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Title: Probing nuclear spin bath dynamics in a self-assembled quantum dot with optically detected NMR
Author: Waeber, Andreas M.
ISNI:       0000 0004 5921 3350
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2016
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This thesis describes experiments using optically detected nuclear magnetic resonance (NMR) techniques to probe and control the nuclear spin bath evolution in single self-assembled InGaAs quantum dots at large external magnetic fields. Strong non-resonant optical pumping is used to create spin bath polarisations ≳ 60% in dynamic nuclear polarisation. Changes of the nuclear magnetisation under resonant radio frequency (rf) excitation of nuclear Zeeman transitions are detected in low-power photoluminescence spectroscopy measurements of the hyperfine shifts of the exciton transition lines. Continuous wave rf excitation shows strong inhomogeneous broadening of the NMR spectra in a quantum dot owing to strain-induced quadrupolar interactions. Hahn echo measurements reveal comparatively long nuclear spin phase memory times T^HE_ M,n ~ 1-4 ms which are attributed to strong suppression of nuclear spin fluctuations due to the inhomogeneous broadening. Further progress towards full control of the spin bath evolution is made using a set of new multiple pulse NMR sequences combining features of Hahn and solid echoes. Measurements demonstrate that spin bath coherence times of up to ~ 20 ms can be achieved within the experimental limitations of this work. Use of these NMR sequences in combination with electron/hole spin control techniques is expected to increase central spin coherence times significantly. The equilibrium spin bath coherence properties are probed using a novel, weakly-invasive rf frequency comb NMR method. Frequency combs with varying tooth spacing are used to determine the homogeneous NMR lineshapes. The sensitivity of the homogeneous linewidths to fluctuations in the spin bath is used to probe the bath dynamics. Few-second-long spin flip-flop correlation times are revealed, demonstrating the potential of self-assembled InGaAs quantum dots to serve as a highly stable host system for spin qubits.
Supervisor: Chekhovich, Evgeny A. ; Tartakovskii, Alexander I. ; Skolnick, Maurice S. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available