systems as the environment in a decoherence experiment. This work has been partially supported by the Spanish Ministerio de Educaci´ on y Ciencia and by the European regional development fund (FEDER) under projects number FIS2005- 01105, FIS2006-12783-C03-01 FPA2006-13807-C02-02 and FPA2007-63074, by Comunidad de Madrid and CSIC under project 200650M012, and by Junta de Analuc´ıa under projects FQM160, FQM318, P05-FQM437 and P07-FQM-02962. A.R. is supported by the Spanish program ”Juan de la Cierva”, and P. P-F., by a grant from the Plan Propio of the University of Sevilla. [1] W. H. Zurek, Rev. Mod. Phys. 75 , 715 (2003). [2] M. Nielsen and I. Chuang, Quantum Computation and Quantum Information (Cambridge University Press, Cambridge, UK, 2000). [3] H. T. Quan, Z. Song, X. F. Liu, P. Zanardi, and C. P. Sun, Phys. Rev. Lett. 96 , 140604 (2006). [4] F. M. Cucchietti, S. Fernandez-Vidal, and J. P. Paz, Phys. Rev. A 75 , 032337 (2007). [5] C. Cormick and J. P. Paz, Phys Rev. A 77 , 022317 (2008). [6] D. Rossini, T. Calarco, V. Giovannetti, S. Montangero, and R. Fazio, Phys. Rev. A 75 , 032333 (2007). [7] P. Cejnar, S. Heinze, and M. Macek, Phys. Rev. Lett. 99 , 100601 (2007). [8] P. Cejnar and J. Jolie, arXiv:0807.3467 (2008). [9] W. D. Heiss, F. G. Scholtz, and H. B. Geyer, J. Phys. A 38 , 1843 (2005); F. Leyvraz and W. D. Heiss, Phys. Rev. Lett. 95 , 050402 (2005); W. D. Heiss, J. Phys. A 39 , 10081 (2006). [10] S. Heinze, P. Cejnar, J. Jolie, and M. Macek, Phys. Rev. C 73 , 014306 (2006); M. Macek, P. Cejnar, J. Jolie, and S. Heinze, Phys. Rev. C 73 , 014307 (2006); P. Cejnar, M. Macek, S. Heinze. J. Jolie, and J. Dobes, J. Phys. A 39 , L515 (2006). [11] M. A. Caprio, P. Cejnar, and F. Iachello, Ann. Phys 323 , 1106 (2008). [12] J. Vidal, J. M. Arias, J. Dukelsky, J. E. Garc´ıa-Ramos, Phys. Rev. C 73 , 054305 (2006); J. M. Arias, J. Dukelsky, J. E. Garc´ıa-Ramos, and J. Vidal, Phys. Rev. C 75 , 014301 (2007). [13] D. Bonatsos, E. A. McCutchan, R. F. Casten, and R. J. Casperson, Phys. Rev. Lett. 100 , 142501 (2008). 9