Researchers at the University of the Witwatersrand (Wits) demonstrated an 11-dimensional quantum state and used it to share sensitive information securely from one sender to 10 parties. They used structured light to achieve a high-dimensional quantum state and then engineered a protocol to ensure information sharing was only among secure and trusted parties. To push the dimension limit, the team used the high-dimensional Hilbert space for orbital angular momentum and used perfect vortex beams as carriers. The dimension of the quantum state has an impact on how large a secret can be. An artistic impression depicting quantum secret sharing using structured light. Courtesy of Wits University. At no stage during the transmission of data from one to several parties was sensitive information revealed through communication among the parties. With this quantum secret sharing scheme, information between more than two people is shared in such a way that its reconstruction requires the collaboration of a certain number of parties. “In essence, each party has no useful information, but if they trust one another then the secret can be revealed. The level of trust can be set from just a few of the parties to all of them,” professor Andrew Forbes said. The researchers experimentally implemented their scheme with a fidelity of 93.4%, for 10 participants in d=11 dimensions. To the best of the researchers’ knowledge, this is the highest number of participants and dimensions realized by a quantum secret sharing scheme to date. The researchers said that the implementation could be scaled to higher dimensions and any number of participants, opening the way for securely distributing information across a quantum network of nodes. In traditional approaches to secure quantum communication, such as quantum key distribution, information is sent from one party to another in a peer-to-peer communication format. This setup has only two nodes: sender and receiver. “Our work pushes the state-of-the-art and brings quantum communication closer to true network implementation,” Forbes said. “When you think of networks you think of many connections, many parties, who wish to share information, and not just two. Now we know how to do this the quantum way.” The research was published in Laser & Photonics Reviews (www.doi.org/10.1002/lpor.202000012).