Toshiba researchers have developed a promising new method called ” dual band stabilization" which consists in sending two signals with different wavelengths which cancel out the effects of the external environment. Credit: Handout.

Researchers from Toshiba announced a major breakthrough in quantum networks, that could change the way nations, financial institutions and intelligence agencies communicate in the future.

Working from the company’s R&D lab in Cambridge in the UK, the team says it has successfully sent quantum information over 600-kilometer-long optical fibers, creating a new distance record and paving the way for large-scale quantum networks that could be used to exchange information securely, ZDNet.com.

The scientists demonstrated that they could transmit quantum bits (or qubits) over hundreds of kilometers of optical fiber without scrambling or damaging the fragile quantum data encoded in the particles.

This was made possible, thanks to a groundbreaking new technology that stabilizes the environmental fluctuations occurring in the fiber, Toshiba said.

“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 (Quantum Key Distribution) are still possible and our solutions can also be applied to other quantum communications protocols and applications.” 

The quantum internet, which will take the shape of a global network of quantum devices connected by long-distance quantum communication links, is expected to enable actions that far surpass today’s web applications, the report said.

But in order to communicate, quantum devices need to send and receive qubits — tiny particles that exist in a special, but extremely fragile, quantum state.

Finding the best way to transmit qubits without having them fall from their quantum state has puzzled scientists for many years. 

Shooting qubits down optical fibers has proved successful but … small changes in the environment, such as temperature fluctuations, cause the fibers to expand and contract.

This is why experiments with optical fiber, until now, have typically been limited to a range of hundreds of kilometers — nowhere near enough to envision the proposed quantum internet, the report said. 

To tackle the instable conditions inside optical fibers, Toshiba’s researchers developed a new technique called “dual band stabilization.”

The method sends two signals down the optical fiber at different wavelengths.

The first wavelength is used to cancel out rapidly varying fluctuations, while the second wavelength, which is at the same wavelength as the qubits, is used for finer adjustments of the phase. 

Put simply, the two wavelengths combine to cancel environmental fluctuations inside the fiber in real time, acting as a kind of shock absorber that protects the qubits during their journey, the report said.

According to a report in Phys.org, Toshiba found it is possible to hold the optical phase of a quantum signal constant to within a fraction of a wavelength, with a precision of 10s of nanometers, even after propagation through 100s of km of fiber. 

Already, the company’s team has used the technology to trial one of the most well-known applications of quantum networks: quantum-based encryption. 

Known as Quantum Key Distribution (QKD), the protocol leverages quantum networks to create security keys that are impossible to hack, meaning that users can securely exchange confidential information, like bank statements or health records, over an untrusted communication channel such as the internet. 

Because of the laws of quantum mechanics, it is impossible for a spy or spy agency to intercept the qubits without leaving a sign of eavesdropping that can be seen by the users – who, in turn, can take steps to protect the information. 

Unlike classical cryptography, QKD does not rely on the mathematical complexity of solving security keys, but rather leverages the laws of physics.

In other words, it would be un-hackable even for the most powerful computers in the world.

When it comes to carrying out QKD using optical fiber, Toshiba’s 600-kilometer mark is a record-breaker, which the company predicts will enable secure links to be created between cities like London, Paris, Amsterdam and Dublin.  

Other research groups, however, have focused on different methods to transmit qubits, which have enabled QKD to happen over even larger distances.

Chinese scientists, for example, are using a mix of satellite-based transmissions communicating with optical fibers on the ground, and recently succeeded in carrying out QKD over a total distance of 4,600 kilometers. 

Governments around the world are actively investing in quantum communications and networks.

The US Department of Defense (DoD) recently published a step-by-step strategy to creating a fully fledged quantum internet; in the EU, the Quantum Internet Alliance was formed in 2018, also with the objective of building up a large-scale quantum network; and China’s latest five-year plan also allocates a special place for quantum networks.

Sources: ZDNet.com, Phys.org