Beams of energy that can move chunks of matter around might seem only to be science fiction, like the tractor beams of Star Trek, but such optical traps have existed for nearly three decades. Now researchers show they can use lasers to both levitate and cool matter. Findings detailed this week in the Proceedings of the National Academy of Sciences could help shed light on how the strange world of quantum physics evolves (or not!) into the familiar classical world.
Light exerts force on partially transparent objects in ways scientists found could help grip and move tiny pieces of matter, a discovery that won a Nobel Prize. Laser beams can also be used to cool targets as well — for instance, when they scatter off atoms, they can make them lose more energy than they absorbed.
Quantum physicists are now using such lasers to control matter in the hopes of uncovering secrets about how the universe operates. They would like to work on larger particles to find out whether there are limits on the validity of the quantum description as one approaches the everyday world–a question which may be crucial for the reconciliation of the prima facie very disparate pictures given by quantum and classical physics. However, the observation of quantum effects such as superposition, where objects can apparently exist in two places simultaneously or spin in two opposite directions at the same
time, is highly vulnerable to disruption — say, from objects they are in contact with, or from heat.
Now quantum physicist Markus Aspelmeyer at the Vienna Center for Quantum Science and Technology in Austria and his colleagues used an optical trap to levitate a glass particle 340 nanometers wide and containing about 1 billion atoms.
“Using optically levitated particles has several possible advantages,” Aspelmeyer says. “The optical trap provides much better isolation from the environment than in conventional mechanical devices. This is important because the environment plays a crucial, mostly deleterious role for quantum experiments.”
The shape of the cavity that the researchers levitated the bead in enhanced the light-scattering effect that cooled the particle. By showing they can both levitate and cool relatively big objects, eliminating two major sources of problems that often bedevil quantum experiments, Aspelmeyer and his colleagues hope they can learn more about quantum effects at large scales.
“The ability to control the motion of massive objects using quantum optics techniques is a fascinating topic,” Aspelmeyer says. “It allows us to perform quantum experiments with truly massive objects, possibly allowing to study the interface between quantum physics and gravity.”
The researchers now are striving to trap particles within the cavity in high vacuum, further reducing any contact an object under study has with the outside world. “This is the last remaining step for showing the full potential of optical quantum control of levitated particles,” Aspelmeyer says.