Events at Physics
Events During the Week of March 24th through March 31st, 2013
Sunday, March 24th, 2013
- Distinguished Lecture Series
- "Cosmology on a Moving Mesh"
- Time: 4:00 pm
- Place: 1310 Sterling Hall
- Speaker: Lars Hernquist, Harvard University
Understanding the formation and evolution of galaxies in a cosmological context using numerical simulations remains an elusive goal. In this talk, I describe a new approach to modeling the hydrodynamics of galaxy formation in which the equations of motion are solved on a moving mesh. The use of a moving mesh makes the scheme fully Lagrangian, unlike popular particle-based codes which are quasi-Lagrangian in nature, and mitigates against advection errors when a spatially fixed grid is used. I present results from an initial study comparing results for a moving mesh with those obtained using a smoothed particle hydrodynamics solver. This preliminary work suggests that the new approach offers promise for resolving the long-standing problems which have plagued this field for nearly two decades.
- Host: Prof Elena D'Onghia
Monday, March 25th, 2013
- Cosmology Journal Club
- An Informal discussion about a broad variety of arXiv papers related to Cosmology
- Time: 12:30 pm
- Place: 5242 Chamberlin Hall
- Abstract: Please visit the following link for more details:
Please feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Le Zhang (firstname.lastname@example.org)
- Host: Peter Timbie
Tuesday, March 26th, 2013
- No events scheduled
Wednesday, March 27th, 2013
- No events scheduled
Thursday, March 28th, 2013
- R. G. Herb Condensed Matter Seminar
- Control and possible applications of valley degree of freedom: Valleytronics?
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Belita Koiller, Federal University of Rio de Janeiro
- Abstract: The conduction electrons in Si are not in a well-defined single Bloch state. Instead, the Si conduction band is six-fold degenerate, with minima (valleys) along the x, y and z crystallographic directions. This imposes limitations to the spin manipulation and coherence. It was recently proposed to encode quantum information directly into the valley degree of freedom, converting the spurious valley Hilbert subspace into a useful ingredient for a quantum computer. In this talk, valley degrees of freedom in Si are addressed in 3 different contexts.
1) Based on an atomistic pseudopotential theory, we demonstrate that ordered Ge-Si layered barriers confining a Si slab can be optimized to enhance the VS in the active Si region by up to one order of magnitude compared to the random alloy barriers adopted so far. We identify Ge/Si layer sequences leading to a VS as large as ~9 meV. The splitting is "protected" even if some mixing occurs at the interfaces.
2) Interface states form spontaneously at some semiconductor-barrier interfaces and they may improve or hinder the electron control and coherence for semiconductor-based qubits. From a simple 1D Tight-binding model, new insights emerge regarding the interface state's energy, as well as the exponential longer (shorter) localization lengths into the Si (barrier) material. The interface state may be probed experimentally by an external electric field, which modulates the capacitance of the system and the lowest level spacing (valley splitting).
3) We analyze the valley composition of one electron bound to a shallow donor close to a Si/barrier interface. A full six-valley effective mass model Hamiltonian is adopted. For low fields, the electron ground state is essentially confined at the donor. At high fields the ground state is such that the electron is drawn to the interface, leaving the donor practically ionized. Valley splitting at the interface occurs due to the valley-orbit coupling, taken here as a complex parameter. A sequence of two anti-crossings takes place and the complex phase affects the symmetries of the eigenstates and level anti-crossing gaps.
1) L. Zhang, J-Wi Luo, A. L. Saraiva, B. Koiller, A. Zunger, arXiv:1303.4932.
2) A. L. Saraiva, B.Koiller, M. Friesen, Phys. Rev. B 82, 245314 (2010).
3) A. Baena, A. L. Saraiva, B.Koiller, M. J. Calderón Phys. Rev. B 86, 035317 (2012).
- Host: Coppersmith
Friday, March 29th, 2013
- No events scheduled