How Many Bits Does It Take to Track an Open Quantum System?
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A D-dimensional Markovian open quantum system will undergo quantum jumps between pure states, if we can monitor the bath to which it is coupled with sufficient precision. In general, these jumps, plus the between-jump evolution, create a trajectory which passes through infinitely many different pure states. Here we show that, for any ergodic master equation, one can expect to find an adaptive monitoring scheme on the bath that can confine the system state to jumping between only K states, for some K=(D-1)2+1. For D=2 we explicitly construct a two-state ensemble for any ergodic master equation, showing that one bit is always sufficient to track a qubit.
Physical Review Letters
Copyright 2011 American Physical Society. This is the author-manuscript version of this paper. Reproduced in accordance with the copyright policy of the publisher. Please refer to the journal's website for access to the definitive, published version.
Quantum Information, Computation and Communication
Quantum Physics not elsewhere classified