  Using quantum Monte Carlo methods we have studied dilute Bose-Bose mixtures
with attractive interspecies interaction in the limit of zero temperature. The
calculations are exact within some statistical noise and thus go beyond
previous perturbative estimations. By tuning the intensity of the attraction,
we observe the evolution of an $N$-particle system from a gas to a self-bound
liquid drop. This observation agrees with recent experimental findings and
allows for the study of an ultradilute liquid never observed before in Nature.
