Evidence for macroscopic vortex--porous-disk interaction in helium II

We describe measurements of the liquid-helium-flow behavior of Millipore (porous) disks. Our findings lead us to hypothesize a novel effect: Quantum vortices, ''destroyed'' when the superfluid passes through the porous material, deposit their angular momentum; an observable, macroscopic torque on the disk results. Many different aspects of our data are shown to be in excellent agreement with this model. We present measurements of the temperature and speed dependence of the vortex-induced torque