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±2 mK and report on record sensitivities for scanning probe force sensors, at the 40zN/Hz1/2 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.
@article{arxiv.2009.02912,
title = {Ultrasensitive nano-optomechanical force sensor at dilution temperatures},
author = {Francesco Fogliano and Benjamin Besga and Antoine Reigue and Laure Mercier de Lépinay and Philip Heringlake and Clement Gouriou and Eric Eyraud and Wolfgang Wernsdorfer and Benjamin Pigeau and Olivier Arcizet},
journal= {arXiv preprint arXiv:2009.02912},
year = {2022}
}