Commentary on “A simple, practical experiment to investigate atomic wavefunction reduction within a Stern‐Gerlach magnet” by Michael Devereux, published in J. Phys. B: At. Mol. Opt. Phys. 57, 152501 (2024), https://doi.org/10.1088/1361‐6455/ad5992

Experimental proof of coherent spatial interference from the logitudinal (1D) Stern-Gerlach (SG) interferometer. (a) A single-shot interference pattern of a thermal cloud with a negligible BEC fraction, with a visibility of 𝑉 = 0.65, clearly showing that a BEC is not needed for the interferometer to work. (b) A multishot image made by averaging 40 consecutive interference images using a BEC (no correction or postselection) with a normalized visibility of 𝑉 = 0.99, proving that the interferometer is phase stable and that no BEC interference (with random fringe position) was involved. (c) Spin oscillations observed at the output of the full-loop SG. The data agrees almost perfectly with the theory developed for a spatial interferometer by the group of Wolfgang Schleich. The excellent agreement again proves that coherent spatial splitting has been achieved. Additional experimental results include clock interferometry and geometrical phase, results which all fit nicely with the theory of a spatial SG interferometer. For a detailed review of the experiments see: Keil, M. et al. (2021). Stern-Gerlach Interferometry with the Atom Chip. In: Friedrich, B., Schmidt-Böcking, H. (eds) Molecular Beams in Physics and Chemistry. Springer, Cham. https://doi.org/10.1007/978-3-030-63963-1_14