A posteriori teleportation

The article by Bouwmeester et al.1 on experimental quantum teleportation constitutes an important advance in the burgeoning field of quantum information. The experiment was motivated by the proposal of Bennett et al.2 in which an unknown quantum state is ‘teleported’ by Alice to Bob. As illustrated in Fig. 1, in the implementation of this procedure by Bouwmeester et al.1, an input quantum state is ‘disembodied’ into quantum and classical components, as in the original protocol2. However, in contrast to the original scheme, Bouwmeester et al.'s procedure necessarily destroys the state at Bob's receiving terminal, so a ‘teleported’ state can never emerge as a freely propagating state for subsequent examination or exploitation. In fact, teleportation is achieved only as a postdiction.Figure 1The teleportation set-up of ref.1PBS, polarizing beam splitter.[graphic not available: see fulltext]