Exploiting the fundamental features of quantum mechanics, an entanglement-based quantum network offers a promising platform for many dramatic applications such as multi-user cryptography. Nevertheless, the implementation of a large-scale quantum network in real-world scenarios remains challenging owing to the multiple scattering events in complex environment, particularly those frequency-sensitive scatterings that disturb quantum correlation both spatially and temporally. When coherent light passes through a scattering
medium, especially those frequency-sensitive complex media like multimode fiber (MMF), the optical field dramatically changes with the frequency of the input field due to the frequency-dependent mode coupling effect and interference, behaving as various output speckle patterns. To implement the best quality of entanglement distribution through a frequency-sensitive MMF in future quantum network, a frequency-independent spatiotemporal shaping technique is required to compensate for both the spatial and temporal distortions for each frequency component of the quantum links.

Here, we demonstrate the frequency-insensitive spatiotemporal control of entangled photons in a fully connected network by leveraging a Fourier-transform setup and the genetic algorithm. The optimization processes achieve a growth factor of over 300% for both linear entanglement distribution process and SFG processes. Such an approach can effectively improve the entanglement distribution process through a multimode fiber while the quantum characteristic of the network can be maintained well after the spatiotemporal shaping. Our scheme can serve as a bridging technology to establish entanglement between remote nodes of spectrally interconnected quantum systems and has great potential applications in future real-world quantum networks.

Fig. 1 Optimization processes. a Performance of the genetic algorithm for the Fourier transform shaping setup. b Enhancement of the entanglement distribution. The inset presents the optimal phase pattern after the shaping process.

Fig. 2 Adaptive spatiotemporal shaping for enhancing the SFG process. a Experimental SFG efficiency versus pump power. b The genetic algorithm performance of spatiotemporal shaping. The inset presents the optimal phase pattern after the shaping process.

This research is published in “Yiwen Huang, Zhantong Qi, Yilin Yang, Yuanhua Li, Yiwei Sun, Yongzhi Tang, Fengchao Ni, Lanting Li, Yuanlin Zheng, and Xianfeng Chen, requency-insensitive Spatiotemporal Shaping of Single Photon in Multiuser Quantum Network, npj Quantum Information, 9, 83 (2023)”.

Link: https://www.nature.com/articles/s41534-023-00752-2