Optical cooling of mechanical degrees of freedom is one of the biggest achievements of cavity optomechanics. Although it has mostly been demonstrated in the dispersive coupling regime, where the mechanical motion modulates the cavity frequency, in the dissipative coupling regime, i.e., when the mechanical motion changes the decay rate of the cavity, cooling can be achieved outside the stringent “good cavity” limit. In the most common experimental configurations of cavity optomechanics, however, where free-standing waveguides are evanescently coupled to an optical micro-cavity, low mechanical Q-factors have so far prohibited observation of dissipative cooling. Recently we reported that glass-fiber nanospikes, fashioned by tapering single-mode fibers, support high-Q flexural resonances (Q > 105) in the few kHz range, at the same time providing low loss, adiabatic guidance of light. Here we report the use of a silica nanospike to demonstrate dissipative cooling and amplification, by coupling it to an ultra-high-quality bottle resonator. In particular an effective temperature of 1.8 K can be inferred from the measurement of the mechanical power spectrum for a launched optical power of only ~200 µW. We believe this system could open the door to optomechanical cooling of low frequency mechanical resonators beyond the sideband-resolved regime.

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