If qubits—the building blocks of a quantum computer—were humans, no-one would employ them. They would be unreliable. They would forget everything they learned. Only trivial jobs could be entrusted to them, and then only after painstakingly marshalling them into teams. On top of all that, they would insist on meticulously prepared and maintained workspaces.

The work itself, though, would happen at lightning speed.

That promise—of a literal quantum leap in computing power—has moved beyond the