A sub-femtosecond stop watch for 'photon finish' races
Using a system that can compare the travel times of two photons with sub-femtosecond precision, scientists at the Joint Quantum Institute (a partnership of the National Institute of Standards and Technology (NIST) and the University of Maryland) and Georgetown University have found a remarkably large difference in the time it takes photons to pass through nearly identical stacks of materials with different arrangements of refractive layers.