Chatterjee, A; (2017) Silicon nanodevice qubits based on quantum dots and dopants. Doctoral thesis , UCL (University College London).

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Abstract

Quantum physics applied to computing is predicted to lead to revolutionary enhancements in computational speed and power. The interest in the implementation of an impurity spin based qubit in silicon for quantum computation is motivated by exceedingly long coherence times of the order of seconds, an advantage of silicon's low spin orbit coupling and its ability to be isotopically enriched to the nuclear spin zero form. In addition, the donor spin in silicon is tunable, its nuclear spin is available to be employed as a quantum memory, and there are major advantages to working with silicon in terms of infrastructure and scalability. In contrast, lithographically patterned artificial atoms called quantum dots have the complementary advantages of fast electrical operations and tunability. Here I present our attempts to develop a scalable quantum computation architecture in silicon, based on a coupled quantum dot and dopant system. I explore industry-compatible as well as industrial foundry-fabricated devices in silicon as hosts for few-electron quantum dots and utilise a high-sensitivity readout and charge sensing technique, gate-based radiofrequency reflectometry, for this purpose. I show few-electron quantum dot measurements in this device architecture, leading to a charge qubit with a novel multi-regime Landau-Zener interferometry signature, with possible applications for readout sensitivity. I also present spin-to-charge conversion measurements of a chalcogen donor atom in silicon. Lastly, I perform measurements on a foundry-fabricated silicon device showing a coupling between a donor atom and a quantum dot. I probe the relevant charge dynamics of the charge qubit, as well as observe Pauli spin blockade in the hybrid spin system, opening up the possibility to operate this coupled double quantum dot as a singlet-triplet qubit or to transfer a coherent spin state between the quantum dot and the donor electron and nucleus.

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