  The dependence of the electric resistance R of nanoperforated graphene
samples on the position of the Fermi level, which is varied by the gate voltage
Vg, has been studied. Nanoperforation has been performed by irradiating
graphene samples on a Si/SiO$_2$ substrate by heavy (xenon) or light (helium)
ions. A series of regular peaks have been revealed on the R(Vg) dependence at
low temperatures in zero magnetic field. These peaks are attributed to the
passage of the Fermi level through an equidistant ladder of levels formed by
orbitally quantized states of edge Dirac fermions rotating around each
nanohole. The results are in agreement with the theory of edge states for
massless Dirac fermions.
