Conventional optical systems are (at best) diffraction limited. But as I understand it, that is solely due to the instrument altering the properties of the incoming radiation -- e.g., an Airy disc only occurs because the direction of the incoming light is altered by some sort of obstacle.
What about (hypothetical) systems that observe the incoming radiation without altering any of its properties? I'm talking about the sorts of systems for which the 2012 Nobel prize was awarded (observing quantum systems non-destructively).
In this context, all I ever hear anyone talk about is quantum computers. But could these sorts of techniques be used in, say, a telescope? Would such a telescope be able to observe individual grains of sand on Mars, while it's standing on the Earth's surface and is no bigger than an ordinary SLR camera?
More generally, suppose there is a device able to determine all properties of all photons in the entire light field accessible to the instrument at some instant, up to the best limits allowed by quantum mechanics. What is the theoretical limit on resolving power for this device?
More theoretically, how much information is actually contained in any light field, and how much of this information can theoretically be extracted from it?