Summary: It may not be quite the tractor beam that you expect from a scifi show like "Star Trek," but we are getting closer. The way these scientists have developed relies on the pressure of sound waves. Instead of trying to create a concentrated beam that holds a particle, they instead create a vacuum of space, bounded by high intensity waves all around it. Then by adjusting the boundaries, they are able to move the trapped particle. Currently the capabilities of the design only apply up to pea-sized particles at less than 40cm away.
Despite the apparent 3D nature of the holding pattern, it only requires a loudspeaker on one side of the particle. For the researchers, this means that it could be applied in the medical field for drug delivery. For those of us thinking of the future, this means that tractor beams on spaceships may be possible in a distant future. (Which the scientists did prove would work on a scaled down model.)
BBC News
Nature
