X (X=Cl,Br and I)*

The gapped spin chains systems are usually non magnetic at low temperature however a break in translational symmetry can create a S = ½ ground state. The defect polarizes a large number of spins around it and pinnes a magnetic soliton [1]. By means of Electron Spin Resonance spectroscopy we report the experimental quantum coherence of a soliton of spin ½  [2,3] and a soliton-dimer with the quantum dynamics of a spin 1. We show the soliton can be either single or paired with a large exchange coupling and a probability of 50 % due to the one-dimensionnal nature of the system [4].