Pattern recognition on the quantum Bloch sphere
  We introduce a framework suitable for describing pattern recognition task using the mathematical language of density matrices. In particular, we provide a one-to-one correspondence between patterns and pure density operators. This correspondence enables us to: i) represent the Nearest Mean Classifier (NMC) in terms of quantum objects, ii) introduce a Quantum Classifier (QC). By comparing the QC with the NMC on different 2D datasets, we show the first classifier can provide additional information that are particularly beneficial on a classical computer with respect to the second classifier. 
Giuseppe Sergioli, Enrica Santucci, Luca Didaci, Jaroslaw A. Miszczak,   Roberto Giuntini
quant-ph cs.CV