  We present a type of dark energy models where the particles of dark energy
phi are dynamically produced via a quantum transition at very low energies. The
scale where the transition takes places depends on the strength g of the
interaction between phi and a relativistic field varphi. We show that a g
\simeq 10^{-12} gives a generation scale E_gen simeq eV with a cross section
sigma simeq 1 pb close to the WIMPs cross section sigma_w simeq pb at
decoupling. The number density n_phi of the \phi particles are a source term in
the eq. of motion of phi and it generates the scalar potential v(phi)
responsible for the late time acceleration of our universe. Since the
appearance of phi may be at very low scales, close to present time, the
cosmological coincidence problem can be explained simply due to the size of the
coupling constant. We unify dark energy with inflation in terms of a single
scalar field phi, and we use the same potential v for inflation and dark
energy. However, after inflation phi decays completely and reheats the universe
at a scale E_RH propto h^2 m_Pl, where h is the coupling between the SM
particles and varphi. The field phi disappears from the spectrum during, from
reheating until its re-generation, and therefore it does not interfere with the
standard decelerating radiation/matter cosmological model allowing for a
successful unification scheme. The same interaction term that gives rise to the
inflaton decay accounts for the late time re-generation of phi. We present a
simple model where the strength of the g and h couplings are set by the
inflation scale E_I with g=h^2 propto E_I/m_Pl giving a reheating scale E_RH
propto E_I=100TeV and phi-generation scale E_gen propto E_I^2/m_pl=eV << E_RH.
