Realization of logically labeled effective pure states for bulk quantum computation

We report the first use of "logical labeling" to perform a quantum computat ion with a room-temperature bulk system. This method entails the selection of a subsystem that behaves as if it were at zero temperature-except for a decrease in signal strength-conditioned upon the state of the remaining sys tem. No averaging over differently prepared molecules is required. In order to test this concept, we execute a quantum search algorithm in a subspace of two nuclear spins, labeled by a third spin, using solution nuclear magne tic resonance and employing a novel choice of reference frame to uncouple n uclei.