BULK QUANTUM COMPUTATION WITH NUCLEAR-MAGNETIC-RESONANCE - THEORY ANDEXPERIMENT

We show that quantum computation is possible with mixed states instead of pure states as inputs. This is performed by embedding within the m ixed state a subspace that transforms like a pure state and that can b e identified by labelling based on logical (spin), temporal, or spatia l degrees of freedom. This permits quantum computation to be realized with bulk ensembles far from the ground state. Experimental results ar e presented for quantum gates and circuits implemented with liquid nuc lear magnetic resonance techniques and verified by quantum state tomog raphy.