Adiabatic conversion for qubit readout: Optimal pulse shapes and dephasing

Adiabatic conversion schemes are commonly used to
measure quantum states. These schemes may include, e.g., spin-to-charge
conversion for spins in quantum dots or parity-to-charge conversion for qubits
based on Majorana zero modes. In all of these schemes, a common element
is that dephasing is minimized at an "operating point" (e.g., for the 'spin' or
'parity' quantum number), but measurement-induced dephasing is maximized
at the "measurement point". The balance between 'adiabaticity' and
dephasing can be optimized to improve performance of these readout
schemes. We give an explicit construction that allows for optimal state
conversion in qubit readouts. Applying this scheme to the specific case of
spin qubits in quantum dots, we show that a high-fidelity (better than 99.9%)
single-shot all-electrical readout is possible.