(ScienceDaily) Researchers at the University of the Witwatersrand in Johannesburg, South Africa, have demonstrated a record setting quantum protocol for sharing a secret amongst many parties. The team created an 11-dimensional quantum state and used it to share a secret amongst 10 parties. By using quantum tricks, the secret can only be unlocked if the parties trust one another. The work sets a new record for the dimension of the state (which impacts on how big the secret can be) and the number of parties with whom it is shared and is an important step towards distributing information securely across many nodes in a quantum network.
Using structured light as quantum photon states, the Wits team showed how to distribute information from one sender to 10 parties. Then, by using some nifty quantum tricks, they could engineer the protocol so that only if the parties trust one another can the secret be revealed.
“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,” says Professor Andrew Forbes from the School of Physics at Wits University. Importantly, at no stage is the secret ever revealed through communication between the parties: they don’t have to reveal any secrets. In this way a secret can be shared in a fundamentally secure manner across many nodes of a network: quantum secret sharing.
“Our work pushes the state-of-the-art and brings quantum communication closer to true network implementation,” says Forbes. “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.”

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