Quantum computers are often described as a glimpse of a faster, more powerful future. The catch is that today’s devices are fragile in a way ordinary computers are not. Their biggest headache is decoherence, the gradual loss of the delicate quantum behavior that makes them useful in the first place. When decoherence sets in, it can trigger two common kinds of mistakes: bit flips and phase flips.

A bit flip is the more intuitive problem. A qubit that should represent ‘0’ can unexpectedly behave like ‘1’. A phase flip is stranger but just as damaging. Even if a qubit stays in a superposition, the relationship between its components can suddenly switch, turning a positive phase into a negative one and scrambling the computation.