Department of Physics, Sapienza University of Rome, 00185 Rome, Italy.
Institute of Semiconductor and Solid State Physics, Johannes Kepler University, 4040 Linz, Austria.
Phys Rev Lett. 2019 Oct 18;123(16):160501. doi: 10.1103/PhysRevLett.123.160501.
Photonic entanglement swapping, the procedure of entangling photons without any direct interaction, is a fundamental test of quantum mechanics and an essential resource to the realization of quantum networks. Probabilistic sources of nonclassical light were used for seminal demonstration of entanglement swapping, but applications in quantum technologies demand push-button operation requiring single quantum emitters. This, however, turned out to be an extraordinary challenge due to the stringent prerequisites on the efficiency and purity of the generation of entangled states. Here we show a proof-of-concept demonstration of all-photonic entanglement swapping with pairs of polarization-entangled photons generated on demand by a GaAs quantum dot without spectral and temporal filtering. Moreover, we develop a theoretical model that quantitatively reproduces the experimental data and provides insights on the critical figures of merit for the performance of the swapping operation. Our theoretical analysis also indicates how to improve state-of-the-art entangled-photon sources to meet the requirements needed for implementation of quantum dots in long-distance quantum communication protocols.
光子纠缠交换，即无需任何直接相互作用即可纠缠光子的过程，是量子力学的基本检验，也是实现量子网络的必要资源。非经典光的概率源被用于纠缠交换的开创性演示，但在量子技术中的应用需要按钮操作，这需要单量子发射器。然而，由于纠缠态产生的效率和纯度的严格要求，这变成了一个非凡的挑战。在这里，我们展示了一种使用 GaAs 量子点按需产生的偏振纠缠光子对的全光纠缠交换的概念验证演示，而无需光谱和时间滤波。此外，我们开发了一个理论模型，该模型定量地再现了实验数据，并提供了有关交换操作性能的关键衡量标准的见解。我们的理论分析还表明如何改进现有的纠缠光子源，以满足在长距离量子通信协议中实现量子点所需的要求。
