Have quantum scars been observed?

Abstract

Fromhold et al. reply — Unstable but periodic classical orbits are of fundamental importance in quantum chaology6,7. They produce regular clustering of the energy levels6 and certain states exhibit regions of enhanced probability density or ‘scars’ in the neighbourhood of the classical periodic trajectories2. The scarring effect seems to have been unexpected in view of the instability of the periodic orbits8. The typical trajectory is chaotic and irregular, which would be expected to correspond to wavefunctions exhibiting irregular and diffuse patterns of probability density. We recently showed1 that scarred and unscarred states can make very different contributions to a physically measurable quantity, in our case the tunnel current through a semiconductor device.