The race to build useful quantum computers has been dominated by devices based on superconducting circuits, which now run to thousands of qubits. But other platforms have certain characteristics that make them competitive even if they can’t yet match those numbers. Computers whose qubits are formed by electron spins in semiconductor quantum dots, for example, have an advantage in that they can be built using complementary-metal-oxide-semiconductor (CMOS) techniques that already underlie the mass-production of integrated circuits. Now Irene Fernández de Fuentes at Delft University of Technology in the Netherlands and colleagues have demonstrated a spin-based quantum computer containing six qubits [1]. The experiment identifies some of the challenges that must be overcome to scale up to tens or hundreds of qubits.
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