## Schedule Spring 2001

**February 2, 2001**

3:00 pm (Friday)

**Dr. Marty Blume**

Editor-in-Chief, American Physical Society and Senior Physicist, Brookhaven National Laboratory

The Physical Review and Physics Publishing: Past and Future

The Physical Review has a remarkable history going back to its founding in 1893. The articles published in its pages have changed our view of the universe and the way we live. We are now in the midst of an electronic revolution in the distribution of the results of physics research, and physicists are playing a leading role in determining the directions of that revolution. This presentation focuses on the past of physics publishing and on new directions. The golden future can be visualized, albeit dimly, but there are many pitfalls in the path to that future. In this talk, with a demonstration of live electronic access, some of these will (with bad luck) be illustrated. So too (with good luck) for the new capabilities.

**February 16, 2001**

3:00 pm (Friday)

**Dr. Marjana Bozic**

Institute of Physics, Beograd, Yugoslavia

Matter Waves from Schrödinger to Quantum Bit

Theoretical and experimental research, motivated by the need to clarify and determine the meaning of the wave function and the nature of distant correlations, is reviewed. About the meaning of the wave function we note three characteristic periods. In the very beginning, Schrödinger and Louis de Broglie argued that the wave function described real waves whose physical nature was unknown. This understanding was followed by the view which denied objective reality of waves described by the wave function. Recently introduced notion qubit, together with the new approach to the EPR paradox, distant correlations and quantum interference, returned us to the understandings of Schrödinger and Louis de Broglie.

**February 23, 2001**

3:00 pm (Friday)

**Prof. Larry Schulman**

Clarkson University

Opposite Thermodynamic Arrows of Time

A model in which two weakly coupled systems maintain opposite running thermodynamic arrows of time is exhibited. The essential conceptual step is the phrasing of the problem as a two-time boundary value problem. Each system experiences its own retarded electromagnetic interaction and can be seen by the other. Causal paradoxes and causality are examined. The possibility of opposite-arrow systems at stellar distances is explored and a relation to dark matter suggested.

**March 20, 2001**

3:00 pm (Tuesday)

**Prof. Colm T Whelan**

Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, UK

Inelastic Electron Scattering from Atoms

An (e,2e) measurement is one where an electron, of well-defined energy and momentum, is fired at a target, ionizes it and the two exiting electrons are detected in coincidence. The energies and positions in space of these electrons are determined by the experiment so in effect all but the spin quantum numbers are then known. We can, therefore, describe it as a kinematically complete experiment; if we could also measure all the spins we would have all the information on a scattering experiment that quantum mechanics will allow. The technique offers both the possibility of a direct determination of the target wave function and profound insights into th nature of few body interactions. What information you extract from such an experiment really depends on the kinematics you chose and the target you use. What is measured is the cross section, i.e. the ratio of the number of measured events corresponding to two final state electrons being detected at fixed position in space with well defined energies per unit time per unit scatterer as compared to the incident flux. Technically we are talking here about a triple differential cross section as opposed to one where we have integrated over one or more electron co-ordinates. Integrated cross sections can be crude things and you need the full power of a highly differential measurement to tease out the delicacies of the interactions. In the last few years, revolutionary advances in experimental techniques and spectacular increases in computer power have offered unique opportunities to develop a much more profound understanding of the atomic few body problem.

In this talk I will consider a) (e,2e) processes with relativistic electrons on the inner most shells of heavy atoms b) double excitation processes: (e,3e), excitation-ionization and related processes I will, briefly, discuss inelastic imaging in the Scanning Transmission Microscope (STEM). The STEM is primarily designed to give spatial information while the (e,2e) technique hopes to yield information about the momentum space wave function of the target. The techniques are therefore complementary.

Examples of how the methods of atomic physics can be applied to good effect in a bulk environment will be given.

**March 23, 2001**

3:00 pm (Friday)

**Prof. Vladimir Privman**

Department of Physics, Clarkson University, Potsdam, NY

Solid-State Quantum Computing in Semiconductor Structures

Quantum information processing is an exciting new paradigm that has generated new emphases and trends in solid-state physics. We offer a general overview of the subject, followed by a survey of our recent work on quantum computing in semiconductor heterostructures. We describe the status of this field and summarize modeling of decoherence, relaxation, and interaction properties in systems which are candidate for quantum computing implementations. Results include systematic investigation of interactions and decoherence in semiconductor quantum wells and heterojunctions, with initial applications for nuclear spins as quantum bits.

**March 27, 2001**

3:00 pm (Tuesday)

**Prof. Mark Novotny**

Center for Computational Science and Information Technology, Florida State University, Tallahassee

Parallel Discrete Event Simulations: A Physicist's Perspective

Discrete Event Simulations (DES) are used in a large number of engineering, scientific, military, and manufacturing applications. Our application is to use a type of DES known as kinetic Monte Carlo to study dynamics of nanoscale ferromagnets. I will introduce DES, and the idea of `virtual time' which is used in parallel DES (PDES) simulations. The importance of avoiding causality violations in PDES will be described, and both the conservative and optimistic approaches to causality violations introduced. One important question to be addressed is the scalability of PDES algorithms, i.e. the computer simulation time required as the number of processing elements and the problem size grow. A recent connection [1] between non-equilibrium surface science and the PDES `virtual time' allows questions of scalability to be addressed. For example, we have recently proven in 1-dimension that ALL conservative short-ranged PDES are scalable for the computation portion of the algorithm [1]. This is independent of the specific PDES problem. I will present numerical evidence that this is also true for PDES in higher dimensions [2]. Methods [3] to make both the computation and the measurement portions of ALL short-ranged PDES scalable will be described.

**March 30, 2001**

3:00 pm (Friday)

**Prof. Klaus Bartschat**

Department of Physics and Astronomy, Drake University, Des Moines, Iowa

Electron Collisions with Atoms and Ions: Recent Developments in Theory, Experiment, and Computer Simulations

Recent developments in the formal description and the numerical treatment of electron collisions with atoms and ions, together with the rapid growth in computer hardware, have opened the opportunity for benchmark comparisons between experimental data and theoretical predictions. In this talk, basic experimental setups to study excitation, ionization, and simultaneous ionization--excitation will be introduced, together with the principal ideas behind state-of-the-art numerical methods used in this field. Furthermore, the reliability of currently available atomic data for electron collisions will be critically assessed. Finally, ways of visualizing the outcome of atomic collision processes by using animated computer graphics to represent the charge cloud of collisionally excited atomic states (see http://bartschat.drake.edu/dloveall for details) will be shown.

**April 6, 2001**

3:00 pm (Friday)

**Dr. Mark M McKinnon**

National Radio Astronomy Observatory, Greenbank, West Virginia

The Orthogonal Modes of Polarization in Pulsar Radio Emission

The polarization properties of the individual pulses from pulsars have been observed in an attempt to understand the radio emission mechanism of pulsars. Upon conducting these observations, one finds that the emission actually consists of two modes of orthogonally polarized radiation. The large variations in the emission's degree of polarization and the random switching between modes suggest that the interaction of the modes is a stochastic process. Indeed, a simple statistical model that describes the emission as the simultaneous interaction of two completely polarized, orthogonal modes can reproduce the observed polarization properties of the emission. The statistical model can be used to determine the intrinsic polarization properties of the orthogonal modes. The superposition of the modes can also account for the observed depolarization of the radio emission.