New Photon Source for Encrypted Communication

Generation of polarization entangled photon pairs at a wavelength of 2.1 micrometers. (Source: M. Kues, PQT)

An international team with the participation of Michael Kues from the Cluster of Excellence PhoenixD at Leibniz University Hannover has developed a new method for gene­rating quantum-entangled photons in a spectral range of light that was previously inacces­sible. The discovery can make the encryption of satellite-based communi­cations much more secure in the future. The new method is used for generating and detecting quantum-entangled photons at a wavelength of 2.1 micrometers.

Until now, it has been only techni­cally possible to implement such encryp­tion mechanisms with entangled photons in the near-infrared range of 700 to 1550 nanometers. However, these shorter wavelengths have disad­vantages, especially in satellite-based communi­cation: 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, but not on sunny and cloudy days.

The international team, led by Matteo Clerici from the Univer­sity of Glasgow, wants to solve this problem with its disco­very. The photon pairs entangled at two micro­meter wavelength would be significantly less influenced by the solar background radiation, says Michael Kues. In addition, transmission windows exist in the earth’s atmo­sphere, especially for wavelengths of two micro­meters, so that the photons are less absorbed by the atmo­spheric gases, in turn allowing a more effective communi­cation.

For their experiment, the researchers used a nonlinear crystal made of lithium niobate. They sent ultra­short light pulses from a laser into the crystal and a nonlinear inter­action produced the entangled photon pairs with the 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 for the use in other appli­cation scenarios”, says Kues. (Source: LUH)

Reference: S. Prabhakar et al.: Two-photon quantum interference and entanglement at 2.1 μm, Sci. Adv. 6, eaay5195 (2020); DOI: 10.1126/sciadv.aay5195

Link: Hannover Centre for Optical Technologies HOT, Leibniz Universität Hannover, Hanover, Germany

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