Subspace confinement: how good is your qubit?

Simon J. Devitt, Sonia G. Schirmer, Daniel K.L. Oi, Jared H. Cole, Lloyd C.L. Hollenberg

Research output: Contribution to journalArticle

18 Citations (Scopus)
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The basic operating element of standard quantum computation is the qubit, an isolated two-level system that can be accurately controlled, initialized and measured. However, the majority of proposed physical architectures for quantum computation are built from systems that contain much more complicated Hilbert space structures. Hence, defining a qubit requires the identification of an appropriate controllable two-dimensional sub-system. This prompts the obvious question of how well a qubit, thus defined, is confined to this subspace, and whether we can experimentally quantify the potential leakage into states outside the qubit subspace. We demonstrate how subspace leakage can be characterized using minimal theoretical assumptions by examining the Fourier spectrum of the oscillation experiment.
Original languageEnglish
Number of pages22
JournalNew Journal of Physics
Issue numberOct
Publication statusPublished - 29 Oct 2007


  • qubit
  • subspace
  • fourier spectrum
  • quantum computation
  • subspace leakage

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