Wave-function collapse models predict a tiny break of energy conservation via a weak spontaneous stochastic force acting on the system, and are attracting experimental studies. Among various physical systems, mechanical based methods provide a direct way to test such collapse induced force without any assumptions on its spectral characteristics. Levitated micro-mechanical oscillator has been recently proposed to be an ideal system. We demonstrated 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 and small mass, the oscillator provides a new upper bound on the wave-function collapse rate, two orders of magnitudes improvement over the previous bound in the same frequency range, and partially ruled out the enhanced collapse rate suggested by Adler. Being performed at room temperature, our experiment has already exhibited advantages over those methods operating at ultra-low temperatures previously reported. Our results experimentally show the potential of magneto-gravitational levitated mechanical oscillator as a promising method for searching wave-function collapse, and cryogenic experiments to further improvements are discussed.

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