Introduce LER

src/thesis/chapters/2_fundamentals.tex

@@ -1660,6 +1660,12 @@ Algorithm \ref{alg:bpgd} shows this process.
 Note that as the Tanner graph only has $n$ \acp{vn}, this is a
 natural constraint on the maximum number of outer iterations of the algorithm.
 
+Quantum degeneracy additionally necessitates some care in the way
+error rates are computed in simulations.
+We must consider the fact that multiple solutions are valid by
+comparing the logical states, computed by measuring the logical operators.
+This way, we obtain the \ac{ler}.
+
 % TODO: Explain that setting the channel LLR to infinity is the same
 % as a hard decision and ignoring the VN in the further decoding
 % tex-fmt: off

src/thesis/chapters/3_fault_tolerant_qec.tex

@@ -1040,9 +1040,8 @@ $p_\text{phys}$.
 
 % Per-round LER
 
-% TODO: Introduce the logical error rate
 Another aspect that is important to consider is the meaning of the
-logical error rate in the context of a \ac{qec} system with multiple
+\ac{ler} in the context of a \ac{qec} system with multiple
 rounds of syndrome measurements.
 In order to facilitate the comparability of results obtained from
 simulations with different numbers of syndrome extraction rounds, we