Events at Physics

<< Summer 2010 Fall 2010 Spring 2011 >>
Subscribe your calendar or receive email announcements of events

Events on Thursday, December 9th, 2010

R. G. Herb Condensed Matter Seminar
Theory of Josephson photomultipliers: current biased Josephson junctions as microwave photon counters
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Emily Pritchett, Institute for Quantum Computing, University of Waterloo
Abstract: Superconducting devices have enabled many experimental demonstrations of on-chip quantum optics in the microwave regime. While microwave fields are usually detected by linear amplification, detection of single low-energy microwave photons remains a challenge to experimental reproduction of quantum optical effects that require photon counting. We analyze the use of single current biased Josephson junctions as Josephson photomultipliers (JPMs) for microwave photon counting. By analyzing the backaction of a switching event in the junction, we show that JPMs are close to binary detectors responding only to the presence or absence of resonant photons. We discuss applications of a microwave photon counter, including on-chip demonstration of the Hanbury-Brown Twiss effect and efficient state tomography.
Host: Robert McDermott
Add this event to your calendar
Astronomy Colloquium
Gas Accretion in Galaxies
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Dusan Keres, Harvard Smithsonian Center for Astrophysics
Abstract: &quot;Most galaxies are actively star forming at all epochs. However, observations of dense, galactic gas indicate that, at any epoch, there is not enough gas in galaxies to support evolution of star formation activity over time. This suggests that galactic gas is being replenished from the intergalactic medium.<br>
I use fully cosmological simulations of galaxy formation to study the gas supply into galactic component from high redshift to present. At high redshift &quot;smooth&quot; infall of cold filamentary gas dominates the gas supply of all galaxies. This &quot;cold mode accretion&quot; is unlike the accretion in the standard model of galaxy formation in which cooling of the hot halo atmospheres is a source of gas supply to galaxies. Cold mode accretion is a major driver of very active star formation of high-z galaxies enabling such activity to proceed for a significant fraction of the Hubble time. Gas accretion rates at a given halo and galaxy mass decrease with time, causing the drop in star formation rates. At low redshift hot virialized gas can cool in some of the halos, but cold gaseous clouds that form from infalling filaments can dominate gas supply in galaxies such as Milky Way.<br>
In this talk I will describe properties, physics and consequences of cold gas accretion from the intergalactic medium as well as predictions for the observational probes of cold halo gas that can provide strong constraints on the models. I will also discuss remaining open questions and future directions in the studies of galactic gas accretion, including new computational methods and observations with upcoming facilities.&quot;<br>
Add this event to your calendar