I Experimental realizatoin of sequential Stern-Gerlach's

[nicholas_eng]

TL;DR Summary

Looking for articles of experimental realizations of sequential Stern-Gerlach experiments

So, an usual introduction to Quantum Mechanics (like the one given by Sakurai) is to refer to sequential Stern-Gerlach (SG) experiments. For example, a first one aligned to the z axis, a second one aligned to the x axis, and a third one aligned to the z axis again (with no relevant dynamical evolution happening in between). The fact that the first and third SG's may give different results leads us to believe in all the quantum weirdness encapsulated by the non-commutation relations for those observables.

There are some details about such experiment that I'm curious to understand a little better. In particular, the way the SG experiment works, is that it deflects into different directions particles with different values for the corresponding spin component. So if I want to plug one of the outgoing beams into a new SG, I should position this second SG in a position where it intercepts that beam, right?. I can't just "realign" the beam (e.g. by using E.M. field to compensate the deflection) because that would violate the "no dynamic evolution" principle, such E.M. field would have a non-trivial effect on the spin state anyway. Is this assessment correct, and is that something taken into consideration in actual realizations of this experiment?

I would love if someone could point me articles like that, as I'm sure there must be many.

 

[PeroK]

Summary:: Looking for articles of experimental realizations of sequential Stern-Gerlach experiments

I assumed that the sequential SG is a thought experiment and practically almost impossible.

 

[vanhees71]

There are some experiments with polarized neutrons, e.g.,

J.E. Sherwood et al, Stern-Gerlach Experiment on Polarized Neutrons, Phys. Rev. 96, 1546 (1954)
https://journals.aps.org/pr/abstract/10.1103/PhysRev.96.1546

T. J. L. Jones, W. G. Williams, A Stern-Gerlach polarimeter for cold neutrons, J. Phys. E 13, 227 (1980)
https://doi.org/10.1088/0022-3735/13/2/025

O. Zimmer, J. Felber and O. Schärpf, Stern-Gerlach effect without magnetic-field gradient, EPL 53 183
https://doi.org/10.1209/epl/i2001-00134-y

 

[PeterDonis]

if I want to plug one of the outgoing beams into a new SG, I should position this second SG in a position where it intercepts that beam, right?. I can't just "realign" the beam (e.g. by using E.M. field to compensate the deflection) because that would violate the "no dynamic evolution" principle, such E.M. field would have a non-trivial effect on the spin state anyway. Is this assessment correct

Basically, yes. Your assessment also illustrates why most experiments involving spin and entanglement are done with photons instead of electrons. The nice thing about photons is that you can "realign" beams of them with simple mirrors, without violating the "no dynamic evolution" principle. That makes it much easier to implement multiple interactions in series on photon beams.

 

[vanhees71]

Of course the action of a mirror on a photon is through interactions between charges making up the mirror and the photon (em. field). The point is, it's described by a unitary evolution (making the mirror of high quality, i.e., with very little absorption), changing the polarization of the photon in a well-determined way. In other words it's easy to manipulate photons in controlled ways using usual optical elements (mirrors, beam splitters, polarizers) without causing (too much) "decoherence".