# Why left and right circularly polarized light have different index of refraction in chiral media?

This is a followup question of (Dependence of the angle of rotation on the wavelength of plane polarized light).

Ron's answer tells about the difference between left and right circularly polarized light. But the explanation isn't in the answer.

So, what's the reason behind different index of refraction?

Also, because it is relevant to the answer, I will reiterate what Ron was saying in the comments. The photon is an inherently quantum object. It is a boson and thus has two possible values of spin angular momentum, $\pm\hbar$. These two values correspond to two allowable states the photon can be in, one which is polarized to the right and the other which is polarized to the left. That is, the electric field vector spins in a circle one way or the other. There also allowable solutions to the state of a photon which are some linear combination of these two polarization states. A 50/50 linear combination gives linearly polarized light. Thus, it seemed like you might have been picturing two photons whose polarizations were cancelling each other out. This is incorrect. Rather, you have to think of a single photon in a superposition of two polarization states.