“…At longer times, the wave packet spreads and begins to exhibit non-classical behaviour. The ® rst experimental observation of a radial wave packet was only reported just over a decade ago (ten Wolde et al 1988), despite some earlier theoretical work (Alber et al 1986, Parker andStroud 1986a, b); however, there has since been a great deal of interest in the subject (for example Yeazell et al (1990Yeazell et al ( 1991, Meacher et al (1991), Broers et al (1993), Wals et al (1994), Jones (1996), Lankhuijzen and Noordam (1996), Schumacher et al (1997), Lyons et al (1998) and Ramswell et al (1999)) (see also the excellent reviews by Alber and Zoller (1991) and Jones and Noordam (1997) and references therein).…”