Probing Nuclear Spin Bath Dynamics in a Self-Assembled Quantum Dot with Optically Detected NMR
Year: 2016
Type: dissertation
Abstract: 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 lowpower 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, weaklyinvasive 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.iii The success of this work would not have been possible without the help of many others.I would therefore like to take the opportunity to thank all those who contributed to the success of this work and made my time with the LDSD group such a pleasant experience.Firstly, I am very grateful to Sasha Tartakovskii and Maurice Skolnick for making this project possible, creating such a nourishing research environment and always providing guidance and support when needed.I am particularly thankful to my supervisor Evgeny Chekhovich, whose mentorship and guidance over the past years were invaluable and whose work ethic and dedication have been truly inspirational.It has been a privilege to work with you.Furthermore, I would like to thank my co-workers Ata Ulhaq and Gau Ragunathan for the fruitful collaboration and numerous thought-provoking discussions, as well as Joe Maguire for his contributions in the course of his SURE project.All experimental physics requires a working setup.A big thank you to Paul Kemp-Russell, Simon Dixon, Jonathan Mercer and their colleagues in the workshop for their readiness to help whenever something needed to be fixed "really urgently" on a Friday afternoon...
Author: A. M. Waeber
Language: English
Subfield: Condensed Matter Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2537815565