TIME AND HISTORY IN QUANTUM TUNNELING

The time a particle spends while tunneling is a subject of long disput e, whose recent history owes much to Rolf Landauer. While I do not hav e the space to say a great deal about the history of the tunneling tim e, I am going to try to argue that the tunneling time itself may have a great deal to teach us about history. After an abbreviated descripti on of some of the surprising results of optical experiments on tunneli ng, this paper outlines a new theoretical approach to the reconstructi on of the past in quantum mechanics; for questions of particles known to have been transmitted through a tunnel barrier, this is precisely t he type of formalism required. We will see that our results have much in common with earlier approaches due to Landauer and Buttiker, althou gh the interpretations may diverge. Roughly speaking, our view is that the history of a tunneling particle may be described more completely than merely by its wavefunction. We will discuss the measurable conseq uences of this claim, and (briefly) an atom optics experiment being as sembled at Toronto in order to test them. Finally, I will present some recent speculations about a quantifiable sense in which a tunneling p article may be 'in two places at one time', which we also hope to be a ble to test at Toronto. (C) 1998 Academic Press Limited.