  We report here numerical results of the low-temperature behavior of a dipolar
spin ice in a magnetic field along the [100] direction. Tuning the magnetic
field, the system exhibit a half-magnetization plateau at low temperature. This
half-polarized phase should correspond to a quantum solid phase in an effective
2D quantum boson model, and the transition from the Coulomb phase with a
power-law correlation to this state can be regarded as a superfluid to a
quantum solid transition. We discuss possible experimental signatures of this
half-polarized state.
