Observation of roton emission from a quantized vortex

Turbulence in inviscid quantum fluids offers unparalleled access to the universal principles of non-equilibrium dynamics, spanning a vast range of length scales from macroscopic flow down to the individual vortex core. In the zero-temperature limit, the microscopic mechanism by which the turbulent energy cascade terminates in the absence of viscosity remains a foundational challenge in quantum hydrodynamics. While prevailing theoretical descriptions prioritize phonon emission, they fail to account for the strong interatomic correlations that give rise to the roton minimum in superfluid 4He. Here, we report the direct observation of roton emission from a single quantized vortex using a high-quality-factor nanomechanical resonator at 10mK. We identify a sharp onset of dissipation at a critical velocity, and measure the energy loss per cycle, which corresponds quantitatively to the roton gap energy. Our findings address the long-standing mystery of zero-temperature energy relaxation by establishing roton emission as the primary dissipation channel in strongly correlated quantum liquids.