  The measurement of the parity of two qubits is a primitive of quantum
computing that allows creating deterministic entanglement. In the field of
circuit quantum electrodynamics, a scheme to achieve parity measurement of two
superconducting qubits has been proposed and analyzed under the usual
rotating-wave approximation (RWA). We show that the same scheme can be carried
over beyond this approximation, to the regime of ultrastrong coupling, with an
improvement in the fidelity.
