  The inflaton is highly likely to settle in a squeezed vacuum state after
inflation. The relic inflaton after inflation and reheating undergoes a damped
oscillatory motion and contributes to the effective cosmological constant. We
interpret the renormalized energy density from the squeezed vacuum state as an
effective cosmological constant. Using the recent observational data on the
cosmological constant, we find the constraint on the squeeze parameter of the
inflaton in the early universe.
