  In a recent publication [Phys. Rev. Lett. 111, 143602] we have shown using a
QED approach that, in the presence of a magnetic field, the quantum vacuum
coupled to a chiral molecule provides a kinetic momentum directed along the
magnetic field. Here we explain the physical mechanisms which operate in the
transfer of momentum from the vacuum to the molecule. We show that the
variation of the molecular kinetic energy originates from the magnetic energy
associated with the vacuum correction to the magnetization of the molecule. We
carry out a semiclassical calculation of the vacuum momentum and compare the
result with the QED calculation.
