We use light created two photons at a time to explore the time needed to cross a barrier. The extreme simultaneity of creation of the two photons allows for very precise timing of optical delays. The time between detection of the two photons is very sensitive to any changes in the optical path of one photon versus the other.
We are studying what happens when a single particle (in this case a photon) crosses a tunneling barrier. This is a particularly interesting question because tunneling is a fundamental distinguishing characteristic of quantum mechanics and it implies remarkable properties such as barrier crossing times that are faster than the speed of light. Using a high reflectance stack of dielectric layers as a proxy for the tunneling barrier, super-luminal traversal times were found to be significantly dependent on minimal changes to the dielectric stack (such as the addition or subtraction of a just a single layer), even changing from super- to sub-luminal regimes. We have also developed a theoretical model explaining these variations in terms of surface states. Current work involves measuring traversal times in a true tunnel barrier, using a frustrated total internal reflection gap.
Demonstration of single photon trapping by a surface mode in a 1D photonic bandgap, ref: Single-photon propagation through dielectric bandgaps, Natalia Borjemscaia, Sergey V. Polyakov, Paul D. Lett, and Alan Migdall, Optics Express Vol. 18, Issue 3, pp. 2279-2286 (2010)