Everyone is familiar with the Doppler shift that occurs when the observer moves relative to some source of waves, but now a rotational effect has been found.

The idea hinges on the fact that a beam of light can carry orbital angular momentum in addition to the spin angular momentum of the photons. So an oncoming wave with orbital angular momentum could be Doppler-shifted depending on how the observer rotated relative to the beam.

The effects are small, but Sergio Barreiro of the University of Montevideo in Uruguay and colleagues have demonstrated them. They used a sophisticated set-up with an exotic transition in rubidium, a magnetic field, and two light beams with different values of orbital angular momentum.

Further reading

S Barreiro et al. 2006 Phys. Rev. Lett. 97 113601.