Householder methods for quantum circuit design

Jesus Urias, Diego Quinones Valles

    Research output: Contribution to journalArticlepeer-review


    Algorithms to resolve multiple-qubit unitary transformations into a sequence of simple operations on one-qubit subsystems are central to the methods of quantum-circuit simulators. We adapt Householder’s theorem to the tensor-product character of multi-qubit state vectors and translate it to a combinatorial procedure to assemble cascades of quantum gates that recreate any unitary operation U acting on n-qubit systems. U may be recreated by any cascade from a set of combinatorial options that, in number, are not lesser than super-factorial of 2n. Cascades are assembled with one-qubit controlled-gates of a single type. We complement the assembly procedure with a new algorithm to generate Gray codes that reduce the combinatorial options to cascades with the least number of CNOT gates. The combined procedure —factorization, gate assembling, and Gray ordering — is illustrated on an array of three qubits.
    Original languageEnglish
    Pages (from-to)150-157
    JournalCanadian Journal of Physics
    Issue number2
    Publication statusPublished - 28 Oct 2015


    • Householder factorizations in tensor-product spaces
    • algorithmic synthesis of quantum circuits
    • quantum simulators


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