Neutron inelastic scattering is a powerful tool for observing spin dynamics in solids. Enhanced quantum fluctuation often dominates low-temperature properties of spin systems, giving rise to novel nonmagnetic ground states. A tool that can observe spin dynamics is indispensable to elucidate mechanism realizing such a nonmagnetic state. Fig.1 shows spin excitation spectra in the quantum kagome antiferromagnet Rb2Cu3SnF12. Strong quantum fluctuations, enhanced by the geometrical frustration, prohibit spins to order even at the base temperature, and instead a nonmagnetic singlet groundstate is formed. Such a singlet state cannot be detected by static magnetic tools. Using neutron inelastic scattering, we measure dynamics of excited triplets from the singlet ground state, with which we uniquely determine the ground-state singlet configuration.