| Popis: |
We present a quantum repeater protocol for distributing entanglement over long distances, where each repeater node contains several qubits that can couple to one single-photon emitter. Photons from the emitters perform heralded entanglement generation between qubits in neighboring nodes. The protocol leaves the emitters disentangled from the qubits and photons, thus allowing them to be reused to entangle other qubits. The protocol can therefore be time multiplexed, which increases the rate of generated EPR pairs. Deterministic entanglement swapping and heralded entanglement purification are used to extend the distance of the entanglement and reduce the error of the entangled qubits, respectively. We perform a complete protocol analysis by considering all relevant error sources, such as initialization, two-qubit gate, and qubit measurement errors, as well as the exponential decoherence of the qubits with time. The latter is particularly important since we analyze the protocol performance for a broad range of experimental parameters and obtain secret key rates ranging from $1 \rightarrow 1000$ Hz at a distance of $1000$ km. Our results suggest that it is important to reach a qubit memory coherence time of around one second, and two-qubit gate and measurement errors in the order of $10^{-3}$ to obtain reasonable secret key rates over distances longer than achievable with direct transmission. |
