Chih-Yung Chen

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My current research project is a study of deep states responsible for the persistent photoconductivity in quantum well structures of Si-doped GaAs.

The weak persistent photoconductivity (WPPC) with an annealing temperature 235 K in quantum well (QW) structures of Si delta-doped GaAs (delta-GaAs:Si) is of great technological interest because of its potential applications in high-density data storage. To understand the nature of the centers responsible for the persistent photoconductivity we will perform the experiment of Shubnikov-deHaas oscillations in magnetoresistance (MR) on a series of delta- GaAs:Si QW structures. From the Shubnikov-deHaas oscillations the subband structure of the two-dimensional electron gas that is confined in the well can be determined. Its temperature dependence will provide important information about the height of the recapture barrier that prevents the electrons from recombining with the defects and results in the persistent photoconductivity.

Thomas D. Donnelly

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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.

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Charlie Doret

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Dr. Doret will join the department in July, 2013, as an assistant professor. He earned his bachelor’s degrees in physics and mathematics from Williams College in 2002, and his master’s and doctoral degrees in physics from Harvard University in 2006 and 2009, respectively. He is presently a postdoctoral fellow in the Quantum Information Systems group at Georgia Tech Research Institute, and previously served as a teaching fellow and tutor while at Harvard. Doret is an experimental physicist who traps atomic ions for studying quantum information processing.

James C. Eckert

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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

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Astrophysics, including accretion flow and emission processes around neutron stars and black holes

Sharon Gerbode

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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.

Richard C. Haskell

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Optical Coherence Microscope (OCM) - An interdisciplinary team of faculty (Haskell and Petersen in Physics) and students have designed and constructed an OCM to study outstanding questions in developmental biology. Laser diodes, interferometers, fast photodetectors, fiber optics, photon statistics, and 3-D computer graphics have been critical topics in this project. For a short but complete description, see the OCM site.

Theresa W. Lynn

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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

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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

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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

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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.

Patricia D. Sparks

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Our work involves the design, making and study of magnetic device structures. Over the past few years an entirely new class of devices, based upon the property of "Giant Magnetoresistance" (GMR), has taken on an increasingly important role in sensor and data storage technology. We are working in collaboration with groups at Oxford and York Universities in England, with the magnetic microscopy group at the University of Minnesota and with the GMR group at IBM Almaden. In addition, we have access to the Cornell National Nanofabrication Facility for making the structures of interest. Our on campus facilities include a state of the art cryosystem with a temperature range of 450 K down to 1.7 K. This system is fully automated and is equipped with a 9 Tesla superconducting magnet and has the ability to rotate samples while making a variety of transport and magnetic measurements, e.g., DC resistivity, AC resistivity, 4 and 5 probe Hall Effect and a sample's I-V characteristics. We also have two state of the art Scanned Probe Microscopes, both of which can operate as either Atomic Force Microscopes (AFM) or Magnetic Force Microscopes (MFM). These systems allow us to image and map both the surface structure and the magnetic structure of our samples. We have recently acquired a pair of high-resolution optical microscopes from Olympus. These microscopes have an upper limit of 1000X magnification and are interfaced to dedicated computers for image acquisition and processing. This summer, we will be receiving delivery of a new thin film sputtering system for making thin film samples. This system will join our thermal evaporator and will greatly expand our capabilities in being able to make new and interesting thin film structures. Over the past five years, we have added in excess of $1,000,000.00 worth of new, state of the art research equipment to our laboratories. At the moment, we are leading the world-wide charge in this exciting new area of research.

John S. Townsend

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My primary research interests have been in particle physics, although I have also done some work in nuclear arms control, an area that might be called public interest science. The Standard Model, which has been developed during the past decades, has been spectacularly successful in explaining the observed phenomena in electromagnetic, strong, and weak interactions at the particle-physics level. While there are still major unanswered questions (such as what is the quantum theory of gravity and how do we unify all the interactions together), these questions are extremely challenging ones. More experimental input is necessary in order to make the next significant step forward. The first step in this direction is the likely discovery in July 2012 of the Higgs boson at CERN.

I have written two textbooks:

Quantum Physics: A Fundamental Approach to Modern Physics is intended as a first introduction to quantum mechanics and its applications. This book, which was published in 2010, shuns the historical ordering that characterizes other so-called modern physics textbooks and applies a truly modern approach to this subject, starting instead with contemporary single-photon and single-atom interference experiments. The text progresses naturally from a thorough introduction to wave mechanics through applications of quantum mechanics to solid-state, nuclear, and particle physics.

A Modern Approach to Quantum Mechanics uses an innovative approach that students find both accessible and exciting. It is pitched toward juniors and seniors. It lays out the foundations of quantum mechanics through the physics of intrinsic spin, and goes on to cover all the standard topics in an upper-division quantum mechanics course. The 2nd edition, which was published in 2012, includes many worked example problems as well as new sections on quantum teleportation, the density operator, coherent states, and cavity quantum electrodynamics.

Liz W. Connolly

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Erik Henriksen

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Thomas Helliwell

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Theoretical general relativity, relativistic astrophysics, and cosmology; the foundations of quantum theory.

Daniel C. Petersen

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Robert P. Wolf

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