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Physics and Astronomy - PhD Thesis Defense - Ethan Williams, Dartmouth College

Title: "Probing central spin decoherence dynamics of electronic point defects in diamond and silicon"

Thursday, February 1, 2024
1:30pm – 3:00pm
Steele 006 and Zoom
Intended Audience(s): Public
Categories: Arts and Sciences, Lectures & Seminars
Abstract: Electron spins of point defects in diamond and silicon can exhibit long coherence times, making them attractive platforms for the physical implementation of qubits for quantum sensing and quantum computing. To realize these technologies, it is essential to understand the mechanisms that limit their coherence. Decoherence of these systems is well described by the central spin model, wherein the central electron spin weakly interacts with numerous electron and nuclear spins in its environment. The net effect of these interactions can sometimes be approximated by a stochastic classical process that causes dephasing. The dynamics of the dephasing can be probed with pulse electron paramagnetic resonance (pEPR) experiments.
 
Using a 2.5 GHz pEPR spectrometer built in-house, we performed multi-pulse dynamical decoupling (DD) noise spectroscopy experiments on ensembles of substitutional nitrogen (P1) and nitrogen-vacancy (NV) centers in diamond, which reveal a 1/f power spectrum of the spin bath interactions. This behavior is indicative of a heterogeneous distribution of nitrogen impurities with varying noise correlation times, reinforcing the emerging picture that nitrogen defects can cluster in diamond. Novel DD analysis methods are introduced which utilize harmonic resonances to extend the frequency range for detecting peaks in the power spectrum. These methods are used to quantify the power spectral contribution of the precession of the 1.1% abundant carbon-13 nuclei and could be used in a variety of ac magnetic field sensing protocols. 
 
Experiments on phosphorus-doped silicon, performed at the National High Magnetic Field Laboratory on the 240 GHz spectrometer, have revealed that the donor-bound electron coherence times are nominally shorter than theory predicts by a factor 2, but when the sample is illuminated with above bandgap light, the coherence times are restored. These results are doubly surprising as they suggest that (i) silicon hyperfine interactions are modified at high magnetic fields; and (ii) optical excitation can extend coherence times, counter to what has been previously observed.  While the microscopic details of this are unclear, these findings could inform models of spin dynamics in silicon.
 
Graduate Thesis Advisor:  Chandrasekhar Ramanathan

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For more information, contact:
Tressena Manning
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603-646-2854
Permanent URL to this event: https://physics.dartmouth.edu/events/event?event=72864

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