  We introduce a straightforward, single-ensemble, path sampling approach to
calculate free energy differences based on Jarzynski's relation. For a
two-dimensional ``toy'' test system, the new (minimally optimized) method
performs roughly one hundred times faster than either optimized ``traditional''
Jarzynski calculations or conventional thermodynamic integration. The
simplicity of the underlying formalism suggests the approach will find broad
applicability in molecular systems.
