Glossary
Every technical term this platform uses, with what it means and — the part that is harder to find elsewhere — the mistake it prevents. On this subject the intuitive reading is often the wrong one, so each entry says what a reader would otherwise get wrong.
Error correction
- Surface code
The most studied way to build a logical qubit, laying physical qubits on a two-dimensional grid where only neighbours interact.
Easy to get wrong: It only suppresses errors below its threshold. Above that, adding more qubits makes the logical error rate worse, not better.
Seen in use on /qec
- MWPMalso minimum-weight perfect matching, matching
A decoder that pairs up detection events so the total 'distance' between paired events is as small as possible.
Easy to get wrong: Fast and accurate on surface codes, but its accuracy depends on the noise matching the model it was given. A decoder tuned for depolarizing noise can do poorly when readout error dominates.
Seen in use on /qec/lab
- Threshold
The physical error rate below which adding more qubits to a code helps, and above which it hurts. Roughly 1% for the surface code.
Easy to get wrong: Results measured above threshold say nothing about behaviour below it. The two are different regimes, not two points on one curve.
Seen in use on /qec/lab