  We report a single-shot-based projective readout of a semiconductor hybrid
qubit formed by three electrons in a GaAs double quantum dot.
Voltage-controlled adiabatic transitions between the qubit operations and
readout conditions allow high-fidelity mapping of quantum states. We show that
a large ratio both in relaxation time vs. tunneling time (~ 50) and
singlet-triplet splitting vs. thermal energy (~ 20) allow energy-selective
tunneling-based spin-to-charge conversion with readout visibility ~ 92.6%.
Combined with ac driving, we demonstrate high visibility coherent Rabi and
Ramsey oscillations of a hybrid qubit in GaAs. Further, we discuss the
generality of the method for use in other materials, including silicon.
