  We explore the spin dynamics emerging from the N\'eel phase of the chain
compound antiferromagnet BaCo2V2O8. Our inelastic neutron scattering study
reveals unconventional discrete spin excitations, so called Zeeman ladders,
understood in terms of spinon confinement, due to the interchain attractive
linear potential. These excitations consist in two interlaced series of modes,
respectively with transverse and longitudinal polarization. The latter have no
classical counterpart and are related to the zero-point fluctuations that
weaken the ordered moment in weakly coupled quantum chains. Our analysis
reveals that BaCo2V2O8, with moderate Ising anisotropy and sizable interchain
interactions, remarkably fulfills the conditions necessary for the observation
of these longitudinal excitations.
