Quantum-gate characterization in an extended Hilbert space

Peter P. Rohde*, G. J. Pryde, J. L. O'Brien, Timothy C. Ralph

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    24 Citations (Scopus)


    We describe an approach for characterizing the process performed by a quantum gate using quantum process tomography, by first modeling the gate in an extended Hilbert space, which includes nonqubit degrees of freedom. To prevent unphysical processes from being predicted, present quantum process tomography procedures incorporate mathematical constraints, which make no assumptions as to the actual physical nature of the system being described. By contrast, the procedure presented here assumes a particular class of physical processes, and enforces physicality by fitting the data to this model. This allows quantum process tomography to be performed using a smaller experimental data set, and produces parameters with a direct physical interpretation. The approach is demonstrated by example of mode matching in an all-optical controlled-NOT gate. The techniques described are general and could be applied to other optical circuits or quantum computing architectures.

    Original languageEnglish
    Article number032306
    JournalPhysical Review A - Atomic, Molecular, and Optical Physics
    Issue number3
    Publication statusPublished - Sep 2005

    Bibliographical note

    A publisher's note for this article can be found at Phys. Rev. A 72, 039906, https://doi.org/10.1103/PhysRevA.72.039906


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