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Events on Wednesday, May 17th, 2023

Graduate Program Event
PhD Final Defense
Nanoscale metrology using the spin and charge states of single nitrogen vacancy centers in diamond
Time: 11:00 am
Place: 5310 Chamberlin
Speaker: Aedan Gardill, Physics Graduate Student
Abstract: The nitrogen-vacancy (NV) center in diamond has shown great success as a nanoscale sensor due to its long coherence times at room temperature, its ability to be optically addressed, its sensitivity to a host of external fields, and having technical and logistical advantages due to being naturally trapped within the diamond. They have been used in a broad range of applications, including condensed matter physics, biology, geographical science, and commercial magnetometers. In this thesis, new nanoscale measurement techniques using single NV centers are presented that utilize their spin and charge states. First, the spin relaxation dynamics of single NV centers in nanodiamonds are measured, which sheds light on the electric noise spectral density of these nanodiamonds. Additionally, these measurements investigate the sources that limit coherence times of NV centers in nanodiamonds. Second, single NV centers are used to capture electrons released from surrounding defects in diamond in a new measurement technique. This allows us to gain new understanding of the charge dynamics of these surrounding defects. Lastly, a novel super-resolution technique is demonstrated with NV centers that uses the naturally formed Airy disk of light focused by a lens. This technique can be readily implemented in other confocal microscopes with little-to-no additional modifications.

The NV center-based measurement techniques introduced in this thesis offer promising new measurement tools that could have large impacts in other research areas, such as quantum computing. For example, the electric field sensing technique could be used to explore the source of surface charge noise in materials used in superconducting qubits or semiconductor quantum dots. The technique using single NV centers to probe charge dynamics also expands our understanding of the charge states of silicon vacancy centers in diamond, which are promising defects for quantum networks. Moreover, the demonstrated new super-resolution technique provides a gateway for other research groups to easily achieve super-resolution in their work and advance their research.
Host: Shimon Kolkowitz
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Preliminary Exam
Investigating the Collisionless Kinetic Regime with the New TREX Drive Cylinder
Time: 11:00 am
Place: B343 Sterling
Speaker: Paul Gradney
Abstract: The Terrestrial Reconnection EXperiment (TREX) at the Wisconsin Plasma Physics Laboratory (WiPPL) can reliably reach the collisionless kinetic regime by driving an induced magnetic field through a cylindrical coil geometry. The enhanced drive reduces the effects of collisionality in the experiment, such that electron pressure anisotropy is expected to develop unimpeded by Coulomb collisions. Comparing the upgraded Drive Cylinder to the previous 4-coil TREX configuration, the reconnection current layer is a factor of two longer, with an absolute system size of L/di = 15, and increases the reconnection rate from Erec ~ 100V/m to 900V/m. These improved parameters allow the Drive Cylinder to reach a Lundquist number of S = 10^5, the highest value achieved by a dedicated reconnection experiment. In this parameter space, the Drive Cylinder can explore plasma physics dynamics that are more applicable to the collisionless settings in many space physics phenomenon, such as planetary magnetospheres.
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