  Within the last decade, experimentalists have demonstrated their impressive
ability to control mechanical modes within mesoscopic objects down to the
quantum level: it is now possible to create mechanical Fock states, to entangle
mechanical modes from distinct objects, store quantum information or transfer
it from one quantum bit to another, among the many possibilities found in
today's literature. Indeed mechanics is quantum, very much like spins or
electromagnetic degrees of freedom. And all of this is in particular referred
to as a new engineering resource for quantum technologies. But there is also
much more beyond this utilitarian aspect: invoking the original discussions of
Braginsky and Caves where a quantum oscillator is thought of as a quantum
detector for a classical field, namely a gravitational wave, it is also a
unique sensing capability for quantum fields. The subject of study is then the
baths to which the mechanical mode is coupled to, let them be known or unknown
in nature. This Letter is about this new potentiality, that addresses
stochastic thermodynamics, potentially down to its quantum version, the search
for a fundamental underlying (random) field postulated in recent theories that
can be affiliated to the class of the Wave-function Collapse models, and more
generally open questions of Condensed Matter like the actual nature of the
elusive (and ubiquitous) Two-Level Systems present within all mechanical
objects. But such research turns out to be much more demanding than the usage
of a few quantum mechanical modes: all the known baths have to be identified,
experiments have to be conducted in-equilibrium, and the word "mechanics" needs
to be justified by a real ability to move substantially the centre-of-mass when
a proper drive tone is applied to the system.
