Exact and approximate complex potentials for modelling time observables A. Ruschhaupt, J. A. Damborenea, B. Navarro, J. G. Muga and G. C. Hegerfeldt Europhys. Lett., 67 1 (2004) 1-7 Published online: 01 June 2004 DOI: 10.1209/epl/i2004-10046-4