Keywords: very low temperature

Solid helium is often referred to as quantum solid and known to deform easily and rapidly even under tiny force, strongly subjected to quantum effect. A number of research have been conducted to study its elasticity, or reversible deformation, but its plasticity, or irreversible deformation, is scarcely understood. In the proposed experiment, we are going to precisely measure the motion of objects sinking in solid helium to elucidate the quantum effects on the plasticity of solid helium. Especially, the local superflow expected to exist in cores of dislocations and grain boundaries are to be examined, in the context of supersolidity.