Why can the wavelength and frequency of a photon be described only for classical electromagnetics, and not photons? Is this Heisenberg's?

Question

jamesj · Answer

In quantum mechanics, we can and do talk about a photon's wavelength, $ \lambda $ and frequency $ f $.  The remain related by
$$ \lambda f = c $$ where $ c $ is the speed of light.  

So I don't understand the concern.

anonymous · Answer

I don't understand the concern either; I was just phrasing exactly as the textbook did. In context of decoherence and entanglement, a photon's wavelength and frequency couldn't be described.

jamesj · Answer

Ok, then this is very special situation and off the top of my head I can't explain it, but it certainly sounds plausible.