Investigating deep defects in 28Si for potential applications in quantum information and communication

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Our modern technology is based on the ability of quantum mechanics to describe perfectly (if only probabilistically) the behavior of nanoscale systems. There is a growing appreciation that the principles of quantum mechanics can be used more directly in new `quantum technologies', which have spectacular potential for completely new and potentially disruptive applications in communications, security, and computing. In a quantum computer (QC), superposition allows the 0 and 1 of a conventional computer bit to be replaced by an infinite range of superpositions of 0 and 1, giving a quantum bit, or qubit. Qubits can be linked using entanglement so that a measurement on one affects the outcome of a measurement on the other, even when separated. This defies our intuition, based as it is on macroscopic reality, but can be completely accounted for by quantum mechanics. We now know that for certain classes of important problems, a QC could be enormously more powerful and faster than the largest imaginable conventional computer. This paradigm-shifting potential is fueling intense research around the world to find a technology for making a QC of sufficient complexity to solve this broad class of problems. A wide range of systems is being investigated, from photons to atoms to subatomic particles such as electrons and nuclear spins. Much activity is focused on silicon (Si)-based approaches, since Si is the basis for our present computing and information technologies. The existing Si materials science and nanoscale device technology could be harnessed to build a QC, if suitable qubits and the means of preparing, coupling and measuring them can be developed. Our discovery that enriched 28Si has a unique property: the linewidths of optical transitions are much sharper in 28Si than in normal Si (or in any other semiconductor), led to new methods for controlling and measuring the electron and nuclear spins of impurities, which are prime candidates for qubits in Si. These techniques demonstrated record-setting coherence lifetimes - the time for which a qubit can be maintained - which attracted significant global attention, including a Physics World Top Ten Breakthrough of the Year (2013). Using these same techniques, we recently identified entirely new possibilities for making highly reproducible single photon sources compatible with Si photonics, which addresses an outstanding need for those trying to build photon-based quantum technologies. These exciting single photon sources also offer a way to link multiple qubits on-chip with individual particles of light, paving the way towards a large-scale silicon-based QC. This grant will allow us to build on our achievements and collaborations, and to continue to set new directions in this field.  Specifically, we will train future leaders, equipped with expertise in semiconductors, optics, cryogenics and quantum information theory, who will contribute to making the promise of quantum technologies a reality.