📡 Longest ultra-secure quantum communication link between continents

• Researchers established a 12,900-kilometer quantum communication link between Beijing and Stellenbosch University via satellite, which uses the laws of physics to make eavesdropping impossible.
• The connection securely transmitted encrypted images using 1.07 million bits of undisturbed photons as the key.
• South Africa became the first country in the southern hemisphere to participate in satellite-based quantum communication.

First quantum connection between hemispheres

In October 2024, researchers created the longest intercontinental quantum communication link ever. The connection stretched 12,900 kilometers between Beijing in China and Stellenbosch University in South Africa. The previous longest quantum satellite link was 7,600 kilometers and existed only in the northern hemisphere.

The researchers used quantum key distribution to create the link. The method allows a sender and receiver to share a secure key that they use to send messages safely. The system sends individual photons, which are small particles of light.

If someone tries to intercept the photons, they become disturbed due to the laws of quantum physics. The sender and receiver use only undisturbed photons, making the key extremely secure. Any eavesdropping attempts leave traces that can be detected.

Microsatellite and ground station enabled the link

To create the quantum communication link between China and South Africa, the microsatellite Jinan 1 was launched into low Earth orbit. The researchers set up a portable optical ground station at Stellenbosch University. The station contains a powerful telescope and special detectors that can detect encoded photons from the satellite.

The secure quantum link functioned during a single pass when the satellite passed over the ground station. The key consisted of 1.07 million bits of undisturbed photons. This made the link not only the longest but also the most secure that has been achieved.

Security based on the laws of physics

Traditional secure communication methods rely on mathematical algorithms and the difficulty of solving certain problems, such as factoring large numbers. Quantum communication draws its security from the fundamental laws of physics instead.

One of these laws is that it is impossible to make an exact copy of an unknown quantum state. Another law is that measurement of a quantum state changes it. This makes eavesdropping detectable.

Quantum key distribution allows two parties to share encryption keys in a way that detects eavesdropping attempts. The keys are encoded using quantum states, typically individual photons. They are transmitted through optical fibers or through free space via satellites.

Fiber-based systems lose signal over long distances. Satellites offer a solution because they operate in the low-loss environment of the upper atmosphere and outer space.

Step towards global quantum internet

Quantum satellite communication is a step towards building a global quantum internet. It would be an interconnected network that enables secure communication, quantum computing, and sensing between continents.

The success of Jinan-1 points towards networks of quantum microsatellites. This would make secure global communication a real possibility.

For businesses, particularly in sectors such as finance, defense, and healthcare, these links enable extremely secure communication systems. They are resistant to hacking even from future quantum computers. This allows companies to protect and communicate sensitive data.

For policymakers, it presents an opportunity to strengthen national security and set global standards for responsible use. It also encourages international cooperation as countries work together to create a secure communication network.

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