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Developing a Microwave Quantum Memory with Rare-Earth Doped Crystals

Alexander, Joseph; (2023) Developing a Microwave Quantum Memory with Rare-Earth Doped Crystals. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Rare-earth doped crystals have attracted a significant amount of attention for use in quantum systems. Available, long-lived, optical and microwave transitions has lead to proposals for quantum transduction and quantum memories, both of which are important in building large scale quantum networks. Ensembles of rare-earth spins can be coupled to superconducting resonators, and high coupling strengths (with cooperativity > 1) readily achievable. While such systems have been constructed, a useful quantum memory which exploits highly coherent transitions has not yet been developed in the microwave domain. In this thesis we couple high-Q superconducting resonators to Yb doped YSO. The spin system of Yb:YSO is explored and the main causes of decoherence are outlined, these are found to be instantaneous diffusion and spectral diffusion. In the process of this, new techniques are developed to determine decoherence sources, where nuclear spins within the YSO crystal are found to limit coherence. Two different regimes are explored to increase the coherence time. Using optimal field orientations and high magnetic field magnitudes, the coherence time is extended to (6±2) ms. While the zero field clock transition is used, along with isotopic purification, to reach the same time ((6±1) ms). Using these techniques to increase coherence, the foundations for a microwave quantum memory with Yb:YSO are laid. Cooperativities > 1 are measured for three different Yb spin systems, this allows for these spin systems to be used in memory protocols and reach unit efficiency. New pulse sequences using adiabatic fast passage are developed to provide control over the spin ensemble and for memory protocols. Finally, we use the knowledge from all of these studies to propose a system which would form the basis of an efficient, long-lived microwave quantum memory using FIB-milled Yb:YSO.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Developing a Microwave Quantum Memory with Rare-Earth Doped Crystals
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2023. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Electronic and Electrical Eng
URI: https://discovery.ucl.ac.uk/id/eprint/10173746
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