Quantum Computing with Spins in Solids

The ability to perform high-precision one- and two-qubit operations is sufficient for universal quantum computation. For the Loss–DiVincenzo proposal to use single-electron spins confined to quantum dots as qubits, it is therefore sufficient to analyze only single- and coupled double-dot structures, since the strong Heisenberg exchange coupling between spins in this proposal falls off exponentially with distance and long-ranged dipolar coupling mechanisms can be made significantly weaker. A scaled-up quantum computer could then be constructed from many single- and double-dot elements. This scalability of the Loss–DiVincenzo design is both a practical necessity for eventual applications of multiqubit quantum computing and a great conceptual advantage, making analysis of the relevant components relatively transparent and systematic. We review the Loss–DiVincenzo proposal for quantum-dot-confined electron-spin qubits, and survey the current state of experiment and theory regarding the relevant single- and double-quantum dots, with a brief look at some related alternative schemes for quantum computing.