  Quantum logic gates for photonic qubits can be implemented using the quantum
Zeno effect based on strong two-photon absorption. The fidelity of quantum Zeno
gates of this kind may be substantially reduced by photon loss. Heralding on
those outcomes in which both of the logical qubits emerge from the Zeno gate
can increase the fidelity at the expense of a limited success rate (P.M. Leung
et al., Phys. Rev. A 74, 062325 (2006)). We analyze the performance of heralded
quantum Zeno gates by solving Schrodinger's equation for a system of photons
coupled to three-level atoms. This approach identifies several potential error
sources that are not described by earlier models that assumed a fixed rate of
single-photon loss and two-photon absorption.
