Comment on "Recurrences without closed orbits"

Abstract

In a recent paper Robicheaux and Shaw [Phys. Rev. A 58, 1043 (1998)] calculate the recurrence spectra of atoms in electric fields with non-vanishing angular momentum <L_z> not equal to 0. Features are observed at scaled actions ``an order of magnitude shorter than for any classical closed orbit of this system.&#39;&#39; We investigate the transition from zero to nonzero angular momentum and demonstrate the existence of short closed orbits with L_z not equal to 0. The real and complex ``ghost&#39;&#39; orbits are created in bifurcations of the ``uphill&#39;&#39; and ``downhill&#39;&#39; orbit along the electric field axis, and can serve to interpret the observed features in the quantum recurrence spectra.