  We report the direct observation by inelastic neutron scattering experiments
of a spin triplet of magnetic excitations in the response associated with the
ladders in the composite cuprate Sr14Cu24O41. This appears as a peak at
q_{Q1D}=\pi and energy \Delta_1=32.5 meV, and we conjecture that all the
triplets making up this conspicuous peak have the same phase and therefore
interpret it as the signature of the occurrence of quantum coherence along the
ladder direction between entangled spin pairs. From the comparison with
previous neutron and x-ray data, we conclude that the temperature evolution of
this mode is driven by the crystallization of holes into a charge density wave
in the ladder sublattice
