  In de Sitter ambient space formalism, the linear gravity can be written in
terms of a minimally coupled scalar field and a polarization tensor. In this
formalism, the massless minimally coupled scalar field can be quantized on
Bunch-Davies vacuum state, that preserves the de Sitter invariance, the
analyticity and removes the infrared divergence. The de Sitter quantum linear
gravity is then constructed on Bunch-Davies vacuum state, which is also
covariant, analytic and free of any infrared divergences. We will conclude that
the unique Bunch-Davies vacuum state can be used adequately to constructing the
quantum field theory in de Sitter universe.
