Tiny particles of glass spun by a laser are the fastest spinning objects we’ve ever seen, at over 1 billion turns per second. Studying them could help us learn more about quantum physics and the big bang.
Two research teams used circularly polarised light to set charged silicon dioxide particles spinning. As a light wave travels, it oscillates up and down, moving in one direction, but this polarised light wave rotates a bit like the hands of a clock.
“It looks like a spinning helix, a little bit like DNA. And this helix is driving the rotation of the particle,” says René Reimann at the Swiss Federal Institute of Technology in Zurich (ETHZ). As the photon turns, it imparts its rotational energy to the particle.
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He and his team trapped a silicon dioxide particle within their polarised laser, placing the whole setup inside a vacuum chamber. As they lowered the pressure inside the chamber, the drag from residual air particles was removed, allowing the silicon dioxide to spin rapidly.
“We were surprised at the high speeds because we thought the particle would disintegrate much sooner,” says Reimann. A large enough centrifugal force will eventually make anything explode, but these nanoparticles can spin for hours before that happens.
Small but mighty
Tongcang Li at Purdue University led another team doing similar work. Again, they used glass nanoparticles, but configured them in a dumbbell shape – two nanoparticles stuck together at one edge – for more strength.
He and his team measured the nanodumbbells rotating at 1.3 gigahertz for several hours. They might even be able to go faster, he says, but detectors capable of measuring higher rotation speeds don’t yet exist.
These rapidly rotating particles could help us study quantum friction. Even in a complete vacuum with no air molecules left, the particles could experience drag created by photons blinking in and out of existence due to the weird rules of quantum physics.
Reimann says we could set these particles spinning and then turn off the laser to watch them fall while measuring how much drag they experience.
They could also shed light on the universe’s origins. Rapidly spinning particles in interstellar space have been suggested as the source of gigahertz radiation in the cosmic microwave background – the light leftover from the big bang, Li says. This technique could also let us test out that theory, he says.
References: , ; due to be published in Physical Review Letters
