Abstract
Spinor wavef unctions change their sign under 2π rotation, an effect observable in interference experiments1,2. Several experiments have used magnetic precession of neutrons to implement rotations3–7. Other investigators have observed phenomena in molecular, nuclear or atomic systems with integral spin that have been identified as interference effects produced by 2π rotation8–11. I describe here a distinction between experiments on spin-1/2 neutrons and those on bosons, one that is crucial to interpreting these experimental results. Following recent work on interpreting magnetic precession as rotation12,13, I show how to resolve Zeilinger's thought experiment12, which actually measures the spin direction of two partial beams, with Byrne's point13 that the recombined beam of neutrons has been rotated only π rad when the relative rotation between two partial beams is 2π. The essential distinguishing step lies in recognizing the lack of geometric significance, in general, of the mathematical parameter that equals 2πin the boson case.
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Bernstein, H. Fermionic and bosonic interference during spin rotation through 2π radians. Nature 315, 42–45 (1985). https://doi.org/10.1038/315042a0
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DOI: https://doi.org/10.1038/315042a0
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