Quantum factor graphs

The natural Hilbert Space of quantum panicles can implement maximum-likelih ood (ML) decoding of classical information. The "Quantum Product Algorithm" (QPA) is computed on a Factor Graph, where function nodes are unitary matr ix operations followed by appropriate quantum measurement. QPA is like the Sum-Product Algorithm (SPA), but without summary, giving optimal decode wit h exponentially finer detail than achievable using SPA. Graph cycles have n o effect on QPA performance. QPA must be repeated a number of times before successful and the ML codeword is obtained only after repeated quantum "exp eriments". ML amplification improves decoding accuracy, and Distributed QPA facilitates successful evolution.