Events at Physics |
Events on Thursday, April 23rd, 2009
- R. G. Herb Condensed Matter Seminar
- BCS-BEC Crossover in Ultracold Atoms: Quantum Fluctuations and Vortices
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Mohit Randeria, Ohio State University
- Abstract: I will first introduce the problem of the BCS-BEC crossover in a Fermi gas with arbitrary interactions and describe the progress in realizing these ideas in experiments with ultracold atomic gases. I will then discuss three questions: (1) How quantum fluctuations about the mean field state impact observable properties in the crossover; (2) How the vortex and core states evolve from the BCS to the BEC limits; (3) Why the most strongly interacting regime at unitarity leads to the most robust superfluid in the entire crossover.
- Host: Andrey Chubukov
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Poincare Invariant Three-Body Scattering
- Time: 1:30 pm - 2:25 pm
- Place: 4274 Chamberlin
- Speaker: Charlotte Elster, Ohio University, Athens
- Abstract: An enormous effort has been made to understand and model the nuclear force. The next step is to apply those models in an environment where three (or four) nucleons interact with each other and thoroughly test underlying assumptions of nuclear physics.
Traditionally three-nucleon calculations are carried out by solving Faddeev equations in a partial wave truncated basis, working either in momentum or coordinate space. We solve them directly as function of vector variables. The key advantage of our approach lies in its applicability at higher energies, where special relativity is expected to become relevant. We investigate relativistic three-boson scattering in the framework of Poincare invariant quantum mechanics. The main point here is the construction of unitary irreducible representations of the Poincare group, both for noninteracting and interacting particles. For three-body scattering the Faddeev scheme is reformulated relativistically.
Comparison of scattering observables obtained from relativistic and non-relativistic calculations based on simple Yukawa-type interactions lead to observations that should be relevant for more sophisticated interactions. These comparisons do not involve taking non-relativistic limits. Instead relativistic and non-relativistic three-body calculations are compared that contain interactions fitted to the same two-body data. All of the observed differences result form the different ways in which the two-body dynamics appears in the three-body problem. - Host: Baha Balantekin
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Searching for exoearths and measuring the acceleration of the universe with femtosecond laser frequency combs
- Time: 4:00 pm
- Place: 4274 Chamberlin
- Speaker: Andrew Szentgyorgyi, Harvard CFA
- Abstract: Octave-spanning, mode locked femtosecond laser frequency combs convert
the most precise instrument available today - the atomic clock - to the frequency domain, providing an equally precise yardstick for wavelength calibration, potentially 1:10^15. Precision at this level enables astronomical radial velocity measurements to 1 cm/sec over decadal time scales. This capability will make it possible to search for earth-like planets orbiting solar type-stars in the habitable zone and to measure the expansion of the universe directly, as well as to explore the local distribution of dark matter and to search for variations of fundamental constants over cosmological time scales. I discuss the techniques, status and potential of this instrumentation as well as ongoing and future observational programs in pursuit of these scientific objectives. - Host: Francis Halzen