Quantum Electrodynamics has Zero Radius of - An outline of why QED is the most tested theory in the universe.

Cavity Quantum Electrodynamics - Since Purcell first realised that atomic decay rates would actually be altered depending on the environment that an atom resides in, there has been a great deal of interest in the field of cavity QED. The essence of cavity QED is that an atom or atoms are stored in a geometric enclosure which has dimensions comparable to the atomic wavelength. Therefore, compared to atoms in free space, the atoms couple not only to a continuum of electric field modes, but also strongly to the modes of the cavity field.