Yichi Zhang, a doctoral student in Materials Science and Engineering, inspects the source of the quantum signal. Credit: Sylvia Zhang (CC BY-SA)
Quantum networking may be one step closer to commercial use with engineers from the University of Pennsylvania in the US designing a ‘Q-chip’ that can transport quantum data onto modern internet networks.
The experiment, published in Science, brought quantum networking out of the lab, where it has traditionally been studied, and into the fibre-optic cables used in commercial settings for everyday online connections.
The researchers hope that this design will set the stage for the potentially transformative “quantum internet” future.
“This feels like the early days of the classical internet in the 1990s, when universities first connected their networks,” says Robert Broberg, an electrical and systems engineering doctoral student at Penn and coauthor of the paper.
“That opened the door to transformations no one could have predicted. A quantum internet has the same potential.”
Quantum networks rely on pairs of ‘entangled’ particles, where a change to one instantaneously causes the same change to happen in the other. Researchers hope that if they can harness this entangled property, it could enable them to combine all the processing power together and link up quantum computers.
This type of network could enable faster, more energy-efficient AI exceeding what can currently be achieved with super computers. The implications could also stretch into the world of medicine, with a study published in January using quantum computing to help design an anti-cancer drug.
However, the unique nature of ‘quantum entanglement’ makes developing such a network very difficult. As discovered by Erwin Schrodinger, quantum particles lose their quantum properties when observed, which makes calibrating a quantum network an almost impossible task for scientists.
“Normal networks measure data to guide it towards the ultimate destination,” says Broberg.
“With purely quantum networks, you can’t do that, because measuring the particles destroys the quantum state.”
Despite this obstacle, the team at Penn has shown that their ‘Q-chip’ can send quantum signals over live commercial fibre. They were able to do so by coordinating quantum signals and classical signals that come from regular light particles.
“The classical signal travels just ahead of the quantum signal,” says Yichi Zhang, the study’s first author from Penn’s Materials Science and Engineering (MSE) faculty.
“That allows us to measure the classical signal for routing, while leaving the quantum signal intact.”
By sending the regular light particles first, the system essentially works like train travelling with precious cargo.
Part of the equipment used to create a node of the quantum network, roughly one kilometer’s worth of Verizon commercial fiber optic cable away from its source. Credit: Sylvia Zhang (CC BY-SA)
“The classical ‘header’ acts like the train’s engine, while the quantum information rides behind in sealed containers,” says Zhang.
“You can’t open the containers without destroying what’s inside, but the engine ensures the whole train gets where it needs to go.”
Their design could also automatically correct for noise and transport quantum signals using the same addressing system and management tools as classical signals. The system’s design means that the entire quantum network system could follow the same Internet Protocol (IP) the online world is organised on.
“By showing an integrated chip can manage quantum signals on a live commercial network like Verizon’s and do so using the same protocols that run the classical internet, we’ve taken a key step toward larger-scale experiments and a practical quantum internet,” says Liang Feng, a senior author of the study and a MSE faculty professor.
However, commercial optic fibre cables exist outside of controlled lab environments leaving them exposed to the weather. This means the cables experience changes in temperature, on top of issues like seismic activity and vibrations from construction and transport.
The researchers overcame this hurdle by developing an error-correction method which uses the classical signals that travel before the quantum ones. Their tests showed that the system was able to maintain an inferred accuracy of over 97%.
“Because we can measure the classical signal without damaging the quantum one, we can infer what corrections need to be made to the quantum signal without ever measuring it, preserving the quantum state,” says Feng.
The team couldn’t amplify the signals without destroying the quantum entanglement, but hopes that because their chip is made from silicon the system will be easy to mass produce, laying the foundations for expanding the network.
“By embedding quantum information in the familiar IP framework, we showed that a quantum internet could literally speak the same language as the classical one,” says Zhang.
“That compatibility is key to scaling using existing infrastructure.”
