MIT Reports to the President 1994-95

Department of Physics

During the past year, the Physics Department maintained its position as a leader across the frontiers of physics research. A flavor of these activities is given in the brief accounts later in this report and in the more detailed reports from laboratories with significant physics participation. On the academic side, several new and continuing thrusts speak to the department's commitment to its educational program.

The members of the Physics Department continue to provide leadership for major MIT interdepartmental laboratories. Currently, the Directors of the Laboratory for Nuclear Science (LNS), Bates Linear Accelerator Center, Center for Space Research (CSR), Center for Materials Science and Engineering (CMSE), Plasma Fusion Center (PFC) and Harrison Spectroscopy Laboratory are members of the Physics Department, as well as the Associate Director of the Research Laboratory of Electronics (RLE). In addition, Professors Robert J. Birgeneau and J. David Litster serve as Dean of the School of Science and Vice President and Dean for Research, respectively. In 1994-95 the total number of faculty was 83. Roger Brooks, Lisa Randall, Paras Sphicas and Xiao-Gang Wen were promoted to Associate Professor without tenure, Richard Milner was promoted to Associate Professor with Tenure. Two Assistant Professors joined our faculty: Takashi Imai and Uwe-Jens Wiese along with one Associate Professor without tenure: Peter Fisher. Faculty on leaves or sabbaticals during this year included: Min Chen, Kerson Huang, Paul Joss, Mehran Kardar, John King, Ali Javan, Paul Schechter, Toyo Tanaka and Jonathan Wurtele. Professor George Bekefi retires from the Physics faculty on July 1, 1995, and Associate Professor Jonathan Wurtele and Assistant Professor Charles Steidel are leaving MIT for other positions.

This has been an extraordinary year for awards and prizes for physics faculty, starting with the 1994 Nobel Prize in Physics awarded to Professor Emeritus Clifford Shull. Four physics faculty garnered major APS awards this year: Professor George Benedek received the Langmuir Prize in Chemical Physics, Professor Roman Jackiw claimed the Dannie Heineman Prize for Mathematical Physics, Associate Professor Jackie Hewitt was awarded the Maria Goeppert Mayer Award, and CMSE Director Marc Kastner received the Adler Award. Professor Henry Kendall was one of seven recipients of the Majorana Science for Peace Prize given by the Centre for Scientific Culture (Italy). The very distinguished Japanese Inoue Prize for Science was given this year to Professor Toyo Tanaka. Assistant Professor Ray Ashoori received the McMillan Award for his work on quantum dots and Assistant Professor Wolfgang Ketterle was the second recipient of the Michael and Philip Platzman Award. Professor Patrick Lee will be on sabbatical next year enjoying his recently received Guggenheim award. Two faculty were recognized by the Institute for their contributions: Professor Daniel Kleppner received the Killian award while the Edgerton award went to Associate Professor Jackie Hewitt. Professor Nihat Berker was recognized with the School of Science Graduate Teaching Award. Professor John Belcher was awarded the Physics Department Buechner Prize for excellence in Teaching. Professors Wit Busza and Tom Greytak joined the ranks of the Institute's MacVicar Fellows. Roman Jackiw was appointed to the Jerrold Zacharias Professorship of Physics. Two junior faculty, Tomas Arias and Takashi Imai were awarded Alfred P. Sloan Foundation Awards, and Assistant Professor Leslie Rosenberg received one of the first NSF "Career" Awards.


The Department continues to maintain a steady number of graduate , undergraduate students and number of credit units per faculty member. This year the number of undergraduate majors was 194 and the number of graduate students was 264. The number of degrees awarded totaled 53 S.B., 3 S.M., 53 Ph.D.

A number of changes took place in the educational program this year or are in the planning stages for implementation over the next several years. The most significant change was in the format of 8.01 which focuses on small classes of no more than 16 students, one plenary lecture per week, formal tutoring sessions, weekly quizzes, and using a study guide in conjunction with a text to help students work through appropriate materials. Student reaction to the new format was mixed, but faculty reaction was enthusiastic. They recommended adding an extra class session, once a week, at which the assigned problems would be discussed. This suggestion will be incorporated in next year's scheduling for 8.01.

8.01L , the extended version of 8.01 completed its third year this Fall. Students continue to be enthusiastic both about its instructors and about the extended time schedule. Part of the academic success of the program is the intensive use of course tutors; each student must spend a half hour with a tutor each week. This year, most of the students in 8.01L had done poorly on the math diagnostic, suggesting that the department is capturing the appropriate population for the course.

The new physics curriculum takes effect for students declaring a physics major in Fall, 1995. As previously reported, the new curriculum adds an intermediate mechanics course in the second year and a third quantum mechanics course to allow the infusion of contemporary applications and examples into the three-term sequence. In addition, students will be required to take one of two IAP courses: advanced mechanics or advanced project laboratory.

The Advanced Project Laboratory was piloted during the past IAP. This course was designed for physics majors who have taken at least the first three courses in the physics sequence. Students are encouraged to use computers on-line for data acquisition whenever possible. Normally, students work in pairs as a research team, proposing a project based on physics phenomena they have learned and would like to investigate. The teaching staff monitors the feasibility of the projects based on time limitations, degree of difficulty of the project, availability of equipment, and background in technical experience and laboratory work of the students.

Changes in the graduate curriculum are being phased in this year. Core requirements have been developed in each subunit (condensed matter, atomic, astrophysics, nuclear and particle experiment, nuclear and particle theory and plasma) that present students with a coherent set of courses in these areas.


The range of high quality forefront basic research activities pursued by the MIT physics faculty is unmatched at any other physics department. This is reflected in the large number of Institute laboratories and centers which support substantial research programs of the Physics faculty. The reports from the Laboratory for Nuclear Science, including the Bates Linear Accelerator Center and the Center for Theoretical Physics, the Center for Materials Science and Engineering, the Research Laboratory of Electronics, the Center for Space Research, the Plasma Fusion Center, the Harrison Spectroscopy Laboratory, and the Haystack Observatory should be consulted for a more complete description of some of these research programs. We can provide only a brief overview in the space made available here.


Research in Astrophysics deals with our attempts to understand the universe on the largest scales. Phenomena ranging from solar oscillations, to accreting black holes in the galaxy, to quasars at cosmological distances are studied. Observational programs involve the collection, analysis, and interpretation of data from a wide variety of ground-based and space-based observatories. Theoretical research is carried out on a wide range of topics that are both complementary to, and independent of, the observational program.

X-ray astronomy continues to be a major area of research. Observational programs utilize the Japanese satellite ASCA, which features a CCD imaging X-ray detector developed at MIT, as well as the German satellite ROSAT. The X-Ray Timing Explorer satellite, containing an all-sky monitor developed at MIT will be launched in the near future. Binary systems with accreting compact objects (e.g., neutron stars), hot plasma in supernova remnants, clusters of galaxies containing dark matter, distant quasars, and the cosmic X-ray background are being actively studied.

Searches for new gravitational lenses, including "Einstein rings", are a major activity of the radio astronomy group. Gravitational lenses provide a probe of the lensed object as well as of the dark matter within the lensing galaxy, and can lead to a determination of the Hubble constant. The VLA radio interferometer in New Mexico is used in many of these studies.

MIT optical astronomers utilize the Michigan-Dartmouth-MIT observatory in Arizona, as well as other telescope facilities around the world. Luminous stars that act as 'standard candles' are being used to map the structure of our Milky Way Galaxy. Several programs aimed at identifying extragalactic objects found in the radio and X-ray bands are underway. Large scale flows in the universe are being investigated with a newly developed fluctuation-distance-indicator technique which yields relative distances accurate to ~5%.

Development work continues on LIGO, a collaborative project of MIT and Caltech to construct a laser interferometer gravitational wave observatory with two 4-km baseline facilities capable of detecting gravity waves from astrophysical sources. LIGO management has been changed substantially. It is anticipated that the LIGO observatory will be operational by the year 2000.

The MIT Plasma Science Experiment on board Voyager 2 continues to measure the properties of the solar wind in the distant heliosphere, and will be the first spacecraft to directly measure plasma conditions in the very local interstellar medium.. A new plasma experiment was recently launched on the WIND satellite which is part of the International Solar Terrestrial Physics program designed to study the nature of solar-terrestrial interactions.

Theoretical research in helioseismology is leading to a better understanding of the internal structure of the Sun, e.g., its internal differential rotation. Theoretical studies are continuing of the formation and evolution of binary systems containing collapsed stars, including "recycled pulsars" and the newly discovered class of "supersoft" X-ray sources. Numerical simulations of cosmic structure formation, including the use of large N-body simulations, and high precision calculations of microwave background fluctuations are being extensively investigated. Activities in theoretical astrophysics have been substantially broadened and bolstered by the appointment of two junior faculty members - Pawan Kumar (three years ago) and Fred Rasio (this year).

Nuclear and Particle Experiment

Nuclear and particle physicists are working to uncover the fundamental particles and forces and to understand how these yield the properties of the strongly interacting matter which makes up nearly the entire mass of the visible universe. These studies are intimately related with cosmological studies of the early universe.

In Intermediate Energy Nuclear Physics, electron scattering research programs included measurements of the neutron charge and magnetization distribution, studies of quasi elastic electron-proton scattering in nuclei at high momentum transfer and high missing energies, study of the phenomenon known as "color-transparency" and use of parity non-conservation as a novel probe of proton structure. Complementary studies of pion-induced reactions are being carried out at Los Alamos and at PSI (Switzerland). The Hermes experiment , under the co-leadership of MIT Prof. Richard Milner, is beginning data taking at the HERA collider at DESY. This experiment uses novel polarized He3 gas targets in conjunction with the polarized electron beam of HERA to, study the spin structure of the neutron.

At Bates, work continued on commissioning the South Hall Ring and on improving the reliability of the accelerator. Important future initiatives are: use of the new Bates Out-Of-Plane Spectrometer and Focal Plane Spectrometer; and the completion of the high resolution spectrometer system for CEBAF.

In Heavy Ion Physics, with the installation of Au beams at the Brookhaven AGS, the systematic study of nucleus-nucleus collisions was extended into the region of higher matter density. A new initiative was started at CERN's heavy ion facility by one of the junior faculty members, Bolek Wyslouch, to search for evidence of the creation of different states of the vacuum. This program is now in the data taking phase.

Following the approval from BNL, the design and construction of the PHOBOS detector began under MIT leadership. It will exploit the opportunities offered by the new collider, RHIC, at BNL. Also at BNL, collaboration in an experiment has been undertaken in the search for strange matter produced in heavy ion collisions.

In Particle Physics, the current research included:

A new proposal led by MIT scientists to study the flux of anti-matter in the cosmic radiation using a permanent magnet spectrometer on a space vehicle(space shuttle/station) has been favorably received by the scientific community and the funding agencies.

Significant effort was spent in exploring the research opportunities at the future accelerator LHC planned at CERN. Involvement in the construction of the world's largest underground cosmic ray laboratory at Gran Sasso, the development of novel nuclear and particle detectors.

Finally, a novel axion search has been mounted in a collaboration with Livermore and others under the leadership of Prof. Leslie Rosenberg, a junior faculty member. This experiment is now being commissioned and data taking should start in the near future.

Nuclear and Particle Theory

Research at the Center for Theoretical Physics seeks to extend and unify our understanding of the fundamental constituents of matter and the theory that governs them. In addition, it uses our present knowledge of this theory to advance our understanding of a variety of subjects, including the structure and interactions of hadrons and nuclei, new forms of matter which may be created experimentally or observed astrophysically, and the behavior of the early universe.

String theory aims to unite the strong, electroweak, and gravitational interactions and to explain the observed hierarchy of particles and interactions. An important contribution at MIT has been the development of a general field theory of closed strings. This theory has now been shown to be independent of the background field that is used in its construction and has been used to calculate off-shell amplitudes. Finite temperature effects have been incorporated into string theory, leading the way to the study of cosmology and radiation from black holes.

Topological terms in field theories, which were introduced by this group several years ago, are now widely studied in problems ranging from gravity to high temperature superconductivity. Recently, these terms were shown to play an important role in QCD at high temperature and used to understand the response function in the quark-gluon plasma.

The role of underlying quark and gluon degrees of freedom in hadrons, hadronic interactions, and nuclear structure is of fundamental interest. New formulations of Yang-Mills gauge theory have been developed in terms of gauge-invariant and geometric variables, and the possibility of observing new multiquark resonances in hadron scattering has been studied.

A major recent thrust has been in the area of lattice gauge theory, which provides a unique tool to solve, rather than model, QCD. Recently, lattice actions have been derived which are free of finite cut-off effects and greatly improve the accuracy with which quarks can be treated in practical calculations. Lattice calculations have also provided strong evidence that the structure of nucleons, pions and other light hadrons is dominated by topological excitations of the gluon field. To exploit the opportunities in this field, a development project to build a Teraflops computer at MIT is continuing in partnership with the Laboratory for Computer Science, Sun Microsystems, and a national collaboration of physicists.

MIT has played a pioneering role in exploiting high energy scattering to determine the quark and gluon structure of nucleons and nuclei. Significant developments include complete classification of observable structure functions and fragmentation functions, the discovery of new ways to measure spin dependent structure functions, and the study of higher twist contributions in the new regime to be studied at CEBAF.

While the Standard Model of Particle Physics is consistent with all reliable experiments, most physicists are nonetheless convinced that it is only the low-energy approximation to a fundamentally simpler theory. An attractive proposal is that the underlying theory includes a set of relationships between integer-spin and half-integer-spin particles known as supersymmetry. CTP theorists have developed several extensions of the Standard Model, including extended Technicolor and supersymmetric models, which agree with known data and make testable predictions. The "Minimal Supersymmetric Extension'' of the Standard Model has also been extensively pursued, with the goal of extracting predictions that can hopefully be tested in future experiments.

To supplement the knowledge that can be gained from accelerators on Earth, particle theorists have turned to the early universe as a testing ground for ideas about high energy interactions. CTP researchers have found that, even in an exactly supersymmetric theory, the differences in the high temperature behavior of integer and half-integer spin particles would lead to a breakdown of supersymmetry in the early universe. There are many consequences, including a new theory of how the universe developed its excess of matter over antimatter.

A subtle feature of the Standard Model is the violation of baryon number conservation, a process which is very improbable under normal circumstances but which becomes large at temperatures above 1016 K. Standard treatments relate the number of baryons produced to a certain integral over the electroweak fields of the theory, but CTP researchers discovered several years ago that this integral is not always an integer. Further studies have shown that the number of baryons produced can be related to the Higgs fields of the theory, in a way that guarantees that the result will be an integer.

Electroweak nuclear interactions are a continuing focus of research. The unique opportunities provided by the new ring at the Bates accelerator have motivated studies of reaction mechanisms, of new ways to use nuclei to test fundamental symmetries, and of spin and polarization observables. The use of neutral current probes to study the strange quark content of the nucleon has been studied. Anti-neutrino and heavy-flavor neutrino production from the sun have been studied to obtain new information on the solar neutrino anomaly and neutrino mixing.

Efforts have continued to understand the nature of periodic solutions in multi-dimensional classical systems and their implications for quantum chaos. Nuclear reaction theory has been used to study parity violation and time reversal symmetry violation in low energy neutron scattering, compound nucleus enhancements in photon production by proton-nucleus scattering, and multi-step compound reactions.

Atomic, Condensed Matter, and Plasma Physics

The past year has been particularly fruitful for researchers in the Division of Atomic, Plasma and Condensed Matter Physics. 'Atom' interferometry has advanced to the stage where molecules can be made to produce sharp interference fringes. Using micro-fabricated gratings, a beam of sodium molecules (Na2 ) is split into two spatially separated beams and then recombined. Changes in the conditions in one of the two paths, such as the presence of a gas of other atoms or an electric field, causes a shift in the phase of the interference pattern. Micro-lasers have been pushed to a new extreme with the demonstration of oscillation in the visible region with less than one atom at a time in the cavity. Correlation of the number of photons emitted per second with the mean number of atoms in the cavity reveals significant differences with predictions of the best current theoretical models. The photoionization spectrum of lithium atoms has been used to study the transition from classical to quantum behavior in a simple, well characterized system. Combined theoretical and experimental investigations provide a detailed physical picture of how the system evolves from one extreme to the other, and give insight into the connections between classical and quantum behavior in chaotic systems as well.

Scientists at MIT are world leaders in understanding the physics of gels. This basic understanding has produced yet another practical application. A gel has been used in a reversible cycle to extract a specific targeted ion from a dilute solution and release it on command in another solution, which could have a high concentration of the ion. It is anticipated that this cycle can be applied to a number of industrial and environmental problems. The aqueous protein solutions present in mammalian eyes are being studied in connection with diseases such as glaucoma and cataracts. These solutions also present model systems for studying critical phenomena in binary solutions composed of large macromolecules and water. A detailed study of the dynamic critical behavior near the phase separation point has shown significant deviation from the behavior characteristic of binary solutions composed only of small molecules.

MIT physicists, collaborating with a group from Stanford University, have used ultra-violet photoemission spectroscopy to map out the dispersion relation for the electrons in a proto-typical high temperature superconductor. The results demonstrate that conventional band theory calculations are inadequate to explain the dynamics of the electrons in these strongly correlated systems. One of the forefront areas in mesoscopic physics concerns `artificial atoms', carefully shaped two dimensional wells in semiconductor hosts. Experimenters and theorists have combined efforts to study an 'atom' with about 30 electrons. They find that Hartree-Fock theory provides a quantitative description of the spin dynamics of the electrons whereas a semiclassical electrostatic model does not. In particular, it explains a divergent spin susceptibility observed at particular values of the magnetic field. The technique of photon correlation spectroscopy has been extended into the x-ray region of the spectrum. The dynamics of an order-disorder transition in the alloy Fe3 Al were probed using x-rays from an undulator-based synchrotron source. The experiments were able to resolve correlation times as long as 1000 seconds for the critrical fluctuations, corresponding to a frequency resolution of 3 times 1021 relative to the X-ray frequency of 3 times 1018 Hz.

In the phenomenon of electronic tunneling into metals there is an anomaly near zero bias (associated with the Coulomb interaction between the electrons) which causes a suppression of the tunneling current. A general theory of tunneling has been developed which is valid even when the Coulomb suppression is strong. This allows the theory to be applied to a number of physical situations which have appeared at the forefront of condensed matter research where the Coulomb effects dominate the behavior, for example disordered metals and semiconductors near the metal-insulator transition and tunneling into two-dimensional electron gases. The discovery of photonic band-gap materials has given rise to many new and ingenious techniques for controlling the propagation of light. MIT's pioneering work in this area has given rise to the first textbook on the subject: Photonic Crystals, published by Princeton University Press.

Ernest J. Moniz

MIT Reports to the President 1994-95