Abstract
In the study of open quantum systems modeled by a unitary evolution of a bipartite Hilbert space, we address the question of which parts of the environment can be said to have a “classical action” on the system, in the sense of acting as a classical stochastic process. Our method relies on the definition of the Environment Algebra, a relevant von Neumann algebra of the environment. With this algebra we define the classical parts of the environment and prove a decomposition between a maximal classical part and a quantum part. Then we investigate what other information can be obtained via this algebra, which leads us to define a more pertinent algebra: the Environment Action Algebra. This second algebra is linked to the minimal Stinespring representations induced by the unitary evolution on the system. Finally, in finite dimension we give a characterization of both algebras in terms of the spectrum of a certain completely positive map acting on the states of the environment.
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Communicated by Claude Alain Pillet.
Work supported by ANR-14-CE25-0003 “StoQ”.
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Bardet, I. Classical and Quantum Parts of the Quantum Dynamics: The Discrete-Time Case. Ann. Henri Poincaré 18, 955–981 (2017). https://doi.org/10.1007/s00023-016-0517-2
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DOI: https://doi.org/10.1007/s00023-016-0517-2