  The coherence of quantum Hall (QH) edges play the deciding factor in
demonstrating an electron interferometer, which has potential to realize a
topological qubit. A Graphene p-n junction (PNJ) with co-propagating spin and
valley polarized QH edges is a promising platform for studying an electron
interferometer. However, though a few experiments have been attempted for such
PNJ via conductance measurements, the edge dynamics (coherent or incoherent) of
QH edges at a PNJ, where either spin or valley symmetry or both are broken,
remain unexplored. In this work, we have carried out the measurements of
conductance together with shot noise, an ideal tool to unravel the dynamics, at
low temperature (~ 10mK) in a dual graphite gated hexagonal boron nitride (hBN)
encapsulated high mobility graphene device. The conductance data show that the
symmetry broken QH edges at the PNJ follow spin selective equilibration. The
shot noise results as a function of both p and n side filling factors reveal
the unique dependence of the scattering mechanism with filling factors.
Remarkably, the scattering is found to be fully tunable from incoherent to
coherent regime with the increasing number of QH edges at the PNJ, shedding
crucial insights into graphene based electron interferometer.
