Open quantum systems are harder to track than open classical systems

  title={Open quantum systems are harder to track than open classical systems},
  author={Prahlad Warszawski and Howard M. Wiseman},
For a Markovian (in the strongest sense) open quantum system it is possible, by continuously monitoring the environment, to perfectly track the system; that is, to know the stochastically evolving pure state of the system without altering the master equation. In general, even for a system with a finite Hilbert space dimension D, the pure state trajectory will explore an infinite number of points in Hilbert space, meaning that the dimension K of the classical memory required for the tracking is… 

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