Oscillating photonic Bell state from a semiconductor quantum dot for quantum key distribution

An on-demand source of bright entangled photon pairs is desirable for quantum key distribution (QKD) and quantum repeaters. The leading candidate to generate such pairs is based on spontaneous parametric down-conversion (SPDC) in non-linear crystals. However, its pair extraction efficiency is limited to 0.1% when operating at near-unity fidelity due to multiphoton emission at high brightness. Quantum dots in photonic nanostructures can in principle overcome this limit, but the devices with high entanglement fidelity (99%) have low pair extraction efficiency (0.01%). Here, we show a measured peak entanglement fidelity of 97.5% ± 0.8% and pair extraction efficiency of 0.65% from an InAsP quantum dot embedded in an InP nanowire. We show that the generated entangled two-photon Bell state can establish a secure key for peer-to-peer QKD. Using our time-resolved technique, we also demonstrate that we can remove the quantum dot detuning as a result of the biexciton-exciton cascade.

Matteo Pennacchietti, Brady Cunard, Shlok Nahar, Mohd Zeeshan, Sayan Gangopadhyay, Philip J. Poole, Dan Dalauct, Andreas Fognini, Klaus D. Jöns, Val Zwiller, Thomas Jennewein, Norbert Lüttkenhaus, Michael E. Reimer