NMR Quantum Computing: Applying Theoretical Methods to Designing Enhanced Molecular Systems

Rob Mawhinney and Georg Schreckenbach

Department of Chemistry and Biochemistry and CERMM
Concordia University
Montreal QC, Canada H3G 1M8


    "Molecular Memory Bank Draws Closer" reads one of the BBC online news headlines of December 3, 2002. This is perhaps the first general public report on NMR quantum computing. The proposal for using NMR techniques for quantum computing was introduced only 6 years ago. Despite the gains made so far, many believe that the potential for NMR quantum computing is very limited, and building systems with more than 10 qubits is practically impossible (a qubit is a quantum bit, in this case it is typically an atom with a nuclear spin of 1/2). So, this first "real life" implementation, using 19 qubits, not only exceeds this limit but demonstrates a practical application of the methodology.
    The two main challenges to implementing NMR quantum computing are: (1) the control of pulse imperfections and (2) the design of molecules with enhanced spectral properties, in particular chemical shifts and spin-spin coupling constants. The predictive nature of theoretical chemistry is particularly geared towards exploring the latter challenge.
    We will present calculated chemical shielding and spin-spin coupling constant results for a number of systems already used for testing NMR quantum computing algorithms. From these results we will assess some of the design criteria required for molecules to be used in NMR quantum computing. From these criteria new, enhanced, systems may be proposed. Future work based on these findings will be discussed.

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