Phys. Rev. A 70, 012111 (2004) [5 pages]Spatial localization and relativistic transformation of quantum spinsReceived 11 March 2004; published 29 July 2004 The purity of a reduced state for spins that is pure in the rest frame will most likely appear to degrade because spin and momentum become mixed when viewed by a moving observer. We show that such a boost-induced decrease in spin purity observed in a moving reference frame is intrinsically related to the spatial localization properties of the wave package observed in the rest frame. Furthermore, we prove that, for any localized pure state with separable spin and momentum in the rest frame, its reduced density matrix for spins inevitably appears to be mixed whenever viewed from a moving reference frame. © 2004 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevA.70.012111
DOI:
10.1103/PhysRevA.70.012111
PACS:
03.65.Ta, 03.30.+p, 03.67.−a
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