Like many quantum fluids, superfluid helium-4 (He II) can be viewed as a mixture of two miscible fluid components: an inviscous superfluid and a viscous normal fluid composed of thermal quasiparticles. [1]Mutual friction between the two fluids can occur due to quasiparticles scattering from the quantized vortex lines in the superfluid. [2]This quantum dissipation mechanism is key to understanding a variety of fascinating behaviors in two-fluid systems. [3,4]However, due to the lack of experimental data for guidance, modeling mutual friction between individual eddies and ordinary fluids remains an open topic despite decades of research. is. [5-10]Here we report experiments to visualize the motion of quantized vortex rings in He II by decorating them with solidified deuterium tracer particles.By examining how the ring spontaneously shrinks and accelerates, only a recent theory [9] This describes the coupled motion of the two fluids due to self-consistent local friction and can reproduce the observed ring dynamics. Our work eliminates long-standing ambiguities in the theoretical description of He II eddy dynamics. This will have far-reaching implications, as similar mutual friction concepts have been adopted in various quantum two-fluid systems, including atomic boses. Einstein Condensation (BEC) [11,12]superfluid neutron star [13-15]and gravity-mapped holographic superfluid [16,17].

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