How to fight against data theft, a real social problem? Quantum physics has the solution. His idea makes it possible to put information (a qubit) into a particle of light (photon) and distribute them in an optical fiber in a safe way. But the use of this mass media technology is mainly hindered by the performance of the single image sensor used. A team from the University of Geneva (UNIGE), with ID Quantique company, succeeded in increasing its (Advanced sensors to combat spies) speed by twenty.
This innovation, which will be discovered in the journal Nature Photonics, makes it possible to produce an unprecedented demonstration of the distribution of keys.
Buying train tickets, booking taxis, getting food are everyday transactions through mobile apps. These are based on payment methods that involve the exchange of confidential information between the user and his bank. To do this, the bank creates a public key, which it sends to its customer, and a private key, which it keeps secret. With the public key, the user can modify the message, make it unreadable and send it to the bank. Because of its private key, it can be hacked by banks.
This system is now threatened by the computational power of quantum computers. To solve this, quantum cryptography – or “quantum key distribution” (QKD) – is the best option. It allows two parties to create shared encryption keys and transmit them using photons, via optical fiber, in a highly secure manner. In fact, the laws of quantum mechanics state that measurements affect the state of the measured system. Therefore, if a spy tries to send a photon to steal the key, the message will be changed immediately and its interception will be displayed.
Limit now
The application of this method is limited by the speed of the single photon detector used to obtain the information. After each discovery, they will actually recover about thirty nanoseconds, which limits the encryption rate to around 10 megabits per second. A UNIGE team led by Hugo Zbinden, assistant professor in the department of applied physics of the UNIGE Faculty of Science, has succeeded in compensating for this limitation by creating an efficient detector. This project was carried out in collaboration with the team of Félix Bussières from the company ID Quantique, which originates from the university.
“Currently, the detectors for this application are single photon detectors with superconducting nanowires”, explains Fadri Grünenfelder, former doctoral student at the Department of Applied Physics of the UNIGE Faculty of Science and the first author of the ‘study. . “These devices have tiny wires that can be cooled down to -272°C. If a photon hits it, it heats up, stops being efficient for a short time, and produces a detectable electrical signal. When the wire cools down again, another photon can be detected.
Record performance
By integrating not one but fourteen nanowires into their sensors, the researchers managed to achieve record detection rates. Hugo Zbinden explains, “Our detector can count 20 gates faster than a single device. “If two photons arrive within a short time in this new detector, they can hit existing wires. separate and detect both, since one wire is not possible.” The nanowires used are also shorter, which helps reduce their recovery time.
Because of these sensors, scientists managed to generate encryption keys at a rate of 64 megabits per second over 10 km of optical fiber. This bit rate is high enough to save, for example, a video chat with many participants. This is five times the performance of current technology over a distance. As a bonus, this new detector is less complicated to create than the devices that are currently on the market.
These results open up new ideas for highly secure data transfers, important for banks, health systems, but also governments and the military. They can be applied in many other areas where light detection is key, such as astronomy and medical imaging.
Source: University of Geneva.
