Forget the X-Men – photons are the true superheroes. Not only do they travel at the universe’s fastest possible speed, now they have been made to both change colour and shape-shift. The feat brings the dream of ultrafast quantum computers a step closer.
Photons are waves of electromagnetic energy that come in different wavelengths, or colours. The wave patterns also vary in shape, depending in part on how they came into being. The shape of a photon produced by a laser resembles a bell curve, for example, while a photon emitted spontaneously by an atom when an electron loses energy has a peak that rises quickly and tails off slowly. The shape can affect how a photon interacts in collisions.
Photons normally maintain their size and shape until they are absorbed by matter. Now Matthew Rakher at the National Institute of Standards and Technology in Gaithersburg, Maryland, has made photons behave like shape-shifting chameleons. They piped infrared photons with a wavelength of 1300 nanometres into a crystal, into which they also pumped photons from a 1550-nm-wavelength laser. Each had different shapes.
The crystal acted as a waveguide, channelling the photons to hit each other at a specific angle and place, making them blend together to form photons with a wavelength of 710 nm with the same shape as the laser photons (Physical Review Letters, DOI: 10.1103/physrevlett.107.083602).