  We propose a Hanbury Brown and Twiss (HBT) experiment of Cooper pairs on the
edge channels of quantum spin Hall insulators. The helical edge channels
provide a well defined beam of Cooper pairs and perfect Andreev reflections
from superconductors. Surprisingly, the Cooper pairs do not bear a bosonic
nature at all once emitted from the superconductor, and the cross correlation
is strongly negative as for free electrons. This result is counter-intuitive,
and seemingly contradictory to the previous theoretical and recent experimental
results. We will point out that our setup is much closer in spirit to the
original HBT experiment (and different) than those in previous works. We will
argue that these differences affect significantly the results.

Mesoscale and Nanoscale Physics