Abstract
It is widely held that Bohr has shown that the spin of a free electron is not measurable. We point out that Bohr's argument has some important ifs and buts. A concrete configuration is calculated to produce a clear spin separation. This is then shown not to contradict Bohr's reasoning.
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In the above discussion, we focused on measurement. If preparation of particles with definite spin is our aim, (17) is not warranted. But the spatial symmetry requirement (21) can be seen to be sufficient to establish a clear-cut correlation between\(\hat \sigma _z \) and\(\hat p_z \) anyway. Hence (17) is also not needed for preparation.
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Martens, H., de Muynck, W.M. On the possibility of measuring the electron spin in an inhomogeneous magnetic field. Found Phys Lett 7, 343–352 (1994). https://doi.org/10.1007/BF02186684
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DOI: https://doi.org/10.1007/BF02186684