  We present a blueprint for building a fault-tolerant quantum computer using
the spin states of electrons on the surface of liquid helium. We propose to use
ferromagnetic micropillars to trap single electrons on top of them and to
generate a local magnetic field gradient. Introducing a local magnetic field
gradient hybridizes charge and spin degrees of freedom, which allows us to
benefit from both the long coherence time of the spin state and the long-range
Coulomb interaction that affects the charge state. We present concrete schemes
to realize single- and two-qubit gates and quantum-non-demolition read-out. In
our framework, the hybridization of charge and spin degrees of freedom is large
enough to perform fast qubit gates and small enough not to degrade the
coherence time of the spin state significantly, which leads to the realization
of high-fidelity qubit gates.
