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 syste ms which are initially only partially polarized. This procedure consists of a sequence of unitary operations and incurs only a quasi-linear overhead i n the number of quantum systems and operations required. The key building b lock involves three quantum systems and was implemented on a homonuclear th ree-spin system using room temperature liquid-state nuclear magnetic resona nce (NMR) techniques. This work was inspired by the state initialization ch allenges in current NMR quantum computers but also shines new light on pola rization transfer in NMR. (C) 2001 Published by Elsevier Science B.V.