Readout and addressability of Si:P qubits with the prospect of scalability

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Embargoed until 2016-09-30
Copyright: Buech, Holger
In this thesis we present single-shot spin readout of precision placed phosphorus donors in silicon. The spin states of an electron bound to phosphorus donors in silicon make promising building blocks for the realisation of a solid state quantum computer due to their remarkably long coherence and relaxation times. Recent progress in scanning tunnelling microscope (STM) lithography has made it possible to place these donors with atomic accuracy, opening the way to individual qubit control and hence scalability. We present spin readout from two different STM-patterned devices where the electron spin qubit is hosted by either a cluster of about four phosphorus donors or a single phosphorus donor and tunnel-coupled to an atomically planar single electron transistor (SET). We demonstrate high fidelity (approx. 90%) single shot spin readout of the cluster qubit via spin-to-charge conversion and show long spin life times of T1 = 1.3 s (B=1.5 T) despite the multi-donor, multi-electron character of the spin qubit. For the single P donor we extrapolate a slightly larger T1 of approx. 6 s at B=1.5 T, consistent with previous measurements of single donor spin life times. Using atomistic tight-binding calculations, we confirm the dependency of the relaxation rate on both donor and electron numbers, where we show that multi-donor single-electron systems provide the highest T1. We also demonstrate the concept of using the single donor as a spectrometer to analyse the energy level structure of the SET island. Finally, the successful spin readout of the cluster qubit with long measured T1 provides an opportunity to use cluster qubits in conjunction with single donor qubits to achieve qubit addressability by a global microwave field with very low error rates. We show by atomistic tight binding modelling, that the electron spin resonance (ESR) frequency of a double donor qubit can be separated by up to 350 MHz from the ESR frequency of a single donor qubit due to the difference in the hyperfine coupling, allowing qubit rotations with error rates as low as approx. 10^(-5). Together, these results advance STM device fabrication technology towards the realisation of scalable donor based qubit architectures in silicon.
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Buech, Holger
Simmons, Michelle
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PhD Doctorate
UNSW Faculty
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