circuit elements rather than measurement and intervention by an external source. I review the basic principles of its operation, benchmark its performance in simulations, and describe ongoing experiments which will hopefully realize it in the next two years. 

Oct 31

Nov 7

Theresa Lynn, Harvey Mudd College
The Entangled Adventures of Alice and Bob

Entangled particle pairs have showcased the weirdness of quantum mechanics ever since Einstein worried about their “spooky action at a distance.”  Now we know that entangled states can be a valuable resource; information processing and communication security can be based on the quantum weirdness itself.  I will discuss some examples of communication and cryptography schemes based on quantum entanglement, and present recent work on my group on two problems related to such schemes:  theoretical limits on how well entangled states can be measured with non-entangling devices, and experimental methods for verifying the presence of imperfect entanglement between particles.

Nov 14

Franklin Dollar, UC Irvine
Bringing Moore’s Law to Lawrence’s device: Miniaturizing the Particle Accelerator

Society has benefited tremendously from the rapid miniaturization of the transistor, to where describing modern nanoscale devices necessitates new physics models and theories. Through the use of high power, short pulse lasers (a technology which warranted the 2018 Nobel Prize in Physics), an analogous revolution is occurring in advanced accelerators where new capabilities and compact form factors are being developed. Intense laser interactions have been shown to generate beams of coherent x-rays with attosecond (10^-18 second) durations, multi-GeV electron beams with nanocoulomb charge, multi-MeV per nucleon beams of light ions with extremely low divergence, and mono-energetic beams of neutrons and positrons. An overview of some of the acceleration mechanisms, both experimentally and numerically, will be presented. 

Nov 21

Nov 28

Junior Qual Information Session