Scientists at the Joint Quantum Institute have developed a new technique to measure the travel time of photons with sub-femtosecond precision. The method involves creating correlated pairs of photons and using a Hong-Ou-Mandel interferometer to detect when the photons arrive simultaneously. This allows them to measure extremely short time intervals by comparing photon travel times through different materials.
The team used the technique to study how the arrangement of refractive layers affects photon transit times. They found that photons take about 20 femtoseconds less to pass through a stack of 31 layers when the stack begins and ends with high refractive index layers. This superluminal effect is possible because the measured transit time is shorter than the time needed for light in a vacuum to traverse the same distance.
The new system could provide an empirical answer to the long-standing puzzle of how fast light crosses narrow gaps that don’t permit conventional electromagnetic waves. The team plans to use the technique to study more perplexing cases, such as light traversing gaps through evanescent waves.
Source: https://www.nist.gov/news-events/news/2008/03/sub-femtosecond-stop-watch-photon-finish-races
Keywords: Photon, Refractive, Interferometer, Femtoseconds, Superluminal
