Applied Physics Department, Royal Institute of Technology, Albanova University Centre, Roslagstullsbacken 21, 106 91, Stockholm, Sweden.
Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628CJ, Delft, The Netherlands.
Sci Rep. 2017 May 10;7(1):1700. doi: 10.1038/s41598-017-01509-6.
Global, secure quantum channels will require efficient distribution of entangled photons. Long distance, low-loss interconnects can only be realized using photons as quantum information carriers. However, a quantum light source combining both high qubit fidelity and on-demand bright emission has proven elusive. Here, we show a bright photonic nanostructure generating polarization-entangled photon pairs that strongly violates Bell's inequality. A highly symmetric InAsP quantum dot generating entangled photons is encapsulated in a tapered nanowire waveguide to ensure directional emission and efficient light extraction. We collect ~200 kHz entangled photon pairs at the first lens under 80 MHz pulsed excitation, which is a 20 times enhancement as compared to a bare quantum dot without a photonic nanostructure. The performed Bell test using the Clauser-Horne-Shimony-Holt inequality reveals a clear violation (S > 2) by up to 9.3 standard deviations. By using a novel quasi-resonant excitation scheme at the wurtzite InP nanowire resonance to reduce multi-photon emission, the entanglement fidelity (F = 0.817 ± 0.002) is further enhanced without temporal post-selection, allowing for the violation of Bell's inequality in the rectilinear-circular basis by 25 standard deviations. Our results on nanowire-based quantum light sources highlight their potential application in secure data communication utilizing measurement-device-independent quantum key distribution and quantum repeater protocols.
全球安全的量子信道将需要高效分配纠缠光子。只有使用光子作为量子信息载体，才能实现长距离、低损耗的互连。然而，一种同时具有高量子比特保真度和按需亮发射的量子光源一直难以实现。在这里，我们展示了一种明亮的光子纳米结构，可产生强烈违反贝尔不等式的偏振纠缠光子对。一个高度对称的 InAsP 量子点产生纠缠光子，被封装在锥形纳米线波导中，以确保定向发射和高效光提取。在 80MHz 脉冲激发下，我们在第一个透镜下收集了约 200kHz 的纠缠光子对，与没有光子纳米结构的裸量子点相比，增加了 20 倍。使用 Clauser-Horne-Shimony-Holt 不等式进行的贝尔测试显示，通过高达 9.3 个标准差的明显违反（S>2）。通过在纤锌矿 InP 纳米线共振处使用新的准共振激发方案来减少多光子发射，在没有时间后选择的情况下，纠缠保真度（F=0.817±0.002）进一步提高，允许在直交-圆基中违反贝尔不等式 25 个标准差。我们在基于纳米线的量子光源上的结果突出了它们在利用测量设备无关的量子密钥分发和量子中继协议进行安全数据通信中的潜在应用。
