SiGe: Materials and Devices for Quantum Computing?

Quantum dots in silicon/silicon-germanium offer several potential advantages for quantum computing, including long spin coherence times and compatibility with silicon device fabrication. Recently, it has become possible to use Schottky gates to define quantum dots in Si/SiGe heterostructures at low temperatures. Here we describe progress in the fabrication and measurement of silicon quantum dots, demonstrating extremely low electron number, low noise, and charge stability over many weeks. In addition to quantum dots and nanostructures, we also show that silicon-germanium single crystals can be fabricated into ultra-thin, freestanding membranes. Thicknesses as thin as one hundred nanometers and lateral widths as large as a centimeter across have been achieved. Such nanomembranes are flexible and, importantly for quantum computing, can be elastically strained without the generation of defects. Nanomembranes can be transferred to essentially arbitrary substrates, including rigid substrates like oxidized silicon for the creation of quantum devices, as well as flexible substrates. Measurements on membranes both before and after the generation of elastic strain confirm that elastic strain sharing generates the required band alignments for the creation of quantum wells. We use this technology to create modulation-doped two-dimensional electron gases