Hybrid continuous-variable (CV) and discrete-variable (DV) entanglement is an essential quantum resource of hybrid quantum information processing, which enables one to overcome the intrinsic limitations of CV and DV quantum protocols. Towards the application of entanglement, it is essential to extend the degrees of freedom of the entangled state, which enables the entangled state to carry more information. Among all the degrees of freedom of photons, orbital angular momentum (OAM) has potential applications in enhancing the communication capacity of quantum communication and precision of quantum measurement. Although quantum state carrying OAM and hybrid CV-DV entanglement have been demonstrated individually, how to prepare the hybrid CV-DV entanglement carrying OAM is still unclear.
Recently, the group led by Xiaolong Su at Shanxi University of China has successfully prepared hybrid entanglement carrying orbital angular momentum, which involves three degrees of freedom including polarization, cat states, and OAM. They experimentally prepare the hybrid polarization-cat entangled state firstly, and then introduce the OAM degree of freedom by inserting a q-plate in the cat-encoded CV part, which converts the Gaussian beam to the OAM beam. In the characterization of the prepared hybrid state, they measure the OAM property in the CV part, and the entanglement between the polarization-encoded DV part and cat-encoded CV part carrying OAM, respectively. The results show that the prepared hybrid entangled states carrying OAM with 𝑙 = 0, +1, +2 have non-zero logarithmic negativities, which confirms the successful preparation of the hybrid entanglement carrying OAM.
The prepared hybrid entanglement has potential applications in increasing the information capacity of quantum communication in the heterogeneous quantum network. The work demonstrates the feasibility of introducing OAM degree of freedom into the hybrid entanglement and takes a crucial step towards hybrid quantum information processing with multiple degrees of freedom. These results have been published in Science Bulletin, under the title "Hybrid entanglement carrying orbital angular momentum", with co-corresponding authors Prof. Xiaolong Su and Prof. Shujing Li, and co-first authors Dr. Meihong Wang and graduate student Fengyi Xu.
