Spectrum - FALL 2017
The Department of Physics at the University of Illinois at Urbana-Champaign is known for its collegial style of research—the “Urbana style”—that often involves collaborations across research areas and among theoretical and experimental physicists. Here is an inside glimpse of what some of our leading physicists are working on.
High Energy Physics
AMO/Quantum Information Science
My research is in the field of particle physics, which focuses on understanding the composition and fundamental laws and symmetries of the universe. In 2012, the Higgs boson was discovered at the world’s most powerful particle accelerator, the Large Hadron Collider (LHC) at CERN in Switzerland. This discovery marked the completion of the standard model of particle physics, which summarizes our understanding of the building blocks of matter and the fundamental forces. While the standard model has been extremely successful, several key open questions indicate that it cannot be the final theory of nature. In particular, the standard model predicts that the Higgs boson mass is 16 orders of magnitude larger than the observed value (the “hierarchy problem”). Additionally, the standard model cannot explain the origin of dark matter, a mysterious, as-yet undiscovered substance believed to permeate the universe. Understanding the nature of physics beyond the standard model is now the centerpiece of the LHC physics program and the focus of my research.
Supersymmetry is an extension to the standard model that may resolve the hierarchy problem, explain the origin of dark matter, and pave the wave to a grand unified theory of nature. Supersymmetry theorizes exotic new particles that may be produced in particle collisions. My research focuses on searching for them in data collected by the ATLAS detector at the LHC. My group is leading searches for supersymmetric particles in collisions containing leptons (electrons or their heavier cousins, the muons) and large missing transverse energy from escaping dark matter particles. We are also adapting machine-learning techniques used in computer vision fields to identify particles produced in LHC collisions and upgrading the ATLAS trigger system to perform fast hardware-based charged particle tracking, which will enhance the sensitivity of these searches. A discovery in these searches would transform our understanding of the composition and fundamental laws of the universe, leading to a paradigm shift in physics comparable in historical scale to Einstein’s relativity superseding classical Newtonian physics in the early 20th century.
My work focuses on astrophysical probes of fundamental physics: the ways in which the deepest workings of the universe are imprinted onto the grandest structures we see through our telescopes. I love the idea that there are deep connections between the largest and smallest scales of our cosmos, and the tantalizing possibility of unlocking new physics inaccessible in terrestrial laboratories. This work has led me to hunt for dark matter deep underground and to take baby pictures of the universe from the Antarctic ice. I look forward to seeing where it takes me next. These kinds of measurements are enabled by the superconducting technologies developed in our condensed matter groups here at Illinois, and I expect fruitful collaborations for the next generation of measurements.
Right now I’m excited about the search for primordial gravitational waves: quantum “noise” imprinted on spacetime by the universe’s earliest moments. LIGO has shown that modern cataclysms leave ripples in spacetime; the theory of inflation suggests that the early Universe did the same, but at vastly longer wavelengths. These waves should have left a unique imprint on the polarization of the cosmic microwave background (CMB): the glow of the hot plasma of the early universe, detectable in the sky today at ~100 GHz. Our “readout system” for this cosmic photograph is a powerful balloon-borne telescope called SPIDER. In January 2015 (just before I joined the Illinois faculty!) we lofted SPIDER for a 16-day flight at 118,000 feet over Antarctica. Our team at Illinois and collaborators worldwide are hard at work on the analysis of this exquisite data set, and new telescopes for SPIDER’s second flight are taking shape on the 4th floor of Loomis. Future efforts include next-generation CMB instrumentation from the ground, balloons, and space, as well as novel instruments (cryogenic and otherwise) for future measurements.
My group studies the trillion-degree matter, the quark-gluon plasma, made in the collisions of two large nuclei. Just as with more conventional substances, we want to study how it’s properties change when we change its temperature. Since the collisions happen in particle accelerators, this process is more challenging than simply adjusting a thermostat. We make the highest temperature matter at the LHC in Geneva and are in the process of building a new detector, sPHENIX, for the Relativistic Heavy Ion Collider in New York, where the lower collision energy translates into a cooler, but still very hot, quark-gluon plasma.
Under the leadership of Illinois Distinguished Postdoctoral Fellow Vera Loggins, at the Nuclear Physics lab we’ve constructed prototype calorimeters for sPHENIX. The calorimeters are of a novel design and are bricks of powdered tungsten with clear fibers running lengthwise. This design allows us to see the light generated when electrons interact with the tungsten. It’s all held together with epoxy. With our collaborators from other institutions, we’ve tested the detectors in particle beams at Fermilab. This testing is designed to tell us whether the detectors are performing as well as we need them to in sPHENIX. The analysis is ongoing, but it is looking very promising!
My lab works at the interface between physics and biology. Generally speaking, we are interested in mechanical processes in biology. What do I mean by this? The living cell is much more complex than a bag of well-mixed molecules that encounter one another by diffusion and undergo chemical reactions. The cell is more like a highly organized factory of molecular machines, proteins that carry out specific mechanical tasks such as moving cargo around the cell, manipulating the cell’s genome, or even propelling the entire cell.
How do we study these processes? We use laser-based techniques—optical tweezers, which utilize focused light to exert forces, and fluorescence microscopy, which detects light emitted from a dye molecule—because they are sensitive enough to measure forces and motions at the level of the individual biomolecule. A recent example is our work applying both techniques to understand helicases—proteins which separate the two strands of DNA (Comstock et al. Science, 2015). We discovered that a class of helicases possess a “switch” that determines the direction in which they move along DNA—akin to the gearbox on a car. We suspect that this switch is used to control what the protein does inside the living cell, but further experiments will be necessary.
Entanglement, the bizarre non-local correlations that can exist between two quantum systems, is the quintessential quantum mechanical phenomenon, distinguishing it from classical lines of thought. In our group we employ the non-local features of entanglement to explore fundamental science, e.g., showing that no local realistic model can explain quantum correlations, and practical applications. For example, we are currently working on projects to implement quantum communication channels (which could allow provably secure ship-to ship communication) for the Navy; one particularly appealing approach is the use of quad-copter drones, which might eventually allow quantum cryptography to be applied to communications to the home. We are also working on a NASA-funded project with the goal of realizing quantum communication from the International Space Station to a receiver on Earth. Such an experiment would be a critical milestone on the path toward an eventual quantum network, whose applications could include secure communication, coherent quantum sensors (imagine the optical equivalent of a radio telescope array, with the collection optics separated by more than the diameter of the planet!), and eventually even distributed quantum computing.
Another area of research focuses on human vision. Although 70+ years have passed since the first low-light vision experiments, it remains an open question whether humans can see single particles of light—“photons.” In our lab we are developing unique hardware and methodology to definitively answer this question, by reliably preparing pulses of light containing exactly one photon. The photon is directed at random to one of two sets of rods in the observer’s retina; by forcing the observer to choose where they believed they saw the photon (including cases where it was lost before detection), single-photon sensitivity can be determined, simply by looking for correct answers better than random guessing would allow. Recent psychology experiments suggest that awareness of visual events may depend on the phase of an observer’s alpha brain waves; therefore, to improve sensitivity we can incorporate signals from an EEG, and send the photons only when the subject is most likely to ‘see’ them. We are also exploring the use of ‘adaptive optic’ techniques to enable us to hit a single rod at will. The payoff would be an extremely powerful measurement system, enabling entirely new types of experiments on the human visual system at the single-quantum level. For example, we can then contemplate tests of nonlocality in which one of the ‘detectors’ is a human observer. Or we can direct the photon in a quantum superposition, simultaneously hitting two separate locations on the retina; the result would be a human-scale version of Schroedinger’s famous cat!