Quantum circuits with mixed states

@inproceedings{Aharonov1998QuantumCW,
  title={Quantum circuits with mixed states},
  author={Dorit Aharonov and Alexei Y. Kitaev and Noam Nisan},
  booktitle={Symposium on the Theory of Computing},
  year={1998}
}
We define the model of quantum circuits with density matrices, where non-unitary gates are allowed. Measurements in the middle of the computation, noise and decoherence are implemented in a natural way in this model, which is shown to be equivalent in computational power to standard quantum circuits. The main result in this paper is a solution for the subroutine problem: The general function that a quantum circuit outputs is a probabilistic function, but using pure state language, such a… 
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422 Citations

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