Official websites use .gov
A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
Summary
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.
Description
Theoretical prediction of propagation delay times for different dielectric stack configurations. Propagation delays are different for different structures due to presence or absence of surface modes on each end of the photonic bandgap structure. The line represents propagation delay of a photon in an equivalent thickness of vacuum. Values below this luminal line represent superluminal propagation. Values above the luminal line represent subluminal propagation. Large symbols show experimental measurements with uncertainties being about half the size of the symbols.
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.
Major Accomplishments
Coalescence of Single Photons Emitted by Disparate Single-Photon Sources: The Example of InAs Quantum Dots and Parametric Down-Conversion Sources, Phys. Rev. Lett. 107, 157402 (2011)
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)