Oscillating photonic Bell state from a semiconductor quantum dot for quantum key distribution
Matteo P. Pennacchietti, Brady Cunard, Shlok Nahar, Mohd Zeeshan, Sayan Gangopadhyay, Philip J. Poole, Dan Dalacu, Andreas Fognini, Klaus D. Jöns, Val Zwiller, Thomas D. Jennewein, Norbert Lütkenhaus, Michael E. Reimer · Communications Physics · 2024
Abstract 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 in an InP photonic nanowire waveguide. We show that the generated oscillating two-photon Bell state can establish a secure key for peer-to-peer QKD. Using our time-resolved QKD scheme alleviates the need to remove the quantum dot energy splitting of the intermediate exciton states in the biexciton-exciton cascade.