  A quantum melting of the spin ice is proposed for pyrochlore-lattice magnets
Pr$_2TM_2$O$_7$ ($TM=$Ir, Zr, and Sn). The quantum superexchange Hamiltonian
having a nontrivial magnetic anisotropy is derived in the basis of atomic
non-Kramers magnetic doublets. The ground states exhibit a cooperative
ferroquadrupole and pseudospin chirality, forming a magnetic analog of smectic
liquid crystals. Our theory accounts for dynamic spin-ice behaviors
experimentally observed in Pr$_2TM_2$O$_7$.
