  We have extracted information about real time dynamics of 4He systems from
noisy imaginary time correlation functions f(tau) computed via Quantum Monte
Carlo (QMC): production and falsification of model spectral functions s(omega)
are obtained via a survival-to-compatibility with f(tau) evolutionary process,
based on Genetic Algorithms. Statistical uncertainty in f(tau) is promoted to
be an asset via a sampling of equivalent f(tau) within the noise, which give
rise to independent evolutionary processes. In the case of pure superfluid 4He
we have recovered from exact QMC simulations sharp quasi-particle excitations
with spectral functions displaying also the multiphonon branch. As further
applications, we have studied the impuriton branch of one 3He atom in liquid
4He and the vacancy-wave excitations in hcp solid 4He finding a novel roton
like feature.
