China Builds the World’s First Quantum Internet in Urban Area

The quantum internet would allow users to establish highly secure cryptographic keys, with near-instantaneous data transfer speeds. This work has increased the distance of realistic quantum entanglement networks from tens of meters to tens of kilometers, a full three orders of magnitude.
May 17, 2024
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Linwen
Editor-in-Chief, The China Academy
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Get ready for a tech revolution like never before – the Quantum Internet is on its way! This isn’t just your regular internet, but a super-powered, ultra-secure network that will blow your mind. Unlike the internet we use today, which is limited by binary bits, the Quantum Internet uses qubits, allowing it to process and transmit information at lightning-fast speeds and in incredible new ways.
Imagine a world where hacking is a thing of the past, thanks to the Quantum Internet’s unbreakable cryptography. Or picture a future where scientists can create virtual telescopes as wide as entire cities, unlocking new secrets of the universe. And that’s not all – the Quantum Internet will also pave the way for the next generation of computing, with interconnected quantum computers that can solve complex problems in the blink of an eye.
And this is about to become reality. In a groundbreaking achievement, Chinese scientists have successfully demonstrated quantum entanglement over several kilometers of existing optical fibers in urban environments. This significant milestone, achieved by connecting parts of a network using infrared photons, brings us one step closer to the realization of a future quantum internet.
Quantum entanglement is a phenomenon where two or more objects share the same information, regardless of the distance between them. This development paves the way for a quantum internet, a network that could facilitate the exchange of information encoded in quantum states. Such a network would allow users to establish highly secure cryptographic keys for protecting sensitive information.
Moreover, full utilization of entanglement could lead to the interconnection of separate quantum computers, resulting in a larger, more powerful machine. This technology could also pave the way for unique scientific experiments, such as the creation of telescope networks with the resolution equivalent to a single dish hundreds of kilometers wide.
Over the past decade, many of the technical steps required for building a quantum internet have been demonstrated in laboratory settings. Researchers have also shown that entanglement can be produced using lasers in direct line of sight, both on the ground and in space. However, transitioning from the lab to a city environment presents a different set of challenges.
To build a large-scale network, it is widely agreed that existing optical-fibre technology will likely be necessary. However, quantum information is fragile and cannot be copied, often being carried by individual photons rather than laser pulses. This limits the entangled photons to traveling only a few tens of kilometers before losses make the whole system impractical.

Led by Pan Jian-Wei at the University of Science and Technology of China (USTC) in Hefei, the team encoded qubits in the collective states of rubidium atom clouds. Qubits, akin to the ‘1’ or ‘0’ of ordinary computer bits, can exist in a combination, or ‘quantum superposition’, of two possibilities. The team set up quantum memories in three separate labs in the Hefei area, each connected by optical fibers to a central ‘photonic server’ up to 12.5 kilometers away. Any two of these nodes could be put in an entangled state if the photons from the two atom clouds arrived at the server at the same time. To ensure that the entanglement process worked smoothly, the researchers actively stabilized the phase variance (fluctuations in the signal) caused by the fiber links and control lasers.

In the experiments, the researchers were able to create entanglement between any two of the memory nodes at the same time. Moreover, the quantum memory was able to store the information for longer than the time it took for the signal to travel back and forth, which is an important requirement for a quantum internet.
The Chinese team has estimated that by the end of the decade, they should be able to establish entanglement over 1,000 kilometers of optical fibers using around ten intermediate nodes, through a process known as entanglement swapping. Initially, such a link would be quite slow, creating perhaps one entanglement per second. Pan, who is also the leading researcher for this project and the earlier  Micius satellite project that demonstrated the first quantum-enabled communications in space, has revealed there are plans for follow-up missions without sharing more details.

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author_image
Linwen
Editor-in-Chief, The China Academy
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