Faraday cages and what constitutes the minimum number of atoms to build an optical mirror I recently asked this question: What is the minimum number of metal atoms necessary to make a mirror?
However it seems I did not make myself clear enough about what I was looking for, even though the question evidently captured interest. So I decided I would reboot, using a different approach.
I am still looking for a minimum mirror made of metal able to reproduce the typical household mirror properties (flat reflection of most incoming visible light).
It was clear to me that a Faraday cage is an example of mirror to electromagnetic radiation that does not require a continuous sheet of metal to operate, i.e. it is a grid. So I asked about the metal density and layout, not just the external size.
There is a question relevant to this one here: What is the relationship between Faraday cage mesh size and attenuation of cell phone reception signals?
I say relevant not because of the question title but because there is a mention of Faraday cages being actual mirrors.
So I am not asking just about the overall size of the minimum mirror, nor just about the spacings of the grid, all being proportional to the wavelength of the incoming light in some way, but also and foremost about the number of atoms necessary and sufficient because this number must take into account other parameters, for example: the number of atoms sufficient to sustain an optical grid (is a one atom wide cable sufficient and possible?), the effects of the width and location of holes on the phase, polarization, etc.
The minimum mirror should be able to reflect any visible light wavelength still respecting the household mirror reflection style, i.e. not just making radiation bounce randomly.
The fact a Faraday cage is not a continuous sheet of metal means the radiation is not reflected by a continuous bed of conduction electrons either and I would appreciate some details about the microscopic physical mechanisms at play, as this seems contradictory with the reflection produced by a gas of delocalized electrons.
 A: This question has an answer here by :
Scientists Built the World's Smallest Mirror With Only 2000 Atoms

The team used a very thin optical fiber, combined with a chain of cesium atoms, to create a highly efficient mirror. The team managed to make the mirror so small because they carefully selected the color of the light, and engineered the cesium atoms so they would be in exactly the right places to reflect the light.
By positioning multiple mirrors in the right way, the team also managed to temporarily trap the light. They could use their mirror to store and retrieve light pulses, creating a kind of optical memory device. This could be used in optical circuits and computers of the future, which could prove to be faster and more efficient than electrical computers.

Publication here.
You say:

I would appreciate some details about the microscopic physical mechanisms at play, as this seems contradictory with the reflection produced by a gas of delocalized electrons.

At the quantum mechanical level one needs the elastic scattering of the photons that carry the image, so that the phases can be  retained between the wavefunctions of the individul photons, as the images carried have to be coherent, and the photon energy ( within the Heisenberg uncertainty) unchanged for a true mirroring. It will depend on the geometry of the collective surface forming the mirror whether a true image reflection will happen. The photon can scatter off electrons and also off spill over electric fields of lattices of various sizes.
