  The Continuous Spontaneous Localization (CSL) model predicts a tiny break of
energy conservation via a weak stochastic force acting on physical systems,
which triggers the collapse of the wave function. Mechanical oscillators are a
natural way to test such a force; in particular levitated micro-mechanical
oscillator has been recently proposed to be an ideal system. We report a
proof-of-principle experiment with a micro-oscillator generated by a
micro-sphere diamagnetically levitated in a magneto-gravitational trap under
high vacuum. Due to the ultra-low mechanical dissipation, the oscillator
provides a new upper bound on the CSL collapse rate, which gives an improvement
of two orders of magnitude over the previous bounds in the same frequency
range, and partially reaches the enhanced collapse rate suggested by Adler.
Although being performed at room temperature, our experiment has already
exhibits advantages over those operating at low temperatures previously
reported. Our results experimentally show the potential of
magneto-gravitational levitated mechanical oscillator as a promising method for
testing collapse model. Further improvements in cryogenic experiments are
discussed.
