Stern-Gerlach interferometer on an atom chip

Ever since Stern and Gerlach (SG) confirmed the existence of the spin and the magnetic moment which accompanies it, as well as the force a magnetic gradient may apply on it, a fierce debate ensued over the feasibility of a SG interferometer (SGI). In such a SGI, a particle with a spin (e.g. a neutral atom) is put into a superposition of two spin states which are macroscopically separated and recombined in space. The fundamental enigma was whether such a macroscopic separation of the partial wavepackets will introduce a large dispersion of phases within the individual wavepackets. Heisenberg and Wigner [1] thought that this was an impossibility due to the very fundamental nature of quantum mechanics. Bohm [2] said that fantastic accuracy will be required. Englert, Schwinger and Scully [3] made an analogy to the Humpty-Dumpty (HD) rhyme and named this impossibility the HD effect. Similar to broken glass, it was thought that extra-ordinary circumstances are required in order to put HD back together again, in a way that would enable all the quantum phases to be accurately restored so that an interference pattern may be observed.