  We investigate coupling an encoded spin qubit to a microwave resonator via
qubit energy level curvature versus gate voltage. This approach enables quantum
non-demolition readout with strength of tens to hundred MHz all while the qubit
stays at its full sweet-spot to charge noise, with zero dipole moment. A
"dispersive-like" spin readout approach similar to circuit-QED but avoiding the
Purcell effect is proposed. With the addition of gate voltage modulation,
selective longitudinal readout and n-qubit entanglement-by-measurement are
possible.
