Events at Physics
|<< Spring 2014||Fall 2014||Spring 2015 >>|
|Subscribe to receive email announcements of events|
Events on Thursday, November 13th, 2014
- R. G. Herb Condensed Matter Seminar
- Generalized Tunneling Model (GTM) for Two Level System (TLS) in amorphous materials and its predictions for their dephasing and the noise in superconducting microresonators
- Time: 10:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Lara Faoro, Universites Paris 6 et 7 and Rutgers University
- Abstract: Thin film high quality superconductor microresonators are important for a number of diverse applications that range from quantum computation to submillimeter and far-infrared astronomy. The performance of these devices has improved dramatically over the past decades and resonator quality factors above 10^6 are now routinely achieved using single-layer structures deposited on high-quality low-loss crystalline substrate. Achieving high-quality factors requires minimizing all potential sources of dissipation and noise. One prominent source of dissipation in microresonators has been found to be Two Level Systems (TLSs) in thin amorphous dielectric surface layers of the microresonators. These TLS are also responsible for an excess frequency noise (jitter) in the resonators. TLS in amorphous materials are usually described by the Standard Tunneling Model (STM). In this theory, TLS are represented as independent quantum two level systems with constant distribution of low energy states. Unfortunately, STM fails to explain the data of noise in the superconducting microresonators so a consistent model for the noise due to TLS in superconducting resonators remains an open issue.
In this talk we shall first review data of recent experiments performed on high quality superconducting microresonator where low frequency noise spectra have been studied in varying temperature and different applied power and argue that the data are inconsistent with the STM. We shall then propose a new model, the Generalized Tunneling Model (GTM) which includes strong interactions between TLS and a slow power law dependence of their density of states. We show that the predictions of this model are in a perfect agreement with the recent studies of the noise in high quality superconducting resonators. The predictions also agree with the temperature dependence of the TLS dephasing rates observed in phase qubits. Finally, we discuss the origin of the universal dimensionless parameter that controls the interaction between TLS in glasses and show that it is consistent with the assumptions of the GTM.
- Host: McDermott
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Atmospheric Neutrinos
- Time: 3:00 pm
- Place: 5280 Chamberlin Hall
- Speaker: Professor Tom Gaisser, University of Delaware
- Host: Karle
- Astronomy Colloquium
- "Faint Lyman-alpha Emitters and the Reionization of the Universe"
- Time: 3:30 pm
- Place: 4421 Sterling Hall
- Speaker: Alan Dressler, Carnegie Observatories
- Abstract: There is general agreement that the photons that reionize the universe beginning at z ~ 12 are produced by young, starforming galaxies, however, the brighter galaxies that are readily detected at z > 5 fall well short of supplying the required flux of Lyman-continuum photons. I will describe an 8-year spectroscopic search with IMACS on Magellan for the faintest Lyman-alpha emitters (LAEs) at z= 5.7. Our study has pushed the detection limit an order-of-magnitude fainter than the prominent narrow-band-imaging surveys,leading to the first robust measurement of the faint-end-slope of the luminosity function. We find that LAEs make a substantial, perhaps dominant, contribution in the final stages of reionization. These young, low-mass galaxies -- more numerous than today's L* galaxies -- are likely to play an important role in the assembly of early galaxies and their chemical enrichment of the early IGM.
- Host: Professor Jay Gallagher
- Graduate Introductory Seminar
- Nuclear Physics and Astrophysics
- Time: 4:30 pm
- Place: 5280 Chamberlin Hall
- Speaker: Balantekin