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

TL;DR

This paper presents a highly efficient, on-demand entangled photon source from a semiconductor quantum dot that can be used for secure quantum key distribution without complex energy level adjustments.

Contribution

It demonstrates a 65-fold increase in pair extraction efficiency from a quantum dot with high entanglement fidelity, enabling practical quantum key distribution.

Findings

Achieved 95.3% raw peak concurrence and 97.5% fidelity.

Enhanced pair extraction efficiency by 65 times.

Generated oscillating Bell states suitable for QKD.

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 entangled photon pairs is based on spontaneous parametric down-conversion (SPDC) in a non-linear crystal. However, there exists a fundamental trade-off between entanglement fidelity and efficiency in SPDC sources due to multiphoton emission at high brightness, which limits the pair extraction efficiency to 0.1% when operating at near-unity fidelity. Quantum dots in photonic nanostructures can in principle overcome this trade-off; however, the quantum dots that have achieved entanglement fidelities on par with SPDC sources (99%) have poor pair extraction efficiencies of 0.01%. Here, we demonstrate a 65-fold increase in the pair extraction efficiency compared to quantum dots with equivalent peak fidelity from an InAsP quantum dot in a photonic nanowire waveguide. We measure a raw peak concurrence and fidelity of 95.3% $\pm$ 0.5% and 97.5% $\pm$ 0.8%, respectively. Finally, we show that an oscillating two-photon Bell state generated by a semiconductor quantum dot can be utilized to establish a secure key for QKD, alleviating the need to remove the quantum dot energy splitting of the intermediate exciton states in the biexciton-exciton cascade.