Ultrasensitive nano-optomechanical force sensor at dilution temperatures

TL;DR

This paper demonstrates an ultrasensitive nano-optomechanical force sensor operating at dilution temperatures, achieving record sensitivities by using minimally perturbing optical readout techniques on silicon carbide nanowires.

Contribution

The work introduces a novel optomechanical readout method at ultra-low temperatures, enabling thermalization and high sensitivity measurements with minimal optical power.

Findings

Thermalization of nanowires down to 32 mK confirmed.

Achieved force sensitivity of 40 zN/Hz^{1/2}.

Detected lateral force gradients in the fN/m range.

Abstract

Cooling down nanomechanical force probes is a generic strategy to enhance their sensitivities through the concomitant reduction of their thermal noise and mechanical damping rates. However, heat conduction mechanisms become less efficient at low temperatures, which renders difficult to ensure and verify their proper thermalization. To operate with minimally perturbing measurements, we implement optomechanical readout techniques operating in the photon counting regime to probe the dynamics of suspended silicon carbide nanowires in a dilution refrigerator. Readout of their vibrations is realized with sub-picowatt optical powers, in a regime where less than one photon is collected per oscillation period. We demonstrate their thermalization down to $32\pm2$ mK and report on record sensitivities for scanning probe force sensors, at the $40\,\rm zN/Hz^{1/2}$ level, with a sensitivity to lateral force field gradients in the fN/m range. This work opens the road toward nanomechanical vectorial imaging of faint forces at dilution temperatures, at minimal excitation levels.