Mike Thewalt: The remarkable optical properties of highly enriched 28Si – new tools and approaches for silicon-based quantum information research

Mike Thewalt, Simon Fraser University

Most schemes for implementing quantum computing using a silicon-based technology already envision the use of enriched ²⁸Si, since the elimination of the nuclear spin of the ²⁹Si provides a completely spin-free host into which impurity electronic and nuclear spins, which are to be used as qubits, can be placed. This results in greatly increased coherence times for these spins – both the electron and nuclear T₂ for the shallow donor ³¹P, one of the main qubit candidates, have recently been shown to exceed one second in highly enriched ²⁸Si. However, we discovered in 2001 another quite unexpected property of enriched ²⁸Si, namely, that the linewidths of a wide variety of optical transitions are more than an order of magnitude narrower than the already very sharp transitions in natural Si. This has lead to the development of new optical methods for the measurement of both the electronic and nuclear spins of ³¹P in ²⁸Si, and for the optical hyperpolarization of both spin systems. I will show how this enables a novel optical NMR measurement of dilute ³¹P in a regime inaccessible to conventional NMR. I will discuss briefly several proposals for the measurement of the electronic and nuclear spins of a single ³¹P using these optical methods, as well as new results for the shallow donor ²⁰⁹Bi, which has a rich hyperfine structure due to the large I = 9/2 nuclear spin.