Researchers Gunter Nimtz and Alfons Stahlhofen of the University of Koblenz have told New Scientist (and other sources) that they’ve broken the light barrier, sending photons faster than the speed of light.
We have reported about superluminal signal velocities in photonic tunnelling. It was observed that the superluminal photonic tunnelling time data measured in the time domain are in agreement with the calculated phase time data. This result is also in agreement with the definition of the barrier transition time given in the Federal Standard 1037 C (NTIA, USA 2000).
To see how far they could make photons tunnel, Nimtz and Stahlhofen sandwiched two glass prisms together to make a cube 40 centimetres on its sides. Since photons tunnel most readily over distances comparable with their wavelength, the physicists used microwaves with a wavelength of 33 cm – long enough for large tunnelling distances yet still short enough that the photons’ paths can be bent by the prism.
As expected, the microwaves shone straight through the cube, and when the prisms were separated, the first prism reflected the microwaves (see Diagram). However, in accordance with theory, a few microwave photons also tunnelled across the gap separating the two prisms, continuing as if the prisms were still sandwiched together.
Nimtz and Stahlhofen found that the reflected microwaves and the few microwaves that tunnelled through to the second prism both arrived at their respective photodetectors at the same time. This suggests an ultra-fast transit between the two prisms – so much faster than the speed of light that the experimenters couldn’t measure it. Moreover, the pair found that the tunnelling time, if any, did not change as they pulled the prisms further apart. Because tunnelling efficiency also drops off with distance, however, Nimtz says that they could not observe the effect across distances greater than 1 metre .
More on the work leading up to this (done with Astrid Haibel) here.