Milestone Hit in Transmission of Data

"Scientists have sent quantum information across a record-breaking 158 miles using ordinary computers and fiber-optic cables.

It is the first time coherent quantum communication -- an ultrasecure means of transmitting data -- has been achieved using existing telecommunications infrastructure, without the expensive cryogenic cooling that is typically required.

"Our equipment was running alongside the fibers that we use for regular communication literally buried underneath the roads and train stations," said Mirko Pittaluga, a physicist and lead author of a study published Wednesday in Nature describing the work.

Integrating the technology into existing infrastructure using largely off-the-shelf equipment is key to expanding the accessibility of quantum communication and its use in encrypting information for more secure transmission of data, according to multiple physicists and engineers who weren't involved in the study.

"This is about as real-world as one could imagine," said David Awschalom, a professor of physics and molecular engineering at the University of Chicago who wasn't a part of the new work. "It's an impressive, quite beautiful demonstration."

Classical digital information is communicated over the internet in units known as bits that have fixed values of 1 or 0. In contrast, quantum information is transmitted in qubits, which can store multiple values at once, making quantum communications more secure.

Pittaluga and his colleagues at Toshiba Europe sent quantum information from regular computers hooked into the telecommunications network at data centers in the German cities of Kehl and Frankfurt, relaying them through a detector at a third data center roughly midway between them in Kirchfeld. The three-location setup enabled the group to extend the distance the messages were sent more than 150 miles, an uninterrupted distance only ever achieved in a laboratory environment.

Working at these types of distances, Awschalom said, means that quantum information could be sent across entire metropolitan areas or between nearby cities, making it useful for hospitals and other institutions, for which secure communications are paramount.

Other groups in the U.K. and U.S., including researchers at the University of Pennsylvania, are also working on extending the distances achievable by quantum communication.

Pittaluga said that his team's work is critical to solving the problem of keeping sensitive data out of the reach of hackers.

Today, bank statements, health records and other data transmitted online are protected using mathematically formulated encryption keys. These keys are the only means of unlocking the data, keeping it secure from cyber thieves. For conventional computers, breaking these keys takes an impractically long time, but quantum computers are up to the task, and as they become more powerful, encryption keys become vulnerable to attack.

"Anything meaningful that's over the internet can be tapped, recorded and saved for the next decade, and can be decrypted years later," according to Prem Kumar, a professor of electrical and computer engineering at Northwestern University, who wasn't a part of the new work. "It's what's called harvest now and decrypt later."

One means of fixing this problem, Pittaluga said, is through quantum cryptography, which relies on the physics of quantum mechanics rather than mathematical algorithms to generate encryption keys.

"The likelihood of them being able to reverse engineer a quantum key, which is the number you would need to decrypt your information, is vanishingly small," according to Awschalom.

But to use quantum encryption keys, you have to successfully distribute them across meaningful distances, a task that has stymied researchers outside the lab for decades.

Internet and telecom infrastructure are based on optical fibers that carry pulses of light containing photons. Classical bits of information are sent as a single impulse of light carrying tens of millions of photons. Quantum information is sent in a package of a single photon.

Efficiently detecting single photons usually requires superconducting detectors that must be cryogenically cooled, using liquid helium, to super low temperatures, making the technology expensive.

Pittaluga and colleagues at Toshiba got around this by using cheaper detectors known as avalanche photodiodes, which cost less and can run at or just below room temperature." [1]

1.  U.S. News: Milestone Hit in Transmission of Data. Woodward, Aylin.  Wall Street Journal
 , Eastern edition; New York, N.Y.. 24 Apr 2025: A2.