 Concatenated quantum error-correcting code

A concatenated quantum code replaces each physical qubit of an outer code by a logical qubit of an inner code. Correction proceeds from inner blocks to outer blocks. For independent errors and ideal correction, a logical-error map $f$ iterates as $p_{\ell +1}=f(p_{\ell })$. This recursion describes the code/channel model and does not by itself include errors in encoding and recovery gates.

// Target: quantum-error-correction.bigb