[1] Department of Physics,
[2] Present addresses: Institute for Quantum Information and Matter,undefined
[3] California Institute of Technology,undefined
[4] Pasadena,undefined
[5] California 91125,undefined
[6] USA (J.M.F.); Quantronics Group,undefined
[7] Service de Physique de l’Etat Condensé (CNRS,undefined
[8] URA 2464),undefined
[9] IRAMIS,undefined
[10] CEA-Saclay,undefined
[11] 91191 Gif-sur-Yvette,undefined
[12] France (K.J.).,undefined