Professor Masatou Kotoru and others at the University of Tokyo have discovered a method to verify security even by using the wave nature of light in communication and using inexpensive general-purpose products for detection, which is expected to reduce the development cost of quantum encryption communication devices to about one-tenth of the cost. It is expected to start cooperation with NEC and aim to be in use by 2025.
Quantum encrypted communication uses the principles of quantum mechanics to generate a secret key for encrypting and breaking confidential information. Information such as the secret key is placed on a photon. Anyone who tries to peek at it, the light creates confusion and leaves a trail of being spied on. Illegal breaking of quantum encrypted information is considered impossible.
Light possesses wave-particle duality (the nature of a particle that possesses linear propagation and reflection, and the nature of a wave after it has been wound around an obstacle, etc.). Quantum encrypted communication, which is already in practical use, mainly utilizes the particle nature of light. To create the secret key to crack the code while monitoring whether it is being peeked at, it is necessary to accurately detect each photon at the receiving end. While a high sensitivity is required, cooling equipment is also needed, sometimes more than 1 million yen is required for 1 detector. In contrast, if the wave nature of light is used, it is possible to increase the received light at the Time of detection, and there is no need to distinguish one photon from another. This method can use the same detector as ordinary optical communication, and the cost is only about tens of thousands of yen. However, the method has previously only been feasible in principle and has not been proven secure.
Quantum encrypted communication only generates errors when it is peeked, and the particle nature of light can be used to calculate the rate of error. Professor Masatou Kotoru and others at the University of Tokyo discovered that the same error rate can be calculated by processing the values obtained when light waves vibrate with special functions. In other words, they have discovered a technique that can accurately detect peeking traces even by using the wave nature of light, thus reducing the cost of the overall equipment for quantum encrypted communication.
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