We propose to employ the neutron Compton scattering (NCS) in the realm of ionic liquids (iL), applying it to the protiated and deuterated variants of an archetipic IL, phosporic acid (PA). PA and its solutions have one of the highest intrinsic proton conductivities among known materials, and the mechanism of this unique conductivity remains a puzzle. A recent study discovered a strong isotope effect in the conductivity: (i) a strong isotope shift of the glass transition temperature and (ii) a significant reduction of the energy barrier by zero-point quantum fluctuations. These results suggest that the high conductivity in phosphoric acids is caused by a very efficient proton transfer mechanism, which is strongly assisted by quantum effects. We propose to measure two samples: (i) 85% wt% H3PO4 in H2O, and (ii) D3PO4 in D2O between 10 and 300K.