Nonlocal Appearance of a Macroscopic Angular Momentum
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We discuss a type of measurement in which a macroscopically large angular momentum (spin) is “created” nonlocally by the measurement of just a few atoms from a double Fock state. This procedure apparently leads to a blatant nonconservation of a macroscopic variable—the local angular momentum. We argue that while this gedankenexperiment provides a striking illustration of several counter-intuitive features of quantum mechanics, it does not imply a non-local violation of the conservation of angular momentum.
KeywordsNonlocality Quantum measurement Bose-Einstein condensate
The research for this work was initially funded by the Templeton Research Fellows Program “Philosophers–Physicists Cooperation Project on the Nature of Quantum Reality” at the Austrian Academy of Science’s Institute for Quantum Optics and Quantum Information, Vienna, which allowed the authors to spend the summer of 2009 at IQOQI Vienna. Special thanks go to our hosts in Vienna, Prof. A. Zeilinger and Prof. M. Aspelmeyer, who have made this visit possible, and additionally to the scientists in the institute for many enlightening discussions. Also, GSP acknowledges support from the Academy of Finland (Acad. Res. Fellowship 00857, and projects 129896, 118122, 135135, and 141559). The contribution by RH to this material is partially based upon work supported by the National Science Foundation under Grant No. SES-0848022.
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