  Levitation offers extreme isolation of mechanical systems from their
environment, while enabling unconstrained high-precision translation and
rotation of objects. Diamagnetic levitation is one of the most attractive
levitation schemes, because it allows stable levitation at room temperature
without the need for a continuous power supply. However, dissipation by eddy
currents in conventional diamagnetic materials significantly limits the
application potential of diamagnetically levitating systems. Here, we present a
route towards high $Q$ macroscopic levitating resonators by substantially
reducing eddy current damping using graphite particle based diamagnetic
composites. We demonstrate resonators that feature quality factors $Q$ above
450,000 and vibration lifetimes beyond one hour, while levitating above
permanent magnets in high vacuum at room temperature. The composite resonators
have a $Q$ that is more than 400 times higher than that of diamagnetic graphite
plates. By tuning the composite particle size and density, we investigate the
dissipation reduction mechanism and enhance the $Q$ of the levitating
resonators. Since their estimated acceleration noise is as low as some of the
best superconducting levitating accelerometers at cryogenic temperatures, the
high $Q$ and large mass of the presented composite resonators positions them as
one of the most promising technologies for next generation ultra-sensitive room
temperature accelerometers.
