We propose and analyze heralded quantum gates between qubits in optical cavities. They employ an auxiliary qubit to report if a successful gate occurred. In this manner, the errors, which would have corrupted a deterministic gate, are converted into a nonunity probability of success: once successful, the gate has a much higher fidelity than a similar deterministic gate. Specifically, we describe that a heralded, near-deterministic controlled phase gate (CZ gate) with the conditional error arbitrarily close to zero and the success probability that approaches unity as the cooperativity of the system, $C$, becomes large. Furthermore, we describe an extension to near-deterministic $N$-qubit Toffoli gate with a favorable error scaling. These gates can be directly employed in quantum repeater networks to facilitate near-ideal entanglement swapping, thus greatly speeding up the entanglement distribution.

• Received 1 January 2015

DOI:https://doi.org/10.1103/PhysRevLett.114.110502

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