CPM Seminar

Optical Spectroscopy in Highly Enriched ²⁸Si: from Isotopic Fingerprints of (Supposedly) Well Known Defects to Applications in Quantum Information

Mike Thewalt

Department of Physics
Simon Fraser University

Natural Si (ⁿSi), the basis of our electronic, communication and information technologies, contains ~92% ²⁸Si, so it is not surprising that many of the properties of highly enriched ²⁸Si are almost indistinguishable from those of ⁿSi. We were therefore surprised to discover[1] that ²⁸Si was remarkably different from ⁿSi in a very important way the linewidths of many different optical transitions can be more than an order of magnitude narrower in ²⁸Si than in ⁿSi, even though those linewidths in ⁿSi are already typically sharper than in other semiconductors.

This huge improvement in spectral resolution has revealed new phenomena and potential applications. Recently[2] we have found that the luminescence of many well known deep centers has resolved fine structure in ²⁸Si which reveals an isotopic fingerprint of the defect constituents, leading to many surprises regarding the actual composition of what were thought to be well-understood defects. We have also resolved hyperfine components in the optical spectra of several centers, and in particular of the bound exciton associated with the shallow donor ³¹P [3]. Both the electronic and nuclear spins of ³¹P have been the basis of many proposed schemes for quantum computation in Si, which all suffer from the problem of reading out the spin state of a single impurity. The new ability to measure the ³¹P nuclear spin optically, and also to polarize it by dynamic pumping, and to selectively ionize donors in specific electronic and nuclear spin states opens up a number of promising new approaches for Si-based quantum computation.

[1] D. Karaskaij et al., Phys. Rev. Lett. 26, 6010 (2001).
[2] M. Steger et al., Phys. Rev. Lett. 100, 177402 (2008).
[3] A. Yang et al., Phys. Rev. Lett. 97, 227401 (2006).