  Quantum particles can penetrate potential barriers by tunneling (1). If that
barrier is rotating, the tunneling process is modified (2,3). This is typical
for electrons in atoms, molecules or solids exposed to strong circularly
polarized laser pulses (4,5). Here we measure how the transmission probability
through a rotating tunnel depends on the sign of the magnetic quantum number m
of the electron and thus on the initial sense of rotation of its quantum phase.
We further show that the electron keeps part of that rotary motion on its way
through the tunnel by measuring m-dependent modification of the electron
emission pattern. These findings are relevant for attosecond metrology as well
as for interpretation of strong field electron emission from atoms and
molecules (6-13) and directly demonstrates the creation of ring currents in
bound states of ions with attosecond precision. In solids, this could open a
way to inducing and controlling ring-current related topological phenomena
(14).
