Impurities as qubits in semiconductors
Much of our recent work is based on our earlier discovery that many optical transitions are much sharper in enriched 28Si than they are in natural silicon. In particular, we have shown that this increased resolution allows us to observe the hyperfine splitting resulting from the coupling of the donor electron and nuclear spins in the donor bound exciton transitions. We can use these transitions to optically measure the donor electron and nuclear spins, and to hyperpolarize them. This has many applications for research in semiconductor-based quantum information, since the donor electron and nuclear spins are prime qubit candidates. It has already lead to the measurement of record quantum coherence times for a solid-state system.
Future directions will expand beyond the prototypical donor in silicon, phosphorus, to study deeper donors such as bismuth, which has a much larger hyperfine interaction, and a large I=9/2 nuclear spin.
The research is in close collaboration with the Quantum Spin Dynamics Group at Oxford University, the Lyon Group at Princeton University and the Itoh Research Group at Keio University, where other aspects of similar systems are being studied.
The lab has state-of-the-art equipment for a wide variety of high resolution and high sensitivity optical spectroscopy in semiconductors spanning the far-infrared to the visible. While most recent work has focused on isotopically-enriched silicon, we also study other semiconductors and heterostructures which are provided by our collaborators.