Erbium implanted silicon for solid state quantum technologies

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Silicon based information technology has revolutionized the modern world. As device features have decreased in size, integrated circuits (ICs) have become subject to quantum mechanical phenomena. Quantum technologies aim to exploit these quantum mechanical phenomena to perform tasks that are difficult or impossible with conventional technologies. One of the main obstacles in developing quantum technologies is the rapid destruction of quantum superposition states caused by interference with the environment in a process called decoherence. Recently, extremely long coherence times (hours) have been demonstrated using small amounts of additives to silicon that have a "spare" electron (donor impurities). Although even longer times can be obtained for atoms in vacuum, an atom trapped permanently in a solid crystal such as silicon is much easier to handle. A major source of decoherence in solids is the nuclear spin of the atoms that make up the host crystals, as they often flop around uncontrollably. This has been eliminated by isotopically purifying the silicon (which normally contains a mix of isotopes, only a small number of which have nuclear spin). Even so, the donor impurities don't interact with telecoms wavelength light, and this is critical for many quantum technologies, quantum communication schemes in particular. There are currently no solid-state quantum technology platforms with long coherence times and optical fibre telecommunications compatibility. The optical transitions of the rare-earth atom erbium are, however, telecommunications compatible. Rare-earth ions are also ideal systems for quantum technologies because the shielding of their electrons offers an atomic scale barrier to decoherence. When doped into relatively high nuclear spin metal oxide crystals, rare-earths show coherence times comparable to donor impurities in natural silicon, but are yet to be investigated in silicon themselves. Ion implantation is a well understood technology used in today's silicon IC manufacture and history has shown that commercial interest in new technologies favours those relying on established fabrication platforms and techniques. Given the expected improvement in coherence time from using erbium implanted isotopically pure silicon, it should be possible to develop a quantum technology platform that has a long coherence time, and is telecommunications and conventional IC tooling compatible.Quantum computation schemes require the entanglement of quantum bits (qubits), this remains challenging in silicon based qubits but has been demonstrated in superconducting circuit qubits. As the latter has short coherence times and lacks optical addressability, I envisage a hybrid scheme where processing is performed with the superconducting resonators and erbium implanted silicon qubits are used as the quantum memory element and as a quantum transducer between telecommunications and microwave wavelength photons. Through this project I will introduce a new quantum technology platform to the research community: erbium implanted silicon. This platform combines the telecommunication capability of erbium and integrated circuit capability of silicon, making it valuable for both quantum computing and quantum communication applications.