  We investigate both experimentally and theoretically the relaxation of
pseudo-pure maximally entangled states (Bell states) of two nuclear spins
1H-13C belonging to a molecule in a liquid. The Bell states are obtained by a
method based on a detuned Hartmann-Hahn cross-polarization condition. Their
entangled character is verified by quantum-state tomography. Our relaxation
measurements reveal different relaxation rates for different Bell states. We
interpret this difference as originating from cross-correlations between
different relaxation mechanisms, thereby demonstrating that the measurements of
the differential relaxation of Bell states are potentially useful for advanced
NMR characterization of liquids.
