High dimensional quantum secret sharing with spatially structured photons

Secret sharing allows three or more parties to share secret information which can only be decrypted through collaboration. It complements quantum key distribution as a valuable resource for securely distributing information. Here we take advantage of hybrid spin and orbital angular momentum states to access a high dimensional encoding space, demonstrating a protocol that is easily scalable in both dimension and participants. To illustrate the versatility of our approach, we first demonstrate the protocol in two dimensions and then extend it to three dimensions. We reconstruct secrets depicted as images with a fidelity of up to 0.979 and 0.946. Moreover, our scheme exploits the use of conventional linear optics to emulate the quantum gates needed for transitions between basis modes on a high dimensional Hilbert space while offering the potential of up to 1.225 bits of encoding capacity per transmitted photon (exceeding the Shannon limit). Our work offers a practical approach for sharing information across multiple parties, a crucial element of any quantum network.