  Here we demonstrate how para-hydrogen can be used to prepare a two-spin
system in an almost pure state which is suitable for implementing nuclear
magnetic resonance (NMR) quantum computation. A 12ns laser pulse is used to
initiate a chemical reaction involving pure para-hydrogn (the nuclear spin
singlet of H2). The product, formed on the microsecond timescale, contains a
hydrogen derived two-spin system with an effective spin-state purity of 0.916.
To achieve a comparable result by direct cooling would require an unmanageable
(in the liquid state) effective spin temperature of 6.4mK or an impractical
magnetic field of 0.45MT at room temperature. The resulting spin state has an
entanglement of formation of 0.822 and cannot be described by local hidden
variable models.
