Quantum condensation of liquid 4He

We present experimental results on the condensation of He-4 atoms on the surface of liquid He-4. 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 He-4 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.