Sania Jevtic, David Jennings, Terry Rudolph
Motivated by thermodynamic considerations, we analyse the variation of the
quantum mutual information on a unitary orbit of a bipartite system state, with
and without global constraints such as energy conservation. We solve the full
optimisation problem for the smallest system of two qubits, and explore
thoroughly the effect of unitary operations on the space of reduced-state
spectra. We then provide applications of these ideas to physical processes
within closed quantum systems, such as a generalized collision model approach
to thermal equilibrium and a global Maxwell demon playing tricks on local
observers. For higher dimensions, the maximization of correlations is
relatively straightforward, however the minimisation of correlations displays
non-trivial structures. We characterise a set of separable states in which the
minimally correlated state resides, and find a collection of classically
correlated states admitting a particular "Young tableau" form. Furthermore, a
partial order exists on this set with respect to individual marginal entropies,
and the presence of a "see-saw effect" in entropies forces a finer analysis to
determine the optimal tableau.
View original:
http://arxiv.org/abs/1112.3372
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