Lens-Free Optical Detection of Thermal Motion of a Submillimeter Sphere Diamagnetically Levitated in High Vacuum

Levitated oscillators with millimeter or submillimeter sizes are particularly attractive due to their potential role in research areas such as detecting high-frequency gravitational waves, dark matter, dark energy, and establishing high-precision compact gravitometers and accelerometers. However, it remains a challenge to achieve efficient measurement of the oscillator's motion. A lens-free highly sensitive submillimeter diamagnetically levitated oscillator is proposed and experimentally demonstrated with detection precision that enables us to observe the oscillator's thermal motion. The acceleration sensitivity measured is down to $9.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$g/$\sqrt{H\phantom{\rule{0}{0ex}}z}$ at room temperature.