  In this paper, we consider two-flavor QCD at zero temperature and finite
isospin chemical potential ($\mu_I$) using a model-independent analysis within
chiral perturbation theory at next-to-leading order. We calculate the effective
potential, the chiral condensate and the pion condensate in the pion-condensed
phase at both zero and nonzero pionic source. We compare our finite pionic
source results for the chiral condensate and the pion condensate with recent
(2+1)-flavor lattice QCD results and find that they are in excellent agreement.
