Foreman, Cameron;
(2025)
Resource-efficient quantum cryptography.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Quantum cryptography leverages quantum mechanics to perform cryptographic tasks and can, in principle, offer security guarantees impossible with classical methods. However, a significant gap exists between current protocols and those required for the practical realisation of this security advantage. This thesis presents several results aimed at bridging this gap, by reducing the required amount and quality of initial resources and improving the computational efficiency of key processing steps -- enabling secure resource-efficient quantum cryptography protocols that can be implemented in the near-term. Part 1 focuses on randomness extractors, classical algorithms that distil uniform and secret randomness from partially random sources, which are essential for quantum cryptography. We introduce seeded randomness extractors with improved finite-size performance and present several two-source extractors that reduce the quality requirements of the seed. For all extractors, we provide efficient, information-theoretically secure, implementations utilising the convolution theorem to achieve quasi-linear computation time where applicable. Next, we introduce a class of extractors specifically designed for quantum protocols which use input sources that violate a Bell inequality. We show that these extractors can be implemented deterministically and provide several efficient and explicit constructions by exploiting a connection with error-correcting codes. Part 2 explores randomness amplification and privatisation, a quantum process that converts weak (non-uniform and public) randomness into uniform and private randomness. We present a device-independent protocol for randomness amplification and privatisation, optimised for practical use, with generation rates linear in the quantum device's repetition rate and quasi-linear computation time classical post-processing. We then demonstrate that this protocol can be experimentally realised in a semi-device-independent manner using current hardware, implementing it on several different quantum computers.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Resource-efficient quantum cryptography |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. 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 > 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 Computer Science UCL |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10209490 |
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