It should be noted that this result was completely expected. It turns out that light traveling through a medium can have 3 different velocities: phase, group and signal. Typically the latter two are the same and we can think of the group velocity as being the real "speed of the particle", but that is not always true. See <a href="http://en.wikipedia.org/wiki/Group_velocity#Physical_interpretation" rel="nofollow">http://en.wikipedia.org/wiki/Group_velocity#Physical_interpr...</a> for more.<p>This experiment manages to measure the signal velocity for the leading photon and verifies what we already knew for larger signals.