  We discuss the conditions for the classicality of quantum states with a very
large number of identical particles. By treating the center of mass as a
Bohmian particle, we show that it follows a classical trajectory when the
distribution of the Bohmian positions in just one experiment is always equal to
the marginal distribution of the quantum state in physical space. This result
can also be interpreted as a unique-experiment generalization of the well-known
Ehrenfest theorem. We also demonstrate that the classical trajectory of the
center of mass is fully compatible with a conditional wave function solution of
a classical non-linear Schr\"odinger equation. Our work shows clear evidence
for a quantum-classical inter-theory unification and opens new possibilities
for practical quantum computations with decoherence.
