Materials issues for quantum computation

The new field of quantum computing uses qubits (quantum bits) in place of classical bits to carry out certain types of computation. Physical systems that act as qubits encompass a wide range of technologies, from ions, to local defect states in crystals, and on to microelectronic devices addressable with wire interconnects. Materials issues arise in all of these, and this issue of MRS Bulletin describes how materials challenges and opportunities arise and have been used to make qubit-based quantum circuits using very different materials systems. In this overview article, we first review the universal ideas of how information is introduced and processed in a quantum computer. Comparing quantum to classical computers, for a given number of bits, the information content in a quantum computer is exponentially larger. But quantum computers face a daunting challenge: How do we keep the information from degrading and eventually disappearing? Maintaining the coherence of a quantum computer comes down to specific materials issues for all the approaches studied so far. Advances in materials design and processing have enabled enormous increases in performance, and we review the work described in each of the articles in this issue.