Foundations of Physics

, Volume 18, Issue 10, pp 1045–1056 | Cite as

Is spin coherence like Humpty-Dumpty? I. Simplified treatment

  • Berthold-Georg Englert
  • Julian Schwinger
  • Marlan O. Scully
Part IV. Invited Papers Dedicated To David Bohm


When Humpty-Dumpty had his great fall nobody could put him together again. A vastly more moderate challenge is to reunite the two partial beams of a Stern-Gerlach apparatus with such precision that the original spin state is recovered. Nevertheless, as we demonstrate, a substantial loss of spin coherence always occurs, unless the experimenter is able to control the magnetic field's inhomogeneity with an accuracy of at least one part in 105.


Magnetic Field Coherence Spin State Substantial Loss Simplify Treatment 
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  1. 1.
    D. Bohm,Quantum Theory (Prentice-Hall, Englewood Cliffs, 1951).Google Scholar
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    Ref. 1, pp. 604 and 605.Google Scholar
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    The Oxford Dictionary of Nursery Rhymes, I. Opie and P. Opie, eds. (The Clarendon Press, Oxford, 1951), p. 213.Google Scholar
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    Other models of SGAs have been considered by M. O. Scully, R. Shea, and J. M. McCullen,Phys. Rep. 43, 487 (1978), as well as by M. O. Scully, W. E. Lamb, and A. Barut,Found. Phys. 17, 575 (1987).CrossRefGoogle Scholar
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    The uncertainty δΦ of the accumulated Larmor precession angle must also be kept very small. This is more easily achieved for magnetic field configurations different from the one in Fig. 1. For details consult J. Schwinger, M. O. Scully, and B.-G. Englert, “Is Spin Coherence like Humpty-Dumpty? II. General Theory,” to appear in the Otto Stern Centennial Issue ofZ. Phys. D (1988).Google Scholar
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    Incidentally, in the original experiment by W. Gerlach and O. Stern,Z. Phys. 8, 110 (1922), and9, 349 (1922), the deflection of the two partial beams showed a strong asymmetry.CrossRefGoogle Scholar

Copyright information

© Plenum Publishing Corporation 1988

Authors and Affiliations

  • Berthold-Georg Englert
    • 1
  • Julian Schwinger
    • 1
  • Marlan O. Scully
    • 1
    • 2
  1. 1.Center for Advanced Studies and Department of Physics and AstronomyUniversity of New MexicoAlbuquerque
  2. 2.Max-Planck Institut für QuantenoptikGarchingFRG

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