Glossary / Quantum computing
Fault-tolerant quantum computing
Running quantum computations so that, even though components fail at some rate, layered error correction lets arbitrarily long calculations finish correctly.
Error correction itself makes errors. Even so, if the error rate per operation is below a certain value — the threshold — then adding more layers of correction can push the overall error as low as you like. That is the threshold theorem, proved in 1996–97[1][2].
The theorem is what turned the quantum computer into a machine that can in principle be built. When companies aim for fault tolerance, they mean hardware whose physical error rates are well below threshold and which can keep correction running indefinitely.
Related terms
- Quantum error correctionSpreading the information of fragile qubits across many of them, so that errors can be detected and fixed.
- Logical qubitA single, robust qubit made by bundling many physical qubits together and running error correction on them.
- DecodingThe calculation that takes the measurements from error correction and works out which qubits suffered which errors.