How does it scale? Comparing quantum and classical nonlinear
... presented there, and then, for we are free to do so, set n̄
n and χ̄ 2 2d0ijk ∕ ε0 , as well as approximate vm ≈ c ∕ n.
Comparing our quantum [Eq. (12)] and classical [Eqs. (19)
and (20)] expressions, we first note that SPDC, DFG, and SHG
all scale the same way with the characteristic power, P, ...