NMR implementation of a building block for scalable quantum computation

We report the implementation of the central building block of the Schulman-Vazirani procedure for fully polarizing a subset of two-level quantum systems which are initially only partially polarized. This procedure consists of a sequence of unitary operations and incurs only a quasi-linear overhead in the number of quantum systems and operations required. The key building block involves three quantum systems and was implemented on a homonuclear three-spin system using room temperature liquid-state nuclear magnetic resonance (NMR) techniques. This work was inspired by the state initialization challenges in current NMR quantum computers but also shines new light on polarization transfer in NMR. (C) 2001 Published by Elsevier Science B.V.