If there is a waveguide involved why does the headline talk about photons in free space? Photons in waveguides are not in free space.
The title should be corrected to something truthful, like "Photons in waveguide-like configuration travel slower than light due to self-interference, as predicted".
Anything else is deliberately, willfully, misleading click-bait (I am a physicist and clicked on the comments specifically to avoid clicking on a click-bait headline I knew was almost certainly a lie.)
Our work highlights that, even in free space, the invariance of the speed of light only applies to plane waves. Introducing spatial structure to an optical beam, even for a single photon, reduces the group velocity of the light by a readily measurable amount.
So it appears there is no actual waveguide involved. I guess that means somehow they construct photons in a "waveguide-like configuration" but in free space?
The title should be corrected to something truthful, like "Photons in waveguide-like configuration travel slower than light due to self-interference, as predicted".
Anything else is deliberately, willfully, misleading click-bait (I am a physicist and clicked on the comments specifically to avoid clicking on a click-bait headline I knew was almost certainly a lie.)