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This Week at Physics

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Events on Thursday, December 1st, 2016

R. G. Herb Condensed Matter Seminar
Controlling Spin Qubits in Diamond with a Mechanical Resonator
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Evan MacQuarrie, Cornell University
Abstract:
The spin state of the nitrogen-vacancy (NV) center in diamond offers a promising platform for the development of quantum technologies and investigations into spin dynamics at the nanoscale. With lengthy coherence times even at room temperature, NV centers present one path towards quantum information in the solid state and enable precision metrology with atomic scale spatial resolution. The NV center spin state can be coherently manipulated with resonant magnetic fields, electric fields, or, at cryogenic temperatures, optical fields. Here, we demonstrate direct mechanical control of an NV center spin by coherently driving magnetically-forbidden spin transitions with the resonant lattice strain generated by a bulk-mode mechanical resonator [1,2]. We then employ this mechanical driving to perform continuous dynamical decoupling and extend the inhomogeneous dephasing time of a single NV center spin [3]. Finally, we experimentally demonstrate that a spin-strain coupling exists within the NV center room temperature excited state and theoretically analyze a dissipative protocol that uses this newly discovered coupling to cool a mechanical resonator [4]. The methods of mechanical spin control developed here unlock a new degree of freedom within the NV center Hamiltonian that may enable new sensing modes and could provide a route to diamond-mechanical resonator hybrid quantum systems.


[1] E. R. MacQuarrie, et al, Phys. Rev. Lett. 111, 227602 (2013).

[2] E. R. MacQuarrie, et al, Optica 2, 233 (2015).

[3] E. R. MacQuarrie, et al, Phys. Rev. B 92, 224419 (2015).

[4] E. R. MacQuarrie, et al, arXiv:1605.07131 (2016).
Host: Eriksson
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Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:15 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
http://cmb.physics.wisc.edu/journal/index.html
Please feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Amol Upadhye (aupadhye@wisc.edu).
Host: Amol Upadhye
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
STUDIES OF GALACTIC COSMIC RAYS WITH DIRECT AND INDIRECT MEASUREMENTS
Time: 2:30 pm
Place: 5280 Chamberlin hall
Speaker: Nahee Park, University of Chicago
Abstract: Cosmic rays, high energy particles originating from outside of the solar system, are believed to be dominated by particles from our Galaxy at least up to the energy of 10^15 eV. Recent results from direct measurements of cosmic rays, including the rise of the positron flux, the hardening of the light nuclei, and the different spectral indexes of the proton and helium spectra, challenge the classical models of the Galactic cosmic rays. Meanwhile, the development of gamma-ray experiments has opened a new window to study the acceleration and propagation of high-energy particles in the vicinity of the source sites, such as supernova remnants.

I will present the Galactic gamma-ray measurements from the VERITAS experiment, an imaging atmospheric Cherenkov telescope measuring gamma rays with energies higher than 85 GeV and up to ~ 30 TeV. Focusing on the supernova remnants, I will discuss what we have learned about the acceleration of high-energy particles with gamma-ray observations. I will also introduce the near-future balloon-borne experiment, HELIX (High Energy Light Isotope eXperiment), which is designed to measure the clock isotope 10^Be up to 10 GeV/n to study the propagation of Galactic cosmic rays. Finally, I will highlight how measurements from different disciplines, such as cosmic-ray and gamma-ray astrophysics, will broaden our perspectives on high-energy particles and advance us towards a new paradigm of Galactic cosmic rays.
Host: Stefan Westerhoff
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Astronomy Colloquium
Do High Equivalent Width LAEs Exist in the Local Universe? Insights from a Flux-Limited GALEX LAE sample at z~0.3
Time: 2:30 pm
Place: 4421 Sterling Hall, NOTE EARLIER TIME 2:30 PM
Speaker: Isak Wold, University of Texas - Austin
Abstract: Observational surveys of Lya emitters (LAEs) have proven to be an efficient method to identify and study large numbers of galaxies over a wide redshift range. To understand what types of galaxies are selected in LAE surveys - and how this evolves with redshift - it is important to establish a low-redshift reference sample that can be directly compared to high-redshift samples. The lowest redshift where a direct Lya survey is possible is at a redshift of z~0.3 via the Galaxy Evolution Explorer (GALEX ) FUV grism data. Using the z~0.3 GALEX sample as an anchor point, it has been suggested that at low redshifts high equivalent width (EW) LAEs become less prevalent and that the amount of escaping Lya emission declines rapidly. A number of explanations for these trends have been suggested including increasing dust content, increasing neutral column density, and/or increasing metallicity of star-forming galaxies at lower redshifts. However, the published z~0.3 GALEX sample is pre-selected from bright NUV objects. Thus, objects with strong Lya emission but faint continuum (high-EW LAEs) could be missed. In this talk, I will present my efforts to re-reduce the deepest archival GALEX FUV grism data and obtain a sample that is not biased against high-EW LAEs. I will discuss the implications of this new sample on the evolutionary trends listed above.
Host: Amy Barger
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