Towards scalable planar donor-based silicon quantum computing architectures

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Copyright: Weber, Bent
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Abstract
In this thesis, we present atomically precise donor-based electronic devices, fabricated using STM hydrogen lithography, combined with a gaseous doping source (PH3) and low-temperature silicon homoepitaxy. Using this technique we address three key issues towards the scale-up of planar Si:P donor-based quantum computing (QC) architectures towards multiple qubits: (i) The fabrication of atomic-scale low-resistive control-electrodes with diameter and pitch comparable to qubit separations. (ii) The independent electrostatic control of donor qubits in predictively modeled device architectures. (iii) The investigation of Pauli-spin blockade towards control and read-out of two-spin states. We demonstrate the formation of ``interface-free'' wires with lithographic widths down to 1.5nm. At T = 4.2K, these wires retain a low diameter-independent resistivity, ρW= (0.3 ± 0.2) mΩcm, comparable to that of bulk-doped silicon and the lowest ever reported for doped silicon wires. Investigating the wire conductance as a function of in-plane gates, we find that Si:P wires remain highly conductive down to millikelvin temperatures, allowing us to use them in more complex device architectures. We subsequently demonstrate the independent electrostatic control of two serially tunnel-coupled quantum dots which are only ~4nm in diameter, separated by ~10nm. Incorporating 4.6nm wide wires as source and drain electrodes, the dots have been embedded within a planar device architecture, optimized using predictive capacitance modeling. With excellent agreement between modeled and measured charge stability data we achieve a similar level of electrostatic control compared to much larger double quantum dots. Finally, we demonstrate independent gate control down to the atomic limit as we investigate Pauli spin blockade of the first few electrons bound to two tunnel-coupled donor-clusters of only 2P and 3P donor atoms. A fundamental manifestation of the spin degree of freedom, Pauli blockade is a main pre-requisite for the control and read-out of two-spin states in double quantum dots and coupled donors. This work therefore demonstrates the potential of STM hydrogen lithography to realize the fundamental building block of Si:P donor-based QC architectures – two precision-placed donor qubits, individually addressable with local electric fields.
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Weber, Bent
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Publication Year
2013
Resource Type
Thesis
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PhD Doctorate
UNSW Faculty
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