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Researchers at the Leibniz Institute of Photonic Technology (Leibniz IPHT) in Jena, Germany, together with international collaborators, have developed two complementary methods that could make quantum communication via fiber optics practical outside the lab.

One approach significantly increases the amount of information that can be encoded in a single photon; the other improves the stability of the quantum signal over long distances. Both methods rely on standard telecom components—offering a realistic path to secure data transmission through existing fiber networks.

From hospitals to government agencies and industrial facilities—anywhere sensitive data must be kept secure—quantum communication could one day play a key role. Instead of transmitting electrical signals, this technology uses individual particles of light—photons—encoded in delicate quantum states. One of its key advantages: any attempt to intercept or tamper with the signal disturbs the quantum state, making eavesdropping not only detectable but inherently limited.

But getting quantum communication out of the lab and into the real world still poses serious technical challenges. A team of researchers from Germany and Canada tackled two of the biggest questions: How can each photon carry more information? And how can signals remain stable across long distances, despite the distortions introduced by fiber-optic transmission?

Their answers are presented in two recent studies published in and . The team demonstrates a new photonic platform that significantly boosts the information density per photon, and a second technique that preserves signal fidelity over hundreds of kilometers of fiber—both using components already deployed in today's telecom networks.

Photons as data carriers: Encoding information in time bins

A central innovation lies in so-called "time-bin encoding." In this method, the information is carried by the precise arrival time of each photon—essentially, which of several tiny time windows it falls into. Traditional systems distinguish only two such time bins. The new platform, developed jointly by researchers at the Institut National de la Recherche Scientifique (INRS) in Canada and Leibniz-IPHT, pushes that number to eight, allowing for a dramatic increase in data throughput.

"It's like a drawer system," explains Prof. Mario Chemnitz of Leibniz-IPHT and Friedrich Schiller University in Jena. "Instead of just one drawer, we can now open several at once—each carrying its own piece of the message."

The platform described in Nature Communications relies on a custom-designed photonic chip built with silicon nitride—an ideal material for guiding light on a tiny scale. It integrates miniature interferometers capable of generating and processing entangled photons, all while using off-the-shelf telecom components.

In lab tests, the system successfully transmitted quantum information over 60 kilometers of optical fiber—the typical distance between two network nodes. That means more users could share secure quantum channels with high data rates across existing fiber networks.

Robust quantum links across long distances

A second challenge was maintaining signal quality over long distances. One key issue is dispersion—a physical effect that stretches out light pulses in time, blurring the precise time-bin distinctions. In the study published in ÌÇÐÄÊÓƵical Review Letters, the team showed how to counter this.

Rather than analyzing photons individually, they tracked the joint arrival time of photon pairs, using a technique called "sum-frequency correlation." This parameter remains stable even under strong dispersion and, for the first time, was harnessed for practical communication.

As a result, the team extended the reach of a secure quantum link to the equivalent of 200 kilometers of fiber—while improving both signal quality and robustness against tampering.

"With the first study, we show how to pack more information into each photon," Chemnitz explains. "With the second, we show how to make sure that information gets through reliably—even in real-world networks. The two approaches complement each other."

From fundamental research to real-world applications

Both advances are part of a larger effort to move quantum communication from the realm of theory and lab experiments into practical use. "Our goal is to make quantum communication viable with systems that integrate into today's telecom infrastructure," Chemnitz says. "We're bridging the gap between fundamental research and application."

At Leibniz-IPHT, Chemnitz leads the junior research group "Smart Photonics," which explores the intersection of nonlinear optics, machine learning, and neuromorphic data processing—inspired by how the human brain works. His long-term goal: to not only transmit information with light, but to analyze and interpret it directly in optical systems—for applications ranging from ultra-fast diagnostics to energy-efficient optical computing.