Quantum computing is exciting and important—really!

Quantum computing, say its champions, promises prodigious power. Its basic currency, the qubit, exists in an on/off limbo until it’s read out, so if you could operate on k qubits, a potentially vast space of 2^k values opens up for computation. The fundamental operation on qubits is a rotation. Combine the rotations, and you have logic gates. Combine the logic gates, and you have algorithms. In principle, these algorithms can perform calculations far beyond classical computing’s conceivable reach.

But to wield that power, you need an actual quantum computer, and building one has proved impossible. Qubits live in small, cold enclaves within the classical macroworld. When heat and other environmental disturbances inevitably intrude, they rob a quantum system of its coherence, its entanglement, and its ability to compute