Quantum condensation of liquid 4He

We present experimental results on the condensation of 4He atoms on the surface of liquid 4He. We show that there is quantum condensation with the creation of phonons and R+rotons in one-to-one processes as atoms go into the Bose-Einstein condensate. These phonon and R+roton signals can be recognized by their time of flight, their angular distribution and their dependence on the ambient temperature. Condensing atoms also create ripplons with a high probability. We derive rate equations for the growth of the ripplon density and the ripplon decay by the creation of bulk phonons. During the atom pulse a dynamic equilibrium is established. The low-energy phonons that are created by ripplon-ripplon scattering can easily be detected and distinguished from the phonons created by quantum condensation. From measured data, estimates are made of the probabilities of creating phonons, R+rotons and ripplons in condensation processes as well as estimates of the quantum evaporation probabilities of phonons and rotons. We clearly detect R+rotons directly with a bolometer in the liquid 4He and show why the signal of R+rotons is obscured by the low-energy phonon signal when both the source and detector are in the liquid helium. Values of the Kapitza conductance for the Zn bolometers are derived