Person: Borregaard, Johannes
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Borregaard
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Johannes
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Borregaard, Johannes
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Publication Long-distance entanglement distribution using individual atoms in optical cavities(American Physical Society (APS), 2015) Borregaard, Johannes; Komar, Peter; Kessler, Eric; Lukin, Mikhail; Sørensen, A. S.Individual atoms in optical cavities can provide an efficient interface between stationary qubits and flying qubits (photons), which is an essential building block for quantum communication. Furthermore, cavity-assisted controlled-not (cnot) gates can be used for swapping entanglement to long distances in a quantum repeater setup. Nonetheless, dissipation introduced by the cavity during the cnot may increase the experimental difficulty in obtaining long-distance entanglement distribution using these systems. We analyze and compare a number of cavity-based repeater schemes combining various entanglement generation schemes and cavity-assisted cnot gates. We find that a scheme, where high-fidelity entanglement is first generated in a two-photon detection scheme and then swapped to long distances using a recently proposed heralded controlled-Z (cz) gate, exhibits superior performance compared to the other schemes. The heralded gate moves the effect of dissipation from the fidelity to the success probability of the gate thereby enabling high-fidelity entanglement swapping. As a result, high-rate entanglement distribution can be achieved over long distances even for low cooperativities of the atom-cavity systems. This high-fidelity repeater is shown to outperform the other cavity-based schemes by up to two orders of magnitude in the rate for realistic parameters and large distances (1000 km).Publication Heralded Quantum Gates with Integrated Error Detection in Optical Cavities(American Physical Society (APS), 2015) Borregaard, Johannes; Komar, Peter; Kessler, Eric; Sørensen, A. S.; Lukin, MikhailWe 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.