  The quantum vortices formed as a result of barrier-suppression ionization of
a two-dimensional hydrogen atom by an ultrashort laser pulse are theoretically
investigated. Using an analytical expression for the wave function of a
photoelectron in the momentum representation, the probability flux density is
investigated. In this case, both the standard definition of a flux and an
alternative one are used. The latter, due to the sensitivity to the phase of
the wave function, makes it possible to identify quantum vortices in the
momentum space.
