Chinese researchers achieved a major breakthrough in quantum communication by securely transmitting encrypted information over more than 100 kilometres of optical fibre using single atoms.
The achievement marks a significant step towards ultra-secure communication systems that cannot be compromised, even if the equipment is faulty or tampered with.
The research team, led by renowned quantum physicist Pan Jianwei at the University of Science and Technology of China, demonstrated the system using two individual rubidium atoms held in place by laser beams at two separate network points. Their findings were published this week in the journal Science.
The scientists used individual photons of light to establish a quantum connection between the two atoms. By measuring and comparing the quantum states of the atoms at each location, the team generated identical strings of digital bits, 0s and 1s, that can be used as secret encryption keys.
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What makes this experiment especially important is the technique behind it. The method, called Device-Independent Quantum Key Distribution, or DI-QKD, remains secure even if the devices used in the system are imperfect or deliberately interfered with.
“The security comes from the laws of quantum physics, not from trusting the devices,” Pan’s team explained in the paper. “This allows secure communication even when the equipment cannot be fully trusted.”
Traditional quantum communication systems rely heavily on the assumption that all hardware works exactly as intended. In the real world, however, tiny flaws or hidden backdoors can be exploited by attackers. DI-QKD avoids this problem by using the quantum behaviour of entangled particles themselves to verify security.
Entanglement is a phenomenon in which two particles remain linked regardless of distance. Any attempt to intercept or alter the signal immediately disturbs the system, revealing the presence of an eavesdropper.
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By far, device-independent quantum key distribution had only been demonstrated over very short distances—typically a few hundred metres inside laboratories. The Chinese experiment extended this range to over 100 kilometres, which the researchers said helped “close the gap between proof-of-principle experiments and real-world applications”.
Quantum physicist Steve Rolston, from the University of Maryland and not involved in the study, praised the achievement.
“This is a big increment over their previous record of 220 metres,” he said, calling it a meaningful step forward for the field.
However, Rolston also urged caution. Being concerned about practical deployment, he pointed out that the system currently generates less than one bit of secure key every 10 seconds.
“That is abysmally small compared to the billions of bits per second handled by standard fibre-optic internet,” he said.
He also stated that the experiment used tightly coiled fibre under controlled laboratory conditions. Real-world telecom networks are far more chaotic, with temperature changes, vibrations, and background noise that could easily disrupt fragile quantum links.
Quantum Encryption
Quantum encryption, based on the principles of quantum physics, is a technique for protecting data.
By encoding information into minuscule particles like atoms or photons, it safeguards data. The quantum state shifts and the intrusion is recognised if someone attempts to intercept the transmission. This makes hacking quite challenging.
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It relies on more than just mathematical codes, unlike conventional encryption. Only the intended recipient will be able to read the message. It is typically employed in delicate fields including government communication, finance, and defence. According to scientists, safeguarding digital networks will be essential in the future.
Most current security systems rely on complex mathematical problems that are difficult for today’s computers to solve. However, future quantum computers could potentially break these codes.
Quantum Key Distribution(QKD) avoids this risk by using quantum physics to generate encryption keys that cannot be copied or intercepted without detection. Any spying attempt alters the system’s quantum state, immediately alerting the users.
China has invested heavily in this technology for decades. In 2016, Pan’s team helped build a 2,000-kilometre quantum communication network between Beijing and Shanghai. That system used relay stations placed every 100 kilometres, but those relays had to be trusted, creating potential security risks.
The new device-independent approach removes the need for such trusted relays. Instead, it relies on a single pair of entangled particles and statistical tests to confirm that the connection is genuine and secure.
Research teams in China, Europe, and the US have worked on DI-QKD for more than 10 years. While the theory has long been established, practical limitations, such as low data rates and technical fragility, have kept the method confined to laboratories until now.
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Rolston stated that China has treated quantum communication as a national priority, while the United States has taken a more cautious approach.
The US National Security Agency has publicly discouraged federal investment in Quantum Key Distribution, citing high costs, infrastructure challenges, and poor scalability. Also, the NSA warns that QKD systems can be undermined by tiny technical flaws.
“Security depends heavily on how well the system is built, not just on the laws of physics as some claim,” the agency argued.
However, the NSA supports post-quantum cryptography, a set of encryption algorithms designed to resist future quantum-computer attacks. These methods are cheaper, easier to deploy, and more compatible with existing networks.
“NSA does not support the usage of QKD or quantum cryptography to protect communications in national security systems,” the agency said. “It does not expect to approve such technologies unless their limitations are resolved.”
Despite these challenges, the Chinese experiment shows that tamper-proof quantum communication over long distances is no longer just a theory, but a reality in the near future.
