Has the 2-stage Stern-Gerlach experiment been performed?

[Ali Lavasani]

In http://www.feynmanlectures.caltech.edu/III_05.html#Ch5-S1, Feynman mentions that the 2-stage Stern-Gerlach experiment, which proves the electron spin states to be in a superposition, has never been actually done! I have also not seen any paper reporting such an experiment. My question is, has this experiment actually been done, and if so, have its results confirmed orthodox QM?

 

[mfb]

It is difficult to keep the beam coherent in the region with a weak magnetic field in between. Nevertheless, it has been done: Double Stern-Gerlach experiments on Mn@Sn12: Refocusing of a paramagnetic superatom
This is probably not the earliest experiment, it is just the first one I found.

 

[Orodruin]

Also note that the Feynman lectures are quite old and therefore are going to be outdated on many things, especially what has been done experimentally and what has not, but that the theory remains solid.