Three-qubit nuclear magnetic resonance quantum information processing with a single-crystal solid

We report the first implementation of NMR quantum information processing in a static single-crystal solid, illustrating pseudopure state preparation and gate manipulations on a three-qubit system, U-C-13(2), N-15-glycine ((H2NCH2COOH)-N-15-C-13-C-13). We consider issues important to single-crystal NMR implementations of quantum information processing and introduce several innovations specific to such implementations. In particular, concurrent cross-polarization of both the C-13 and N-15 spins from proton magnetization enhances and equalizes populations on these nuclei in a single step. This multiple cross-polarization step simplifies preparation of pseudopure spin states relative to previously described multiple-pulse sequences. Also, proton decoupling, which prolongs coherence during spin-evolution and detection periods, is switched off to dephase unwanted coherences during preparation of pseudopure spin states. Such "relaxation averaging" (or T-2 averaging) is an alternative to spatial averaging, which requires special hardware and large gradient strengths for small crystals. (C) 2003 American Institute of Physics.