The Physics Department had a very productive year. While enrollments in our introductory physics course for premedical students have dropped, the enrollments in our introductory course for potential physics majors and in our courses for non-science majors are booming. Sixteen juniors and seniors enrolled as physics majors and we shared six astrophysics majors with the Astronomy Department, giving us a very lively and talented group of students in our upper-level courses. Graduating seniors report to us that the physics faculty members are unusually accessible and that the department has a strong sense of community.

Student-faculty research continues to be an essential part of our program. Under the leadership of Professor Bill Wootters, our department serves as a National Science Foundation Research Experiences for Undergraduates (REU) site. This program and other grants allow us to hire several students to work with us full time on our research in the summer. During summer 1998, six Williams students and five students from other colleges joined our faculty to work on experimental and theoretical projects. Two of those students continued their research during the academic year, completing honors theses. This coming summer (1999) we will have nine students from Williams and two from other colleges. The students meet regularly for tea and cookies, as well as for more formal talks given by faculty or students. Those students doing experimental projects take a short course on machine shop work and another on electronics.

During the academic year, Eric Kramer joined the department as a visiting assistant professor. Professor Kramer had earned his Ph.D. from University of Chicago in 1996 and came to us from a postdoctoral research fellowship at Brandeis University. This coming Fall, he will begin a new position as an assistant professor of physics at Simon's Rock College, in nearby Great Barrington, MA.

Assistant Professor Daniel Aalberts presented two new courses: a tutorial Classical Mechanics and Fluid Mechanics and a Winter Study course Science of Sports co-taught with Steve Swoap of the Biology Department, which included ten new hands-on experiments. He and Lee Park of the Chemistry Department designed a new course, Chemistry and Physics of Materials. He advises the Society of Physics Students.

With summer research students Brian Gerke '99, Qiang Sun '00, Jonathan Pyle '99 (Swarthmore), and Lucas du Croo de Jongh (Leiden Ph.D. '00), Aalberts studied ultrafast dynamics of photoactive molecules. In November, Aalberts and Gerke visited collaborators at Leiden University to begin preparation of a journal article. In the spring, Ian Eisenman '99 joined the group, studying structural properties of double-bonded molecules. Gerke and Pyle both wrote honors theses based on their collaborations.

Aalberts participated in the Princeton Lectures on Biophysics, hosted by the NEC Research Institute. He was one of 1% of 11,000 participants at the American Physical Society's Centennial Meeting asked to contribute a lay language version of their work. (See <http://positron.aps.org/meet/CENT99/vpr/layfc19-05.html>.) His research also was highlighted in the Williams Record. (See <http://record.williams.edu/articles/11054.html>.)

Aalberts gave an on campus presentation for the Bronfman Summer Research program entitled "Ultrafast Dynamics of Rhodopsin, the Molecule that Makes Us See". He also gave an on campus presentation for the Physics Summer Research program entitled "Sequencing DNA in a New Way: the Old Ball and Chain".

Assistant Professor Sarah Bolton was on sabbatical leave during the 1998-1999 year. She spent the year at Lawrence Berkeley National Laboratory in Berkeley, CA studying ultrafast dynamics in semiconductors. In this work, a laser producing very short pulses of light (less than 5 x 10^-14 seconds = 50 femtoseconds in duration) is used to explore the motions of electrons in semiconductors. The laser pulse acts much like a strobe light, allowing observation of electronic processes which take place on the femtosecond time scale. The processes which can be explored with this technique include interactions among electrons, as well as interactions of electrons with thermal vibrations. Bolton's work this year focused on dynamics in the compound ZnSe, which has particularly strong electron-electron interactions, leading to well defined new resonances. Bolton returns to Williams for the summer program in July 1999, to continue this research with students Mark Acton '00, Camille Burnett '01, and Ricky Joshi '01.

In August of 1998, Bolton was awarded a National Science Foundation grant of $79,000, to be used for equipment and student summer stipends in the continuation of research at Williams on the behavior of ultrafast lasers. This project was started with Sarah Dugan '97, Rob Jenks '98, and Chris Elkinton '98, and will be continued by Mark Acton '00.

Professor Stuart Crampton completed his fourth and last year as the college's Provost. He also completed his terms on the National Academy of Sciences Board of Assessment of the Physics Programs at the National Institute of Standards and Technology and on the National Research Council's Committee on Atomic, Molecular, and Optical Sciences. He continues to serve on the Board of Directors of Research Corporation and as a consultant to the Sherman Fairchild Foundation Scientific Equipment Program. Next fall he will be on leave as a Visiting Scholar at the Center for Theology and the Natural Sciences in Berkeley, CA.

Professor Kevin Jones was on sabbatical at the National Institute of Standards and Technology in Gaithersburg, MD. He has a long-standing research collaboration with a group there headed by William Phillips. When Phillips was awarded the 1997 Nobel Prize in Physics he invited Jones to come to Gaithersburg for an extended two-year sabbatical. This research group has developed techniques for slowing atoms to near absolute zero. Jones, working with Paul Lett and others, has been "photoassociating" these cold (< 0.001 degrees Kelvin) sodium atoms to produce Na₂ molecules. With assistance of Ginel Hill '00 he has explored some molecular states in which both of the two chemically active electrons are excited to higher orbitals. Molecules in these states vibrate perhaps 20 times (on average) and then eject an electron. He has also been looking directly at the dynamics of the ionization process using a short pulse laser to produce excited atoms which then collide to produce molecular ions.

In March Jones attended the international workshop "Cold Atomic Collisions: Formation of Cold Molecules," at the Centre de Physique des Houches, Les Houches, France. A paper written with co-authors from China and Canada was recently accepted for publication. Jones is in the process of writing two others, one with co-authors in France and the other with a group in Holland. More locally, he has just written a paper on the theory of photoassociation lineshapes with a theoretical chemistry group one floor up at NIST.

Despite being away from Williamstown, Jones notes that he has still had numerous Williams Physics connections. In addition to having Ginel Hill '00 back at NIST for another summer of research, Jones shares an office with Chad Orzel '93 who has just completed a Ph.D. through a NIST/University of Maryland program (run by Michael Coplan '60). Gordon Jones '89 is a post doc at NIST. At a recent laser conference in Baltimore, Jones saw Tom Gallagher '66, Dan Kleppner '53, Guy Beadie '90, James Heyman '85, Dave Citrin '85, and Matt DeCamp '96 as well as Prof. Sarah Bolton.

Visiting Assistant Professor Eric Kramer published two papers in which he applied the theory of liquid crystals to the behavior of biological macromolecules in solution. He also continued work on the topological classification of patterns in wood grain. The goal of the classification is to illuminate the developmental mechanisms at work as the tree grows new wood.

In the fall of '99, Professor Kramer used peer instruction techniques to enliven his lectures in Physics 131, Particles and Waves.

During the 1998-99 year, Assistant Professor Tiku Majumder taught Physics 301, Introductory Quantum Mechanics, Physics 010 Light and Holography (during winter study), and Physics 109, Sound, Light, and Perception. Physics 109 is a course developed recently by Profs. Majumder and Bolton to offer a hands-on, interactive physics course for non-majors. During the summer of 1998, Majumder supervised four students in the summer research program. Leo Tsai '98 stayed on for the summer after his senior year to complete his thesis research project (results to appear in the journal, Physical Review A in July, 1999). Also during the summer, Rob Lyman '99 began his thesis work, while Alex Jarvis '99 and J.J. Ackles (Vassar) '99 spent their summer completing a number of laboratory projects. During the academic year, Prof. Majumder again organized the department colloquium series.

With the aid of funds from a new NSF/RUI grant, Dr. David S. Richardson joined the Majumder research group and the department in December as a postdoctoral research associate. Dr. Richardson recently received his D. Phil. in experimental physics from the University of Birmingham, UK, and will be working closely with Prof. Majumder and his research students on all aspects of the experiments. The Majumder group continues to pursue thallium laser spectroscopy experiments in his atomic physics lab. A better understanding of the structure of this complex atom is essential to be able to interpret recent precise measurements of parity nonconservation in thallium in terms of fundamental physics. Rob Lyman '99 completed a successful thesis project in which he completed construction of a new atomic beam apparatus (worked on previously by Julie Rapoport '97 and Peter Nicholas '98). Rob also helped to bring on-line a new frequency-doubled diode laser system, and used the UV light to obtain our first spectroscopic data of the thallium 6P1/2 - 7S 1/2 transition at 378 nm.

In October, Professor Majumder gave a pair of general-audience lectures on his research for the Williams College Sigma Xi Lecture Series titled "Tests of Fundamental Symmetries and Searches for New Physics: I. Recent History and II. Current Atomic Experiments".

In March, Majumder, Lyman, and Richardson (along with 11,000 other physicists!) attended the exciting Centennial Meeting of the American Physical Society in Atlanta, GA, at which they presented two posters on current experimental work.

Emeritus Professor David Park, encouraged by the success of The Fire Within the Eye, has begun to think about a new book, to be known as The Grand Contraption. What it will be about is anybody's guess.

Associate Professor Jefferson Strait served as chair of the department this year. In addition to the routine duties of a chair, he spent a good deal of time planning for the Physics Department's part of the science facility renovation and expansion project. While the department will not occupy space in the new building, we are excited about converting the present Physics and Astronomy library space into an introductory teaching laboratory named after Professor David Park. Also we look forward to a 2,800 square foot laser research laboratory that will be constructed in the Bronfman Science Center.

Strait and his students have built an optical fiber laser designed to produce pulses of light about 10^-12 seconds long. Unlike most lasers which use mirrors to confine light to the laser cavity, an optical fiber laser uses a loop of fiber as its cavity. A section of fiber doped with erbium serves as the gain medium. Strait and his students pump the gain medium with 1.06 µm light and it lases at 1.55 µm, conveniently the same wavelength at which optical fiber is most transparent and therefore most suitable for telecommunications. During the summer of 1998, Allegra Martin '99 and Meredith Dill (Brown University '00) improved stability of the laser and prepared to measure its pulse duration. Clay Stein '00 and Adam Halverson (Reed College '00) will continue this work during the summer of 1999. The eventual goal is to study how these short pulses propagate in optical fiber.

Strait attended both the fall and the spring meetings of the American Physical Society New England Section as a member of its Executive Board. He also served as the pre-engineering advisor at Williams.

Professor William Wootters continued his theoretical research on quantum entanglement (a peculiarly quantum mechanical kind of correlation between two objects), collaborating not only with students but also with researchers at IBM's Watson Research Center. In the summer of 1998, he worked with two students from other institutions, Nurit Baytch of Harvard and Alex Wong of Carleton, who were supported by the department's Research Experiences for Undergraduates grant. Together they made progress towards generalizing a formula derived earlier by Prof. Wootters and Scott Hill '97, which expresses the amount of entanglement contained in a state of two simple quantum particles such as electrons.

Prof. Wootters developed and taught three new courses during the 1998-1999 academic year: How Things Work, a technologically oriented course for a general audience; Mathematical Methods for Scientists, an up-to-date version of a course the department had taught many years ago and revived this year; and, with Prof. Susan Loepp of the math department, a new interdisciplinary winter study course called Building and Cracking Codes: How Will We Protect Information in the Coming Centuries?

• Brian Gerke '99
• Robert Lyman '99
• Allegra Martin '99
• Laura Brenneman '99
• Ian Eisenman '99
• Alexander Jarvis '99
• Ginel Hill '00
• Sara Kate May '00
• Rebecca Cover '00
• Mark Acton '00
• Andrew Speck '00
• Kevin O'Connor '00
• Kevin Russell '00

 

Chad Orzel '93, National Institute of Standards and Technology/University of Maryland

Dr. Steve Peil, Harvard University

Dr. Andres Corrada-Emmanuel, Dragon Systems, Inc.

Prof. Michael Brenner, Massachusetts Institute of Technology

Prof. A. Nihat Berker, Massachusetts Institute of Technology

Prof. David Goldsman, Georgia Tech School of Industrial and Systems Engineering

Benjamin Evans '96, MIT/WHOI Joint Program in Oceanography and Applied Ocean Science and Engineering

Prof. Kiko Galvez, Colgate University, Physics Department

Dr. Maureen Fahey, 3M Corporation, Austin, Texas

Prof. Rob Carey, Boston University, Physics Dept.

Dr. John Birmingham, Brandeis University - Volen Center

Prof. Daniel Aalberts

Prof. Sarah Bolton

Prof. Kevin Jones

Prof. Protik (Tiku) Majumder

Prof. William Wootters

PHYSICS

• Ian L. Eisenman: Research assistant with Prof. Daniel Aalberts, Williams College; then graduate school in physics
• Brian F. Gerke: Two years as a Herchel Smith fellow at Cambridge University (UK) studying mathematics; then physics graduate school in the U.S
• Andrew D. Henderson: Teach for 1 year in a Catholic school in South Central Los Angeles, CA; then graduate school in environmental engineering (most likely Clemson or University of Texas)
• Alexander C.R. Jarvis: Uncertain
• Robert N. Lyman: Living in Germany for one year; then graduate school in physics
• Allegra L. Martin: Working in Boston, MA

ASTROPHYSICS

• Laura W. Brenneman: Uncertain
• Jeremy D. Burr: Investment banking at a mergers and acquisitions boutique headquartered in Los Angeles, CA
• Craig C. Westerland: Ph.D. program in mathematics at the University of Michigan

Astrophysics

The question of how spiral galaxies evolve over their lifetimes is a focal point in the modern study of cosmology. Given what we now know -- that our own world resides within the delicate framework of such a galaxy -- our pursuit of an answer to this query is personally relevant as well as scientifically compelling. Each year, more studies are conducted, searching for these solutions through a variety of different methods. Herein, I present the results of my own work on one such project, which I began involvement with during my internship at the Hubble Space Telescope Science Institute in the summer of 1998. Working with Dr. Paul Goudfrooij and using data obtained with the WFPC2 (Wide Field and Planetary Camera 2) instrument on the Hubble, I examined the globular cluster populations (GCPs) in the halos of several edge-on spiral galaxies of varying Hubble types. The goal of this project is ultimately to find a relationship between the characteristics of the globular cluster populations and the type of central bulge in their parent galaxy. This technique, if successful in finding such a relationship, would prove useful in the future for gauging the age and stage of evolution of other nearby observable spiral galaxies. Chapter one is an introduction to galaxies and how we observe them. The next two chapters discuss how a spiral galaxy in particular is formed, and how we have arrived at our current theories of galactic evolution, also highlighting the ideas behind using globular cluster populations as a "smoking gun" to tell us more about changes in galactic morphology over time. Observations, data reduction and analysis consume chapters four and five, and our most recent results and conclusions are presented in chapter six.

Physics

Photoisomerizations are light-induced shape-changing reactions. They occur with striking speed in many conjugated polyenes. Although many theoretical studies of conjugated polyenes have been undertaken, a theory that satisfactorily describes these striking dynamical behaviors has remained elusive. We present a model aimed at illuminating the mechanism behind ultrafast photoisomerization. We find that competition between electronic and steric interactions, as well as the quantum mechanical correlations of the electrons are both important contributors to these reactions. As a test of the model, we present a complete calculation for the simple case of ethylene, where we find that the molecule's shape-change reaction proceeds within approximately 30 fs, in good agreement with experiment. We also present preliminary calculations for longer molecules, which also look promising.

We have undertaken a measurement of the excited state hyperfine splitting and isotope shift of the 6P_1/2 Æ 7S_1/2 transition in atomic thallium using a frequency-doubled diode laser. The operation of the experimental apparatus is explained and current preliminary experimental results are presented. Continuing work on an atomic beam, which offers dramatically reduced linewidth and enables a measurement of the Stark shift on this transition, is described.

Physics

Physical Review B 58, 16326 (1998)

To study the effects of confinement by quantum-well potential discontinuities on ultrafast carrier dynamics, we performed pump-broadband probe studies of a series of InGaAs quantum wells excited 30 meV above the band edge. Our measurements show that the rate of carrier thermalization is well width independent, however, the rate of carrier cooling to the band edge is strongly influenced by confinement. This influence has two separate physical origins. First, the dimensionality dependence of the density of states results in a larger proportion of thermalized electrons that can emit LO phonons in three dimensions than in two. Second, modification of the phonon density of states by the ionic mass discontinuity at the well boundaries may reduce the electron-LO-phonon coupling.

Journal of the Optical Society of America, B 15, 2847 (1998)

We study the effect of cavity topology on the nonlinear dynamics of additive-pulse mode-locked (APM) lasers configured in the Fabry-Perot and Michelson geometries. In experiments the Fabry-Perot laser often exhibits such behaviors as period doubling and quasiperiodicity as the nonlinearity is increased, whereas the Michelson APM (M-APM) exhibits none of these effects. Numerical studies confirm that the M-APM appears to be more resistant to such behavior, and thus is more tolerant of excessive nonlinearity in the control cavity. Using the concepts of intensity- and phase-dependent two-beam and multiple-beam interference, we obtain a general empirical rule connecting cavity topology to pulse train instabilities for fast saturable absorber modelocked lasers employing coupled cavities.

Journal of the Optical Society of America, B 16, 339 (1999)

We made pulse resolved observations of subharmonic oscillations in the pulse train of a Kerr lens model locked Ti:Sapphire laser. Pulse-resolved beam profiles demonstrate that these oscillations, which include period doubling as well as P3, P4, and quasi periodicity, are accompanied by spatial modulation of the beam. A pulse resolved autocorrelation technique, believed to be novel, is used to show that temporal pulse reshaping does not accompany these dynamics. The power dependence of subharmonic oscillation frequencies exhibits the frequency locking characteristic of nonlinear dynamics in systems of coupled oscillators.

Physical Review E, 58, 5934-5947 (1998)

Journal of Chemical Physics, 110, 8825-8834 (1999)

Physics Review A, 60, (to appear July 1999)

We have measured the ratio of the electric quadrupole (E2) to magnetic dipole (M1) transition amplitude within the 6P1/2 Æ 6P3/2 transition in atomic thallium. We find that c E2/M1 = 0.2387 (10) (38), where the first error is statistical and the second represents a combined systematic error. In addition to providing a stringent test of theoretical wavefunction calculations in thallium, accurate knowledge of this amplitude ratio is essential for existing and future measurements of parity nonconserving optical rotation on this same 1283 nm line in thallium.

Phil. Trans. R. Soc. London A, 356, 1717-1731 (1998)

Quantum mechanical objects can exhibit correlations with one another that are fundamentally at odds with the paradigm of classical physics; one says that the objects are "entangled." In the past few years, entanglement has come to be studied not only as a marvel of nature but also as a potential resource, particularly as a resource for certain unusual kinds of communication. This paper reviews two such uses of entanglement, called "teleportation" and "dense coding." Teleportation is the direct, though not instantaneous, transfer of a quantum state from one object to another over a distance. Dense coding is the effective doubling of the information-carrying capacity of a quantum particle through prior entanglement with a particle at the receiving end. The final section of the paper presents various quantitative measures of entanglement and considers novel features that arise when entanglement is shared among three objects.

Physical Review A, 59, 1070-1091 (1999)

We exhibit an orthogonal set of product states of two three-state particles that nevertheless cannot be reliably distinguished by a pair of separated observers ignorant of which of the states has been presented to them, even if the observers are allowed any sequence of local operations and classical communication. It is proved that there is a finite gap between the mutual information obtainable by a joint measurement on these states and a measurement in which only local actions are permitted. This result implies the existence of separable superoperators that cannot be implemented locally. A set of states is found involving three two-state particles that also appear to be nonmeasurable locally. These and other multipartite states are classified according to the entropy and entanglement costs of preparing and measuring them by local operations.