Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 57, Number 11
Friday–Saturday, October 26–27, 2012; Socorro, New Mexico
Session B3: Condensed Matter I |
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Chair: Barry Zink, University of Denver Room: Macey Center Agora |
Friday, October 26, 2012 10:40AM - 11:04AM |
B3.00001: Pattern Formation in Nature: What Could Be Behind It Invited Speaker: V.M. Kenkre Pattern formation in nature is a ubiquitous and fascinating phenomenon. A simple description will be given of one possible mechanism among many: spatial nonlocality in competitive interactions [1-2]. A tutorial explanation will be presented of random walks or diffusion, then of the logistic equation, then of their combination to produce the Fisher equation, and finally of a generalization of the Fisher equation with spatial nonlocality which is capable of producing patterns. The role of diffusion in the pattern formation process will be discussed with possibilities of a remarkable shape shifting consequence of controlled motion that we have discovered recently [3].\\[4pt] [1] Nonlocal Interaction Effects on Pattern Formation in Population Dynamics, M. A. Fuentes, M. N. Kuperman, and V.M. Kenkre: Phys. Rev. Lett. 91, 158104-1 (2003).\newline [2] Analytical Considerations in the Study of Spatial Patterns Arising from Nonlocal Interaction Effects, M. A. Fuentes, M. Kuperman, and V. M. Kenkre: J. Phys. Chem. B 108, 10505-10508(2004).\newline [3] Shape Shifting in Patterns Produced by Control of Diffusion: Theoretical Considerations, M. Kuperman and V. M. Kenkre, Consortium Preprint, UNM (2012). [Preview Abstract] |
Friday, October 26, 2012 11:04AM - 11:16AM |
B3.00002: Landau-Lifshitz-Gilbert Model and Ferromagnetic Pattern Formation Soyoung Jung, Manuel Berrondo We study the dynamics of multi-spin systems with energy dissipation. The Heisenberg model constitutes an essential stepping stone to understand ferromagnetic materials. Individual two-spin short-range interactions of magnetic dipoles give rise to coherent long-range behavior in a lattice structure. The spins are free to rotate and can arrange themselves in a parallel configuration in the ordered state. The local magnetic field acting on each spin arises as the result of the addition of nearest neighbors (NN) spins. The addition of dissipative effects allows us to study the onset of ordered states as a dynamical process. In addition to NN spins interactions, we include anisotropy to simulate the layer structure of the experimental samples. We also included a long range interaction as an opposing force. As a result, we have been able to observe the formation of domains in simulated 2-d ferromagnetic lattices. Depending on the external transverse magnetic fields, different patterns are formed. These patterns correlate very well with experimental observations in Co-Pt thin magnetic films. [Preview Abstract] |
Friday, October 26, 2012 11:16AM - 11:28AM |
B3.00003: Neural Network Solutions to Optical Absorption Spectra Conrad Rosenbrock Artificial neural networks have been effective in reducing computation time while achieving remarkable accuracy for a variety of difficult physics problems. Neural networks are trained iteratively by adjusting the size and shape of sums of non-linear functions by varying the function parameters to fit results for complex non-linear systems. For smaller structures, ab initio simulation methods can be used to determine absorption spectra under field perturbations. However, these methods are impractical for larger structures. Designing and training an artificial neural network with simulated data from time-dependent density functional theory may allow time-dependent perturbation effects to be calculated more efficiently. I investigate the design considerations and results of neural network implementations for calculating perturbation-coupled electron oscillations in small molecules. [Preview Abstract] |
Friday, October 26, 2012 11:28AM - 11:40AM |
B3.00004: Where Exactly are the Quantum Cheshire Cats? Prashanna Simkhada, Jean-Francois S. Van Huele We present Aharonov's concept of a Quantum Cheshire Cat (QCC) (arXiv: 1202.0631) to illustrate how physical properties can be disembodied from the objects they belong to. We compute weak-measurement expectation values and look for correlations of spin and path observables associated with a Mach-Zehnder interferometric set-up. By including ancilla states we are able to (a) confirm Aharonov's correlations, (b) find new QCCs, and (c) provide a new interpretation of the occurrence of QCCs. We conclude that where we find the Cheshire cats depends on the precise question we ask about the entire set-up. [Preview Abstract] |
Friday, October 26, 2012 11:40AM - 12:04PM |
B3.00005: Quantum control and measurement of spins in laser cooled gases Invited Speaker: Ivan Deutsch Quantum information processing (QIP) requires three important ingredients: (i) preparing a desired initial quantum state, usually highly pure; (ii) controlling the dynamical evolution, usually via a desired unitary transformation; (iii) measuring the desired information encoded in the final quantum state. Many physical platforms are being developed for QIP, including trapped ions, semiconductor quantum dots, and atoms in optical lattices. In these cases, it is the spins of the system that encode the quantum information. Spins are natural carriers of quantum information given their long coherence times and our ability to control them with a variety of external electromagnetic fields. In addition, spins in laser-cooled atomic gases are an excellent testbed for exploring QIP protocols because of our ability to initially prepare highly pure states and employ the well-developed tools of quantum optics and coherent spectroscopy. In this talk I will give an overview of recent theory and experiment in the control and measurement of spins in laser-cooled atomic gases. We consider the hyperfine magnetic sublevels in the ground electronic states of $^{133}$Cs, a 16-dimensional Hilbert space. We can explore all three ingredients described above: preparation of an arbitrary superposition state, evolution through an arbitrary unitary matrix, and readout through quantum state reconstruction of the full density matrix. We employ the tools of optimal quantum control and quantum estimation theory. The implementation involves atoms controlled by radio-frequency, microwave, a optical fields, and measured via polarization spectroscopy. The experiment is performed in the group of Prof. Poul S. Jessen, University of Arizona. This work was supported by the National Science Foundation. [Preview Abstract] |
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