Optimal entanglement generation for efficient hybrid quantum repeaters

We propose a realistic protocol to generate entanglement between quantum memories at neighboring nodes in hybrid quantum repeaters. Generated entanglement includes only one type of error, which enables efficient entanglement distillation. In contrast to the known protocols with such a property, our protocol with ideal detectors achieves the theoretical limit of the success probability and the fidelity to a Bell state, promising higher efficiencies in the repeaters. We also show that the advantage of our protocol remains even with realistic threshold detectors.

Figure 1

(Color online) (a) Schematic diagram of our protocol. (b) The performance of protocols with ideal detectors: fidelity of the obtained entanglement to a Bell state as a function of the success probability when $l_0=25\text{km}$ (corresponding to $\sim 0.17\text{dB}/\text{km}$ attenuation) and $\theta =0.01$ for (i) protocol I [12, 13], (ii) protocol II [14], and (iii) our protocol.

Figure 2

(Color online) The performance of protocols with realistic detectors: (i) protocol I with an ideal homodyne detector, (ii) protocol II with a TD1 $\left(\eta =0.89,\nu =1.4\times {10}^{-6}\right)$, $\left({\text{ii}}^{\prime }\right)$ protocol II with a TD2 $\left(\eta =0.12,\nu =3.2\times {10}^{-7}\right)$, (iii) our protocol with TD1s, and $\left({\text{iii}}^{\prime }\right)$ our protocol with TD2s.