## Research in Physics at HMC

Each student is encouraged to do individual experimental or theoretical research in an area of his/her special interest in conjunction with a faculty member. The department has a rigorous student-faculty research program in a wide variety of fields in experimental and theoretical physics. Current student-faculty research areas include: observational astronomy, astrophysics, biophysics, geophysics, laser and atomic physics, quantum theory, solid state physics, and string theory.

 Jessica Arlett Prof Arlett is an experimental physicist with interest in biochemical sensors, particularly the development of novel approaches to neurochemical detection that can aid in our understanding of neural activity, neurodegenerative diseases, and ultimately the development of advanced neurological treatments.Prof Arlett works in the intersection of physics, chemistry, and biology. Immediate goals are to design, test, and optimize neurochemical sensors for in vivo measurements in mice. We are particularly focused on the question: How can we maximize the sensing of target neurochemicals, while minimizing the noise from other chemicals present in the brain? Nicholas P. Breznay Early in our careers we learn that electrons are antisocial – they never want to be in the same place at the same time, and their mutual interactions can often be ignored, especially when considering just a few (or a few hundred). But as you crowd more and more into the same space, electrons begin to talk to one another; in solid materials, they sometimes decide to spontaneously organize, condense, and rearrange themselves—collectively assembling into patterns and phases that we never would have predicted from a “one-electron” picture. Our lab studies the properties and applications of these quantum materials, where the tremendous number (1023) of electrons, and their collective interactions, leads to new and fascinating behavior. These electronic states of matter can have familiar classical analogs—noninteracting gas, strongly interacting “Fermi” liquid, or crystalline solid—but they can also be fundamentally quantum-mechanical states that have no classical analog. We investigate these exotic states of matter—superconductors, spin-liquid magnets, charge-ordered oxides, and amorphous Anderson insulators—using hands-on low-temperature experiments with thin film and bulk crystal samples. Since thermal energy can disrupt fragile quantum states, we cool the samples to temperatures below 1 kelvin, and examine how their electrons respond to intense electromagnetic fields. Thomas D. Donnelly A century ago, the shortest time interval that could be measured, a millisecond, was available from streak-recording methods, and by 1965 the capabilities of high-frequency electronic circuitry had reduced this limit to a nanosecond. The time-resolution limit dropped precipitously after 1965 due to the invention of the laser and is now less than 1 fs ($$10^{-15} {\rm s}$$). These ultrafast laser pulses provide a tool for exploring nature in a previously inaccessible time domain; the evolution of nonequilibrium materials can be resolved, chemical reactions can be controlled, phase transitions can be monitored, and energy can be impulsively deposited into materials to create high-energy-density states of matter. The Donnelly group carries out experiments to study the interaction of high-intensity laser light with novel microstuctured targets. We develop machines that are capable of producing novel micron and sub-micron sized targets that are developed to study topics such as laser-driven nuclear fusion and the heating mechanisms which allow laser energy to be absorbed on short timescales by solid-density materials. We build, characterize, and do science with our machines at Harvey Mudd, as well as with our collaborators at the University of Texas at Austin where we have access to some of the most powerful laser systems ever built. James C. Eckert Magnetic device technologies are playing an ever expanding role in our day to day lives. Magnetic storage dates from the 1930's with the advent of tape recording and the recent high capacity computer hard drives are simply a variation on that same theme. However, the past few years has seen an explosion in the number and type of magnetic devices that have appeared on the scene. Position and location sensors, magnetic switching, and non-volatile computer memory based upon magnetoresistance have all come into common usage within recent years. This was brought about by the discovery of and the exploitation of the effect known as giant magnetoresistance (GMR). The phenomenon of giant magnetoresistance is the large change in electrical resistance of a system when a magnetic field is applied. Samples exhibiting GMR consist of separated regions of ferromagnetic, such as iron or cobalt, and non-magnetic materials. Devices that make use of GMR require a third region of antiferromagnetic material, such as CoO or IrMn, that serve to produce a locking effect, known as exchange coupling, on the direction of the magnetization in one or more of the ferromagnetic regions. This exchange coupling is the central feature in all of these devices and is not well understood. Our research employs electrical transport, magnetization, thermodynamic, and optical measurements to study exchange coupling in thin film magnetic nano-structures with the dual goals of shedding light on the origins of exchange coupling and of enhancing the effect with an eye towards improving and developing magnetic device technologies through the control of the magnetism associated with the spin of the electrons as they move through magnetic structures. This is the budding new field of spintronics. See my research page for more information. Ann A. Esin Astrophysics, including accretion flow and emission processes around neutron stars and black holes Sharon Gerbode In introductory physics courses, we learn about an idealized frictionless world of rigid bodies and smooth surfaces. Yet the physics of everyday life is complex: soft, sticky, squishy and often far from equilibrium. Many materials, ranging from biological tissues to piles of sand evade traditional classifications as either liquid or solid. Further incorporation of such soft matter into modern engineering requires a deeper understanding of these materials. Soft matter physics explores the fundamental physical principles that underlie the complexity of such systems, and has opened up an exciting new class of questions with applications to industry, biology and materials science. The Gerbode Lab focuses on two areas at the forefront of experimental soft matter physics: (i) colloids — where microscopic solid particles suspended in a fluid self-assemble into thermodynamic phases; and (ii) adaptive biomaterials — where soft microstructured biological tissues actuate complex motions. Visit our research website to learn more. Mark Ilton Soft matter physics: the study of soft, squishy, and deformable objects. Examples of soft matter are all around us. Most parts of our body (e.g. skin, tendon, blood) and many engineered materials (e.g. plastics, rubbers, foams, gels) fall under the category of soft matter. More precisely, the field of Soft Matter Physics encompasses systems where room temperature thermal energy is comparable to that of applied mechanical or thermal stresses. Soft Matter often includes structure on mesoscopic size scales (sizes anywhere from roughly 10 nm up to about 100 um; between that of a single atom but smaller than we can easily see with the naked eye). The PoSM Lab at Harvey Mudd College studies both soft elastic solids and non-Newtonian fluids from a curiosity-driven approach. Currently, we are interested in green technologies that use soft materials to address our environmental footprint. In particular, we are studying the fluid dynamics of water-processible polymers and the elastodynamics of mechanical batteries (batteries made of materials that store and release elastic energy). By studying the underlying fundamental physics related to these systems, we aim to inform further development of green technologies. Theresa W. Lynn When we save an mp3, search our files, or submit an online banking request, the information we care about must be encoded – and often sent around the world – in the state of some physical system. What if that physical system is a single atom, an individual electron spin, or one photon of light? As computers get smaller and faster and communication bandwidth gets more crowded, information technology will eventually run up against the microscopic realm of quantum mechanics, where an object can be in a superposition of two or more states at the same time, and where measurements alter the state of the thing being measured. Though this may sound like a hopeless muddle, many physicists, mathematicians, and computer scientists have discovered that there are reasons to be excited about the advent of quantum information technology. Since 1995, we have known that a full-scale quantum computer would be able to factor large numbers quickly, enabling it to break the current worldwide standard of data encryption. On the other hand, quantum mechanics can come to the rescue with communication technologies where security against eavesdroppers is guaranteed by the laws of physics themselves. The Lynn lab focuses on quantum communication protocols using photon pairs that are quantum mechanically entangled in their polarization states, spatial modes, or both properties at once. We investigate the role of entanglement – a type of correlation that doesn’t exist in classical physics – in providing communication bandwidth and security in protocols including quantum secret sharing. In experimental and theoretical investigations, we explore the advantages and limitations of using simple (linear) optical devices for quantum communication with entangled photons. Gregory A. Lyzenga Geophysics, including observational study of crustal deformation and earthquakes using geodetic, seismological and gravimetric methods; computer simulation of tectonic processes. Solar system astronomy. Peter N. Saeta Photovoltaics are the fastest-growing renewable energy source over the last three years and have the potential to supply a significant fraction of our electricity needs. Conventional silicon cells are made of thick crystals because silicon is a weak absorber in the infrared and much of the visible. Thin solar cells require less energy and material to make and may lead more swiftly to widespread deployment of photovoltaics. A challenge facing thin cells is to maximize the absorption of the solar spectrum. We explore the enhancements to absorption in thin-film cells made possible by metallic nanoparticles and other structures designed to scatter incident radiation into guided modes propagating parallel to the cell's surface. Vatche Sahakian String theory may be viewed as a framework for exploring new exotic ideas on the frontier of theoretical physics. At its heart, the subject aims at describing a consistent theory of quantum gravity, in addition to being a short length scale completion of the Standard Model of particle physics. The subject’s most prevalent successes to date are twofold: convincing evidence that the theory resolves various long standing puzzles arising in black hole physics; and phenomenological realizations of models that appear to mimic the world we see at low energies. While the theory itself as a whole may still evolve beyond its current form, several of the new concepts that it has developed are expected to survive at the foundation of a future formulation of the laws of physics. My research focus is string theory. I am interested in understanding the small scale structure of space, in a context where both gravitational dynamics and quantum mechanics become important. This realm often involves studying black holes, unravelling exotic dynamics such as non-commutative geometry, and exploring new frameworks that extend the Standard Model of particle physics and standard inflationary cosmology. A list of my publications can be found at the preprint arxiv. Brian Shuve My research is in the area of theoretical particle physics, and my work seeks to answer questions about the fundamental workings of nature: What is matter made of on the most basic level? How do the interactions of elementary particles shape the structure of the Universe and everything in it? What is the mysterious dark matter that fills the Universe but does not seem to be made of the same stuff as we are? Why are we made of matter and not anti-matter? In researching answers to these questions, I seek to uncover and test what kinds of new particles and forces could exist in nature, as well as to come to a better understanding of our current theories of physics and their limitations. My work is firmly grounded in the experimental efforts needed to confirm or refute extensions of our current understanding of particle physics. In particular, I research how the discovery (or lack thereof) of new particles at high-energy colliders such as CERN’s Large Hadron Collider sheds light on the physical processes taking place in the early universe that influence the structure of our world, and I build connections between current experiments and dark matter (and other poorly understood phenomena in particle physics). This leads to close collaboration with experimentalists at the Large Hadron Collider and other, smaller-scale experiments, as well as physicists in related fields.