Dark energy condensate and vacuum energy

Many candidate models for dark energy are based on the existence of a classical scalar field. In the context of Quantum Field Theory (QFT), we briefly discus the condensation of such a field from a light quantum scalar field produced by gradual decay of a heavy particle during cosmological time. We obtain the necessary conditions for survival of the condensate in an expanding universe and show that this process is directly related to quantum nature of the field which preserves the coherence of the condensate at cosmological distances. We also suggest a new interpretation of {\it vacuum energy} in QFT in curved space time which can potentially solve the puzzle of huge deviation of what is considered to be the vacuum energy from observations of dark energy.