Steering towards a quantum internet

Quantum entanglement is a unique and powerful phenomenon that can facilitate correlations between distant locations. Among other things, it can allow for the exchange of private messages between two parties with absolute security.

However, linking two different places with high-quality entanglement is not easy, and few have created links robust enough to be applicable beyond proof-of-principle demonstrations. Harder still has been the challenge of linking multiple parties, which is thought to require more entangled particle pairs or more complex quantum states.

Working with elementary particles of light, Pepper et al. demonstrated a novel method for linking multiple parties with quantum correlations using just a single pair of entangled photons. They mixed the pair with many normal photons and then distributed qubits to “quantumly steer” targeted recipients.

“By randomly sending the recipients either an entangled photon or a normal one, we found out that all parties still shared enough entanglement to guarantee secure communication,” said author Alex Pepper.

In an experiment, the researchers entangled three parties and rigorously tested the result, confirming the presence of non-classical correlations. The scenario is like adding an unknown and untrusted user to a trusted network, representing situations where people connect to mobile banking applications from unknown locations, for instance.

“We have mathematically and experimentally proven that our method can not only create useful multiparty entanglement but also can form a very large secure network, even when some photons are lost,” said Pepper. “It turns out that you don’t need a big complex quantum system to have a big network. You can get away with only having a small amount of quantum spread thinly over many people.”

Source: “Scalable multiparty steering using a single entangled photon-pair,” by Alex Pepper, Travis J. Baker, Yuanlong Wang, Qiu-Cheng Song, Lynden. K. Shalm, Varun B. Verma, Sae Woo Nam, Nora Tischler, Sergei Slussarenko, Howard M. Wiseman, and Geoff J. Pryde, AVS Quantum Science (2024). The article can be accessed at http://doi.org/10.1116/5.0197186 .