  Electron spins confined in silicon quantum dots are promising candidates for
large-scale quantum computers. However, the degeneracy of the conduction band
of bulk silicon introduces additional levels dangerously close to the window of
computational energies, where the quantum information can leak. The energy of
the valley states -- typically 0.1 meV -- depends on hardly controllable
atomistic disorder and still constitutes a fundamental limit to the scalability
of these architectures. In this work, we introduce designs of complementary
metal-oxide-semiconductor (CMOS)-compatible silicon fin field-effect
transistors that enhance the energy gap to noncomputational states by more than
one order of magnitude. Our devices comprise realistic silicon-germanium
nanostructures with a large shear strain, where troublesome valley degrees of
freedom are completely removed. The energy of noncomputational states is
therefore not affected by unavoidable atomistic disorder and can further be
tuned in situ by applied electric fields. Our design ideas are directly
applicable to a variety of setups and will offer a blueprint toward
silicon-based large-scale quantum processors.
