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@article{PY07a,
Abstract = {We analyze a quantum mechanical gyroscope which is modeled as a large
spin and used as a reference against which to measure the angular
momenta of spin-1/2 particles. These measurements induce a
back-action on the reference which is the central focus of our study.
We begin by deriving explicit expressions for the quantum channel
representing the back-action. Then, we analyze the dynamics
incurred by the reference when it is used to sequentially measure
particles drawn from a fixed ensemble. We prove that the reference
thermalizes with the measured particles and find that generically, the
thermal state is reached in time which scales linearly with the size
of the reference. This contrasts a recent conclusion of Bartlett et
al. that this takes a quadratic amount of time when the particles are
completely unpolarized. We now understand their result in terms of a
simple physical principle based on symmetries and conservation laws.
Finally, we initiate the study of the non-equilibrium dynamics of the
reference. Here we find that a reference in a coherent state will
essentially remain in one when measuring polarized particles, while
rotating itself to ultimately align with the polarization of the
particles. },
Author = {D. Poulin and J. Yard},
Date-Added = {2007-02-01 08:54:10 -0800},
Date-Modified = {2010-05-06 13:47:34 -0400},
Eprint = {quant-ph/0612126},
Journal = {New J. Phys.},
Keywords = {Reference frame},
Local-Url = {PY07a.pdf},
Pages = {156},
Title = {Dynamics of a Quantum Reference Frame},
Volume = {9},
Year = {2007}}