This object is a small ball made of silica, which can rotate around billions of times per second and that can be used as a sensor capable of measuring torque forces to a quadrillionth of a newton-meter. This is around 700 times more sensitive than was possible with the existing technology. The device provides sufficient sensitivity to be able to detect the small amounts of drag caused by the friction within vacuum.
Wait a minute, an attentive reader could say, vacuum is empty, right? How come is there any drag force? But it seems like this space, some time back named as empty space, is not empty at all. Researchers already know that vacuum is filled with quantum fluctuations. Quantum mechanics suggests that there is a drag due to electromagnetic fields that constantly fluctuate: appear and disappear, which leads to a friction drag forces acting on any spinning object in vacuum. These forces are extremely small and measuring them is not trivial at all. Currently researchers are only starting to develop capable detection devices.
By using a 1,550-nm laser beam, the researchers suspended 150 nanometer silica nanoparticles in vacuum. The physicists had to fine-tune the device to make the particles to levitate and to apply spin on it. The spin is applied using polarised pulses from a second laser. The spin achieved is incredible – 300 billion rotations per minute (rpm) – the fastest man-made rotation ever created. For a comparison, the fastest motors of Tesla (and also Formula 1 vehicles) rotate with a maximum of around 18 thousands rpm.
The scientists were able to measure the torque forces in the device by measuring the particle’s spin speed evolution during the laser pulse cycles with the optical sensor. This new device could be so sensitive, that it could in theory be used to measure fainting electromagnetic fields that create friction in vacuum.
Further information: Jonghoon Ahn et al. Ultrasensitive torque detection with an optically levitated nanorotor, Nature Nanotechnology (2020). DOI: 10.1038/s41565-019-0605-9
 Jonghoon Ahn et al. Ultrasensitive torque detection with an optically levitated nanorotor, Nature Nanotechnology (2020). DOI: 10.1038/s41565-019-0605-9
Administration of the project