With this system, the researchers showed that they could control the states of the logical qubits in a fault-tolerant way and correct any single-qubit errors that occurred.

A type II error is a statistical term referring to accepting a false null hypothesis. It contrasts with a type I error that occurs when rejecting a true null hypothesis.

Errors inevitably occur, for example, during computations. An ancilla is used to repeatedly perform measurements that detect errors.