Week In Science

This week scientists at the National Institute of Standards and Technology managed to control the transfer of rotational motion from beams of light to sodium atoms at the quantum level.

Rotation has been tranferred from light to particles before, but this is the first time it has been done in quantized increments.

The scientists used a cloud of sodium atoms called a Bose-Einstein condensate (BEC), which is a set of particles operating as though they were a single particle.

What is interesting about transferring rotation at the quantum level is that only discrete quantities of rotation can be transferred, and nothing in between.

And most unusually, some of the states that can occur are very strange. For example, the cloud can be set to rotate as a vortex (like a tornado), or set to rotate simultaneously in opposite directions (yes, this is possible at the quantum level, even though it makes no sense in the macroscopic world that we are familiar with), or simultaneously rotate and stand still.

The scientists used two laser beams focused on about a million sodium atoms in a magnetic trap to perform the experiment. A single photon at a time was absorbed by the condensate, whilst one was emitted. The difference in rotation between the two photons was thus transferred to the condensate.

It has previously only been possible to control the internal states (excitation levels and other internal quantum states) and movement (translation) of atoms with light. Being able to control their rotation at the quantum level gives complete control over all aspects of atoms.

Some nice photographs of the unusual quantum states induced can be viewed at PhysOrg.com, along with further information about the experiment.