Thursday, September 8, 2011

Weird Quantum Effect Can Make Materials Transparent

When you shine light on a substance, part of the light is reflected, part is transmitted and part is absorbed. If you choose the color of light and the substance sensibly, you can arrange things so that all the light is absorbed. Nothing special about that, right? OK, but what if you could shine a second light on the substance and make it transparent for the first light field? That would be a bit strange, wouldn’t it?

Electromagnetically induced transparency (EIT), as it is called, is a bizarre phenomenon all by itself. But there is nothing like taking the bizarre and making it even more so. A group of researchers has shown that, under the right conditions, this second light field doesn’t have to hit the substance to make EIT work—it only has to have the potential to be there. My response: OMFG, that is too cool to be true.

EIT occurs due to an interaction between two light fields that is mediated via an atom. Atoms absorb light in discrete chunks. Normally, an atom would be sitting in a single ground state, but some atoms have two states that are at about the same energy and are about as stable. In this case, we can think of the atom as having two ground states. Through careful preparation, we can generate a group of these atoms so that they are all in just one of the two ground states. If I turn on a light field (called the probe light) with the right color, it will be absorbed by the atoms, putting them into an excited state. more