  Motivated by recent experimental progress towards the measurement and
manipulation of Majorana fermions with superconducting circuits, we propose a
device interfacing Majorana fermions with circuit quantum electrodynamics. The
proposed circuit acts as a charge parity detector changing the resonance
frequency of a superconducting $\lambda/4$ - resonator conditioned on the
parity of charges on nearby gates. Operating at both charge and flux sweet
spots, this device is highly insensitive to environmental noise. It enables
high-fidelity single-shot quantum non demolition readout of the state of a pair
of Majorana fermions encoding a topologically protected qubit. Additionally,
the interaction permits the realization of an arbitrary phase gate on the
topological qubit, closing the loop for computational completeness. Away from
the charge sweet spot, this device can be used as a highly sensitive charge
detector with a sensitivity better than $10^{-4} \text{e} / \sqrt{\text{Hz}}$
and bandwidth larger than $1$ MHz.
