Realizing the potential of quantum computing requires finding viable ways to store and manipulate representations of the binary bits, 0 and 1. The many two-level quantum systems being explored for such qubits include not only the up and down spins of trapped atoms or ions and the polarized states of photons, but also the quantum states of superconducting Josephson junctions and electron spins trapped in quantum dots. A quantum dot is a nanostructure that confines a conduction-band electron in three spatial dimensions.
Quantum-dot qubits take advantage of the extensive experience gained over decades of engineering and manufacturing semiconductor devices. They were proposed1 in 1998 by Daniel Loss (now at the University of Basel, Switzerland) and David DiVincenzo (RWTH Aachen University). A central challenge is to manipulate the electron spin in a time that’s short compared with the time for it to lose coherence, and to do it in a...
