### Abstract

In recent papers (Refs [1-4]) it is shown that if N copies of an SU(2) gate are available, one can estimate it with a square error that goes to 0 as 1/N^2 (instead of 1/N as one normally expects in statistics). This is achieved by using an Nfold entangled state as input. In my talk I will try to show that this is also possible for SU(d) with d > 2.

[1] M. Hayashi, (2004), quant-ph/0407053. [2] E. Bagan, M. Baig, and R. Munoz-Tapia, Phys. Rev. A 69, 050303 (2004), quant-ph/0303019. [3] E. Bagan, M. Baig, and R. Munoz-Tapia, Phys. Rev. A 70, 030301 (2004), quant-ph/0405082. [4] G. Chiribella, G. D.Ariano, P. Perinotti, and M. Sacchi, (2004), quant-ph/0405095.