As the quantum information technology has gradually reached a mature level, how to realize a large-scale quantum communication network effectively has become a thriving research field. Entanglement based quantum network offers the promise platform. Recently, the fully connected quantum communication network based on quantum entanglement has attracted much attention in constructing a large-scale metropolitan network. Such type of network configuration enables multi users’ communication with each other at the same time when minimizes the infrastructure and hardware. Hyperentanglement in multiple degree of freedoms (DOF) enables significant enhancement of information capacities and has stimulated new quantum protocols. The higher data capacity and stronger error resilience make it an attractive candidate for many quantum-secure information processing such as dense coding, entanglement distillation, and superdense teleportation. Hyperentanglement in polarization and orbital angular momentum (OAM) DOFs has great potential for long-distance quantum information applications. A multiuser fully connected network based on hyperentanglement in polarization and OAM would provide a promising platform that can support the end users perform multiple quantum tasks.

Here, we proposed a hyperentangled multiuser network with a fully connected network architecture encoded in polarization and OAM DOFs. By using a polarization entangled source and dense wavelength division multiplexing technique, three hyperentangled states in polarization and time-energy DOFs are multiplexed to three single mode fibers to form the fully connected network architecture. Then, three interferometric quantum gates consisting of a Mach-Zehnder interferometer with spiral phase plates inserted in different paths are utilized for transferring quantum entanglement from time-energy to OAM DOF. The two-photon interference visibility is measured to be higher than 95% for both polarization and OAM entanglement, revealing a high quality of hyperentanglement in these two DOFs of the constructed network. Our approach can provide a novel way to construct a large-scale hyperentangled network that can support various kinds of multiuser quantum communication tasks, such as multi-DOF quantum entanglement swapping, superdense coding, and teleportation.

Figure 1 Wavelength multiplexing and temporal cross correlations. (a) Independently measure transmission of all the wavelength channels during the network construction. (b) Temporal cross-correlations between the time traces of the three users’ detectors.

Figure 2 Experimental results for OAM entanglement. (a) Typical two-photon interference fringes of the OAM entangled state shared by Alice and Bob. (b) Measured two photon interference visibility for all OAM entangled photon pairs with horizontal and vertical polarization.

This research is published in “Yiwen Huang, Yuanhua Lil, Zhantong Qi, Yilin Yang, Yuanlin Zheng and Xianfeng Chen, A fully-connected three-user quantum hyperentangled network, Quantum Frontiers, 2, 4 (2023)”。

Link: https://doi.org/10.1007/s44214-023-00030-4