  Neutron time-of-flight spectroscopy has been employed to study the
crystal-field splitting of Pr$^{3+}$ in the pyrochlore stannate
Pr$_{2}$Sn$_{2}$O$_{7}$. The crystal field has been parameterized from a
profile fit to the observed neutron spectrum. The single-ion ground state is a
well isolated non-Kramers doublet of $\Gamma_3^+$ symmetry with a large
Ising-like anisotropy, $\chi_{zz} /\chi_\perp \approx 60$ at 10 K, but with a
significant admixture of terms $| M_J \neq \pm J >$ which can give rise to
quantum zero-point fluctuations. This magnetic state satisfies the requirements
for quantum spin ice behavior.
