  We report on nanomechanical resonators with very high-quality factors
operated as mechanical probes in liquid helium \(^4\mathrm{He}\), with special
attention to the superfluid regime down to millikelvin temperatures. Such
resonators have been used to map out the full range of damping mechanisms in
the liquid on the nanometer scale from \(10\,\mathrm{mK}\) up to
\(\sim3\,\mathrm{K}\). The high sensitivity of these doubly-clamped beams to
thermal excitations in the superfluid \(^4\mathrm{He}\) makes it possible to
drive them using the momentum transfer from phonons generated by a nearby
heater. This so-called "\textit{phonon wind}" is an inverse thermomechanical
effect that until now has never been demonstrated, and provides the possibility
to perform a new type of optomechanical experiments in quantum fluids.
