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Harvard physicists took a giant step towards full-scale quantum internet networks this month, creating the longest quantum network so far with cables running between Boston and Cambridge.
In collaboration with Amazon Web Services, researchers led by University Professor Mikhail D. Lukin successfully transmitted qubits — bits of quantum information — between two quantum nodes in the Laboratory of Integrated Science and Engineering. The nodes were connected by 35 kilometers of existing telecommunications fiber running in a loop through Boston and Cambridge, according to the Harvard Gazette, a University-run publication.
The work, led by Lukin — a co-director of the Harvard Quantum Science and Engineering Initiative — and Can M. Knaut, a researcher in Lukin’s lab group, was done alongside Electrical Engineering and Applied Physics professor Marko Lončar, Chemistry professor Hongkun Park, and Bart J. Machielse, a research scientist at AWS. The group’s findings were published in Nature in May.
These advancements have the potential to revolutionize various fields, according to Knaut. For instance, quantum networks could enable ultra-secure data transmission, protecting sensitive information on quantum computers. They could also transform astronomical observations, allowing telescopes to extract “exponentially more information” from light.
“There’s a wide variety of applications in this technology for long-distance communication, which is sort of long-distance ultra-secure communication, which is really what we were trying to prove out of here,” Machielse said.
The research, though, has been years in the making.
“This idea of actually using multiple network nodes and connecting them via deployed fiber is something we’ve been working on for a long time. And it’s just a very important demonstration of the fact that this technology works in real-world environments,"”he said.
Lukin — who began working on quantum networks nearly 25 years ago — wrote in a statement that the work is “necessary and important” because “as quantum computers are becoming a reality, there is a need to wire them up into a quantum network.”
“Showing that quantum network nodes can be entangled in the real-world environment of a very busy urban area is an important step toward practical networking between quantum computers,” Lukin told the Gazette.
Knaut said that the fact that the experiment was conducted in the real world — as opposed to a controlled lab environment — meant that the researchers had to approach their work differently.
“We had to basically work with what we were given,” Knaut said. “You have to really relinquish a little bit of your ability to control every small aspect and more focus on optimizing the final output you care about — and that was a change in operations as compared to other experiments in the lab where you can at least try to control every single aspect.”
Machielse — who was a doctoral student under Lukin — said that doing the experiment “in the real world” was crucial to showing the success of the technology.
“In principle, the fundamental science, we always knew that it was there,” Machielse said. “But really the novelty of this experiment is actually been stringing all of this together and showing that it works when you actually do this in the real world, because it wasn’t clear that would come together.”
The experiment came with challenges, including preventing environmental disturbances and ensuring precision “up to the nanosecond,” according to Knaut. The setup, which mimicked realistic network operations, faced additional difficulties from noise sources introduced by the deployed fiber.
With a successful demonstration in Boston, the researchers are now planning to improve the technology and expand the size of the network.
“The key technology that would be necessary to build these large quantum networks is being built,” Knaut said, adding that a demonstration could be possible “in the next couple of years.”
But while Lukin wrote that the research “is still in the early stage,” he added it had the potential to change modern-day communication technology.
“This approach can result in a new way of communication that is both secure and equitable,” he wrote.
—Staff writer Mandy Zhang can be reached at mandy.zhang@thecrimson.com. Follow her on X @mandyzhang08.
