More Efficient Purifying scheme via Controlled- Controlled NOT Gate
  A new modified version of the Oxford purification protocol is proposed. This version is based on the controlled-controlled NOT gate instead of controlled NOT in the original one. Comparisons between the results of the new version and the original and an earlier modification are given. It is found that the new version converges faster and consumes fewer initial qubit pairs of low fidelity per final qubit pair of high fidelity. 
Nasser Metwally and Abdel-Shafy F. Obada