  In quantum optomechanics, finding materials and strategies to limit losses
has been crucial to the progress of the field. Recently, superfluid 4He was
proposed as a promising mechanical element for quantum optomechanics. This
quantum fluid shows highly desirable properties (e.g. extremely low acoustic
loss) for a quantum optomechanical system. In current implementations,
superfluid optomechanical systems suffer from external sources of loss, which
spoils the quality factor of resonators. In this work, we propose a new
implementation, exploiting nanofluidic confinement. Our approach, based on
acoustic resonators formed within phononic nanostructures, aims at limiting
radiation losses to preserve the intrinsic properties of superfluid 4He. In
this work, we estimate the optomechanical system parameters. Using recent
theory, we derive the expected quality factors for acoustic resonators in
different thermodynamic conditions. We calculate the sources of loss induced by
the phononic nanostructures with numerical simulations. Our results indicate
the feasibility of the proposed approach in a broad range of parameters, which
opens new prospects for more complex geometries.
