World-Record-Breaking Boffins Reveal the Fastest Spinning Thing on Earth

Arthur T Knackerbracket has found the following story:

The fastest spinning object on Earth - a pair of nanoparticles - can complete over five billion revolutions per second in the laboratory, according to a paper published in Nature Nanotechnology on Monday.

Here's how the team at Purdue University in the US pulled it off: they formed a dumbbell-shaped object roughly 300nm across in a vacuum chamber from two silica particles. Next, the eggheads zapped the dumbbell with a laser to trap it in place, a process dubbed optical levitation.

A second, slightly less powerful laser beam is focused on the particle to make it spin. The laser light used to trap the nano-dumbbell is passed through a lens and projected onto a series of photodetectors. As the teeny object spins, it alters the polarization of the beam, and that change is used to determine the nanoparticle's record-breaking rotation rate. Thus, the dumbbell also acts as torque detector, we're told.

The goal isn't to keep breaking records for the sake of it, however. [Tongcang Li, an assistant professor of physics and astronomy, and of electrical and computer engineering at Purdue, who led the study] hopes these strange nanoparticles will help scientists understand so-called "vacuum friction," a quantum effect in which a particle is slowed down by frictional forces in empty space. Physicists reckon virtual photons pop in and out of existence in a vacuum, such as space, to exert a tiny amount of drag on real particles.

The nanoparticles could be used to measure that drag because, as the university was keen to remind us, the dumbbell forms "the world's most sensitive torque detector, which researchers hope will be used to measure the friction created by quantum effects."

Journal Reference:
Ahn, J., Xu, Z., Bang, J. et al. Ultrasensitive torque detection with an optically levitated nanorotor, Nature Nanotechnology (DOI: doi:10.1038/s41565-019-0605-9)

Abstract:

Torque sensors such as the torsion balance enabled the first determination of the gravitational constant by Henri Cavendishand the discovery of Coulomb's law. Torque sensors are also widely used in studying small-scale magnetism, the Casimir effect and other applications. Great effort has been made to improve the torque detection sensitivity by nanofabrication and cryogenic cooling. Until now, the most sensitive torque sensor has achieved a remarkable sensitivity of 2.9"i-"10^a'24"N"m"Hz^a'1/2 at millikelvin temperatures in a dilution refrigerator. Here, we show a torque sensor reaching sensitivity of (4.2""1.2)"i-"10^a'27"N"m"Hz^a'1/2 at room temperature. It is created by an optically levitated nanoparticle in vacuum. Our system does not require complex nanofabrication. Moreover, we drive a nanoparticle to rotate at a record high speed beyond 5"GHz (300 billion"r.p.m.). Our calculations show that this system will be able to detect the long sought after vacuum friction near a surface under realistic conditions. The optically levitated nanorotor will also have applications in studying nanoscale magnetism, and the quantum geometric phase.

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