  Quantum Hall edge modes are chiral while quantum spin Hall edge modes are
helical. However, unlike chiral edge modes which always occur in topological
systems, quasi-helical edge modes may arise in a trivial insulator too. These
trivial quasi-helical edge modes are not topologically protected and therefore
need to be distinguished from helical edge modes arising due to topological
reasons. Earlier conductance measurements were used to identify these helical
states, in this work we report on the advantage of using the non local shot
noise as a probe for the helical nature of these states as also their
topological or otherwise origin and compare them with chiral quantum Hall
states. We see that in similar set-ups affected by same degree of disorder and
inelastic scattering, non local shot noise "HBT" correlations can be positive
for helical edge modes but are always negative for the chiral quantum Hall edge
modes. Further, while trivial quasi-helical edge modes exhibit negative
non-local "HBT" charge correlations, topological helical edge modes can show
positive non-local "HBT" charge correlation. We also study the non-local spin
correlations and Fano factor for clues as regards both the distinction between
chirality/helicity as well as the topological/trivial dichotomy for helical
edge modes.
