This Week at Physics

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Events on Thursday, February 6th, 2014

R. G. Herb Condensed Matter Seminar
Electrically controlled spin qubits in coupled quantum dot systems
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Vanita Srinivasa, UMD
Abstract: The spins of electrons confined in semiconductor quantum dots represent versatile building blocks for solid-state quantum information processing devices. Within these systems, manipulation via electric fields enables both rapid control and protection from noise. I will describe our theoretical investigations of single-electron and multi-electron quantum dot systems with electrically controllable spin relaxation, highly tunable exchange interactions, and quantum gates robust against charge noise. These features yield approaches for rapid single-spin initialization as well as for controllably coupling donor electron spin qubits in silicon.

Host: Coppersmith
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Searching for Q-balls with the High Altitude Water Cherenkov Observatory
Time: 2:30 pm
Place: 4274 Chamberlin Hall
Speaker: Peter Karn, UC Irvine
Abstract: The High Altitude Water Cherenkov (HAWC) Observatory is a gamma-ray experiment currently under construction at Sierra Negra in Mexico. When complete it will consist of a 22,000 square meter array of 300 water Cherenkov detectors. Although HAWC is designed to study gamma rays from galactic and extra-galactic sources, the large volume of instrumented water (each tank holds ~188,000 liters) gives the opportunity to search for rare objects. One such target is the Q-ball, a very massive, subrelativistic particle that can have a large baryon number and can be stable since their creation in the early universe. If stable, Q-balls would make up some of the dark matter of the universe, but their large mass means their flux is very low. HAWC has a flexible data acquisition system which, with a dedicated trigger algorithm for non-relativistic species, allows a search for Q-balls traversing the detector. The Q-ball trigger, simulation, and analysis will be presented.
Host: Vandenbroucke
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Astronomy Colloquium
Measuring Magnetic Fields Near and Far via the Zeeman Effect
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Tim Robishaw, Dominion Radio Astrophysical Observatory
Abstract: The Zeeman effect is the only observational tool that allows us to directly measure the magnetic field strength and direction in the interstellar medium. We provide an overview of ongoing projects in which we are using the Zeeman splitting of the 21-cm line and the 18-cm hydroxyl (OH) transitions in order to probe astrophysical magnetic fields. We will highlight the first detection of extragalactic Zeeman splitting in the OH<br>
megamaser emission from starburst galaxies. Results will be shown from a southern survey of Zeeman splitting in OH masers in our Milky Way's spiral arms that suggest field reversals relative to the field directions probed by Faraday rotation. We will also discuss previous measurements of the Zeeman effect in Galactic 21-cm radio emission, some of the instrumental challenges involved in such measurements, and plans for a large-scale<br>
survey underway on the 64-m Parkes telescope and the 26-m John A. Galt Telescope at the Dominion Radio Astrophysical Observatory.
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