We report direct spectroscopic evidence of correlations between monopoles in a quantum spin ice. A hierarchy of unequally spaced magnetic excitations has been observed via low energy inelastic neutron spectroscopy in Pr2Sn2O7, resembling the confinement of spin defects in low-dimensional quantum magnets., Using a simple linear potential model to fit the excitations, we have estimated the monopole pair creation energy, and calculated a lower bound for the tension between monopole-like quasiparticles. The linear potential model provides a natural explanation as to why detection of these correlations have been so elusive in the canonical dipolar spin ices. This is the first spectroscopic measurement of an effective “Dirac string” between magnetic monopoles.
 P. M. Sarte et al 2017 Journal of Physics: Condensed Matter Vol. 29, 45LT01.
 P. M. Sarte et al 2018, submitted to Physical Review Letters.