China Achieves Tamperproof Communications Over A 100Km Distance

Chinese researchers have pushed the frontiers of quantum encryption, demonstrating a powerful new way to send secure information over more than 100km (62 miles) of optical fibre – without having to trust the equipment being used.

A team led by Pan Jianwei at the University of Science and Technology of China used a pair of individual rubidium atoms, trapped in laser beams at two separate network nodes, as the foundation for their system, according to a paper published in Science this week.

The researchers created quantum links between the atoms using single light particles, or photons. By comparing the atoms’ states at each end, the team generated identical strings of 0s and 1s – a shared secret key for encryption.

What sets the experiment apart is that the approach, known as Device-Independent Quantum Key Distribution (DI-QKD), would still work securely even if the devices were flawed or had been tampered with.

The method derives its security from the quantum-mechanical behaviour of the entangled atoms, protecting against the real-world vulnerabilities that have long challenged quantum communication systems.

DI-QKD had previously only been demonstrated over short distances in the laboratory, the researchers wrote, adding that their study helped to “close the gap between proof-of-principle experiments and real-world applications”.

Quantum physicist Steve Rolston from the University of Maryland, College Park, who was not involved in the study, called the result “a big increment” on the research team’s previous record of 220 metres (722 feet).

But he cautioned that the system was still far from ready for practical deployment, noting for example that it produced less than one bit of secure key every 10 seconds – “abysmally small” compared with the billions of bits per second handled by standard fibre-optic internet.

Rolston also noted that the test used coiled fibre in laboratory conditions – a far cry from the unstable, noisy environment of real-world telecoms networks, where temperature swings and vibrations could easily disrupt the delicate quantum link.

Unlike conventional encryption, which relies on hard maths problems that could be cracked by future quantum computers QKD uses the laws of quantum physics to generate keys that are extremely hard to intercept or copy without detection.

QKD emerged in the late 1990s using direct links between users. In 2016, Pan’s team built a 2,000km network between Beijing and Shanghai using relay stations every 100km. But these relays themselves had to be trusted, creating a security risk.

The new device-independent approach removes the need for relays. Instead, it uses a single pair of entangled particles and a statistical test to confirm that the link is genuine, even if the equipment is faulty or malicious.

Teams in China, Europe and the US have been testing this method for more than a decade. The physics has long been proven but the low key rates and fragile requirements made it impractical beyond a few hundred metres – until now.

Rolston said that, while China seemed to have made quantum communications a national priority, the United States had taken a much more cautious stance.

The National Security Agency (NSA) has openly discouraged federal funding for QKD and quantum cryptography, citing technical limitations that include infrastructure challenges, high costs and poor scalability.

On its website, the NSA warns that communication needs and security goals may conflict in QKD systems, which could be undermined by tiny technical flaws. The agency argues that security in these systems depends heavily on how well they are built – not on the “laws of physics” as some have claimed.

The NSA favours post-quantum cryptography – a class of conventional algorithms designed to withstand attacks from quantum computers, which are cheaper and easier to deploy at scale.

“NSA does not support the usage of QKD or QC to protect communications in national security systems and does not anticipate certifying or approving any QKD or QC security products for usage ... unless these limitations are overcome,” it said.

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How did the USTC team achieve device-independent quantum encryption over a record-breaking 100km distance? The researchers trapped individual rubidium atoms in laser beams to create a quantum link via entangled photons; this DI-QKD approach uses Bell tests to verify security through the laws of physics, ensuring the link remains tamper-proof even if the physical equipment is compromised.