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  • Feeling the Ultrasensitive Force with a Levitating Nanoparticle

Photonics.com
Nov 2013
BARCELONA, Spain, Nov. 26, 2013 — Optically levitating nanoparticles in high-vacuum conditions have led to the measurement of the highest quality factors (Q-factors) in nano- and micromechanical oscillators. Oscillators with high Q-factors are gaining attention for their potential as ultrasensitive detectors.

Unlike microfabricated devices, optically trapped nanoparticles in a vacuum do not suffer from clamping losses, resulting in much larger Q-factors. The work overcomes limitations to advances in mechanical resonator fabrication and design and makes the devices more suitable for sensing, signal processing and transduction, and for fundamental research into quantum effects in increasingly larger systems.


A silica nanoparticle trapped by tightly focused laser beams. Courtesy of ICFO.


A recent study led by the Institute of Photonic Sciences (ICFO) reports that the combination of an ultrahigh Q-factor and the tiny mass of the nanoparticles led to an unprecedented force sensitivity at room temperature. In fact, the system is so sensitive that the weak forces arising from collisions between the nanoparticle and residual air molecules are enough to drive it into the nonlinear regime, the scientists said.

The work shows, for the first time, that ultrahigh Q-factor nanoresonators intrinsically behave nonlinearly. It also showed that, when combined with feedback cooling, the levitating nanoparticle can be used as a force-sensor, sufficiently sensitive to detect ultraweak interactions such as non-Newtonian gravitylike forces and tiny forces arising from quantum vacuum fluctuations.

”Thermal motion is commonly observed in nanomechanical systems. However, observing nonlinear features of thermal motion is a true novelty and, thus, challenges our understanding of how these high-Q nanomechanical systems behave,” said Jan Gieseler.

The research involved collaboration between the Plasmon Nano-optics group, led by ICREA professor at ICFO Romain Quidant, and the Nano-Photonics group, led by professor Lukas Novotny of the Photonics Laboratory at ETH Zurich.

The research appears in Nature Physics (doi:10.1038/nphys2798). 

For more information, visit: www.icfo.eu


GLOSSARY
nanoparticle
A small object that behaves as a whole unit or entity in terms of it’s transport and it’s properties, as opposed to an individual molecule which on it’s own is not considered a nanoparticle.. Nanoparticles range between 100 and 2500 nanometers in diameter.  
plasmon
Calculated quantity of the entire longitudinal wave of a solid substance's electron gas.
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