Figure 4: Quantum dot spin–photon entangled pairs for quantum repeaters.
From: Complete tomography of a high-fidelity solid-state entangled spin–photon qubit pair
(a) A schematic diagram of a quantum repeater based on optical quantum dots. When a spin–photon pair is generated, the spin is stored in the repeater node, whereas the photon is sent into the communication channel. Two such photons from different repeater nodes interfere to (probabilistically) produce spin–spin entanglement between two repeaters. (b) Plot of the simulated net communication rate of entangled spin–spin pairs after consumption (in purification) of ‘raw’ spin–photon states and EPR-Bell-pairs (Einstein-Podolsky-Rosen) suitable for use in the network. Entanglement distillation consumes many raw pairs generated at Fss=
+(1/3)(1−Fsp)2 (assuming depolarizing noise). As Fsp approaches the threshold 0.71 from above, the net communication rate goes to zero. The communication rate in entangled bits per second (ebits s−1) is calculated, assuming spin–photon pairs interfering at a rate of 100 s−1. The final spin–spin entanglement fidelity is at least 0.995.
