Marshall Stoneham speaks at E-MRS Spring Meeting in Strasbourg (30 May 2007)

The E-MRS 2007 Spring Meeting took place in Strasbourg and was co-chaired by LCN's Prof Ian Boyd. Another LCN researcher, Prof Marshall Stoneham gave a presentation formally entitled "The Quantum in Your World: What Could the Quantum Do for You?". In this presentation he built a case for the emergence of simple demonstration quantum computers based on silicon technology by 2010. While admitting that "when you think of quantum you think of things that are non-intuitive," Stoneham also contends that "nanoscales force us to think quantum."

In answering the question "Why do we need quantum?", he cited inevitability and opportunity. The inevitability comes from the fact that present trends indicate that by 2020 the number of electrons required to switch a transistor will be exactly one. The opportunity lies in the possibility of seeking a radical quantum technology that lives alongside Si technology, according to Stoneham. "Ideally, the quantum technology would be based on silicon, using off-the-shelf techniques," he stated. He quickly added the proviso, "But not just any shelf, only the best of shelves."

After reviewing the nature of classical computing, Stoneham delved into quantum computing with its strange and non-intuitive qubits, entanglement ("a quantum dance"), and decoherence properties. He then proposed one method to produce a quantum computer based on optically controlled spins in an Si-based device. The process starts with a bare Si wafer, followed by a 20-nm to 100-nm-thick layer randomly doped with qubits. Next, "control donors" are randomly doped alongside the qubits. You can control the qubits by optical excitation of the control donor materials, and read out the state of the qubits through the reverse process. The random doping will result in patches of material (approximately 2 microns in diameter) where qubits and control donors are in close enough proximity to be effective. This will give a maximum of 20 gates per patch, which Stoneham called "useful, but not brilliant." So you need "flying qubits" that will connect the patches into a larger system with many more gates. He says that we already think we have the way to do this, and he is applying for a patent. "All the methods to produce and run a quantum device have been done by someone somewhere already," he says. "Putting it all together is very hard."

Stoneham has gone so far as to conceive a business plan for quantum computing devices. He divides their usage into 5 categories:

• The probable (factorization, searches);
• The possible (modeling quantum systems);
• The conceivable (hard problems like turbulence)
• The frivolous (quantum games, which he believes will inevitably come first); and
• The not-yet conceived.