  Chiral quasiparticles in Bernal-stacked bilayer graphene have
valley-contrasting Berry phases of 2{\pi}. This nontrival topological
structure, associated with the pseudospin winding along a closed Fermi surface,
is responsible for various novel electronic properties, such as anti-Klein
tunneling, unconventional quantum Hall effect, and valley Hall effect1-6. Here
we show that the quantum interference due to intervalley scattering induced by
atomic defects/impurities provides further insights into the topological nature
of the bilayer graphene. The scattered chiral quasiparticles between distinct
valleys with opposite chirality undergoes a rotation of pseudospin that results
in the Friedel oscillation with wavefront dislocations. The number of
dislocations reflects the information about pseudospin texture and hence can be
used to measure the Berry phase7. As demonstrated both experimentally and
theoretically, the Friedel oscillation, depending on the atomic defect/impurity
at different sublattices, can exhibit N = 4, 2, or 0 additional wavefronts,
characterizing the 2{\pi} Berry phase of the bilayer graphene. Our results not
only provide a comprehensive study of the intervalley quantum interference in
bilayer graphene, but also shed lights on the pseudospin physics.
