  Wave-particle duality is an inherent peculiarity of the quantum world. The
double-slit experiment has been frequently used for understanding different
aspects of this fundamental concept. The occurrence of interference rests on
the lack of which-way information and on the absence of decoherence mechanisms,
which could scramble the wave fronts. In this letter, we report on the
observation of two-center interference in the molecular frame photoelectron
momentum distribution upon ionization of the neon dimer by a strong laser
field. Postselection of ions, which were measured in coincidence with
electrons, allowed choosing the symmetry of the continuum electronic wave
function, leading to observation of both, gerade and ungerade, types of
interference.
