Feedback-cooling the fundamental torsional mechanical mode of a tapered optical fiber to 30 mK

TL;DR

This paper demonstrates active feedback cooling of a tapered optical fiber's torsional mode from room temperature to 30 mK, achieving high quality factors and paving the way for advanced fiber sensors and quantum optomechanics.

Contribution

It introduces a feedback cooling method for the torsional mode of a tapered optical fiber, reaching near-quantum ground state temperatures.

Findings

Achieved a quality factor of up to 10^7.

Damped thermal motion from room temperature to 28(7) mK.

Established potential for fiber-based sensors and quantum platforms.

Abstract

Tapered optical fibers (TOFs) are used in many areas of physics and optical technologies ranging from coupling light into nanophotonic components to optical sensing and amplification to interfacing quantum emitters. Here, we study the fundamental torsional mechanical mode of the nanofiber-waist of a TOF using laser light. We find that this oscillator features a quality factor of up to $10^7$ and a $Qf$ product of 1 THz. We damp the thermal motion from room temperature to 28(7) mK by means of active feedback. Our results might enable new types of fiber-based sensors and lay the foundation for a novel hybrid quantum optomechanical platform.