Fiber: Researchers create “inviolable” quantum network spanning hundreds of kilometers

Toshiba teams have successfully sent quantum information over optical fibers 600 kilometers long. A new distance record that paves the way for large-scale quantum networks, used to exchange information securely between cities and even countries.

From Toshiba’s UK R&D lab, scientists have demonstrated that they can transmit quantum bits (or qubits) over hundreds of kilometers of optical fiber without scrambling the fragile quantum data encoded in the particles, thanks to a new technology that stabilizes the environmental fluctuations occurring in the fiber. This could help create a next-generation quantum internet that scientists hope will one day span global distances.

The quantum internet, which will take the form of a global network of quantum devices connected by long-distance quantum communication links, is expected to allow uses that are not possible with current web applications. This ranges from generating virtually tamper-proof communications to creating clusters of interconnected quantum devices that together could exceed the computing power of conventional devices.

At the heart of qubits

But, in order to communicate, quantum devices must send and receive qubits – tiny particles that exist in a special, but extremely fragile, quantum state. Finding the best way to transmit qubits without them dropping out of their quantum state has challenged scientists around the world for many years.

One approach is to send qubits through the optical fibers that connect quantum devices. This method has worked well, but it is spatially limited: small changes in the environment, such as temperature fluctuations, cause fibers to expand and contract and may disrupt qubits. This is why, so far, fiber optic experiments have been limited to a range of a few hundred kilometers, which is nowhere near enough to create the large-scale global quantum internet that scientists dream of. .

To cope with the unstable conditions inside optical fibers, Toshiba researchers have developed a new technique called “dual band stabilization”. This method involves sending two signals through the optical fiber at different wavelengths. The first wavelength is used to cancel out rapid fluctuations, while the second, which is at the same wavelength as the qubits, is used for finer phase adjustments.

Towards a quantum internet?

In other words, the two wavelengths combine to cancel fluctuations in the environment inside the fiber in real time, which Toshiba researchers say allowed the qubits to move around in real time. completely safe for more than 600 kilometers. Toshiba teams have already used this technology to test one of the most well-known applications of quantum networks: quantum encryption.

Known as quantum key distribution (QKD), this protocol relies on quantum networks to create secure keys that cannot be hacked, meaning that users can securely exchange confidential information, such as statements. banking or medical records, over an unreliable communication channel such as the Internet.

During a communication, the QKD works by asking one of the two parties to encrypt a piece of data by encoding the encryption key on qubits and sending these qubits to the other person through a quantum network. Due to the laws of quantum mechanics, however, it is impossible for a spy to intercept qubits without leaving a listening sign visible to users, who can then take action to protect the information.

An inviolable network

Unlike classical cryptography, QKD therefore does not rely on the mathematical complexity of resolving security keys, but rather relies on the laws of physics. This means that even the most powerful computers would be unable to hack qubit-based keys. It then becomes easy to understand why the idea is attracting the interest of actors from all walks of life, from financial institutions to intelligence agencies.

Toshiba’s new technique to reduce fluctuations in optical fibers allowed researchers to perform QKD over a much greater distance than was previously possible. “This is a very exciting result,” said Mirko Pittaluga, research scientist at Toshiba Europe. “With the new techniques we have developed, further extensions of the communication distance for QKD are still possible and our solutions can also be applied to other quantum communication protocols and applications. “

When it comes to achieving QKD using fiber optics, Toshiba’s 600-kilometer mark is a record, which the company says will create secure links between cities like London, Paris, Brussels. , Amsterdam and Dublin.

Brussels is coming

Other research groups, however, focused on other methods of transmitting qubits, which made it possible to perform QKD over even greater distances. Chinese scientists, for example, use a mixture of satellite transmissions communicating with optical fibers on the ground, and recently succeeded in performing a QKD over a total distance of 4,600 kilometers.

Each approach has its advantages and disadvantages: the use of satellite technologies is more expensive and could be more difficult to scale. But one thing is certain: Research groups in the UK, China and the US are experimenting at a rapid pace to make quantum networks a reality.

Toshiba’s research has been partially funded by the European Union, which shows a keen interest in the development of quantum communications. At the same time, China’s latest five-year plan also places special emphasis on quantum networks, while the United States recently released a master plan outlining a phased approach to establishing a global quantum internet.

Source: .com

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