  We have developed a nanomechanical resonator, for which the motional degree
of freedom is a superfluid 4He oscillating flow confined to precisely defined
nanofluidic channels. It is composed of an in-cavity capacitor measuring the
dielectric constant, which is coupled to a superfluid Helmholtz resonance
within nanoscale channels, and it enables sensitive detection of nanofluidic
quantum flow. We present a model to interpret the dynamics of our superfluid
nanomechanical resonator, and we show how it can be used for probing confined
geometry effects on thermodynamic functions. We report isobaric measurements of
the superfluid fraction in liquid 4He at various pressures, and the onset of
quantum turbulence in restricted geometry.
