Optical coupling to nanoscale optomechanical cavities for near quantum-limited motion transduction

TL;DR

This paper presents a highly efficient fiber-optic coupling method for nanoscale optomechanical cavities, achieving near-quantum-limited displacement measurement, advancing the development of quantum and classical sensing devices.

Contribution

It introduces an adiabatic waveguide taper for efficient fiber coupling to nanoscale cavities, enabling high collection efficiency and low noise in displacement measurements.

Findings

Achieved 52% collection efficiency at 1538 nm wavelength.

Imprecision noise floor is 2.8 times above the standard quantum limit.

Predicted total added noise of 1.4 phonons at optimal probe power.

Abstract

A significant challenge in the development of chip-scale cavity-optomechanical devices as testbeds for quantum experiments and classical metrology lies in the coupling of light from nanoscale optical mode volumes to conventional optical components such as lenses and fibers. In this work we demonstrate a high-efficiency, single-sided fiber-optic coupling platform for optomechanical cavities. By utilizing an adiabatic waveguide taper to transform a single optical mode between a photonic crystal zipper cavity and a permanently mounted fiber, we achieve a collection efficiency for intracavity photons of 52% at the cavity resonance wavelength of 1538nm. An optical balanced homodyne measurement of the displacement fluctuations of the fundamental in-plane mechanical resonance at 3.3 MHz reveals that the imprecision noise floor lies a factor of 2.8 above the standard quantum limit (SQL) for continuous position measurement, with a predicted total added noise of 1.4 phonons at the optimal probe power. The combination of extremely low measurement noise and robust fiber alignment presents significant progress towards single-phonon sensitivity for these sorts of integrated micro-optomechanical cavities.