The Quantum Information Science and Technology (QIST) Grand Challenge is a three-year research effort aimed at producing the world’s first silicon spin based quantum bit (qubit). Qubits are the basic information storage elements of quantum computers, which perform quantum information processing and offer the opportunity to efficiently solve problems that are numerically challenging for classical computers. Quantum computers, therefore, may someday augment conventional classical computers by employing some of the unusual properties of quantum systems to speed up computation.

A critical challenge in building a quantum information processing system is the need to couple and manipulate tiny qubits in the form of a quantum circuit that produces a useful function. Sandia researchers are focused on the basic questions related to the feasibility of manufacturing a simple qubit and simple quantum circuits – a task that includes demonstrating a silicon qubit, integrating the qubit with classical CMOS (Complementary Metal Oxide Semiconductor) technology, and designing quantum error correction circuits that are tuned to the physical qubit’s unique properties. Sandia’s approach is to physically encode quantum information in the spin state of an electron that is confined in a silicon quantum dot. Although gallium arsenide quantum dots have been demonstrated, quantum dots made from silicon are expected to have longer decoherence times and improved integration with silicon-based classical circuitry. A significant challenge is to engineer the Si qubit and the surrounding electronics all operating at ~ 0.1K (0.1 degrees above absolute zero).

Figure 1 (a) scanning electron microscope image of Sandia's dual quantum dot structure fabricated in silicon (the dots suggest single electrons confined by the surrounding gates); (b) schematic cross section of the quantum dot structure showing the position of the single electron locations; and (c) schematic representation of spin manipulation using rotation and precession of two different spins.