Professor Hideo Kosaka of Yokohama National University Graduate School of Engineering and his colleagues have collaborated with Stuttgart University, Osaka University, and Tokyo University in Germany to transfer photons used for quantum communication into diamonds, which are quantum memories, using the principle of quantum teleportation. Then, he announced that he succeeded for the first time in the world in demonstrating a new principle of long-term storage.It is expected that the absolutely safe quantum communication network will be dramatically longer and more reliable.
Quantum communication is a cryptographic communication technology that cannot be eavesdropped by applying quantum mechanics, and uses automatic distribution (QKD) of cryptographic keys made of quantum.Currently, it is in the process of being put into practical use at a distance of about 100 km, but for longer distances, quantum relay that reproduces the quantum state to a distant place where photons cannot reach at once is indispensable based on the principle of quantum teleportation.It is necessary to generate entanglement (quantum correlation state between two quanta) between quantum nodes arranged every several tens of kilometers that photons reach, and to detect entanglement within the quantum node.
The relay node has a nucleon in a diamond that becomes a quantum memory, and the quantum state of the photon is quantum teleportated to the nucleon via an electron.By performing such transcription in each section every several tens of kilometers and performing quantum measurement instead of classical measurement, quantum relay that cannot be eavesdropped becomes possible.With this method, it is possible to transmit 10 megabits of information per second over a 1000 km line.The spins of the electrons and nucleons that make up an atom are connected by a force that leads to quantum entanglement called hyperfine interaction.In quantum teleportation, we have succeeded in transferring the quantum state of a photon to a nucleus by applying the quantum entanglement detection by absorption of a photon to the seed of the quantum entanglement in this substance.
With this achievement, it is possible to expand the quantum communication network to the world and continue to develop a safe and sound information society whose safety is guaranteed by the laws of physics.
