Mitigating the unexpected with quantum error correction

As we saw in the previous recipe, it is good to understand how your measurements behave, to statistically be able to correct incorrect readouts. But in the end, a measurement is just a measurement, and a measurement of a qubit will result in either 0 or 1. If the state of the qubit that you measure turns out to be instead of the expected , it doesn't matter that you statistically corrected for measurement mistakes; your qubit is off by 100%.

There are a lot of things that can perturb our qubits, from gate errors to just plain physics that causes the qubit to decohere and dephase (remember the T1 and T2 times). In the classical computing world, we can periodically check in on our bits, and apply error correction coding to make sure that they behave. Digital error correction is one of the reasons that digital communication works and that you can play digital media, CDs, DVDs, and Blu-ray disks and actually hear or see what...