University of the Witwatersrand (Wits) scientists have achieved a major advance in the field of secure quantum communications, the university announced on Friday.

The team, led by School of Physics Professor Andrew Forbes, has had its research paper published online by Laser & Photonics Reviews. 

The team set a new record for the number of parties to whom information could be securely and simultaneously sent by means of quantum communication. “In traditional secure quantum communication, information is sent securely from one party to another, often named Alice and Bob,” noted Forbes. “In the language of networks, this would be considered peer-to-peer communication and by definition has only two nodes: sender and receiver.”

In the real world, that is quite inadequate. Information must often be shared between a number of people or parties, with a sender and several receivers. “Traditional quantum key distribution does not allow this, and is only of the peer-to-peer form,” he pointed out. Now, however, the Wits team has demonstrated how to send information securely by quantum communication from a single sender to ten receiving parties, with a fidelity of 93.4%.

“Our work pushes the state-of-the-art and brings quantum communication closer to true network implementation,” he highlighted. “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 Wits scientists achieved this by using ‘structured light’, which is light that has been shaped or tailored, often by controlling its polarisation, amplitude and phase, but could also be formed by controlling its time and frequency. The structured light they created was used as quantum photon states. 

Structured light can also be described as ‘patterned light’  and the team could create a lot of patterns to increase the number of quantum dimensions they were working with. The more dimensions, the more information the light could carry, and the larger the secure message could be. In their experiment, they created 11 dimensions.

Not only that, but they also demonstrated that by using certain quantum techniques, they could set the information protocols so that the encoded information could only be revealed if the sender and receiver trusted each other. “The level of trust can be set from just a few of the parties to all of them,” reported Forbes. The secret could never be revealed during communication between the parties. The parties did not have to reveal any secrets. The communication of the secret was fundamentally secure throughout the network. 

The other members of the research team were post-doctoral fellow Dr Najmeh Tabebordbar and students Jonathan Pinnell, Isaac Nape and Michael de Oliveira. Their paper is entitled “Experimental Demonstration of 11-Dimensional 10-Party Quantum Secret Sharing”.