Toward measurement-based quantum computing using solid state spins

Recent developments in the theory of measurement-based quantum computing reduce the problem of building a quantum computer to that of achieving high quality rotation and measurement of single qubits. The first generation of such machines may well therefore consist of individual modules each containing a single quantum system that embodies the qubit. The first demonstrations of entanglement of electronic qubits by measurement have been performed recently in ion traps. The leading contenders for physical qubits in the solid state are the negatively charged nitrogen-vacancy defect in diamond and the Stranski Krastanow quantum dot, each of which offers long electronic spin dephasing times and convenient spin-sensitive optical transitions. In this article we will compare the strengths and weaknesses of these two systems and discuss some of the challenges to be met in constructing a measurement based quantum computer in the solid state.