The tractor beam is a long-serving staple of sci-fi, but now Australian researchers have created a new type of real-world version. While it won't exactly be capturing enemy spaceships anytime soon, the device can use light to pull in and trap atoms, which may be handy for quantum communications or memory systems.
There are plenty of ways to build tractor beams. Some use sound waves to push or levitate small objects and particles, while others can direct energy behind the target and pull it towards the source. A separate class uses light, either through the pressure of photons bouncing off objects, or creating tiny thrust through the photophoretic force that keeps particles suspended in a dark core when surrounded by laser light.
The new design from researchers University of Adelaide also uses light, but in this case it's invisible infrared and it affects the target in a different way. When light from an optical fiber strikes cold rubidium atoms floating in a vacuum chamber, it triggers a change in the dipole moment of those atoms, which guides them towards the most intense part of the light. The way the device is set up, that point is the center of the optical fiber that's emitting the beam.
"Every atom that enters the tractor beam is pulled into the fiber – there is no escape," says Ashby Hilton, the PhD student who developed the technology. "And once sucked into the interior of the optical fiber the atoms can be held for long periods of time. Our experiments show that we can very precisely control light to produce exactly the right conditions to control atoms."
So what can you do with these tiny tractor beams? The team says the trapped atoms could be used in quantum communications systems, or as sensors that detect specific molecules in the air or disease biomarkers in a patient's breath.
"What is really exciting is that now we have the possibility to do quantum experiments on these trapped atoms," says Philip Light, lead researcher on the study. "Our first experiments intend to use these stored atoms as elements of a quantum memory. We hope that our work may eventually form part of absolutely secure communications channel that is of obvious high interest to defence, intelligence and industry."
The research was published in the journal Physical Review Applied. A simulation of how the tractor beam works can be seen in the video below.
Source: University of Adelaide