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An international team has developed a new method for generating quantum-entangled photons in a previously inaccessible spectral range, making the encryption of satellite-based communications much more secure in the future.
A 15-member research team from the UK, Germany, and Japan has developed a new method for generating and detecting quantum-entangled photons at a wavelength of 2.1 micrometers. In practice, entangled photons are used in encryption methods such as quantum key distribution to completely secure telecommunications between two partners against eavesdropping attempts. The research results are presented to the public for the first time in a recent issue of Science Advances.
Until now, it has been possible to implement such encryption mechanisms only in the near-infrared range of 700 to 1550 nanometers. These shorter wavelengths have disadvantages, especially in satellite-based communication, because they are disturbed by light-absorbing gases in the atmosphere as well as the background radiation of the sun. With the existing technology, end-to-end encryption of transmitted data can only be guaranteed at night.
Entangled photon pairs at two micrometers wavelength are significantly less influenced by the solar background radiation. Also, a so-called “transmission window” exists in the earth’s atmosphere for wavelengths of two micrometers. That means these photons are less absorbed by atmospheric gases, allowing more effective communication.
For their experiment, the researchers used a nonlinear crystal made of lithium niobate. When they sent ultrashort light pulses from a laser into the crystal a nonlinear interaction produced entangled photon pairs with a new wavelength of 2.1 micrometers.
The next crucial step will be to miniaturize this system by converting it into photonic integrated devices, making it suitable for mass production and use in other application scenarios.