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Quantum Circuits with Mixed States Dorit Aharonov \Lambda Alexei Kitaev y Noam Nisan z
 

Summary: Quantum Circuits with Mixed States
Dorit Aharonov \Lambda Alexei Kitaev y Noam Nisan z
Abstract
Current formal models for quantum computation
deal only with unitary gates operating on ``pure quan­
tum states''. In these models it is difficult or impossible
to deal formally with several central issues: measure­
ments in the middle of the computation; decoherence
and noise, using probabilistic subroutines, and more.
It turns out, that the restriction to unitary gates and
pure states is unnecessary. In this paper we general­
ize the formal model of quantum circuits to a model in
which the state can be a general quantum state, namely
a mixed state, or a ``density matrix'', and the gates can
be general quantum operations, not necessarily unitary.
The new model is shown to be equivalent in compu­
tational power to the standard one, and the problems
mentioned above essentially disappear.
The main result in this paper is a solution for the
subroutine problem. The general function that a quan­

  

Source: Aharonov, Dorit - School of Computer Science and Engineering, Hebrew University of Jerusalem

 

Collections: Physics; Computer Technologies and Information Sciences