Ions in SuperfluidHe4

A quantum model is proposed to describe the motion of ions in the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ superfluid. The interaction between the ions and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ atoms is expressed in terms of the structure factor and quasiparticle operators of the quantum liquid. This model Hamiltonian is solved by a variational scheme. On the basis of the nonparabolic energy-momentum spectrum of the dressed ions, an explanation is given for the linear temperature dependence of the ion effective mass observed in the experiments. The study reveals some interesting aspects of the interaction between classical particles and quantum fields.