ICFO: Spain overtakes China in one of the biggest quantum communication problems | Science

Spain-based researchers have bypassed China in one of the most complex problems in creating quantum communications networks that are impossible to spy or hack.

For years, China, the United States, and Europe have been vying to be the first to achieve quantum supremacy, a broad term referring to the creation of computers with computing power and speed much higher than those currently connected to an impenetrable communications network.

Last year, China built a quantum computer that replaced the one made by Google and solved a mathematical problem in just over three minutes. It would take an average computer about 2.5 billion years to solve.

China is also a pioneer in quantum communication, which consists of sending keys to decode secret messages using the amazing properties of light particles: photons. These microscopic particles can get entangled with each other, so they are in the same state even though they are separated by thousands or millions of kilometers. Sending messages with entangled photons is probably the most secure method of communication: if a spy tries to get into the system, the photons break their link, the encrypted message is lost, and an intrusion alarm goes off. Quantum supremacy is a strategic goal for both countries that want to send confidential messages and companies that handle sensitive data of billions of people.

China has a quantum computer that solved a mathematical problem in just over three minutes that an average computer would take about 2.5 billion years to solve

Last summer, China sent a quantum key from space to two ground stations more than 1,000 kilometers apart, 10 times the distance achieved so far. It was one of the greatest victories of Jian Wei Pan, head of the Chinese Quantum Communication System. Jian trained at the University of Austria in the late 1990s before returning home to start developing this technology. The concept of quantum communication was formulated in Europe and this is where the first basic experiments were conducted, but years ago, China invested large sums of money to perfect this technology.

Today, a group of researchers from the Institute of Photonic Sciences of Catalonia (ICFO) is winning a big, small battle against the Asian giant. One of the biggest unsolved problems in quantum communication is that optical fibers cannot transmit entangled pairs of photons for more than 100 kilometers. The signal has been lost. In order to scale, repeaters must be manufactured, a trivial question in conventional communications but diabolical when it comes to quantum, since photons must be stored in quantum memories made up of crystals whose atoms can hold the entangled particle inside for some time.

team led by Hugo de Redmaten, ICFO, explains in an article on the cover of the prestigious magazine nature Storing two entangled photons in two quantum memories separated by a distance of 10 metres. studying It is a major proof of concept, as the researchers used photons with properties that would allow quantum messages to be sent using the traditional optical fibers already used by the Internet. They are also the first to show that their communications have up to 60 different ways to store photons, a major milestone in the field.

“This work is a demonstration of a first step toward a quantum repeater,” Redmatten explains. The memories store a photon for 25 millionths of a second, enough to prove that a viable repeater network can be created that works with particles traveling at the speed of light.

Samuele Grandi, another member of the team, explains that they are already setting up a similar experiment between a quantum memory located at ICFO, based in Castelldefels, and one in Barcelona, ​​​​35 kilometers away.

Today, a Chinese team publishes A very similar study In the same journal they described their quantum repeaters that were capable of storing two entangled photons, but only three meters apart from each other. The work is led by researchers from the State Quantum Information Laboratory of China University of Science and Technology, of which Jian is vice president.

“This is a very important step towards creating the first ground-based quantum communication network,” acknowledges Juan José García Ripoll, a quantum communications expert at the Supreme Council for Scientific Research. García-Ripoll says the Spanish team’s study “has immediate application”: “Create the first urban quantum network using commercial optical fibers.”

Jelena Rakonjak, another author of the ICFO study, explains that this future quantum internet will not replace the current internet, but will complement it. Quantum networks will transmit keys that allow messages sent to be decrypted in a traditional way. If someone tries to hack the quantum memories to spy, the key disappears and the message becomes indecipherable. “This can be very useful for confidential official communications, for banking services and also for sharing highly sensitive personal data, such as medical records between hospitals,” the researcher says.

Redmatten warns that we are still at the dawn of quantum computing and communication. Perhaps in this decade we will see the first quantum networks at distances of up to 500 or even 1,000 kilometres. But having a functional network that reaches everyone like the Internet will take many years, if not decades,” he explains.

At the end of this summer, the European Union’s first major project in this field was known as Alliance for Quantum Internet. The project cost more than 10 million euros. Its goal is to paint a close-up of what will be Europe’s first quantum communications network.

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