  Semiconductor spin qubits are an attractive platform for quantum computing,
but their performance is degraded primarily by fluctuating electromagnetic
environments. We introduce the concept of ballast charges, which are induced
charges on the surface of an additional screening layer situated below the
qubits. The counteractive behavior of these charges can significantly reduce
the power spectral density associated with fluctuations from two-level systems
that contribute to charge noise. Our simulations show that the dephasing time
of a spin qubit in a Si/SiGe device increases by a factor of 4 to 6 on average
when using this method. We also discuss the physical implementation and
potential challenges of this approach.
