CARNEGIE MELLON UNIVERSITY -
UNIVERSITY OF PITTSBURGH

Monday, February 1, 2010, Astro Coffee, 2:00 PM, 416 Allen Hall, PITT.

Monday, February 1, 2010, Cosmo Faculty Candidate, Dan Kasen, University of California, Santa Cruz, “Characterizing the Transient Sky” 3:00 PM, 106 Allen Hall, PITT.

Abstract:  In the coming years, several astronomical surveys will scan the night sky with unprecedented depth and field of view, revealing an enormous number of supernovae and other optical transients -- many never before seen. The study of these stellar explosions is not only a vibrant field in itself, but also impacts our understanding of cosmology, nucleosynthesis, compact objects, and the sources of gravitational waves.   I discuss advances in the theory and simulation of explosive transients as the critical means to interpret, classify and exploit these observations.  I focus on the physics of thermonuclear -- or Type Ia -- supernova explosions, and on refining these as measures of cosmic expansion.  I show how variations in Type Ia brightness are driven by the breaking of spherical symmetry, and explain the physics of the empirical width-luminosity relation used to calibrate them.  I then present predictions for two other kinds of important transients:  the disruption of extremely massive stars via the electron-positron pair instability (believed to characterize the first generation of stars) and the faint optical transients from the merger of neutron stars (considered promising targets for gravitational wave observatories).

Monday, February 1, 2010, CM/Nano Faculty Candidate, Rudolph Bratschitsch, University of Konstanz, “Ultrafast quantum optics with solid-state nanosystems" 4:30 PM, 102 Thaw Hall, PITT.

Abstract:  Semiconductor quantum dots and color centers in diamond are promising solid-state systems for fundamental quantum optical experiments and robust quantum information processing. In quantum dots, ultrafast sequences of coherent quantum operations may be envisioned with femtosecond light pulses. We present the first femtosecond pump-probe experiment on a single CdSe nanocrystal. In this few-fermion system, Coulomb renormalization and single-photon gain are observed on an ultrafast timescale. The ability to add or remove single photons to and from photon bunches is explored [1]. To not only reach single-electron but also single-photon sensitivity, we present two ideas to efficiently couple light from the far field into nanometer sized objects: metal nanoantennas [2, 3] and dielectric microcavities [4]. Color centers in diamond allow for single spin initialization, manipulation and readout at ambient conditions. We present imaging magnetometry on the nanoscale with a single diamond color center [5]. Furthermore, new concepts to fabricate nanophotonic elements based on diamond are demonstrated.

[1] F. Sotier et al., Nature Physics 5, 352 (2009).

[2] J. Merlein et al., Nature Photonics 2, 230 (2008).

[3] T. Hanke et al., Phys. Rev. Lett. 103, 257404 (2009).

[4] M. Kahl et al., Nano Lett. 7, 2897 (2007).

[5] G. Balasubramanian et al., Nature 455, 648 (2008).

Tuesday, February 2, 2010, Cosmo Faculty Pizza lunch, Dan Kasen, University of California, Santa Cruz, 12:00 pm, 106 Allen Hall, PITT.

Tuesday, February 2, 2010, CM/Nano Faculty Pizza lunch, Rudolph Bratschitsch, University of Konstanz, 12:00 pm, 319 Allen Hall, PITT.

Wednesday, February 3, 2010, Joint Medium Energy/High Energy Seminar, Haiyun Lu University of South Carolina, "Exclusive Photoproduction of K+ Mesons and Sigma*- Hyperons Off the Deuteron", 4:30 P.M., WEH 7316, CMU.

Thursday, February 4, 2010, Astro Coffee, 2:00 PM, 416 Allen Hall, PITT.

Thursday, February 4, 2010, Cosmo Faculty Candidate, Haojing Yan, Ohio State University, “Galaxy Formation and Evolution in the Early Universe” 4:00 PM, 103 Allen Hall, PITT.

Abstract:  A fansinating subject in observational cosmology is the origin of galaxies.  While we have not yet found the "first galaxies" in the universe, we are approaching this goal. In this talk, I will review our understanding of the formation and evolution of galaxies in the first billion years of the universe, or in terms of redshift ("z"), z ~ 6 and beyond. The number density of galaxies in this early stage of the universe seems to be significantly less than that in one billion years later. However, the ratio between the number of faint galaxies to the number of bright galaxies seems to be significantly higher than that at the later stage of the universe; such faint galaxies could have
played an important role in an important event in the history of the universe, namely, the reionization of hydrogen. Some of the brightest galaxies at this stage are "matured" and have already assembled a large amount of stars, indicating that the universe must have started forming galaxies at even earlier time.  This has been confirmed by the most recent result from the refurbished Hubble Space Telescope, and we have moved one step forward in probing the early universe.

Friday, February 5, 2010, CMU/Pitt Astro Lunch, Dr. Shiv K. Sethi, "Primordial magnetic fields and the epoch of reionization", 12:00 PM, WEH 8327, CMU.

Abstract: The presence of primordial magnetic fields can alter the thermal and ionization history as well as cause early formation of structures in the universe. This can leave imprints on the HI signal from the epoch of reionization. The scale of density perturbation in the magnetic field case is close to magnetic Jeans' length which, for reasonable values of field strengths, is much smaller than the scale of density perturbation in the usual lambda CDM case. In addition, the first collapsed objects are closer to one-sigma events and their HII regions are smaller. Therefore, both the density and ionization inhomogeneities in this case are smaller than in the usual case. This scale lies in the range 0.4 to 2 Mpc for the range of acceptable values of magnetic field strengths. It is possible the upcoming instruments might indirectly detect this signal. The future interferometer SKA will easily detect this signal in less than a week of integration.

Friday, February 5, 2010, Costmo Faculty Pizza lunch, Haojing Yan, Ohio State University, 12:00 p.m., 105 Allen Hall, PITT.

Friday, February 5, 2010, Astrophysics Seminar, Michael Wood-Vasey, PITT, "The Astrostatistics of Galactic Tidal Streams", 1:30 PM, BH 232Q, CMU.

Monday, February 8, 2010, CM/Nano Faculty Candidate, Mark Foster, Cornell University, “Photonic Nanowires: Ideal Ultrafast Elements" 4:30 PM, 102 Thaw Hall, PITT.

Abstract:  Optical processing enables functionality beyond the bandwidth limitations of electronic devices. In extreme situations, bandwidths approaching a petahertz are available to photonic devices. Ultrafast nonlinear optical interactions in which a material’s optical properties are altered by the presence of light on a femtosecond time scale provide a path for applying this bandwidth toward useful devices. Unfortunately, nonlinear optical interactions are often limited to specific materials, bulk interactions, and high optical powers.I will discuss maximally confining dielectric waveguides, known as photonic nanowires, as a solution to the common shortcomings of traditional nonlinear optical elements. The miniscule dimensions of these structures allow for a maximal nonlinearity as well as widebandwidth control over the optical propagation through nano-scale changes in size. This geometric control yields favorable propagation regimes with little dependence on the waveguide material. For this reason, efficient ultrafast elements can be designed from a wide range of glasses and semiconductors including the important technological materials of silica glass and silicon. I will finish the talk with the realization of several ultrafast systems that incorporate silicon nanowaveguides and utilize the space-time duality of electromagnetic waves. This duality results from the similarities between spatial and temporal propagation of light and allows for the design of temporal imaging systems inspired from common spatial systems. For example, I will discuss a temporal magnifier and a time-domain telescope. Demonstrations of this style are not only capable of capturing one’s imagination but also yield practical devices for ultrafast science.