Feedback cooling of a cantilever's fundamental mode below 5 mK

TL;DR

This paper demonstrates active feedback cooling of a silicon cantilever's fundamental mode from 2.2 K down to approximately 3 mK, achieving near quantum-limited noise suppression and surpassing shot noise levels.

Contribution

It presents the first experimental realization of feedback cooling of a cantilever's fundamental mode below 5 mK using optomechanical techniques.

Findings

Achieved cooling of the cantilever to 2.9 +/- 0.3 mK.

Suppressed optical interferometer noise below shot noise at high feedback gain.

Demonstrated limits set by cantilever properties and measurement noise.

Abstract

We cool the fundamental mechanical mode of an ultrasoft silicon cantilever from a base temperature of 2.2 K to 2.9 +/- 0.3 mK using active optomechanical feedback. The lowest observed mode temperature is consistent with limits determined by the properties of the cantilever and by the measurement noise. For high feedback gain, the driven cantilever motion is found to suppress or "squash" the optical interferometer intensity noise below the shot noise level.