Ultranarrow-linewidth levitated nano-oscillator for testing dissipative wave-function collapse

Levitated nano-oscillators are promising platforms for testing fundamental physics and quantum mechanics in a new high mass regime. Levitation allows extreme isolation from the environment, reducing the decoherence processes that are crucial for these sensitive experiments. A fundamental property of any oscillator is its linewidth and mechanical quality factor Q. Narrow linewidths in the microhertz regime and mechanical Q's as high as 1012 have been predicted for levitated systems. The insufficient long-term stability of these oscillators has prevented direct measurement in high vacuum. Here we report on the measurement of an ultranarrow linewidth levitated nano-oscillator, whose width of 81±23μHz is only limited by residual gas pressure at high vacuum despite residual variations of the trapping potential. This narrow linewidth allows us to put new experimental bounds on dissipative models of wave-function collapse including continuous spontaneous localization and Diósi-Penrose and illustrates its utility for future precision experiments that aim to test the macroscopic limits of quantum mechanics.